Bonded Porcelain Restorations in the Anterior Dentition: A Biomimetic Approach

Library of Congress Cataloging-in-Publication Data Magne, Pascal. Bonded porcelain restorations in the anterior dentition: a biomimetic approach / Pascal Magne, Urs Belser. p.; em. Includes bibliographical references and index. ISBN 0-86715-422-5 (hardback) 1. Crowns (Dentistry). 2. Dental ceramics. 3. Dental bonding. 4. Dentistry-Aesthetic aspects. [DNLM: 1. Dental Bonding-methods. 2. Dental Porcelain. 3. Esthetics, Dental. 4. Tooth Preparation, Prosthodontic. WU 190 M196b 2002] I. Belser, U. II. Title. RK666 .M24 2002

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© 2002, 2003 by Quintessence Publishing Co, Inc All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission of the publisher. Quintessence Publishing Co, Inc 551 Kimberly Drive Carol Stream, IL 60188 www.quinlpub.com

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Bonded Porcelain Restorations in the Anterior Dentition:

A Biomimetic Approach

Pascal Magne, PD, DR MED DEI\lT Senior Lecturer

Deportment of Fixed Prosthodontics and Occlusion

University of Geneva

School of Dentistry

Geneva, Switzerland

Urs Belser, PROF, DR MED DENT

Professor and Head

Deportment of Fixed Prosthodontics and Occlusion

University of Geneva

School of Dentistry

Geneva, Switzerland

r

Quintessence Publishing Co, Inc quintCllCftcc Chicago, Berlin, London, Copenhagen, Tokyo, Paris, Barcelona, Milano, boolu Sao Paulo, New Delhi, Moscow, Prague, Warsaw, and Istanbul

4

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DEDICATION

To my wife, Ceibi. and my father, Albin, who supported me and encouraged me in all situations. To my brother, Michel, who shared and brought to light his passion for dentistry and dental technique. In memory of my mother, Agnes, who was token from us by cancer too early.

-PM

In memory of my mother, Heidi. To my father, Theodor.

To my wife, Christine, for her unfailing support and patience.

To my children, Marc and Michele.

-UB

TAB LE OF CONTENTS

FOREWORD PREFACE

19

20

CHAPTER

I

UNDERSTANDING THE INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

23

Biology, Mechanics, Function, and Esthetics

1

1

Optimal Compliance and Flexibility Rationalized Anterior Tooth Shape Mechanics and Geometry During Function Ph y s i 0 log icE n am e I C r a c kin g and the D Ej Natural Tooth Aging and Enamel Thinning Biomimetics Applied to Mechanics

\

CHAPTER 1

2

NATURAL ORAL ESTHETICS

57

General Considerations

Fundamental Criteria

Esthetic Integration

1

CHAPTER

3

ULTRACONSERVATIVE TREATMENT OPTIONS Chemical Treatments and Biomimetics Nightguard Vital Bleaching Microabrasion and Megabrasion Nonvital Walking Bleach Technique Reattachment of a Tooth Fragment Simplified Direct Composites

99

CHAPTER

4

EVOLUTION OF I~IDICATIONS FOR ANTERIOR BONDED PORCELAIN RESTORATIONS

129

Historic Perspective Type I: Teeth Resistant to Bleaching Type II: Major Morphologic Modifications Type III: Extensive Restoration in the Adult Combined Indications Biologic Considerations Perspectives for Occlusal Veneers in Posterior Teeth

CHAPTER

INITIAL

5

TREATME~IT PLA~INING A~ID

DIAGNOSTIC APPROACH

179

Interactive Patient-Operatory-Laboratory Relationships Patient Management by the Operatory Team Patient Management by the Laboratory Team Treatment Planning and l n i.t i o l Therapy Diagnostic Waxup Diagnostic Mock-up Peculiar Cases Summary of Diagnostic Approaches Clinical Photography Shade Documentation

CHAPTER

6

TOOTH PREPARATION, IMPRESSION, A~ID PROVISIONAUZATION General Considerations Tissue Reduction Margin Configuration and Localization Peculiar Situations Immediate Dentin Bonding Definitive Impressions Direct Provisionals and Provisional Bonding

239

CHAPTER

7

LABORATORY PROCEDURES

293

Choice of Restorative Material and Technique Master Casts in the Refractory Die Technique Ceramic Layering and Finishing Special Effects Configuration of the Ceramic Workpiece

CHAPTER

8

TRY-IN A",ID ADHESIVE LUTING PROCEDURES

335

Choice of Luting Composite Resin Try-in and Preparatory Steps Conditioning of the Ceramic Surface Conditioning of the Tooth Surface Plocement of the Ceramic Restoration Final Adjustments and Occlusal Control Special Considerations

CHAPTER

9

MAINTENANCE AND REPAIRS

371

Maximum Performance, Reduced Maintenance Routine Professional Hygiene Complications and Repairs Replacement of Class 3 Composite

GUIDE TO CLINICAL CASES

387

INDEX

400

FOREWORD

It is with considerable pleasure that I write the foreword to Dr Magne and Prof Belser's book, which takes the science of esthetic dental reconstruction to a new level both clinically and academically. Dr Magne spent 2 years as a visiting associate professor in the Minnesota Dental Research Center for Biomaterials and Biomechanics at the University of Minnesota, where many of the ideas pro­ mulgated in this book were hotly debated, refined, and tested in a modeling and experimental en­ vironment. In this book, the clinician will find all that he or she could wish for in terms of indications and the classic clinical steps for tooth preparation, laboratory procedures, adhesive luting proce­ dures, and maintenance protocol. Those who have heard Dr Magne lecture will not be disop­ pointed. In fact, they will find much more that is practically and intellectually satisfying. The central philosophy of the book is the biomimetic principle, that is, the idea that the intact tooth in its ideal hues and shades, and perhaps more importantly in its intracoronal anatomy and loca­ tion in the arch, is the gUide to reconstrudion and the determinant of success. The approach is ba­ sically conservative and biologically sound. This is in sharp contrast to the porcelain-fused-to-metal technique, in which the metal casting with its high elastic modulus makes the underlying dentin hypo­ functional. The goal of the authors' approach is to return all of the prepared dental tissues to full function by the creation of a hard tissue bond that allows functional stress to pass through the tooth, drawing the entire crown into the final esthetic result. I hope that this book will receive a wide readership and that its principles will be carefully studied and become fully established in teaching and research, as well as de rigueur in the practice of restorative dentistry.

William H. Douglas, BDS, MS, PhD Director, Minnesota Dental Research Center for Biomateriais and Biomechanics; Chair, Department of Oral Science, University of Minnesota Minneapolis, Minnesota

19

PREFACE

The most exciting developments in dentistry have emerged within the past decade. Oral implant dentistry, quided tissue regeneration, and adhesive restorative dentistry are strategic growth areas both in research and in clinical practice. However, the many advances in dental materials and tech­ nology have generated a plethora of dental products in the marketplace. Clinicians and dental tech­ nicians are faced with difficult choices as the number of treatment modalities continues to grow. Fur­ ther, changes in technology do not always Simplify technique or decrease treatment costs. Prudence and wisdom need to be combined with knowledge and progress when it comes to improving our patients' welfare. In this perplexinq context, no one will contest the need for less expensive, satisfactory, and rational substitutes for current treatments. The answer might come from an emerging interdisciplinary bioma­ terial science called biomimetics.' This concept of medical research involves the investigation of the structure and physico] function of biologic "composites" and the design of new and improved substi­ tutes. Biomimetics in dental medicine has increasing relevance. The primary meaning for denlistry refers to processing material in a manner similar to that by the oral cavity, such as the calcification of a soft tissue precursor. The secondary meaning refers to the mimicking or recovery of the biome­ chanics of the original tooth by the restoration. This. of course, is the goal of restorative dentistry. Several research disciplines in dental medicine have evolved with the purpose to mimic oral struc­ tures. However, this nascent principle is applied mostly at a molecular level, with the aim to enhance wound healing, repair, and regeneration of soft and hard tissues2,3 When extended to a macro­ structural level, biomimetics can trigger innovative applications in restorative dentistry. Restoring or mimicking the biomechanical, structural, and esthetic integrity of teeth is the driving force of this process. Therefore, the objective tistry based on biomimetics.

of this book

is to propose new criteria for esthetic restorative den­

Biomimetics in restorative dentistry starts with an understanding

of herd

tissue structure and related

stress distribution within the intact tooth, which is the focus of the opening chapter of this book. It is immediately followed by a systematic review of parameters related to natural oral esthetics. Because the driving forces of restorative dentistry are maintenance of tooth Vitality and maximum conserva­ tion

of intact

hard tissues, a brief chapter describes the ultraconservative treatment options that can

precede a more sophisticated treatment. The core of the book centers on the application of the bio­ mimetic principle in the form of bonded porcelain restorations [BPRs). The broad spectrum of indi­ cations for BPRs is described, followed by detailed instruction on the treatment planning and diag­ nostic approach, which is the first step in learning this technique. The treatment is then described step-by-step, including tooth preparation and impression, laboratory procedures related to the fab­ rication of the ceramic workpiece, and its final insertion through adhesive luting procedures. The book ends with discussion of the follow-up, maintenance, and repair of BPRs.

20

I would have been unable to achieve this work without the valued collaboration of other dentists, dental technicians, specialists, and researchers. We should always remember that a key element for successful and predictable restoration is teamwork and an essential ingredient for teamwork is humility, to consider others better than oneself. We must try to serve each other rather than expect to be served. I am fortunate to have studied under Prof Urs Belser; his teaching and gUidance have been invalu­ able to me. Speciol thanks goes to Drs William Douglas, Ralph Delong, Maria Pintado, Antheunis Versluis, and Thomas Korioth at the University of Minnesota for their help and friendship during my 2-year re­ search scholarship there. They expanded my vision and knowledge of scientific research in bio­ materials and biomechanics. I extend appreciation to Michel Magne, CDT, for his significant contributions to the chapter on lab­ oratory procedures and for his skills in fabricating the ceramic restorations for all of the cases in this book. I also acknowledge my patients, who indirectly contributed to the realization of this book, and the private practitioners who donated extracted teeth for the studies and illustrations. Special thanks in this regard goes to Drs Rosa Serrano of Geneva, Switzerland, and Jose de Souza Ne­ grao of Sao Paulo, Brazil. Finally, I give honor and glory to my lord and Savior, Jesus Christ, who has made all possible through his gracious love.

of

my projects

Pascal Magne :-

References 1. Sarikaya M. An introduction to biomimetics: A structural viewpoint. Microsc Res Tech 1994;27:360-375.

2 Slavkin He. Biomimetics: ReplaCing body parts is no longer science fiction.

J Am

Dent Assoc 1996; 127: 1254-1257.

3 Mann S. The biomimetics of enamel: A paradigm for organised biomaterial synthesis. Cibo Found Symp 1997;205:261-269.

21

CHAPTER

l

UNDERSTANDING THE

INTACT TOOTH AND THE

BIOMIMETIC PRINCIPLE

Mimicry in the field of science involves reproducing or copying a model, a reference. If we as dentists want to replace what has been lost, we need to agree on what is the correct reference. The accepted frame of reference must be the same for the entire profession, and it should be timeless and unchanging. Once this is established, we can then construct appropriate research designs, devise valid concepts, and create rational dental treat­ ment plans. For the restorative dentist, the unquestionable reference is the intact natural tooth. Remains of Inca civilization in South America as well as mummies in Egypt 1 demonstrate age-old principles: the original number, dimensions, and structure of teeth have not changed. While the pattern of oral disease (infections, wear, parafunctions) has been influenced by the ever-changing human lifestyle, the original structure of enamel and dentin appears to be the same today as it was 3,000 years ago. In this context, it seems commendable to study and understand the marvelous design of natural teeth before considering any further concepts in restorative dentistry.

1

I

UNDERSTANDING THE INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

BIOLOGY,

MECHA~IICS,

FUNCTION, AND ESTHETICS

Physiologic performance of intact teeth is the result of an intimate and balanced relationship between biologic, mechanical, functional, and esthetic parameters (Fig 1-1 a). The most educational situations supporting that fact are found in cases of traumatic lnjuries like lhot illustrated in Fig 1-1. The price of on injury can be paid in the form of either a mechanical (hard tissue involvement) or a biologic failure (pulpal involvement). In both cases, the influ­ ence on the esthetic and functional parameters is obvious. Fortunately for the patient in Fig 1­ 1, simple and economic treatment strategies could be used [fragment reattachment on the left central incisor, root canal therapy and bleaching on the other]. Yet a critical question can be raised: What would have been the out­ come if, instead of being intact, these central incisors had been previously restored by two

rigid and extremely resistant full crowns? We know from impact experiments" that a more profound fracture [root involvement], which would be problematic to restore, is encoun­ tered when stiff and unyielding crowns are used. This contrasts with the behavior of the more fragile jacket crowns, which often shatter, leaving the remaining tooth substance intact. A partial crown fracture might be preferable if one considers that the energy dissipated during fracture can prevent further biologic damage or root injury. In consideration of the above-mentioned parameters, it is of primary importance to ask ourselves: Is it better to pursue the development of strong and stiff restorations or, instead, to find treatment modalities that reproduce the biomechanical behavior of the intact tooth? Stronger and stiffer might not always be better.

FIGURE 1-1: PHYSIOLOGIC PERFORMANCE OF TEETH. Performance of teeth is the result of an intricate physio­ logic puzzle including biology, mechaniCS, function, and esthetics (1-1 ol. Illustrative case: The moxillorv left central incisor fractured follOWing trauma that involved both moxillory central incisors [1-'1 b). The tooth fragment was recov­ ered [1-1 c). The situation was potentially compromised by pulpal exposure (1-1 d). After direct capping under rubber dam, the tooth fragment was rebonded to the remaining tooth substance [see Fig 3-10). A 1-week postoperative view reveals the favorable situation [1-1 e). One month later, the unfractured right central incisor showed signs of pulpal damage (1-1f). The severe organic discoloration was completely removed by internal bleaching ("walking bleach technique," see Fig 3-6) after root canal treatment was accomplished. [The root canal therapy was indicated only by the presence of symptoms and radiographic evidence.) The tooth was slightly overbleached to anticipate the initial color relapse [1-1 g). The 5-year postoperative view shows stable results i 1-1 h). (Figures 1-1 b to 1-1 g are reprinted from Magne and Magne 2 with permission.)

24

1

I UNDERSTANDING THE

INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

OPTIMAL COMPLIANCE AND FLEXIBILITY

The previous section calls for a strong and nat­ ural protection concept present in natural teeth called compliance or flexibility. The latter is an essential quality that enables a structure to absorb the energy of a force. In other words, a compliant structure will cushion a sudden impact by bending elastically under a given load. Up to a certain point, the more resilient a structure is, the better. This ability to store energy without undergoing permanent damage is inherent to intact anterior teeth and can be considered a reference. Dentin is the key ele­ ment in this capability. Figures 1-2a and 1-2b show the exact shape and structure of this essential "resilient" component. It was demon­ strated by Stokes and Hood" that during impact, an intact tooth is able to absorb the

highest energy of fracture when compared to teeth restored with different types of crowns. Although resilience promotes protection against impact through energy absorption, excessive elasticity might also render a structure too "floppy" for its purpose (Fig 1-2b, lett). The dentin core alone would be functionally inade­ quate without its rigid outer shell of enamel (Fig 1-2b, right). In this respect, natural teeth,rhrough the opti­ mal combination of enamel and dentin, demonstrate the perfect and unmatched com­ promise between stiffness, strength, and resilience. Restoralive procedures and alter­ ations in the structural integrity of teeth can easily violate this subtle balance.

FIGURE 1-2: RESILIENT COMPOt\IENT OF TEETH. An extracted tooth was specially acid treated to eliminate the enamel shell 11-20) and expose the dentin core (proximal view, left; palatal view, right), The lost enamel volume is evident in 1-2b. The dentin core alone is weak, and bending under 5 kg can be perceived with the naked eye (1­ 2b, bottom left, incisal edge displacement about 0.5 mm). The enamel shell provides the tooth crown with sufficient resistance to bending (1-2b, bottom right, incisal edge displacement about 0.1 mm). (The bottom diagrams in Fig 1­ 2b were produced with the finite element method.]

26

1

I UNDERSTANDING

THE INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

RATIONALIZED ANTERIOR TOOTH SHAPE Moving from the posterior segment in the ante­ rior direction within the dental arch, the process of "incisivization" tokes place (Fig 1-3a),

the cutting efficiency of the tooth. In some instances, vertical lobes rising from the cingu­

whereby the

of the crown

occlusal

table

is gradually

replaced by an incisal edge that has the obvi­ ous function of cutting. Anatomically, incisors show a distinct contrast between facial and palatal surface morphol­ ogy. The labial aspect of the crown features smooth and mainly convex contours, whereas the palatal surface displays a deep concavity extending oxiollv from the dental cingulum to the incisal edge and laterally between the two pronounced proximo] ridges (Fig 1-3b). With

lum interrupt the palatal concavity. The portion featuring the thinnest enamel layer, namely the cervical third, is also the area of

maximum thickness of dentin. Inversely, the thick incisal enamel is supported by a thin dentin wall. Canines display a different morphology. The cingulum is large and the marginal ridges are strongly developed. All of these convex ele­ ments are confluent and there is no palatal fossa [Figs 1-3b to 1-3d). The peculiarity of

this shape, the incisal edge is desiqned like a

such architecture will be explained later in view of the specific functional requirements of this

blade, which undoubtedly plays a major role in

strateg ic tooth.

INCISIVIZATION

FIGURE 1-3: BASIC ANATOMY OF THE ANTERIOR DENTITION. Comparative views showinq functional surfaces right; 1-3c; 1-3dj display soft and convex curva­

of extracted teeth. Palatal surfaces of canines [1-30, center; 1-3b, tures compared to the concavities of incisors (1-3b, left).

28

1

I

UNDERSTANDING THE INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

MECHANICS AND GEOMETRY DURING FUNCTION Thorough understanding of stress and related strain allows restorotive techniques to be opti­ mized. Load-to-failure tests have been popular among the wide range of mechanical testing approaches. However, these "conventional" strength studies, no matter how accurately con­ ducted, are not always sufficient to guarantee structural integrity under operational conditions. Failure under load conditions well below the yield stress often occurs in structures with small cracks or cracklike flaws, such as teeth and some dental materials. Therefore, modern test­ ing approaches must include nondestructive methods. For instance, the effect of functional loading can be quantitatively determined by the crown flexure, which can be measured under simulated conditions by bonded strain

gauges (Fig 1-4a) and numeric methods, such as the finite element method (FEM, Figs 1-4b to

1-7).5-9 Such investigation instruments must reproduce the loading configuration of anterior teeth, which has been clearly established and can be characterized as follows: • Because of the arrangement and position of the anterior dentition, mechanical loads act primarily in the buccolingual plane of each tooth. Proximal contact areas restrain mesiodistal loads [Fig 1-4b). • The horizontal component of realistic biting loads induces bending, which is the major challenge for the incisor.

FIGURE 1-4: NONDESTRUCTIVE EXPERIMENTAL METHODS IN MECHANICAL TESTING. Experimental specimen (intact central incisor) mounted with gauges for comparison of strains at the fossa and cingulum; strain gauges were oriented along the long axis of the tooth (1-4a1. Numeric modeling of anterior teeth can be achieved using bucca­ lingual cross sections and two-dimensional finite element methods* 11-4bl. [Figure 1-4a is reprinted from Magne et al 9 with perrnission.]

*In a finite element analysis, a large structure is divided into a number of small simple-shaped elements (Fig 1-4bl, for which individual deformation (strain and stress) can be more eosily calculated than for the entire, undivided structure. By determining the deformation of each small element simul­ taneously, the deformation of the entire structure can be reconstructed. The finite element method has become an accepted modeling tool, and new trends in research tend to combine both the experimental strain gauge approach and FEM evaluation in the same investigation.

30

I

1

UNDERSTANDING THE INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

of

the yield criteria

MOVing toward an edge-to-edge position (Fig

used for failure prediction in numeric analyses.

1-5bL significant tensile stress concentrations

The VOt) Mises criterion (VMj is commonly used.

are detected in the palatal fossa.

It is important to be aware

It works well with materials for which the yield stresses measured in uniaxial tension and com­

Even in that challenging position, which in­

pression are equal. However:

duces maximum bending moments, the facial half of the tooth and the cingulum area still do

Both enamel and dentin are brittle materials

not display detrimental stresses. It is appropri­

that present a higher strength in compression

ate to analyze stresses in a direction for which

than in tension.

the x and y components

of stresses

will display

their maximum values. The resulting analysis The ratio between compressive strength and

(upper right of Figs 1-5a and 1-5b) outlines the

tensile strength has been incorporated in an

principal stresses in the form of areas of com­

adapted failure criterion for brittle materials: the

pression and tension. The original maxillary

modified Von Mises criterion (mVM).lO Figures

incisor is separated into two distinct areas

1-5a and 1-5b illustrate the stress distribution

when subjected to maximum

[using the mVM criterion] throughout the central

palatal half of the tooth exhibits positive values,

incisor during protrusive movements.

namely tensile stresses, whereas the facial half

bending:

the

of the tooth displays compressive stresses. Note Initial guidance starting at the intercuspal

again the quiescent area of the cingulum

position (Fig 1-5a) does not cause significant

regard ing tensiIe stresses.

stresses. as determined by mVM. In this position. most of the tooth crown is sub­ jected to compressive lorces. and bending is minimal.

FIGURE 1-5: STRESS DISTRIBUTION ON A NATURAL MAXILLARY CENTRAL INCISOR DURING FUNCTION. Non­ linear finite element contact analysis. The mandibular incisor is sliding in protrusion starting at the intercuspal position (1-5a) and moving toward an edge-to-edge position (1-5b). Real tooth deformation is magnified 5x to emphasize the bending mode of the crown. In 1-5a, most of the cross-sectional area is subjected to compression (gray area in the principa! stress) or negligible tensile stresses. In 1-5b, the tooth behaves like a cantilever beam with a compres­ sive side [facial half) and a tensile side [palatal half) separated by a neutral axis. Maximum tensile forces are found at the level of the fossa. The external force created by the mandibular incisor is about 50 N, and real horizontal defor­ mation at the maxillary incisal edge is about 100 ~m [1-5b, distance from dotted !ine). The tooth is fixed (zero dis­ placement) at the cut plane of the root.

32

1

I UNDERSTANDING THE

INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

One may wonder what happens to mandibu­ lar incisors (Fig 1-60) when subjected to simi­ lar loading conditions. As with maxillary incisors, initial quidonce starting at the inter­ cuspal position does not produce significant mVM stresses. In this position, the mandibular crown is subjected only to compressive forces [Fig 1-6b). Moving toward an edge-to-edge position, tensile stresses begin to develop at

the facial surface (Fig 1-6c). This stress pattern is exactly the opposite of that of the antago­ nistic tooth. Because of the favorable facial geometry of mandibular incisors, which dis­ plays flat or convex contours (Fig 1-60), the level of facial tensile stresses remains moder­ ate and less detrimental compared to those found at the antagonistic fossa (see Figs 1-5b and 1-6c).

FIGURE 1-6: STRESS DISTRIBUTION ON A l'-lATURAL MANDIBULAR INCISOR DURING FUNCTION. Nonlinear finite element contact analysis. The facial aspect of a mandibular incisor exhibits extremely simple morphology with mostly flat or slightly convex surfaces (1-6a]. As in Fig 1-5, the mandibular incisor is sliding in protrusion starting at the intercuspal position (1-6b) and moving toward an edge-to-edge position (1-6c]. Real tooth deformation is magni­ fied 5 X. In 1-6b, most of the cross-sectional area is subjected to compression (gray area in the principal stress). In 1­ 6c, the tooth behaves like a cantilever beam with a compressive side [lingual half] and a tensile side (facial half] sep­ arated by a neutral axis. Maximum tensile forces are found at the facial middle third of the crown but are minor compared to the stresses of the antagonistic tooth at the palatal fossa. The external force created by the contact is about 50 N, and real horizontal deformation at the mandibular incisal edge is about 60 IJm (1-6c, distance from dot­ ted line). The tooth is fixed (zero displacement) at the cut plane of the root.

34

1

I UNDERSTANDING THE

INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

As previously outlined, form (ie, geometry) and function are essential determinants of stress dis­ tribution. It is important to remember that low stress lev­ els are found in surfaces of maximum convex curvature, ie, the cingulum and the cervical part of the facial surface. Therefore, it is con­ cluded that convex surfaces with thick enamel experience fewer stress concentrations than do concave areas, which tend to accumulate them.9 This statement is clearly supported by Fig 1-7a, which shows the influence of enamel geometry and thickness after modification of the palatal surface contour of a mandibular incisor. The resulting contour might be assumed as the prox­ imal aspect of an incisor (Fig 1-7b) or as verti­ cal lobes extending from the cingulum. The addition of enamel discloses a seemingly better balance and stress distribution. In this regard, it can be presumed that moderate stress concen­ trations would occur on the totally convex palatal surfaces, such as that found on canines. Canines have very curvilinear facial surfaces that may better withstand compressive forces.

A canine with its accentuated biconvex con­ tour (buccolingual section) displays an almost perfect convex design, which leads to a favor­ able mechanical configuration. An irregular surface anatomy, ie, the palatal surface anatomy of an incisor [Fig 1-7bl, logi­ cally yields to a different stress pattern. Stress concentration in the palatal fossa contrasts with the low stresses observed on smooth and con­ vex areas (ie, the cervical half of the crown for both palatal and facial surfaces). Accordingly, the following conclusions can be mode": • The palatal concavity provides the incisor with its sharp incisal edge and cutting abil­ ity but is shown to be an area of stress con­ centralion. • Specific areas featuring thick enamel, such as the cingulum and the marginal ridges, can compensate for this shortcoming and act as stress redistri butors. Cingula and marginal crests also represent essential palatal stops that allow for mainte­ nance of the vertical dimension of occlusion in the anterior segment.

FIGURE 1-7: STRESS DISTRIBUTIONS WITH VARYING ENAMEL THICKNESS AND GEOMETRY. An original buc­ copalatal cross section (1-7 a, left) is compared to a modified incisor with a thickened, convex palatal enamel [1-7 a, right). The modified tooth displays the lowest palatal surface stresses. Two small stress peaks still subsist in the palatal surface and correspond to concave areas delimiting the thickened enamel. * The modified finite element model repro­ duces the prominent distal crest of the tooth [1-7b). This typical incisal feature helps to improve stress distribution along the palatal surface.

* Although the loading condition [50 N palatally) was chosen to reflect a realistic situation, it should be emphasized that the conclusions are based only on this one loading condition. However, the conclusions about the effect of shape (convex versus concave) and composition [enamel-dentin dis­ tribution) are universal and do not depend on the load direction or magnitude.

36

1

I UNDERSTANDING THE

INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

PHYSIOLOGIC ENAMEL CRACKING AND THE DEJ The assembly of two tissues with distinctly dif­ ferent elastic moduli requires a complex fusion for long-term functional success. Stress transfer in simple bllorninote structures with divergent properties usually induces increased focal stresses at the interjoce.!' If enamel and dentin at the functional surfaces of a tooth comprised such a simply bonded bilaminate, then enamel-initiated cracks would easily cross the dentinoenamel junction (DEjl and propagate into dentin. In reality, the situation seems to be quite different. Although multiple enamel cracks are typically encountered in aged teeth, they seldom affect the structural integrity of the enamel-dentin complex. The explonotion ture inherent to fusion at the DEj be regarded as

lies in the most fascinating fea­ the natural tooth-a complex (Figs 1-8a to 1-8cl, which can a fibril-reinforced bond. 1'2

The DEj is a moderately mineralized interface between two highly mineralized tissues [enamel and dentin). Parallel, coarse collagen bundles (probably the von Korff fibers of the mantle dentin) form massive consolidations that can divert and blunt enamel cracks through considerable plostic deformation. Scanning electron microscopy fractographs of DEj specimens have demonstrated crack deflec­ tion to another fracture plane when forced through the DEl 14 The structure of the DEj shows two levels of scalloping (Fig 1-8a), which increase the effective interfacial area and strengthen the bond

between enamel

and

dentin. The scalloping is most prominent where the [unction is subject to the most functional stresses.

FIGURE 1-8: SPATIAL DEJ ARCHITECTURE AND FORMATION. Schematic representation of the spatial relationship of collagen fibrils 11-80). Thick bundles and tufts reinforce the fusion of enamel and dentin (middle). Coarse collagen bundles form "mieroscallops" (bottom, black dotted arrows) within the major scallops of the DE;] outline (middle, white dotted arrows). These bundles merge with other fibrils before or after entering the enamel matrix (bottom). [The top fig­ ure is reprinted from Sieber l 3 with permission. The middle and bottom figures are modified from Lin et 01 12 with per­ mission.]

38

1

I UNDERSTANDING THE

INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

Intereslingly, the DEJ is preformed in the earliest developmental stage of the tooth crown, at the time of incipient mineralization and much ear­ lier than an identifiable pulp (Fig 1-8d). This chronology is not coincidentol, and another sequence would not allow the creation of such a complex dentinoenamel fusion. It is probably

more correct to regard the crown of the tooth as growing out bidirectionally from the DEj, rather than from the pulp. In other words. the DEJ is the "center" of the tooth, not the pulp.

FIGURE 1-8 (CONTINUED). Thin tooth section under polarized light showing the collagen tufts in the enamel 11-8b; original magnification x250; courtesy of N. Allenspach, University of Geneva). Low-voltage field-emission scanning electron microphotograph of the DEj decalcified with neutral ethylenediaminetetraacetic acid: 80- to 120-nm-diame­ ter collagen fibrils merge with dentin matrix fibrils (arrowheads) and splay out into the enamel matrix (open arrows); note the cross banding of the collagen fibrils every 600 A (black arrows) (1-8c; original magnification x50,000). This deep penetration of collagen into the enamel, which is the sine qua non of the DEj, could not take place with fully calcified enamel (99% mineral by weight]. This points to the fact that the DEj forms early in embryonic develop­ ment and subsequently calcifies. The DEj of a primary tooth is being formed at the late bell stage (early crown stage] of tooth formation; dentin and enamel have begun to form at the crest of the folded internal dental epithelium. At this stage and in the continuing early growth, interpenetration of collagen into the contiguous enamel organ takes place. At maturity, this forms the fully functional DEj, which should be considered an interphase rather than an interface [1­ 8d; courtesy of Dr W. H. Douglas, University of Minnesota). (Figure 1-8c is reprinted from Lin et al 12with permission.)

40

1

I

UNDERSTANDING THE INTACT TOOTH AND THE BIOMIMETIC PRINCIPLE

Due to the inherent brittleness of enamel and the collagenous consolidation of the DEl enamel cracking should be considered a nor­ mal aging process. In addition, there are other effects of enamel cracks, which are visible in finite element models. Stress in the enamel is redistributed around the crack through the DEl which creates a stress concentration at the crack tip and leaves the tooth surface in the area of the crack relatively quiescent (Fig 1-8e).

Thus, enamel cracks can be considered an acceptable enamel attribute, and the DEJ plays a significant role in assisting stress trans­ fer (as opposed to stress concentration) and in resisting enamel crack propagation (Fig 1-8f). The fascinating properties of the DEJ must serve as a reference for the development of new dentin bonding agents, which should allow for the recovery of the biomechanical integrity of the restored crown.

FIGURE 1-8 (COt'--ITINUED). A photomicrograph of a strain gauge study specimen displays multiple cracks on the palatal surface [1-8e, top). Similar experimental conditions including modeling of Single and multiple cracks were sim­ ulated in FEM. Enamel surrounding the flaws appears to be totally quiescent with regard to tensile forces (gray areas correspond to mVM stresses between 0 and 1 MPa). Stresses at the crack tip are well above 200 MPa (1-8e, bot­ tom; teeth are loaded horizontally with 50 N on the incisal edge, 7x deformation factor). Scanning electron micro­ graphic view 11-8f) of palatal enamel cracks above a strain gauge (G). This appears to be the area of maximum ten­ sile stresses in the numeric model. The full thickness of enamel lEI is cracked, but the flaws never propagate into dentin (PI. (Figure 1-8e is reprinted from Magne et 01 9 with permission. Figure 1-8f is reprinted from Magne and Douglas 7 with permission.)

42

Equivalent mod ified Von M ises (MPa)

--

-

----

-------

-

---

-=

= --

-----

~~----

-

-

-

-

--

~----

-

-

--=

----

-

.

1

I U NDE RSTAND ING THE

INTA CT TOO TH A ND THE BI OMI ME TI C P RIN CIPLE

NATURAL TOOTH AGING AND ENAMEL THINNING As previously mentio ned, enamel and dentin exhibit different phy sical properties . Enamel can resist occlusa l wear but is fragile and cracks eas ily. Dentin, o n the o ther hand , is flexible and co mplia nt but is not wear resis­ ta nt and does not age favora bly w hen dir ectly ex posed to the ora l environment.

O rig ina l mo rphology and thickness of the ena mel shell (Fig 1-9a) seem to have been d esigned to a ntic ipa te w ear a nd function requirements 16 : ma ximum w ear ar eas ar e specifica lly those w ith grea ter bulks of ena mel, ie, the incisal edge o f an terior teeth. This " pre­ ventive" arch itecture still a llows physio log ic w ear to create dentin expos ure in the incisa l area (Figs 1-9b to 1-9d). By the same to ken,

Becau se

of

their respective shortco mings, nei­

ther enamel nor dentin independentl y wou ld be co nsidered effec tive restorati ve materials. How­ ever, they form a "co mposite" structure, w hic h prov ides a tooth w ith unique characteristics 's : the hard ness of enamel protects the soft under­ lying dentin, w hile the cra ck-arresti ng effect o f dentin and the thick co llagen fibe rs at the DEJI 4

teeth in the posterior regi on , w here ma sticator y force s are stronger, have thicker ena mel tha n do an terior teeth. 17 The dynami c w ear pa ttern of the incisal edg e must stand as a reference for the develo pment of new materia ls, w hich sho uld be abl e to age Similar ly to ena mel a nd dentin.

co mpe nsa te for the inherently brittle nature of ena mel. This structural a nd physical interrela­ tionshi p betwee n an extremely hard tissue an d

Na tural tooth ag ing a lso impacts the oplico l interactio n betwee n ename l an d dentin (Figs 1­

a more pliable tissue provides the natura l too th

g e and 1-9f). Her e ag a in, the inci sa l ed ge is the most a ffec ted (see Fig 2-8).

wi th its o rig ina l bea uty but a lso its a bility to w ithstan d mastication , thermal load s, a nd wear dur ing a lifetime .

FIGURE 1-9: THE SEASONS OF TOOTH LIFE. Anterior teeth initia lly present typica l mamelons a nd surfac e texture (1-9 0 ]. These elements are progressively eliminated by we ar. On going enamel cracking and dentin exposure (1-9 b to 1-9 d ) o re linked to o bvious co lor cha nges. Extreme w ea r a llow s for understanding the op tical interaction betw een enamel and dentin, especially the crucia l role of den tin in limiting lig ht tra nsmissio n in the incisal area (1-ge, 1-9f) . O ptimized cera mic or com posite stratificatio n technique s a re needed to reproduc e the selective light transmission of enamel a nd dentin.

44

=--- -

_

r

-

- - - . =

- .= ~_ ='i::: = --= .......:--==-- ~ - -- " - - -.- -- -

.

c'*'

..

t-

-

~~~.

=

_

--a=

_

.

~_

~~--~-

­

I U NDE RSTA NDING

1

T HE I NTAC T T OOTH A ND T HE BI O M IM ET IC P RINCIPLE

Age-related cha ng es o f the d entitio n are the main cha llenge of modern dentistry, whi ch is faced w ith a po pula tio n that is getting old er a nd keeping mo re

of

In the physiologi c aging process, the o rig inal ena mel thickness is prog ressively red uced [Fi g s 1- 1Oc to 1- 1Oe).

its natural teeth . The colo r a nd cosmetic pro blems related to

Smiles ca n show physica l a nd esthetic sig ns o f

tooth agi ng should not be the o nly co ncern o f

agi ng . Amo ng these, excessive w ear in the incisal area co ntributes to the loss of an terio r tooth pro minence a nd insuffic ient a nterio r gUid­ ance, thus gene ra ting new respo nsib ilities fo r

the resto ra tive de ntist.' As mentio ned previ­ o usly, dentin pla ys a cruc ial role in provid inq the toot h w ith co mp lia nce a nd fleXibil ity,

the restoralive dent ist. This degenerative phe­

w hereas the enam el shell w ill assure its rig id ity and strength . The increased crow n fleXibility o f

nomenon is ove rshadowed by col or cha nges

worn teeth ca n be assoc ia ted w ith functional

fol low ing dentin exposure, ena mel cracking, a nd related extrinsic infiltra tio n (Figs 1-1 Oa a nd 1-1 Ob). The Wides pread interest in vita l bleach­

and mechanical prob lems.

ing has beco me the dr iving fo rce o f esthetic dentistry to rejuve nate tooth a ppearan ce a t a limited cos t. How ever, this ultraco nserva tive

A sufficient a nd unifor m thic kness o f fa cia l ena mel is essential to the ba lan ce o f func­ tional stresses in the anterior dentiti on ."

chemical trea tment addresses o nly the cosmetic compone nt

of a

com p lex p rob lem .

FIGURE 1-10: ENAMEL IN THE AGING PROCESS. Teeth o f a 70-yea r-old pa tient w ith o bvious age-rela ted enamel w ear, crac king, and extrinsic infiltratio n of both ce ntral inciso rs (1-100 , 1-10b). Bleaching w ill nol add ress the bio me­ cha nical issues, w hic h req uire cro wn stiffness recove ry through ad eq uate resto rative ap proaches (see treatment steps in Fig s 5 -4 a nd 6 -22 ) Detail views of extracted ce ntral incisors (1 - 1Oc to 1-10 e) Tan gentia l lig ht is used to revea l the loss of tooth form, surface architecture, a nd pa latoinc isa l w ear.

46

·

---~

-

~-

­

I UNDER STANDIN G TH E INT ACT

1

Comb ined results

of

TO OTH A N D TH E BI O MI M ETI C PRIN CI PLE

different stu di es yi eld sig­

facial ena mel negatively aff ects the be havior

of var io us

rema ining pal ata l ena mel . Similar ly, loss

nificant infor ma tion about the effec t tissue red uction s on anterior c rown

flexure 7- 9 :

of of

pa latal enamel w ill sig nifica ntly a ffect rema in­ ing faci a l ena mel.

Substantial loss

of fa ci al

ena mel o r p resence

o f end od onti c a ccess cav ities is mo re likely to

Recovery of the o rig ina l ename l thic kness a nd

a ffect crown rigi d ity than is the interdenta l

arc hitecture is necessary for the b io mec ha nica l

redu ction

of ena mel o r

large C lass 3 ca vities

[Fig 1-1 1a ). As a ma tter

ba la nce

of

the tooth c rown. The c ho ice o f

restorative ma teria l is c ritica l in this matter (Fig 1-1 1d an d 1-1 1e).

of

fa ct, thin, a ged fa ci a l ename l

ca n lea d to hig h stress co ncentra tio ns dur ing

Restitution of ena mel thickne ss is therefore a

function . Surfac e cracks typ ica lly found o n

com b ined esthetic a nd b io mec ha nica l en­

ag ed teeth ac co unt for this p rob lem. The sig nif­

d ea vor . Bonding

ican t effec t

of the

enam el shell on stress d istri­

a nd

adh esive

resto rative proce d ures have the pot entiol to

b utio n w a s d emon strated using bo th stra in

reverse the esthetic mani festati on s

ga ug e ex periments an d finite element mod els (Fig s 1-1 1b a nd 1-1 1C).7-9 The total lo ss o f

teeth (Figs 1-1 1b to 1-11 e).

.c -

-

1. 8

-

~ 0

1.6

-

Q)

1.4

-

0 Q)

1.2

'x Q) = c

U >

of ag ing

in

2.2 2 0

.:0

ce ram ic

1. 15

cY:

1.0 lnlocl"

Proximal ena mel?

1. 30

1. 37

1.40

Facia l Cl ass 3 Endo Facia l ena mel, covitites" occess" ena mel, %) 9 76 9

2 . 16 Facia l enamel ,

16 9

Ha rd tissue remova l from inciso rs "1

-,

FIGURE 1-11 : IMPACT OF ENAMEL LOSS AND ENAMEL RESTITUTION. G rap hic representa tion of relative flexi­ bility (cha nges in flexibi lity rela tive to the baseline) for natural inciso rs a fter remova l of co ro na l tissues [ 1-1 1c]: tota l remova l of p roximal enamel (second col umn) does not a ffect crown rig id ity, but total remova l of facial enamel [last co lumn] is most ad verse; %), 76, a nd YJ ind ica te the a mount o f fac ia l ena mel thickness removed . Tooth preparati on by total facial enamel remova l w as simulated in FEM (1- 1 1b to 1-1 1e); the plot o f ta ngentia l stresses (red line) proceed s for each tooth al o ng the pa latal surface from cervica l to incisal; a dra matic increase in tensile stresses is found in the rema ining enamel of the pa lata l fossa (too th loaded palatal ly wi th 5 0 N onto incisa l edge, defo rmation factor l Ox on mVM stress ma pp ing) (1- 1 1b, 1-1 1c]. The o rig ina l profile of ta ngentia l stress is co mpletely recovered after bond­ ing a feldspathic por cela in veneer (1-11 d ); the use of composite a s the veneering material a llows only par tial recov­ ery of stiffness (1- 1 1e]. The orig ina l stress distrib ution of the natural tooth (gray line) is reported as a reference .

48

.. - - - -

-----

I

-

-

-

-

­

1

I

UND ERSTAND IN G THE INTA CT TO OT H AN D T HE B IOM IM ETIC PRINCI PLE

BIOMIMETICS APPLIED TO MECHANICS A natural tooth's uniq ue ab ility to with stand

recovery of tooth stiffness, wh ic h wa s not pos-

masticatory a nd thermal loads d uring a lifetime is the result of the structural a nd physical inter-

sib le w ith a ma lga m fillings .

rela tionship between an extremely hard tissue (ename l) and a more pliable tissue (dentin). The

How ever, it should be rememb ered that the

recog nition of this relati o nship has led to a g rowing co ncern about the bio mecha nica l respo nse o f intact hard tissue to restorati ve pro-

physica l properties o f co mposite resins are so mewha t limited. One limita tion is the elastic modu lus, w hich fo r a n a verage microfil led

cedures. The situation has been parti cularly

hybrid can be up to 80% lower [a p proxima tely 10 to 20 G Pa) tha n the elastic mod ulus of

informative about po sterior teeth. A sign ificant step wa s made w hen researcher s focused their

ename l (a pproxima tely 80 G Pa). A s mentioned before, the ena mel shell p roves to be instru-

attentio n o n the b io mec ha nica l side effects of am al gam restoratio ns (ie, cuspa l fractures a nd

mental in the w ay stresses are d istrib uted w ithin the crown.

crac ked tooth synoro rncs]." >" In respon se, a number of stud ies2i-24 analyzing biophysica l

When a more flexible materia l rep laces the

stress a nd stra in have shown the fol lOWing : •

Resto ra tive pro cedure s ca n ma ke the tooth crow n more deformable.

• The tooth ca n be streng thened by inc reasing its resistance to cro wn deformation .

ena mel shell, only par tia l recovery of crow n rigi d ity ca n be expec ted . Studies conducted by Reeh et 01 26 and Reeh and ROSS6 showed a recovery of 76% to 88% in crown stiffness aher the placement of co mposite resto rations a nd co mposite veneers. O n the

Based on these principles, tooth reinfo rcement w as obtained by some form

of

full o r par tia l

other hand , it wa s demonstra ted that crow n rig id ity ca n be recovered 100% w hen feld-

co verage (extracoro na l streng thening ) a t the expense of the intac t too th substance .25-27

spathi c

Today, adhesi ve technolog y has pro ved its efficiency in Simu ltaneou sly reestab lishing cro w n

os w ith porcelain veneer restorations (see Fig 11 1d ).7 Teeth resto red with de ntin-bo nded po rce-

stiffness a nd o llow inq maximum preserva tio n o f

lain

the remain ing hard tissu e (intraco rona l streng thening ).28-30 These stud ies demonstrated tha t

bio mimetic be havior w hen sub jected to cumula-

bon d ed

com posi te restoration s pe rmit the

porcela in (elastic modulu s approxi-

mately 70 GPa) is used as an ename l substitute,

ve neers

a lso

proved

the ir

absolu te

tive restorative procedures" and ca tastrophic testing [Fig 1-1 2).

FIGURE 1-12 : CATASTROPHIC FAILURE OF INTACT INCISORS VERSUS INCISORS RESTORED WITH DENTIN BONDED PORCELAIN VENEERS . * Natural (1 -120, 1-12b) and veneered (1 -1 2c, 1-12dji ncisors have been subjected to cumulative restora tive procedures (endo dontic treatment fol low ed by C lass 3 restorations) fol low ed by simulated ag ing (thermocycling lOOOx at SOC to 55°C) and impac t testing (catastrophic palata l load at incisal edge, notched palatal surface). Note the similar fracture pattern. Both teeth behaved like ca ntilever beams. Due to stress distribution w ithin the tooth, cracks d id not propag ate horizontally. but obl iquely by respecting the facial compressive stress area (see Fi g 1-5b) . Crack prop ag ation in the restored tooth (1 -12c , 1-12dl; how ever, followed a characteristic path that precisely avoid s the dentin-bonded veneer. A sig nifica nt a mount of dentin cohesively foi led (1-1 2d l, leaving the restoration intact and uncracked. The restoration wa s made of feldspathic porcelain.

*The veneered specimen in Figs 1-12c' and 1-12d w as initially prepa red by compl etely removing enamel from the buccal surface, reducinq the incisa l edge i .5 to 2 mm, and creating a mo derate interdental w rep ping (penetrating half of the proximal surface). A special den tin bo nd ing proced ure w as then used ? The extensive removal of enamel and de ntin exposure is not a tradi tiona l app roa ch for veneer preparation. This risky exper' imental design w as chosen to creole a maximum cha tlenge for the teath-restora tio n complex. .

. -

J -

--

-

-

-

1

I U NDERSTA NDIN G TH E INTA CT TO OT H A ND THE

B IOM IM ETIC PR INCI PLE

Fro m Figs 1-1 1 a nd 1- 12 , it is ea sy to understa nd the impa ct o f the b io mime tic princ ip le,

The closest substitute fo r den tin is represented

whic h log ica lly lead s to a nalysis of w hich materia ls ca n best simulate the behav io r of enam el

by hybrid co mposites, due to thei r similar elastic modulus. M ost co mpo sites, howeve r, develop shrinkage stresses a nd exhibi t high ther-

a nd dentin. Part of this approac h is represented in Tabl e 1-1 . Simple feldspa thic po rcelain ca n

mal expa nsio n (up to 4x the thermal expan sion o f the natural tooth or po rcela in). This wi ll ra ise

be compared to ename l. It is important to mention that :

sign ifican t problems w hen co mbining thin layers

Most den tal ceram ics ha ve a higher ultimate

of

porcela in a nd luting composites, espec ia lly w hen thick d ie spacers (> 20 0 ~ m ) are used dur ing the fabricat ion of the restora tions (see Fig

tensile streng th than natural enam el. H ig hstrength material s such as reinfo rced cerami cs

8-13) .42-4.1

do not seem to be requ ired to comply w ith the

The most cha lleng ing parameter is the simula-

b io mimetic principle.

tion of the DEj, the co mp lexity of w hich seems to be o ut of reach. 12 , 14 Nevertheless, prog ress

W ear properties (a brasiveness) of feldspathic

in adhesion has a llowed improvement in the

materia ls, how ever, remain a co ncern." espe-

integr ity of the tooth-resto rati o n interface (Figs 1-

cia lly fo r full cover age o f lateral segm ents of the d entitio n, as we ll as inlay s and on lays . In this

12ca nd 1-12d ;seea lsoFig 8-11 ).

reg ard , bioa c tive g lass ce ram ics mig ht bring sig nifica nt imp rove ments in the near future. O n

Applying the biomimetic princ ip le, it seems reaso nabl e to co nclude that new restorati ve

the other ha nd :

approac hes sho uld aim to crea te not the

Po rcelain veneers migh t no t subject o pposi ng

stro ngest restora tion but ra ther a restorat ion that is co mpati ble w ith the mechanical, bio-

teeth to significant wear prob lems because o f the conservative nature o f the treatment : the

logi c , and optica l properties of underly ing dental tissues.

pa latal a nd funcl io nal side

of the

tooth often

rema ins intact .

FIGURE 1-1 2 (CONTINUED) . The in vitro simula lio n in 1-12a to 1-12d a ppears to be clinically releva nt, os illustrated by this case of fracture, a crack started in the pa lata l co ncavi ly and pro paga ted o bliquely tow ard the facial aspect o f the root ( 1-12e, 1-1 2 f; courtesy o f Dr L. N . Bara tieri et ol , Fed eral Universily o f Santa Ca tar ina). The similar ily betvveen 1-1 2a a nd 1-1 21 is striking . Such a clinica l situation is not a necdo tal, as demonstrated by Baratie ri et a l.45

Table 1-1 Physical properties of dental hard tissues and correspo nd ing bio materials * Thermal expan sion coefficient

Ultimate tensile streng th (MPa)

Dental hard tissue

Elastic modulus (GPa)

Enamel

80"

17 32

1033

Dentin

1437

1 ]32

105 37

(x 10-6/ o q

* All values ore approxima tions.

Correspond ing material

Elastic modulus

Therma l expansion coefficient

Ultimate tensile strength

Feldspathic ceramic s

60-70'
90%) and unstable anterior g Uida nce (4-60 to 4-6 d). Composites w ere originally used to restore the incisal edges of the maxillary anterior teeth (4-6 c) The dia gnostic a pproach included a laboratory-made acrylic template (see Fig 5-10 ). Signifi ca nt improvements occurred offer the veneering proced ure (incisal ceramic coverage ab out 3 mm), in­ cludi ng harmony of the incisal edges with the low er lip line (4-6e), Width/height ratio of the clini cal crowns (4-6f; now about 84%), a nd function (4-6g ). Frequently, obvious signs of improved appearance a lso include changes in hairstyle (4-6h). The specific changes related to the incisal edge line are detail ed in 4-6i and 4-6 j. (Fig ures 4-4b , 4­ 4e, 4-4i, a nd 4-4j are reprinted from Mag ne a nd Douglas20 wi th permission .)

146

I

--

." ;W_----=-

~~-

~

-~~- --~--~ ~

-

---

v • -.

4 [ EVOL UTIO N OF I NDICATI O N S FO R A NTER IO R B O N D ED P O RCELAIN RE STOR ATI ON S

To minimi ze stresses durin g tooth-guided pro tru­

There is no scientific evide nce indi cating that

sive movements, some clini cians redu ce the

this ideal occlusa l status is no t a ppl icable to pre­

length of esthetica lly correct teeth . This inade­ q uate approach results in a reverse smile line and may ag e the potient sig nifica ntly.49 As proven c1i nica lly,24 there sho uld be no fear to re­

viously worn dentitio ns a nd pa tients wi th oc­ clusa l para functions. In fact , BPRs placed in w o rn a nd fractured teeth in the ear ly 19 9 0 s

juvenate the patient's smile by increas ing cen­

and followed over 5 years co mpared favora bly w ith traditiona l porcelain veneers a nd inlcvs."

tra l incisor prominence and leng th, because

This success rate is empowered by the minimally

ideal occl usion refers to bo th an esthetic a nd physiol ogi c ideal .48.50

invasive approach, which should always be the first choice for patients with w orn den titio ns.

Another rea son not to systema tica lly di stribute

Especially for indication types IIC and IliA [see

the anteri or g uida nce ove r a maximum number of teeth is the favora ble mec han ica l be havior of

next section ), the comfort a nd esthetic o utco me should be anticipa ted by a spec ially devel­

bonded porcelai n restorat io ns IBPRs).

oped d iagn ostic strategy21 (described in C ha p­ ter 5 ) to rcvcrsiblv redefine a smile line tha t a lso

In other words, the functio na l features of teeth

ma tches the unique character a nd perso na lity of the pa tient (Fig s 4-6i a nd 4-6 jl. In most

restored by bonded po rcela in restorations ca n be co nsidered identica l to those of intact nat­ ura l teeth. Particular empha sis must be ad­

ca ses, recovery o f a nterio r tooth prom inence

dressed, how ever, to the ma intena nce or reesta blishment of an adequat e a nd [uncnonc l

mately repo rted by the pati ent (co mpare Fig s 4 ­ 6a a nd 4-6 h).24

an terior q uido nce regard less

of w hether

has a pos itive socia l a nd personal impact, ulti­

this

g uidance involves the new restorati ons or not.

FIGURE 4-6 (CONTINUED). The low er lip line proved extremely imporlanl in gUid ing Ihe new incisal edge co nfig u­ ration (see Fig 2-12) The lower lip a nd incisal edge lines did nol co mplement eac h other, produ cing visua l tensio n 14-6i). Abo ut 2 mm had to be added to the centra l incisors to achi eve a more har mo nious situatio n [4-6 jl. In some sit­ uations, the lowe r lip has been modeled by inad equa te preexisting restorations. Under such ci rcumstances, it is highly reco mmended to "deprog ram" Ihe lip using , for insta nce, a n ocryllc mock-up for 1 to 2 w eeks (see Fig s 5-8 k to 5­ 8m)2 1

148

.

-

~

;;'

- - --

-

.

--­ -

.

..

.

'.

_

• -

'c - -

_ -

­

\

4

I

EVOLUTI ON OF IN DI CATI O NS FO R A NTE RIO R BONDED P OR CEL AI N RE STORATIONS

of inci sal function of

As w as said for type I indi cati on s, there are no reason s not to veneer nonvital teeth w ith type II

There is so me evide nce that the type

ind ica tion s (Fig 4-7 ) except in case o f severe brea kdown of too th substance . Genera lly, it is not recommended to ovs rlc p the endodontic

the type and amount of inc isal coverage. The pal atal mini-cha mfer, w hich is routinely used,

finish line to be recomm end ed is a

access cav ity with the veneer nor to use posts.

should occasio na lly be repl aced by a simpler fini sh line like a butt marg in,23.sl espec ia lly on

These precautio ns al low an ea sy reentry to the

w or n incisors. These opti ons w ill be scientifi­

o rig ina l pulp cha mbe r a nd pe rmit rebleach ing w hen required .

ca lly exp la ined in view o f functio nal stress dis­ tribution d uring protrusive movemen ts man dible [see Fig s 6 - 1 1 to 6 - 16).

of

the

FIGURE 4-7: RECOVERY OF CENTRAL INCISOR PROMINENCE IN AN AGING SMILE . The pa tient's main com­ plaint w as the lock of volume and leng th of both central incisors (4-70 , 4-7b). The left central incisor w as nonvital and d iscolored (4-7c). Preparatory steps included internal bleac hing of the left central incisor and replacement of preex­ isting interdental comp osites [4-7 d). The endodon tic access cavity w as par tia lly filled w ith glass ionomer, then cov­ ered w ith a layer of compo site (see Fi gs 3-7 to 3-9]. Porcelain veneering allo wed substantial recovery of the facial coro nal vol ume and length (4-7e to 4-7g ). The low er lip has "remod eled " itself to perfectly confo rm to the newl y de­ fined incisal edges (4-7f). Intraoral view after more than 4 years of clinical service (4-7h) . Intact teeth have age d and dar kened, but veneered teeth and related periodontium remain unchanged. Tooth prepara tion steps of this ca se are deta iled in Fig 6-4.

150

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4

EVOL UTIO N O F IN DICATI ON S FO R A NTERIOR BO ND ED PO RCELA IN RE STOR AT IO N S

TYPE III : EXTE N SIVE RES TOR ATIO N IN THE ADULT

Extensive cor ona l fractures (type IliA , Fig 4-8 ), extensive loss o f ena mel [type IIIB), a nd ma lfor­ mations (type III C ) ore ind icoti o ns fo r this type

These challengin g types of dam aged dentition

sometimes involve a maj ori ty of the coro nal vol­

ume or too th surface ,

of bo nded porcela in resto ra tio n,

4 -.30

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FIGURE 4-8: CONSERVATIVE TREATMENT OF SEVERE CROWN FRACTURES. Facial preopera tive view (4-80) , Due to trauma, significa nt volume of the central incisors has been lost (4 -8 b, pala tal view) The fracture line ends parag ingi­ va lly at the mesial aspect of the rig ht central incisor, Ha rd tissue loss estimated at more tha n 5 mm in heigh t is evident (silico n ind ex from waxup) (4 -8c ), (Figures 4-80 and 4 -8d are reprin ted from M ag ne and Magne 52 w ith permi ssion .)

152

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FIGURE 4-8 '(CONTINUED) , Final. bonded' porcelciin ve neers (4 -8d ). Details of di ag nostic steps are shown in Fig .5 -5 , a nd too th preparati on is presented 'in Fig 6 -3 . Restoratio nswere bonded only to enam el beca use effective dentin adhe­ sives were still under development at the time of plccement, Uncha nged situation 4 years la ter (4-8e) . Light enamel stains ere detected on the palata l aspect, but' clinlcol morg indladaptation and sea l are n ot altered (4-8f). No porcelain fa il­ .ires are recorded in spi te of obvious functio n and marked an terior g Uida nce (4-8g). Optima l esthetic inteqrotion: smile ine (4 -8 h) a nd pati ent's pe rsona lity ~ere respected throug h the di agnostic steps. The situation remains unchanged 7 years later (4- 8 i). ' ' .. .

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4

I EVO LUT IO N OF INDICATIO NS FO R AN T ERIO R B OND ED

Type IliA: Extensive coronal fracture Porc ela in veneers a llow the vitality of the teeth to be ma intained despite con siderable cor onal brea kdown . In chil dren , such co nd itio ns would

PO RCEL AI N R ESTO RATI ONS

investigati on surprising ly clai med ultimate coro­ nal streng ths of restored teeth far exceed ing those o f intac t teeth (Fig 4 -9a) . This co nclusio n mig ht even be stro nger today co nsidering the prog ress of dentin ad hesives. How eve r, dentin

be prefera bly trea ted wi th d irect compos ites as

ad hesion might no t be as cri tical as initia lly

transient restorati o ns, rather tha n porcela in resto ra tions, w hich sho uld ba sically be used in

tho ugh t for this type of indi cati on. It wa s clear ly de mo nstrated that the potentia l o f the co ncept lies in the desig n o f the restorati on , w hic h is ex­

adu lts. Extensive incisa l edge spa ns of ce ramic ma teria l ha ve been investigated o nly recen tly23

plain ed through favorabl e load co nfig urat ion,

a nd subseq uently used cli nica lly w ith succe ss." For severely fractured inciso rs (F ig 4 -8L the ex­

ge o metry, and tissue arran gement of maxillary incisors [Figs 4 -9b a nd 4 -9c).23.46As a conse­

treme desig n of the restorati ons suggests tha t terminol ogy may need to be chang ed : ca n we still call these restorat ions "lamin ates" or "ve­

q uence , co rona l streng th proves to be sufficient even w hen using BPRs wi th extensive incisal

neers"? Co nseq uently, the term "bo nde d porce­ lain restorati on s" (BPRs) has been p ropose d instead 24

of scientific stud ies ha ve field of indi cat ion s. Wa ll et that up to 2 mm of inci sal

ed g e spa ns of cera mics. In a cli nica l eva lua­ tion , no probl ems w ere de tected w hen up to

5 .5 mm of avera g e freestand ing feldspathic material was used ."

O nly a limited number

BPR-resto red c rowns wi th extensive inc isal ed ge

exp lored this new a l45 de mon strated

spa ns

edge span o f ce ra mics co uld be crea ted o n ma ndibu lar inci sors w itho ut a ffec ting the ulti­ ma te coron a l streng th, but An d reasen et ai lS may have been the first authors to study the treat ment

of crown-frac tured

inci so rs w ith la mi­

nate-type BPRs in the ear ly 19 9 0 s. Their in vitro

of

ceram ics are characterized by their

"lo w-stress" desig n and increased crow n stiff­ ness w hen co mpared to intact teeth.53 As men­ tio ned in C hapter 1, how ever, fleXi bili ty proves to be an essential qual ity in any structure . O th­ erwi se, it woul d be unabl e to a bsorb the en­ ergy of a traumati c blow. Up to a point, the mo re resilient a structure, the better s 3.54

FIGURE 4-9: STRENGTH OF INTACT AND FRACTURED INCISORS RESTORED WITH DIFFERENT TREATMENT MODALITIES . The results of stud ies by Andreasen et 01 (w hite bo r!" a nd g ray bo rs" ) a nd M unksgaard et 01 (black bo rs-"] have been com bined in this g ra ph . Ce ra mic restorati o ns co nsisted o f traditi onal facial la minates [no incisal coverag e) except for the last g roup [fra ctured tooth plus bulk veneer}, w hich featured the hig hest average strength a nd co rrespo nded to teeth for w hich the veneers included the missing par t of Ihe incisal edge as w ell the faci al surface . G ro ups that w ere not statistica lly different are linked by brackets on the left (4-90). Fac ia l load ing w as a pplied {light

gray arrowheads}.

154

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FIGURE 4-9 '(CO N TIN UED):' MODIFIED VON MISES STRESS .DISTRIBUTION THROUGHOUT BUCCOLINGUAL SECTIONS OF RESTORED 'INCISORS (FI NITE ELEMENT ANALYSISj. The thick do tted orrow shows the loca tion and di rectionol the 50-N load , The' w hite dotted line represents the luting co mposite. Despiteextreme differences in-the design of the restoration, the tooth-restoration interface and the restoration itself ore not sub jected to elevated stresses for both the minimum veneer \ (4~9 b ) a nd ,the veneer restoring the fra ctured tooth (4 -9 c). l n bo th cases, the interface , ' does not cross the pcila tal conca vity. Stresses in the rema ining pala tal enamel ore even higher in 4-9b compared to stresses at the same loca tion in the concavity of the ceramic piece in 4-9c. The !wo incisors are restored w ith the sa me feldspa thic ceramic (see also Fig 6- 1,2).

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I

EVOLUTI O N O F IN DI CATION S FOR ANTE RI OR B ONDE D PO RCEL AIN RE STORATI ON S

Fu rther

research

is required

to d etermi ne

o f a por cela in veneer beca use of unifo rm ther­

w hether modu lated streng th through high er­

ma l expa nsio n a nd the absence of hygro sco pic expa nsio n of the rebonded fragment.

compli a nce des igns mig ht be ind ica ted , ie, by including underlyin g co mpos ite buildups. This modali ty w as includ ed in the Ioad-to-fa ilure study by A nd reasen et 01 15 (see Fig 4-9a ) and yielded favo ra ble ultima te crown streng th. The related stress dis tribution w as ca lculated in a fi­ nite element study.23 Presen ce of the co mposite provides a sig nifica nt effec t, simultaneo usly a l­ low ing the decrease of stresses in the pa la ta l co nca vity (stress redi stributi o n into the more flex­ ib le compos ite) and relocatin g the margin of the veneer into the "safe" inci sal area . How­

W hen the fractured tooth fragmen t is not avail­ a ble, the simplified "ce ra mic o nly" design is rec­ o mmended (Figs 4 -8 a nd 4-1 0 ) beca use it is straig h ~orward and fea tures optimal esthetic re­

sults . The de nta l technici an ca n use spec ific po rcela ins to accurately reproduce the a natomy a nd o ptical charac teristics of de ntin, ie, opa que dentin fo r an ad eq uate translucency a nd fluo­ rescent stains for a n adeq uate luminescence (see Figs 7 -8 and 7 -9 ). M ost composite resins

ever, unde rlying composite buildups must be carefully considered. Fu rther scien tific investiga­

do not a llow such precise characteriza tio n.

tions are needed w ith regard to the high ther­

Fractured mandibul ar teeth ca n be treated w ith

ma l expa nsio n

of

ce rta in com posite resins.

the same approach [Fig 4-1 0) . Even though

Composi te resins prove d to have a signi fican t influence o n the developm ent o f cera mic post­

functio nal stresses can gen erate tensile force s a t the facial surfac e o f mand ibu lar incisors [see Fig 1-6 ), this is not a co ntraind ica tion for BPRs. Due

bo nd ing flaw s w hen a pplied too thic kly as a luting ag ent56-58 or w hen used in the form of p re­ existing Cl ass

3 restorotio ns."

For the time being , the rebonding of the frac­ tured tooth fragment,55.60 w hen possible, is ce r­ ta inly ind ica ted beca use it has been proven to gi ve g ood results w hen supplemented with a veneer (see Fig 4 -9 a ).1 4 In fact, this treat ment

to the favo rable facial geometry of mandibular incisors, the morphology of w hich dis pla ys flat o r soft con vex contours, such facia l tensile stresses remain mod erate. The loading confi g u­ rat ion o f mandi bular teeth (ie, facial load ) w as reprod uced in stud ies by Wal l et a l45 and A n­ dreasen et a l 14

15

and y ielded favo ra ble results

co mpared to intact teeth.

moda lity seems appro priate prio r to place ment

FIGURE 4-10 : PREVIOUSLY FRACTURED MANDIBULAR INCISORS. This case features com bi ned ind icati ons for BPRs: recover y of incisa l pro minence in the maxilla and de finitive restora tions of the righ t ce ntral and latera l mandibu­ lar incisors previously restored w ith co mposites (4- 100) . Detailed views of the tooth prepara tion (4- 1Obi a nd fina l ce­ ra mic restorations [4- 1Oc]. Marked anter ior gUidance ensures adequate function, and the situatio n remains stable after 3 years of cli nical service (4-1 Od; this view a lso show s porcela in laminates on the moxillo rv right central incisor to the left ca nine). Addi tiona l views of this case , as well a s de tailed diagnostic procedures , are presented in Fig 5-8 .

156

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I

EVOLUTION OF INDICATIONS FOR ANTERIOR BONDED PORCELAIN RESTORATIONS

Type IIIB: Extensive loss of enamel

tralizing mouth rinse leg, bicarbonate solution) and topical application of neutral fluoridated

Extensive tooth abrasion is typically found in

gels can be recommended. Adhesive dentistry

people of older age groups; of the maxillary teeth, the anterior teeth often exhibit the most

should be used whenever possible if restora­ tion is necessary.

wear (Fig 4-1 1). However, tooth surface loss is a growing problem in younger individuols." Di­

Localized loss of enamel can be easily treated

etary acids are increasingly popular (especial ly

by direct application of composite resins. In

soft drinks). Bulimia, consumption of acidic

case of a more extensive wear pattern, bonded

foods, acid reflux, and chlorine consumption

porcelain restorations can be proposed and

[from swimming) are other typical etiologic fac­

may include posterior teeth. Type IIIB indications

tors in young patients.

can appear somewhat similar to type lie, but the former features a more generalized nature

Tooth erosion, particularly in young people, presents a considerable challenge to restora­

(often more then four teeth to treat) as compared to the latter (which often involves only two

tive dentists. In all cases, preventive and con­

teeth). Another typical type IIIB patient is fea­

servative strategies are essential. Use of neu-

tured in Figs 8-8g to 8-8j.

FIGURE 4-11: ENAMEL EROSION OF MAXILLARY ANTERIOR TEETH. The patient presented with severe facial wear of maxillary anterior teeth and infiltrated Class 3 composite resin restorations (4-11 a to 4-1 1c). Note definite dentin exposures on the facial surface of the right and left central incisors (4-1 1b) Treatment planning included replacement of preexisting restorations, and teeth were prepared according to a diagnostic template; note the proximal margins extending within the new interdental restorations (especially between the central and lateral incisors) to minimize the volume of remaining composite restorative material 14-11d). The final porcelain restorations feature minor changes of tooth form and length but substantial recovery of the facial volume (4-1 1e to 4-1 '1 hi.

158

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4

I EVOLUTION O F IN DICATION S FOR A NTERIOR

B OND ED P ORCELAI N R ESTOR ATION S

'lie:

Type Generalized congenital and acquired malformations A number of loc a lized malfor mations of the crown surface ca n be ~r eated by rather co nser­ va tive mea ns, includin g freeha nd composite restorati o ns (see Fig s 3-5 and 3- 1 1) 6 263 G en­

w hic h are preferab ly used in the adu lt. Prema­ ture placement of po rcela in restora tions (before ag e 16 or 18 ) may not be appro priate be­ cau se of the sig nifica nt chang es that still take place w ithin the dentitio n leg , pa ssive eruptio n a nd resid ua l a lveolar c rest growth).

era lized ena mel dysplasia (F ig 4 -1 2), how ever,

G enera lized enamel dysplasia must be d istin­

req uires a more g lob al a pproach a nd may be trea ted successfully a nd conser va tively w ith

gu ished fro m a melogenesis imperfecta . The la t­

BPRs if the de ntinoename l junctio n has not been al tered 2 9 As w as said for type IliA, direct co m­ posites can be used as interim restorat ions in the child prio r to the final porcelai n bond ing s,

ter req uires particular prud ence: most freque ntly a full-coverage prosthetic proc ed ure rema ins the treatment o f choic e ." Further research is re­ q uired to d etermine w hether amelogenesis im­ perfecta ca n be trea ted w ith bo nded ce ramics.

FIGURE 4-1 2 : COMPREHENSIVE TREATMENT APPROACH FOR G EN ERA LI ZED ENAMEL DYSPLASIA. M axillary teeth w ere previously trea ted wi th PFM crowns, w hich sig nifica ntly a ltered the pa tient's self-confidence: her eyes flee the ca mera a nd her lips try to hide her teeth (4-120 , 4 -12 bj . The mand ibular teeth still exhibit the orig inal surface de­ fects (4 -12 c) The mand ibular situatio n is co mplica ted by marked crow d ing (4-12d). The preprosthetic phase included provisio naliza tion of rnoxillo rv teeth a nd extractio n of a mandi bular incisor follow ed by orthodontic therapy (4- 12e). [Fig ure 4 -1 2c is rep rinted from Magne and Magne 52 wi th permission.)

160

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FIGURE 4.121CONTINUEDI . Once realigned, (4·1 2fl. mandibular incisors, canine s, and first premolars w erepre­ pared [4 ~12g),resto red with po rcelci nlcrn motes (4-12hl. and stabi HzecJ w ith a lingua!.b onded ' retainer. Definitive ' restora tions on maxillary teeth w ere then carried out in a seco nd, stage [4-12il ,' wh ich allowed [orthe exoctshcde re­ production ol .inteqroted mandibular veneers (4, 12j , 4-12 k), Significcint irnpcct .on 'the patient's confidence and .sccio! life is expected 14: 12iiq '4 -1) m). Theserestoia tions have been in cliniccl servicelor moo re than 9 vec rswilhout mcijor problems, Detailed steps for the fapricatjon of mandi bular veneers'arEl shown in Fig '7· 1 1,

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4

I EVOLUTI ON

OF IN DICATI ON S FOR AN T ERIO R BO ND ED P ORCEL A IN R ESTORATIONS

COMBINED INDICATIONS It is uncommon to find patients wi th o nly one

The pa tient in Fig 4-1 3 par ticular ly illustrates

rea son to justify the use o f BPRs . Most pa tients in

that fac t bec ause there we re a t least three mai n

this book present a combina tio n

of

fa ctors that

rea son s to use BPRs . The restora tio ns simultane­

finally lea d to the decisio n to use po rcela in ma­

o usly permitted solving the prob lem

of

terial in an indi rect approa ch.

stain ing of a nonvita l too th, closure

of di a stem­

a ta, and redefinit io n

of

residua l

to o th form an d length .

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FIGURE 4-13: TYPICAL PATIENT WITH COMBINED INDICATIONS FOR BPRs . Preoperative views: the patien t's re­ quest included the closing of interdental spaces betw een maxillary incisors (4 -13a ). In ad d itio n, the left centra l incisor presented bleaching-resista nt staining , a nd analysi s of the smile revealed a sig nifica nt space betw een the low er lip a nd maxillar y incisors (4 -13b) . Io o lh volume and leng th were redefined acco rding ly; the approxim ate curva ture of the lip (dolled curve) served a s a reference (4-13c; unprepared teeth a nd silicon index of the waxup) , Baseline (4­ 13d l, co rrespond ing views of tooth prepara tions (4- 13e , 4- 13fl, a nd final BPRs (4-13g to 4 -13i ) Cohesiveness be­ twee n the rnoxillo rv teeth a nd the low er lip ca n now be ob served (4- 13 hl, and there is a significa nt improvement in the pa tient's denfofacial compositio n (4- 13 i) [Pa lient treated in co llaboratio n w ith Dr Va lerie Favez, University o f C enevo .]

164

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I

EVOLUTI ON OF IND ICATION S FO R AN TERIOR BON DED PORC ELAIN R ESTORATIONS

BIOLOGIC CONSIDERATIONS A co mp rehensive discuss io n

of new

indications

for BPRs must includ e biologi c co nside ratio ns. For those pa tients showing types II an d III indi ­ ca tio ns, tradition al treatment ap proaches (full­ cove rage crown) wou ld involve the removal of large amounts of sound too th substance, w ith a dverse effects o n pulp, g ing ivae , a nd crown biomechanics , not to mentio n the serio us finan­ cia l cons eq uences. The use

of

adhesive tech­

no logy instead al low s maximum preservation of tissues (incl ud ing ma intena nce o f tooth vita lity) a nd limits cos ts, w hich a lso contrib utes to the sa tisfactio n

of the

pati ent.

even demonstra ted sig nifican t reduc tio ns in Pla que Index a nd plaque bacteria vitality a fter the placement of po rce la in ve neers. Such re­ sults ca ll into question the gene ral assumption that so-cal led high-end adhesive restoralion s are not indi cated fo r pa tients w ith poo r oral hy­ g iene. In fact, beca use of the ir "friend ly " be­ havior, bonded ce ra mics mig ht be the most fo rgiv ing resto ra tio ns fo r patients strugg ling w ith o ra l hygi ene (Fig 4-140 ). It can be anti ci­ pa ted that those pa tients' period ontium might respond be tter to ceram ic materials, co nside r­ ing that d ental porcela in is less susceptib le to accumu lation of bacteria l p laq ue than are

A sig nifica nt outcom e is the excel lent peri­

gold , resin, o r even minera lized tooth struc­

odontal respon se (see follow-up photog ra phs in Figs 4-5r, 4 -7h , 4 -8e to 4- 8 i, 4-1 ad , and 4­

tures M .67 There is Virtua lly no surface degrada­ tio n of the ceramic materia l, w hich is co rro bo­

14), w hich w as first noted by Ca la mia in the late 1980s 9 Due to thei r favo ra ble intrinsic es­

rated by the absence of plaque accumu lation (Fig 4- 14b).24 An add itio na l a dva ntage o f BPRs

thetics in the marg ina l area, bon ded cera mic restorations do not require penetration into the

from the periodo nta l pe rspective is the avoid­ ance of cro wn-l engthening proced ures, be­

gingiva l sulcus, which prevents po tential dam­ ag e to the periodontal tissues. Kourkouta et 0 165

cause even very short clinical crow ns can be recovered (see Fig . 4-8 ).

FIGURE 4-14 : FOLLOW·UP VIEWS OF PERIODONTAL SO FT TISSUES AROUND BPRs AFTER 5 TO 6 YEARS OF CLI ~"CAL SERVICE W ITHOUT SPECIFIC MAINTENANCE . Posto perative view 6 years after placement of a po rce­

lai n veneer on the lateral incisor showin g a favorable periodo ntal situa tio n despite poo r o ra l hygi ene; there has been significa nt evolutio n of the ce rvica l lesio n on the ca nine (4-14a ), This case w as de tai led in Fig 4 -4 (baseline view o f the lateral incisor in Fig 4 -4g) . Magnified view from another pa tient 5 years after the placement of a BPR (4-14b). The po rcela in surface is still glossy, the margi n is invisible, and there is no plaque accumulation despite the fact thai no specific profess ional maintenance has been car ried o ut (the sa me ca n be sa id for the pat ient in Fig 4-140).

166

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4

I EVOLUTI ON

OF INDI CATION S FOR A NTERIO R B ON DE D PORC ELA IN RE STO RATIO NS

Finally! optima l esthetics

of

the marginal peri­

is increased by the up per lip : the p roxi mity

of the

ll

odo ntium in the presence of BPRs is ensured

lip can genera te a n "urn brello effed (s hadow)

through the so-ca lled esthetic w id th inherent to

c haracterized by grayish margin al g ingivae and

these restorations (Fi g 4-15 ).35 With conven­

dar k interd ental

tio nal full-coverag e resto rat io ns, extend ed metal

4-15 d ; see also Fig 4-12b). BPRs, o n the other

frameworks a nd opaque a luminous ce rami c

han d , ex hib it an excellent optica l behav io r and

papillae

(Fig s 4-1 5 b a nd

of the

cores are assoc ia ted w ith unplea sant optica l ef­

promote a na tural ap peara nce

fects in the surround ing soft tissues. This pro blem

soft tissues (Fig s 4 -15c a nd 4 -15d ).

marginal

FIGURE 4-15: ESTHETIC WIDTH AND UMBRELLA EFFECT ON THE SOFT TISSUES . The restorat ions (full-coverage ceramic crow ns on the right can ine to left canine) are too opaque and are respo nsible for gray ish papillae ob served only in the presence of the lip (compare 4-150 and 4-15b; see 4 -15d, upper pari) . In contra st, per iodontal lissues a round BPRs [rig ht central incisor to left canine) or jacket crowns ap pear healthy and naturally illuminated (4-15c, 4-15d, lower pari). (Fi g ure 4 -15d is reprinted from Magne et 0 135 with permissio n.)

168

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4

I EV O LUT IO N OF

IND ICAT IO N S FO R AN T ERIOR B O N D ED PORCELA IN R ESTO RATIONS

PERSPECTIVES FOR OCCLU SAL VENEERS IN PO STERIOR TEETH Patients' req uests an d cl inicians' interest in es­ thetic restora tions are not limited to an terior teeth. As a result, posterio r tooth-colored adhe­ sive restorat ive techni ques have g row n consid­ era bly over the lost de code .

cuspa l flexure d ue to their mo rphology a nd oc­ clusion. Res torative p rocedures ca n increase cuspal movement under occlusa l load ,68,72 w hic h in turn ma y result in a ltered streng th, fa­ tigu e fracture , a nd c rocked-too th syn­ drom es.73 - 75 Such know ledge a llowed consid­

The b io mimetic principl es that have been di s­ cussed for an te rio r teeth can be similarly ap­ plied to molars a nd premolars. The fol loWing bio mecha nica l co nside ra tio n shou ld be re­ membered : As w as the case for crown flexure in anterior teeth, cuspal flexure rep resents the most importa nt biomecha nica l fea ture in pos­ terior teeth .

erab le development of methods improving frac ture resistance of teeth76,77 throug h var io us fo rms of full or partia l co verage 78-80 an d , mo re recently, throug h the use sive techni qu es.69.81,82

of

co nse rva tive ad he­

M arg ina l rid g e integ rity is o n important a nat o mic feature limiting c uspa l flex ure, w hic h is the most sig nifican t con tributor to

C hief adva nces have resulted from the study a nd understandin g

of

cuspa l flexure a nd plas­

tic y ie ldi ng , w hich are key para meters in the per forma nce of the tooth -restora tive co m­ plex .68.69 Subclinica l cuspa l mlcrodelorrnotion. ie , be low the threshol d

of cha irside

observa ­

lion. has been id entifi ed since the early 1980s by Do ug las68 a nd Morin et 0 1/0,7 1a nd it is now accep ted that intact posterior teeth dem onstrate

stiffness a nd strength

of

the posterior tooth

crown. " A s mentio ned in C hapter 3 for a nterio r teeth, a number of posterior teeth can be treated ultra­ con servatively with freeha nd composites,84,85 especial ly if the proxima l ridges are intac t to ensure the b io mec hanica l integ rity crown (Fig s 4-16 and 4-17).

of

the tooth

FIGURE 4-16 : SMALL- TO MEDIUM-SIZED REPLACEMENT OF TOOTH SUBSTANCE WITH FREEHAt'-ID COM­ POSITES . Proximal ridges a re intact o n this molar, w hich presents the ideal ind ica tion for d irect co mposite restoration (4-16 a ). C ovlty preparati o n after car ies removal (4- 16b) a nd beveling (4-16 c). Composite w as stratified using the sa ndw ich technique;" w hich co mprises a base o f ena mellike shad es (4-16d ) tha t are characterized w ith intense stains and covered w ith more translucent masses (4 -16 e) Each cusp and anato mic lobe ca n be cured separate ly (4-1 6 fl, w hich a llows the elaboration of a sophistica ted morpholog y and functiona l masticatory surface (4-16g to 4 -16 i) Finishing of the restora tion is significan tly simplified ; the fina l contou rs and luster are easily obtained w ith "home-made" notched SofLex disks (3M) (4-16 j to 4 -16 1) .

170

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FIGURE 4-1 SEVEN-YEAR FoLLOW-UP OF FREEHAND COMPOSITE. Preoperative view of Ol d amalgam restora­ tion (4-17 o j a nd postope rative .view . aher 7 years of cli nica l service (4-17b), Staining of the restoration closely matches the natural occlusolsulcus.ofn eig hboring teeth. The detail view shows no alteration of margin and excellent behavior of the motericl (4-17c). The clinical success mig ht be attributed to the limited a mount of tooth substa nce re­ . '" ' ,. . . pbced .

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P ORCELA IN REST ORA TI ON S

The co mparatively low elastic modu lus of most

Luting procedures for these po sterior BPRs w ill

co mposites, however, ca n never fully co mpen­

follow the sa me steps that are described in C hapter 8 for anterior BPRs,28 ie, immed ia te

sate for the loss of strong proximal ename l ridges , especially in large Cla ss 2 restorat ions. In these situations, espeda lly w hen cusp cover­

appl icat ion impre ssion

of the den tin bon d ing agen t (befo re taking) and use of a reg ular light-cur­

age is required , indirect cera mic inlays/on lays seem to be the best option. 84.35 Adeq ua te stiff­

ing com po site as the luting age nt; dua l-cure co mpos ite cement ca n be o mitted in this ap­

ness of the porcelain materia l po tentia lly a llow s for complete recovery of crow n rigi d ity. Cu rrent co mposites suffer not o nly from low elaslic mod­

proa ch beca use BPRs seem to o ffer sufficient tran slucency for effec tive lig ht curinq. " The rig­

ulus and limited to ug hness but a lso fro m high therma l expansio n; in this co ntext, their use as a restorative ma teria l fo r large oc clusa l and stress­ bear ing rehabilitation seems questionable .

o ro us a pplicat io n of this seq uence is impera tive to avo id postoperative sensitivity. As d iscussed for type III ind ica tions for ante­ rior BPRs, the use of posterio r BPRs in the form

of cera mic In the ca se of tota l occl usal cov erage in vital

o nlays a nd overla ys is indeed a [ud icio us way to avoid tradi tiona l prosthetic

teeth w ith a short clini cal crown , ind irec t ce­

procedures that would require root-cana l ther­

ramic overlays are indicated (Figs 4-18 a nd 4­

apy and surgica l crown leng thening . Maxi­

19 ).86 .85

mum tissue preservation an d biom imetics, the dri vin g force s of modern restorati ve den tistry, are enabled.

FIGURE 4-18 : FIVE-YEAR FOllOW-UP OF AN "OCCLUSAL VENEER" OF A VITAL TOOTH WITH A SHORT CLIN­ ICAL CROW N . Compara tive view of a PFM crow n a nd cera mic overlay (4 -180 ). The ad va ntage of the overlay for this molar with a short clini ca l crown is ob vious: the too th is still vital and functions w itho ut prob lems after 5 years of clin ica l service (4 -18 b, 4 -1 8c; now 8 year s of clini ca l service) N ote that no effective den tin bo nd ing age nts were avai lab le at the time of placeme nt. Ad hesion to marg inal ename l is solely responsible for this clinical success. FIGURE 4-1 9 : CO NSERVATIVE REPLACEMENT OF AN AM A LG AM RESTORATI ON WITH CERAMIC OVERLAY­ 7-YEAR FOllOW-UP. Insufficient remaining thickness o f cusps (4-190) justified complete coverage of the too th, but it wa s kept vital . Final view of the cera mic overlay on its sing le d ie (4-19 b) and after ad hesive luting (4-19 c). C lose-up view af ter mo re tha n 7 yea rs o f cli nical service w ilho ut intervention (4 -19 d; now 10 years of clini cal service) Here aga in, no effective dentin bonding agents w ere availab le a t the time of placement. Ad hesion to margina l ename l is solely responsible for this clini ca l success.

172

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PORCEL AIN RE STOR ATI ON S

2 1. Mag ne P, Doug las W Ho Ad d itive co ntour of porcela in ve­

References 1. Pincus CR. BUild ing mouth personality. J South Ca lif Dent Assoc 193 8;14:125-129 . 2 . Horn HR. Porcelain laminate veneers bonded to etched enamel. Dent C lin North Am 1983 ;27 671-6 84. 3 . Ca la mia JR. Etched po rcelain facial veneers: A new treot­ ment mod a lity based on scien ific and c1 inico l evide nce. NY J Dent 1983;53:255-259 4 . Rochette AL. A ceramic restoration bonded by etched enamel and resin for froctured incisors. J Prosihet Dent

1975 ;33: 287- 293 . 5 . Touati B, Pissis P, Miora P. Bond ed sing le restorations ond the co ncept of pelliculor preporotions. Cah Prothese

neers: A key element in enamel preservation, adhesio n and esthetic for the ag ing dentition. J Adhes Dent 1999; 1:

8 1-9 1. 22. Magne P, Douglas W Ho Optimisa tion des concepts me­ caniqu e en medec ine denlaire esthetique. Inf Dent 1999 ; 81 :37 3- 38 1. 23. Magne P, Douglas W H DeSig n optimization a nd evolu­ tion of bo nded ceramics for the anterior dentition: A finile element a nalysis. Qui ntessence Int 1999;30:66 1-672.

24 . Magne P, Perroud R, Hod ges JS, Belser UC C linica l per­ formonce o f novel-design po rcelain veneers for the recov­ ery of co ronal volume and length. Int J Periodontics Res­ torotive Dent 2000; 20 44 1-4 57

25. Jordo n RE, Boksman L. Co nservative vital bleac hing treot­

1985 ; 13 95-1 30. 6. Toual i B, Bersay L. Enameling of teeth using g lass ceromic veneers. C ah Prothese 19 87 ; 15 167-1 89

ment o f d iscolored dentition . Compend Con tin Educ Dent

7 . Touati B, Pli ssart-Vanackere A C eramic bo nded veneers. Toward a minimol prosthesis Reol C lin 1990 ; 1:51 - 66 .

26 . Hoyw ood VB, Leono rd RH, Dickinson G L. Efficacy of six

8 . Cai amio JR . Etched porcelai n veneers: The current state o f the cr t. Q uintessence Int 19 85 ;16:5-1 2. 9 Ca lomia JR. C linica l eva luation o f etched po rcelain ve­ neers. AmJ Dent 1989 ;2:9-1 5

10. C ala mia JR. The current stotus of etched porcelain veneer restora tions. J lndi ono Dent Assoc 1993 ;72: 10-1 5 . 1 1. C hristensen Gj. Veneering of teeth: Sta te of the cr t. Dent C lin North Am 19 85 ;29:373-391 .

12. Garber AD, Goldstein RE, Feinman RA Porcelain Lami­ nate Veneers. C hicago : Q Uintessence, 1988 . 13. Friedman Mj. Aug menting resto rative dentistry wit h porce­ lain veneers. J Am Denl Assoc 1991 ; 122:29-34 . 14. Andreasen FM, Daug aard~e n s en J. Mun ksgaard EC Re­ inforcement o f bo nded crown fractured inci sors w ith po r­ celain veneers. Endod Dent Tra umatol 1991 ;7 :78- 83. Da u ga ard~e n se n J. M unks­ gaard EC Treatment o f crow n fractured incisors w ith lam­ inate veneer restoratio ns: An experimental study. Endod Dent Traumatol 199 2;8:30-35 .

15 And reasen FM, Flugge E,

16 . Mag ne P, Magne M , Belser U. Na tural a nd restorative o ral esthetics. Part II: Esthetic treatment modal ities. J Esthet Dent 1993;5: 239-246 . ] 7 . Magne P, HoIz J. Restauration des den ts o nterieures. Principe, indic alion s el limites des techniques de traite­ rnent. Rev Mens Suisse Odontostomatol 1994; 104 :

124 7-1254. 18. W alls AW. The use o f ad hesively rela ined all-porcela in ve­ neers during the manage ment o f fractured and worn a nte­ rior teeth: Part 1. C linica l technique. Br Dent J 1995;

178:333-336. 19 . Walls AW. The use of adh esively retained all-porcelain ve­ neers d uring the manag ement of fractured and worn ante­ rior teeth: Part 2 . C linical results after 5 years o f follow-up Br Dent J 1995 ;178:3 37-3 40.

20 . Belser UC , Mag ne P, Magne M. Ce ramic laminate ve­ neers: Continuous evolution

of indicat ions. J

1997;9 197-207.

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months o f nightguord vital bleach ing of tetrocycli ne-stai ned teeth J Esthel Dent 1997 ;9 .13- 19.

27 . Hoyw ood VB, Porker M H . N ig htguord vital bleaching be­ neoth existing po rcelain veneers: A case report. Qu in­ tessence Int 1999;30:743-747

28. Magne P, Doug las W H o Porcelain veneers: Dentin bo nd­ ing optimiza tion and biomimetic recovery o f the crown . Int J Prosthod ont 1999; 12:1 1 1- 12 1.

29. M ag ne P, Douglas W H oRationaliza tion o f esthetic restora­ tive dentistry based on biomimetics. J Esthet Dent 1999 ; 11:5-1 5. 30 . Mag ne P, Dougla s W H oC umulative effects of successive reslorative proced ures o n a nterior crown flexure: Intact ver­ sus veneered incisors. Q uintessence Int 2000;3 1:5- 18.

3 1. Sedg ley CM , M esser HH. Are endodontica lly treated teeth more brittle? J Endod 199 2; 183 32-3 35 32 . Papa J, C a in C, Messer HH . M o isture co nlent of vita l vs endodontica lly treated teeth. Endod Dent Traumatal

1994 ;10:91-9 3 33 . Princej, Donova n T. The esthetic metal-ceramic margi n: A com pa rison o f techniq ues J Proslhe! Dent 1983;50:

185-192. 34 . W ohlwend A, Sirub JR, Scharer P M etal-ceramic a nd 011­ po rcelain restora tio ns: Cu rrent co nsiderations. IntJ Prostho­ dont 1989 ;2 13-26.

35 . M agne P, M agne M, Belser U. The esthetic wi d th in fixed proslhod ontics J Prosthodont 1999;8: 106-11 8. 36 . Schoeneberg AJ. Di Felice A, Cossu M . The esthetic po­ tential of the ceramic-fused-to-metal technique . In: Fischer J led) Esthetics a nd Prosthetics: An Interdi scipl inary Con sid­ era tion of the Sta te of the Art. C hicago : Q uintessence,

1999 :31-70 . 37 . Peumans M , Van Meerbeek B, Lambrechts P, Vanherle G, Q Uirynen M The influence of direct composite ad ditio ns fo r the cor rectio n o f loo th form a nd/ o r position o n peri­ od o ntal health: A retrospective study. J Periodontal 1998;

69:422-427.

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EVOLUTI ON O F INDI CATI ON S FOR A NTE RIO R B ON DED P OR CEL AI N RE STO RAT IO NS

38 . Burke S, Burch j G , Telz j A Incidence and size of pre­ treatment overlap and posttreatment g ingival embrasure space belween maxillary cenlral incisors . Am j O rthod Dentofac ial O rthop 1994 ; 105 50 6-511.

I

4

57 . M ag ne P, Kwon KR, Belser U, Dougla s W H o C rack prop ensity of porcelain laminate veneers: A Simula ted o p­ eratory evaluation. j Prosthet Dent 1999;81 :327-33 4 . 58 . Mag ne P, Versluis A, Douglas W H o Effect of luting com­ posite shrinkage a nd thermal load s on the stress d istribu­ tion in porcelain laminate veneers. j Pro slhet Dent 19 9 9 ; 8 1:3 35- 34 4.

39. Allen EP, Koisj, Tornow D, Takei H. Progress in interdental papilla construction. Presented at the 21 st Annua l M eeting of the American Academy of Esthetic Dentistry, Aspen, August 8, 19 9 6 .

59 . Mag ne P, Douglas W H o Interdental desiqn of porcela in veneers in the presence of composite fillings: Finite ele­ ment ana lysis of composite shrinkage and therma l stresses. Inl j Prosthod onl 20 0 0 ; 131 17- 124 .

40. Kopp FR: Esthetic principles for full crown restorali ons. Part II: Provisionalization. j Esthet Dent 19 9 3;5258-264 . 41 . Lombardi RE. The principles o f visua l perception and their clinical ap plica tion to denture esthetics. j Pro sthet Dent 19 73 ;29 :35 8-3 8 2 .

60 . Baratieri LN el 0 1 [eds]. Direct Adhesive Restorations on Fractured Anterior Teeth. Sao Paulo: Q uintessence, 19 98: 135-205.

42 W alls AW, Murray jJ. M cCabe jF. Co mposite laminate veneers: A clinical study. j O ral Reha bil 1988 ; 15 : 4 39-454 .

61 . Deery C , W agner M L, Longbottom C , Simon R, N ugent Zj. The prevalence o f denial erosion in a United States and a United Kingdom sample of adolescents. Pediatr Dent 2000; 22 :505-5 10

4 3. Tyas Mj. Correlation belween fracture properties and clin­ ical performance of composite resins in C loss IV cavities. Aust Dent j 1990 ;35 :4 6-49.

6 2. M agne P Megabrasion A conservative strategy for the anterior dentition. Pract Periodontics Aesthet Dent 19 9 7 ; 9:389- 39 5.

44. Peumans M , Von Meer beek B, Lam brechts P, Vanh erle G. The 5-year clinical performance of di rect co mposite add i­ tions to correcl tooth form and position. I. Esthetic q ua lities. C lin O ral lnvesfig 19 9 7 ; 1: 12-1 8 .

63 . Dietschi D, Krejci I. Trai lements chimiques des dyschromies dentaires. Rea l C lin 1999; 10:7-2 4 .

45. Wa ll jG, I~eis bi ck M H, john ston W M . lncisol-edqe strength of porcelain laminate veneers restoring mandi bu­ lar incisors. Intj Prasthodont 199 2;5 :4 4 1- 4 4 6 .

64 . Bouvier D, DuprezjP, Pirel C, Vincent B Amelogenesis im­ perfecta- A prosthetic rehabilitation: A clinica l report. j Prosthet Dent 19 9 9 ;8 2 : 130-1 3 1.

4 6 . M agne P, Versluis A, Douglas W H o Rationa lization of in­ cisor shope: Experimental-numerical analysis. j Prosthet Dent 19 9 9; 81 34 5-35 5 .

65 . Kourkouta S, W alsh Tl. Davis LG . The effect of porcelain laminate veneers on gi ngival health and bacterial plaque characteristics. j C lin Periodontol 19 94;2163 8-640 .

47. O keson jP led) Ora facia l Pain. C hicago : Quintessence, 19 9 6 : 12 2-12 3 .

66 . C hon C , Weber H. Plaque retention on teeth restored w ith full-ceramic crown s: A comparative study. j Prosthel Dent 19 86 ;56 :6 66-671 .

4 8. Ramfjord S, Ash NWI . Occlusion, ed 3. Phi ladelphia : Sounders, 19 8 3 : 166- 168 .

6 7 . Koidis PT, Schroeder K, j ohnston W, Campagni W. Co lor consisiency, plaque accumulation, and external marginal surface characteristics of the collarless metal-cera mic restoratio n j Prosthet Dent 19 9 1;6 5 :39 1-4 0 0 .

49. Daw son PE Evaluation, Diagnosis, and Treatment of O c­ clusal Problems, ed 2. St Louis: M osby, 1989:274-29 7. 5 0 Beyron H. O ptimal occl usion. Dent Clin N orth Am 19 6 9 ; 13 :5 37-35 4

68 . Douglas W H o Co nsiderations for mod eling. Dent Mater 19 9 6 ; 12: 20 3-20 7 .

5 1. Castelnuovo j, Tja n AH, Phillips K, N icholls j l, Koi s j c. Fracture load and mode of failure of ceramic veneers w ith different preparati on s. j Prosthet Dent 2000 ; 8 3 : 17 1-1 80

6 9 . M orin D, Delong R, Douglas WH oC usp reinforcement by the acid-etch technique j Dent Res 19 84 ;6 3: 10 75-1 078 .

5 2 . M ag ne P, M agne M . Porcelain veneers at the turn of the millenium: A w indow to biomimetics [in French] . Real C lin 19 9 8;9 3 29-34 3 .

70. M orin DL, Dougla s W H, C ross M , Delong R. Biophysical stress a nalysis of restored teeth: Experimental strai n mea­ surements. Dent M ater 1988;4:41-4 8.

53. M agne P, Douglas W H o Optimization of resilien ce and stress distribution in porcelain veneers for the treatment of crow n-fractured incisors. Inl j Periodontics Restorative Dent 19 9 9 ; 19 :543-5 5 3 .

71 . M orin DL, Cross M , Voller VR , Douglas WH , Delong R. BiophYSical slress ana lysis o f restored teeth: Modeling a nd analysis. Dent M a ter 19 8 8;4 :7 7-84 . 72 . Assif D, M arshak BL, Pilo R Cuspal flexure associated w ith amalgam resto rat ions. j Prosthet Dent 19 9 0 ;63 258- 26 2 .

54. Gordon j E Structures: W hy Things Don't Fall Down . N ew York: Do Capo, 19 7 8 :7 0-109. 55 . Mun ksgaard EC, Ho jrved L, j orgensen EH, AndreasenjO , Andreasen FM . Enamel-dentin crown frac tures bonded w ith various banding age nts. Endod Dent Traumatol 199 1;7 :7 3- 77

7 3 . Cameron CE The crocked tooth syndrome. j Am Dent Assoc 19 64 ;6 8 :4 0 5- 4 11 .

56. Borghi N , Berry TG . Post-bonding crock formation in po rcelain veneers. j Esthet Dent 19 9 7;9 :51-54 .

75 . Covel VVT, Kelsey W P, Blankenau RJ An in vivo study o f cuspa l fracture. j Pro sthet Dent 19 85 ;5 3 :3 8-4 2 .

7 4 . Cameron CEo The cracked tooth synd rome: Addi tional findings j Am Dent Assoc 197 6 ;9 3: 9 71-975.

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O F INDI CATI ON S FOR A NTERIO R B ONDED PO RCELAIN R ESTO RATI ON S

76 HoodJ M i\!\ethods to improve fracture resistance of teeth [di scussion]. In: Vonh erle G, Smith DC (eds) . Internationol Symposium on Posterior Composite Resin Restorative M a­ terials [sponsored by 3M]. St Poul: M innesolo Mi ning & M anufacturing , 19 8 5:44 3- 4 50 . 7 7. Douglas W H o Met hods to improve frocture resi stonce of teeth. In: Vanherle G , Smith DC [eds]. Internationol Sym­ posium on Posterior Composite Resin Restorative M aterials [sponsored by 3M ]. St Pa ul: IvYnnesota Mi ning & M anu­ facturing , 19 854 3 3-44 1. 78. M olcolm PJ, HoodJ M The effect of cast restorations in re­ ducing cusp flexibility in restored teeth. J Dent Res 19 71 ;5 6 :D207 . 7 9 Reeh ES, Dougla s WH , M esser HH . Stiffness of en­ dodontically-treated teeth related to restoration technique. J Dent Res 19 89;6 8 : 1540-1 5 44 80 lin n J, Messer HH . Effect o f restorative procedures on the strength of endodontically treated molars J Endod 19 9 4 ; 20:479-4 85 .

81 . McCullock AJ, Smith BG. In vitro studies of cusp rein­ forcement with adhesive restorative material. Br Dent J 19 86 ; 161 :4 50-4 5 2. 82 . MacPherson LC , Smith BG . Reinforcement of weokened cusps by od heslve restorative materials: An in-vitro study. Br Dent J 1995 ; 17 8 :34 1- 34 4 . 83 . Reeh ES, M esser HH, Douglas W H Reduction in tooth stiffness os a result of endodontic and restorative proce­ dures. J Endod 19 89 ; 15 :5] 2- 5 16 . 84 . M agne P, Dietschi D, Holz J Esthetic restorations for pos­ terior teeth: Proctica l ond clinical considera tions. IntJ Peri­ odontics Restorative Dent 1996 ; 161 0 5- 1 19 . 85 . Dielschi D, Sprec lico R Adhesive M etal-Free Restorations. Berlin: Quin tessence, 1997 :60-7 7. 86 . Mag ne P, Holz J Stratification of composite reslorations: Systematic and durable replication of natural aesthetics. Pracl Periadonlics Aesthel Denl 19 9 6 ;8: 6 1- 6 8 . 87 . Besek M , Mormann W H, Persi C , l utz F. The curing o f comp)osites under Cerec inlays. Schw eiz Monalsschr Zahnmed 19 9 5 ; 105 : 112 3-11 28

176

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CHAPTER

5

INITIAL TREATMENT

PLANNING AND

DIAGNOSTIC APPROACH

Previous chapters have empha sized that (I ) esthetics and function are equal concern s when restoring the anterior dentition a nd (2) mod ern co n­ cepts in restorative denti stry have introd uced new so lutio ns thro ug h bonded porcelain restoration s (BPRs) that d istribute stress and involve the tooth crown as a w hole in supporting occlu sal force and masticatory functio n. The resulting biom imetic nature of BPRs is par ticular ly interesting w hen co n­ sidering the restoration of an aging dent ition ; both functio n and appear­ ance are affe cted by the physical chara cteristics of agi ng teeth. Erosion and surface wear lead to prog ressive thinning of enamel , ultimately ca us­ ing increa sed crown fleXibility and high er surface stra ins. Restorati on of tooth vol ume w ill not o nly restitute the or ig inal , yo ung er appearance of the smile but w ill al so allow the com prehen sive biomim etic recovery of the crown . This treatment o utco me strong ly depends o n the therapeutic ap­ proach chosen, the driving force of wh ich should be preserva tio n of the thin remain ing enamel. W hile a number of preparation techniques w ill lead to ma jor dentin exposur es, the princ iple

of

ena mel preservation ca n be fulfilled by the use of a speci fic approach , This chapter describes a treatment rationale that incor porates a d iagnostic template resulting from the interactive relationships be twe en the cl inician , the pa tient, a nd the den­ tal laboratory. This type of w ork stra tegy, documented wi th cli nical case s, integ rates additive w axups a nd acrylic mock-ups. The latter w ill p rovide a sign ificant a mo unt of di ag nostic info rmation a nd eco nomy of tooth sub­ strate inval ua ble to the rea lizatio n and prognosis of the fina l restora tio n.

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5

INIT IAL TRE AT MENT PL AN NIN G A ND DI A GN OSTIC A p PROA CH

INTE RACTIVE PATI ENT-O PERATO RY-LABO RATO RY RELATION SHIP S In most ca ses of esthetic rehabilitati on, the treat­ ment o b jective w ill be reached by means o f a d iag nostic effo rt. 1 The d iag nostic stage ca n be achi eved in a two­ step approach including ( 1) the elabo ratio n of a d iagn osti c wa xup and (2) the fabrication of a cor responding template to be eva luated in vivo by both clinic ian a nd pa tient. In the ca se of BPRs, a speci fic approa ch needed to be de­ veloped . Simple but essentia l tool s w ill be pre­ sented in this cha pter: the add itive dia g nostic w axup an d the acrylic mock-up, to be used du r­ ing d iag nostic steps a nd tooth preporotion pro­ ced ures for the o ptima l resto ra tion of the ag ing dentition w ith BPRs. Two elements are empha­ sized : (1) the ob jectiveness and the simp licity of the app roach and (2) the significa nt amount of d ia g nostic informa tion a nd economy of tooth substra te manda tory for the rea liza tion and pro gn osis of the final restoratio n.

I

This strategy depends co mpletely o n ade­ quate patient management a nd a clo se inter­ acti ve relation ship wi th the dental lab orat o ry. The mastering of restorativ e techniques, optim al co ntrol of the esthetic para meters, a nd adeq ua te thera peutic choices w ill significantly enhance the chances of success, but the final o utco me has a rea l impac t only if the co mmunica tio n betwee n the clinician 's and the technician 's teams is ef­ fective. This exchange of knowl edge also in­ cludes the pat ient,2.3 w ho is eva luated by both cli nician and technician a nd partici pates ac­ tively with them in the "triad of success" (F ig 5­ 1). Patient management a nd initia l therapy w ill therefore be discussed in the first sections of this chapter.

I

I FIGURE 5-1 : TRIAD OF SUCCESS AND FLOW CHART FOR SYSTEMATIC PATIENT EVALUATION AND MAN­ AGEMENT. The triad of success is defined by a har monious relationship betwee n the pa tient a nd the o peratory and la boratory teams. The restorati ve de ntist o nly represents o ne "finger" o f the o peratory tea m's "hand" in the circle o f this relation ship. Ot her "fingers" incl ude the pe riodon tist, orthodonti st, etc. A systematic approac h is proposed. Both the cl inic ia n a nd the dental technician must understand the pa tient's req uest. It is therefore recommended that the pa­ tient visit the den tal lab o ratory befo re trea tment planning beg ins. The denIal techni cian develops on esthetic status in the form of image s a nd notes. Shade ca n be documented at this stage, but it is recommended that the pa tient visit the la boratory aga in, espec ia lly w hen blea ching a nd other preliminary proced ures are probable . In the case o f d is­ co lored teeth, ad diti onal shade do cumenta tion should be ca rried out fol lowin g too th preparatio n. Amo ng preliminary la bo ratory proced ures, the d iag nostic waxup is o f pa ramount impo rtance for the initia l thera py. The diagn ostic phase represents the most crea tive a nd interactive part of the treatment, and the diag nostic mock-up must a llow envisio ning of the final o bjective. In this wa y, the crea tive effort du ring the restorati ve phase rema ins minimal and will be limited to the reproductio n of the d iag nostic mock-u p in the form of BPRs.

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INITI AL TRE ATMENT PL ANNIN G A ND DI A GN OSTIC ApPR OA CH

PATIENT MANAGEMENT BY THE OPERATORY TEAM Appropriate management and co unseling of patients with esthetic problems undoubtedly represents the most c ritica l phase of the treat­ ment. The task may be parti cularl y challe ng ing if the co nfidence of an indi vidual (wh o suffered from a previ ous therapeuti c failure ) has to be re­ co vered . A co mbined and structured manage­ ment by the dental o pera tory and the dental laborator y w ill provid e adequate ba ses for full co o peratio n from a co nfident patient. During the initial pha se, the clinician sho uld respect the following seq uence (see Fig 5-1 ):

1. Kn ow the patient. This first step aims at un­ derstanding the patient's primary request. It is of utmost imp ortance that the clini cian listen care­ fully to the patient's expla nal ions in o rder to de­ fine the main expectations. The patient must not sit in the dental chair at this stage (Fig 5-2 ). Use of models of intact dentiti ons, photographs, and fashion magazines ca n sig nifica ntly help in co mmunica ting w ith the patient.

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I

3 . Inform the patient. Based o n the aforemen­ tioned documents, the clini cian explains the ex­ isting probl ems to the patient, using the radi o­ graphs, photographs, and study casts as aids. The use of simple and comprehensible termi­ nology is essential . A patient w ho thoroughly understands the information w ill better perce ive possibiliti es and limita tio ns of the treatment. Fi­ nally, the maj or elements of the treatment o p­ tions ore expla ined . In that co ntext, demonstra­ tion models [Fig 5-2 ) and / or cl inic al pictures of o ther patients ca n be helpful in expla ining the d ifferent types of restoration s.

4. Sequential treatmen t plan. At this time , the clini cian ela bo ra tes a sequential treatment plan including possible alternatives. Duration and costs are determined. The laboratory fee should be presented separately. W hen treatment and patient mana gement are share d eq ua lly by the cl inici a n and techn ician , it is not unusual for la bo rato ry and clinical fees to be similar.

2. In itial documentation . After the patient has

5 . Final phase of initial patient management.

expressed his o r her d esires, the clini cian col­ lects the ba sic elements of an inilial documen­ tation , ie, a radi ogra phi c survey and a system­ atic cl inical examination [eva lua tio n of periodontal and end od ontic co nd itions, exist­ ing restorati ons, etc ]. Photogra phs and study casts, possibly mounted in an articulator, com­ plete the initia l documentati on.

This stage is not clini cal but involves a di scus­ sion in w hich the cl inici a n explain s the para me­ ters of treatment (ob jective , sequence, duration , co sts, limitations, prog nosis, a nd alternatives) .

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FIGURE 5-2: FIRST CONTACT WITH,THE PATIENT. Patients often feel dominated and restroined if they.sit in the'den­ tal chair. Cornrminicotion can be op timized by "same-level" seating (middle), Useol photoqrcphs. a rid fashion mag­ az ines helps.the clinlcionu ndersto nd lheIndlviduc ls lifestyle a nd tcistes(top)" Simulation model sqndexamples of restora tio ns cn d.lntc ct-dentltions he lp op timizethe patient's informatio n (bottom) ,

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INITI AL TRE AT MENT PL A NI\JIN G AN D D IA GNO STI C A p PROAC H

PATIENT MA NAGEMENT BY THE LABORATOR Y TEAM

The development of sophistica ted techniq ues for esthetic restorations increas ing ly involves close

The first co nta ct between the pati ent a nd the den ta l labo ra to ry is o f primary impo rtance . Un­

cooperatio n with the denta l laborat o ry. The pa ­ tient should visit the cera mist as ear ly as possi­

fortunately, in da ily practice , such an approach is frequently negl ected . Undou btedly, man y cl i­ nician s hesitate to send their pati ents to a den­

ble durin g the initial stages of pa tient manage­ ment (see Fig 5- 1). The first visit to the dental la bo ra to ry is essential for tw o reason s: (1) hav­

ta l la borator y, perha ps because they fear inad­ eq uate reception a nd lack of hyg iene. Fo r tha t rea son , den ta l tech nicia ns must be ed ucated

ing so me know ledge a bo ut the technica l as­ pects , the individ ual wi ll better understand the treatment that has been pro posed, and (2) it of­

o n how to a pproach the pa tient. A dental la b­ o ra to ry should have a special area for pa tient

fers the cera mist the opportunity to complete an initial documentation , w hich rep resents the ba sis

co nsulta tio ns that includ es basic items, such as a co mfortabl e chai r, sink w ith a hand-di sinfect­

for the w o rking pla n. Pa tient man agement by the labo ratory is q uite similar to that by the o p­

ing device, exa minatio n gloves, a nd a protec­ tive napkin (Fig 5-3 ).

erato ry. The cera mist's documentatio n co mprises a photog raphic status and shad e selection.

FIGURE 5-3 : RECOMMENDED LABORATORY ENVIRONMENT. This co mmercia l la boratory (O ral Desiq n C enter, M o ntreux, Sw itzerla nd) integrates a specia l area fo r the pa tient (5-30 ) The dental technicia n should never touc h the pati ent's face o r mouth w ithout wea ring examinati on g loves. A "touch-free" d isinfeclio n device (5-3b , ar row) a lso ai ds in manipula ting shad e ta bs and other ob jects w ithout co nta minatio n. Seeing the ceramist's la boratory w ith its multi­ tude of ceramic powders and sta ins 15-3c, 5 -3d ) helps the pati ent understand the fa brica tion process a nd price of these unique cera mic pieces. The patient 's ac ceptance of future treatment is sig nificantly enhanced by this visit to the la bo rato ry.

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I NITI AL T REAT M ENT PL A NNI N G A ND D IA GNO ST IC A pP RO A CH

TREATMENT PLA NNIN G A N D INITIAL THERAPY Treatment planni ng co nsists of determining the sequence o f treat ment and coo rd ina ting cli nica l and tech nica l interventio ns. The clini cian de­

of

fines the number

cl inica l sessio ns corre­

sponding to the sequence o f trea tment. On this basi s, the la bo rato ry is infor med about the ini­ tial treatment pla n an d the da tes of the princ i­ pa l restorat ive phases: w ax up, fina l impres­

in the next sec tio ns ca n sig nifica ntly influence this phase . The follo w ing interventions ore most freq uently underta ken w hen esthetics plays a key rol e : mucog ingi va l surgery, bleac hing , o r­ thodo ntics, an d di rect compos ite restorati ons.

Mucogingival surgery

sion s, cl inica l trial s, and fina l placement. The initial phase o f trea tment typica lly com­ prises preventive, pe riodontal, a nd opera tive asp ects, w hich ore too o ften neg lected . They repr esent essentia l "touch-ups," so metimes o nly minor correctio ns that w ill have a sig nifica nt ef­

Adeq ua te health and mo rphology of the peri­ o don tium or e responsible for 50% of the final esthetic o utco me. Eve n the best restorati on w ill not be a ble to com pe nsate for pe riodontc l de­ fects. In some situa tio ns, g ra ft-type interventi o ns (Fig 5 -4 ] o r mino r remod eling of gi ng iva l con ­

fect on the ~i n al outcome . The d ia g nostic

to urs (see Fig 5-6 ) can ensure the final o utco me

waxup a nd cor respondin g moc k-up descr ibed

of the

resto ro tions.

FIGURE 5-4: CONNE CTIVE TISSUE GRAFT TO IMPROVE GINGIVAL CONTOUR BEFORE REALIZATION OF BPRs. There is sig nifica nt tooth agi ng and ena mel thinning of the right a nd leN central inciso rs a nd the left laleral inci sor, plus on unsig htly block triang le between the central inc iso rs (5-4 0 , 5 -4 b) Progressing recession around the left central a nd latera l incisors is responsible for asymmetric g ing iva l contours (5-4b ) A co nnective tissue graft from the pal ate w as first placed using the "envelo pe" techniqu e4 5 (clin ician , Dr Jea n-Pierre Ebner, University of G eneva). Und ermining par­ tial-thic kness inc isions create Ihe envelope . Vertica l releasing inci sio ns a re not necessary [5 -4 c). The co mbined ep­ ithelia l a nd connective tissue g raft is plac ed over the de nuded areas, and the fla p is sutured w ith 7-0 po lypropylene sutures, the graft being secured w ith two add itio nal sutu res (5-4 d ) O ne-w eek posto perative view (5-4e ). C o mpariso n of preope rative (5-4f) a nd 3-mo nth postoperative view s (5 -4 g ) show s co nside ra ble enhancement of g ing iva l contours. The preexisting Clo ss 5 co mposite w as removed except for the most co ronal part , w hich temporar ily suppo rted and maintained the gi ngiva l profile. A specific di agnostic phase was then carried out, follow ed by preparatio n of the in­ volved teeth fo r laminates, some aspec ts of whic h are deta iled in Fig 6-22 . Maximum interdental preparatio n a llowe d the ce ramic to be extended w ith "mini-w ings" to close the interdental bloc k triangl e (5-4 h; see a lso Figs 6-20 a nd

6-2 1).

186

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INI TIAL T REATM ENT P LANN ING AND DI AG NOSTIC A p PROAC H

Bleaching

5 ). In some rare cases, orthog nat hic surgery might be indica ted in conjun ction w ith o r-

The o ptica l co nd itio ns o f und erly ing d enta l tissues can have a negative influence o n the fina l esthetics; blea ching proc edures a llow

thodontics, w hich requ ires specia l treatment planning (see Fig 5 -1 2) .

reesta b lishment o f a tooth color that will facil itate integra tion of the BPRs [see Fig 4-7), The treat ment of non vi ta l di scol o red teeth to be resto red with BPRs is recomm end ed exa ctly as described in Chapter 3 , The restora tive phas e must be delayed for 2 to end

of

b lea ching be cause

4 w eeks after the

of

the ln hibi linq ef-

fect o f oxygen resid ues on the bo nd streng th o f co mpos ites. The sa me protocol is followed for vita l ble a ching ,

Direct composites Min o r modi fica tions o f neig hboring teeth are o ften nece ssary before pla cin g venee rs. A typical situatio n is the o ptimiza tio n of latera l inciso r shape and vol ume before veneering central inci sors (Figs 5-5 and 5 -6 ). Lateral incisor s are ideal targets fo r freehand applica tion of co mposites. C o rrectio n of sha pe and position ca n be easily add ressed w ith direct co mposites

Orthodontics and orthognathic surgery Realignmen t

of

teeth to be veneered is g ener-

a lly undertaken be fo re the restorative phase . However, the provisional crow ns [see Fig 4- 12)

w hen the resto rative material is fully supported by intact underlying enam el, and lateral inciso rs are norma lly not sub jected to sig nifica nt functio na l loads.

o r "touch-up" composites may improve crown

The wa xup and cor responding acryl ic mock-

sha pe a nd faci litate the fine position ing of eac h tooth by the o rthodontist; the latter must, in turn,

up help sig nifica ntly in detecting a nd correc ting minor problems of crown shape and length in neig hboring teeth (Figs 5-5 and 5 -6).

be g Uided by the o rthod o ntic setup (see Fig 4-

FIGURE 5-5 : FREEHA ND CO M POS ITE TO ENHAN CE CRO WN SHA PE OF NEIGHBORI NG TOOTH PRIO R TO PLACING VENEERS . Preliminary mod els (5-5a , 5 -5b; orig inal situation and dia gnostic w axup, respecfively) show the recovery of crow n length o f both central incisors. This situation is tested in vivo using a removable ac rylic mock-up derived from the waxup (5-5c to 5-5 elltechnique described in sections that follow) . The length of the central incisors is adeq uate in relation to low er lip co ntour, but the mock-up reveals insufficient length o f the left lateral inciso r (5-5e), the clinical crown of wh ich also presents an inad equate Wid th/heig ht ratio (5-5f). A silicon index of the w axup reveals the missing tooth substance (5 -5g ). After ena mel etching and bonding , a smal l a mount of den tinlike co mposite is placed and cured (5-5h ), then covered by translucent enamel and incisal shades using the silicon index as a mold to be pressed onto the incisa l edge [5 -5 i, 5-5 jl. C rown shape is sig nificantly enhanced by this procedure (5 -5k) Such detail is essential to the outcome of porcela in veneers on neig hboring central incisors and show s harmony wi th the lowe r lip 15-51) Other aspects and fol low-up of this case are presented in Figs 4-8 and 6-3.

188

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FIGURE 5-6 (CONTINUED) : DETAILED ,STEPS. Preliminary procedures (first clinica l session) are described in Figs 56d to 5-6m. Articulating paper has bee n rubbed on the surface of the right lateral incisor to hig hlig ht the missi ng mesial crow n volume and co rresponding transition line ang le (5'6d) . Freehand bonding was carried out a fter place' ment of a deflection cord and enamel etching (5-6el .The tooth ca n be slightly enlarged by the add ition of enamel. like and incisa l co mposites (5-6f). The modi fied too th shape shows adequa te mesial crest qnd mesio l volu.me(5-6g ). Second , the left la teral incisor is too short (5-6h) a nd must be modified wi tH the same technique as described in 'Fig 5-5, using the silicon index of thew axup (5-6 i). Immedi a tely postoperative, the tooth is still dehydrated (5-6jl but dis.plays a form that is now compatible wi th the planned increase of the central incisor length. Fina lly, the g ingivOi contour around the left central.incisor is too flat (5-6k). A minor gin g ivectomy w as necessary (5'61). Two w eeks. later (5o rn ], the pa tient is ready for tooth p repara tions. Step-by-step tooth prepara tions for this par ticular case ca n be found in Fig 6-10 and 'the fab rica tianof m~ster costs and ceramic layering in, Figs 7-4 to 7-8 . "

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intrc orcl -view s show a harmonious , r~lotio ns h ip'belV'Veen teeth a nd soft tissue's (5~6n ; 5-6 0). .Preoperative face and smile (5-6p ; 5-6q) for direct comparison with the new situ, alion .(5-6r, 5-6s).' ..

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IN IT IA L TREATMENT PL A NNING AN D D IAGN OST IC ApPR OA CH

DIAGN O ST IC WA XUP General considerations

dure , a uniform tooth reduction of a t least 0. 5 mm is per formed using d ia mo nd burs wi th

Ena mel is a high ly spec ia lize d tissue . It has been particularl y va luable to the cl inicia n since

cal ibra ted ring s. A nother cla ssic preparation method , using the preexisting tooth surface as

19 5 5 , w hen Buonoco re proved it to be a n es-

a gUide , co nsists of takin g silicon index es o f the

sential substra te fo r bondinq ." Today, the predi c table va lue of ena mel bonding is wi tnessed in the mediu m- to lon g-term clini cal success of porce la in veneers.7- 10

labi al surface of the unprepared tooth. Significa nt den tin exp osures are to be exp ec ted wh en such freehand proced ures are used o n inta ct

Ena mel is a brittle substra te, and its integ rity is dependent o n the crac k-arresting ca pac ity of the thick lon gitud ina lly o riented col lagen fib ers of the den tinoename l [unctio n J 1 (DEj) (see Figs 1-8a to 1-8c). Therefo re, both enam el a nd the

central inci sors, as demonstrated by Nattress et ol ." The situation is most cri tica l w hen treating ag ing denlili o ns w ith thin residual ena mel. Accord ing ly, a key element fo r ena mel preserva tion d uring tooth prepara tio n is prio r delinilion of the final tooth vo lume .

DEj must be car efully preserved d uring tooth prep arat io n.

W hen a sig nifica nt thickness of ena mel

It is extremely importa nt to identify the ena mel

tially missing beca use o f w ear o r erosion (Fig 5 -7d l, the future restora tio n should a im to resti-

IS III 1-

faci al wear pattern of teeth to be restored [Figs 5-7a to 5-7 d ). W hen the residual enamel is

tute the or igina l vo lume of the tooth that has

thin, as is the case w ith aged or wo rn inc isors,

approp riate tooth pro minence and biomi metic

prepara tio n methods using the preexisting tooth surface as a reference fo r enamel red uction are absolutely co ntra indi ca ted . The "simplified lam-

behavior of the crown" : a bo ve al l, it w ill a llow sig nifica nt preserva tio n of ena mel substrate a nd

inate prepara tio n, " w hich uses specific cutting tools to avo id so-cal led freeha nd prepara tion, 12

Therefore, a silico n index of a n add itive wa xup

is a lso contra indica ted . In the pro posed proce-

(see Fig s 6 -2 to 6 -5 ).

been lost over time. This in turn w ill restore an

suppo rting

DEj d uring

is essentia l as a refe rence for tooth reductio n

196

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FIGURE 5-7: TYPICAL ENAMEL AGING ·' AND'EFFECT ON CROWN ARCHITECTURE . Schema"

S E .V E RE

W EA R

fie incisal ,view showmq th ~ volume loss and "rounding" o f facial crow n, architecture (5-7a), Central incisors. originally present strong ena mel rid ges and 'marked transition line an, gles(5-7b , tangential fad 01 v iew), Examples of teeth exhibi ting different. ..wear ' patterns: little facial w ear w ith '. a textured surface (5-7c) or severefacial wear wi th a soh g lo~sy surface . (5-7d), Thin enamel requires special , preparation methods .using an cddi- ' tive w axup, ,

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INITIAL TREATMENT PLANI\)ING AND DIAGNOSTIC ApPROACH

Esserl'~ials for the cdditive waxup

surfaces. Because

of

their prominence, these

ridges are the first to wear off and therefore In this first stage

of

the diagnostic approach, in-

should be the first element to be restored by the

of the

addition of wax on the preliminary model (Fig 5-7g).

tuition, sensitivity, and a good perception

patient's personality should allow the dental technician to define a preliminary restorative

of

goal, As previously described for the aging

The position and arrangement

dentition, this is mostly obtained by the oddition

will influence the tooth form. The differential

of wax onto the preliminary model

(Figs 5-7e to

placement and contouring of the transition line

5-7k), This procedure requires precise knowl-

angles can easily generate the illusion of a

edge

of

the strategic elements

of

these lobes

tooth anat-

shorter or wider tooth. A special section related

omy, which can be learned through systematic

to these effects is included in Chapter 7 [Fig 7-

observation

of

natural teeth (see Figs 5-7b and

10).

5-7c; see also Chapter 2). A secondary step of the waxup procedure is to The basic tooth shapes are defined by the ver-

recreate the superficial developmental lobes

tical proximal crests. They represent transition

and horizontal components

line angles between the facial and proximal

phy resulting from the line

of surface of growth.

topogra-

FIGURE 5-7 (CONTINUED): "FINGERTIP-ASSISTED" ADDITIVE WAXUP (SAME PATIENT AS II'\J FIG 5-6). Original models showing insufficient facial volume and length (5-7e, 5-7f; see also Figs 5-60 and 5-6q). The additive waxup can be easily carried out with an electric spatula, starting with the redefinition of proximal crests and transition line angles (5-7g). The thumb is pressed onto the palatal surface and used as a quide to elongate the crests and build the missing part of the incisal edge 15-7h, 5-7i) Final views show volumes and shapes [5-7j, 5-7k). Compare with baseline views (5-7e, 5-7f) Although the main diagnostic effort was focused on the central incisors, the shape of the lateral incisors was also optimized by augmentation of the mesial crest of the right lateral incisor and slight lengthening of the left lateral incisor (5-7jl.

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I

INIT IA L T REAT ME NT P LANN ING AND DI AGN OSTI C A pPROAC H

DIAG N OST IC M O CK -U P Predicting the treatment outcome is essential when planning a substan tial esthetic reha bilitalion .' The diagnostic cno lysis is the founda tio n

of the

future thera py. N evertheless this should remain a simp le and rationa l proced ure. If subl

tle chan ges are con sidered , it is advisable to co mmunica te with the pa tient using most co ncre te de vices to avo id even the slighte st misun-

Beca use of the reduced thickness of the laminate and the intrinsica lly conse rva tive approoc h. the tooth pre parahon itself is inlimately rela ted to the final vol ume of the restoration . The in vivo eva lua tio n a nd full approva l of the template by the patient should therefore precede tooth preparation procedures. The simplest method involves fabrica tio n

derstand ing .

of an

acry lic template directly in the po tient's mouth At this stage of the diag nostic op prooch, the new vo lume of teeth must be ap proved by the po tient, resulting in tota l ag reement o n the definitio n of tooth shope, size, a nd length . In trcdilio ne l prosthodontics (full-cove rage cro wn], preliminary tooth preparat ion usually precedes fa brication of the d iag nostic tern plo te . wh ic h is used as the prov isio na l restorati on itself . I ,2, i 6, 17 Such treatment plann ing is not possib le w ith BPRs.

(or o n an intact study model) using self-curing resin mold ed o n the unprepared tooth surfaces w ith a silicon matrix of the wa xup (Figs 5 -7 1to 5-7t) . Subseq uenllv, the pa tient ca n easi ly appreciate this removable mask, A hig hly accurate silicon ind ex ca n be fabrica ted by firmly applying the materia l onto the model. then immedi ately sub jecting it to approxima tely 4 atm o f press ure durin g setting (Fig 5 -7 m). In this

waYI the silicon matrix will also present an increa sed stiffness, w hich facil itates handlin g a nd repositio ning (w hich, in turn, should genera te o nly minor excess resin).

FIGURE 5-7 (CONTINUED) : DIRECT ACRYLIC MOCK-UP (SAME PATIENT AS IN FIG 5-6) . A stiff a nd accurate silico n index mus t first be ob tained by ada pting the putty o nto the w axup (5-7 1) and immediate ly applying a pressure over 4 atm wi th a hydrauli c press, a com pactor (5-7m), or a press ure pot The silico n must ove rlap at least one tooth o n each side of the mod ified segment, but the pa lata l surfaces must remain accessible to al low premature elimi nation of pa latal excess resin (5-7n ). A thick layer of Vaseline must be applied to the teeth and surroundi ng soft tissues to prevent adherence of the acrylic resin to preexisting restora tions a nd g ingiva (5-70), pa latal a nd interdental undercuts being blocked o ut w ith sticky wax. The silico n matrix is then filled par tia lly w ith liquid resin (eg New O utline, Anaxdent), a nd the resin surface is allowed to become d ull in appeara nce (5-7p) . The index is then applied to the teefh and mainta ined in positio n (5-7q) until the resin is compl etely cured (the mock-up is usually thin and would be deformed by prema ture removal ), the oper ato ry field being cooled w ith abun da nt rinsing. l

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I

INITI AL TRE ATMENT P LA NNI NG A ND DI AGNOSTI C A p PROAC H

A common situa tion must be po inted out. W hen lookin g at the template for the first time, the patient is likely to compla in about the excessive tooth volume . This reacl'ion is norma l a nd understand a ble . The process leading to wear a nd erosio n is slow a nd extends over year s; cha nges in tooth leng th and sha pe take place progressively, w itho ut genera ting sudde n mod ification s in the patient's smile . When this long degenera tive pro cess is coun teracted by an insta nt restorati ve procedure (the mock-up) invol ving rnojor changes in the smile desig n, the pa tient can be surprised . The indi vid ua l must therefore be info rmed that an objective esthetic eval ua tion req uires a cl inica l tria l of severa l days. Accordi ng ly, the unchanged mock-up is g iven to the pa tient for assess ment for 1 to 2 weeks . Hand ling of the thin acrylic template requ ires specific instructions [see Figs 5 -9k an d 59 1). The templ ate ca n al so be temp orarily bonded by enamel spot etching if necessary. At the next a ppo intment, the patient ge nera lly feels mor e co mfo rta b le and will di scuss cha nges w ith enhanced objectivity.

Rem odeling o f the lip by the mock-up has been o bserved in some cases (Fig 5- 8) , w hich ern phcs ize the imp ortan ce of this subtle c hro no logy. Since the method is not time-consuming , modifications of the initia l di agn ostic study ca n be carried out and integ rated into a new template . Ph otographi c prints of the mock-up can be presented to the pa tient for di scussion (Fig s 5-8 n a nd 5-80). The actual tooth preparation s wi ll be pe rfo rmed o nly after the pa tient's formal approva l. The moc k-up can a lso be prepared indirectly in the denta l laboratory, w hich all ow s for more sophisticated resu lts an d characteriza tio ns (see Fig 5- 10 ). For bo th d irec t and indirect techniq ues, it is recomm end ed that simple acryl ic resins be used instead of com posite materials or stiffer resins that w ould be too brittle. Self-curing resins have optima l pro perties for a mock-up because of their e lasticity a nd favora ble handling properties.

FIGURE 5-7 (CONTINUED) . The resin template cov ers the fo ur inc iso rs (5 -7 r to 5 -7t; a preo perative view is inset for compar iso n). It ca n be eosilv unlocked a nd removed by inserting a sca ler interproxima lly. The removable acrylic mockup is g iven to the pa tient fo r a prolonged trial. It ca n a lso be bo nded by enamel spo t etching , w hich reduces the tria l pe riod to a few days . In co mbi na tio n w ith the patient's input at the end of the trial , the mock-up helps to detect defects in the g ing iva and neigh bo ring teeth a nd gUide opti mizat io n of the enviro nment (see Fig 5-6) for the future BPRs . Details of tooth prepara tio n procedures for this case are presented in Fig 6-1 0 , a nd fabricati on of master ca sts and cera mic stratification in Figs 7-4 to 7-8.

202

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INIT IA L T REATM ENT PL AN NI NG AND D IAGNOS TIC ApPROACH

PECULIAR CA SE S Retracnon/displacement of coronal volumes Und er some spec ific circumstances aim ed at retracti ng o r d isplacing the o rig ina l tooth vol ume (eg, correction of tooth position), the prev iously desc ribed a pproach is not applica ble . Such exceptional situations will requ ire pre liminary co rrectio ns of the crown shape to create the nec-

essary space for the mock-up, w hich w ill a lso act a s a provisiona l restoratio n (Fig 5 -8) secured by ena mel spot etching and light-cured unfilled resin (spot etch ing is d escribe d in Figs 6-25g to 6-25 i). Only after the pa tient's app rova l or o b jective modi fica tion of the mock-up con fig uration can the tooth preparations be final ized .

FIGURE 5-8 : CORRECTIONS OF CROWN SHAPE BEFORE MOCK-UP. Initial clinica l view s showing combined ind icati ons for porce lain veneers: restitution of incisa l prominence and restoration of previously fractured crow ns (5-8a to 5-8c l. Composite restorations o n Ihe facial a nd incisal po rtio ns of the maxillary righl central inciso r to left ca nine and the ma nd ibular rig ht central and lateral inciso rs are w o rn. Note the tilting of the maxillar y central incisors (5-8b) . The treatment ob jective w as de fined by a n add itive w ax up proced ure. The cor responding sectio ned silico n indexes are placed intraorally (5-8d , 5 -8e). N ote the repositioning and shift of the midline (interincisalline) and Ihe insufficient space left for the mock-up (arrows), especia lly a t Ihe level of the left cenlra l and laleral inciso rs. These areas are mar ked , and corrections of preexisting com posites are carried out (5 -8f) to create adequa te space for the d irect acr ylic mock-up (5 -8g ]. This thin removab le mask (5 -8 h, 5 -8;) is g iven to the pa tient for a we ek. If necessar y, the mock-up can be sta bilized wi th unfilled resin and ena mel spot etching. Significan t improvements w ere o bta ined w ith this simple technique, which allowed eslablishmenl of co rrect too th length a nd smile line 15-8 i, 5-8jl.

204

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'FIGURE 5-8 (CONTINUED): MODELING OF THE LOWER LIP BY THE MOCK:UP. Rest~rati on of incise]. prornjnence generated by the mock-up is ,often .occornported by rernodelinglnatural reconJouring)of ,the k)~e rli p; cor(lpore flot lip at baseline (S-Sk)with contoured lip -ol "mock~u p dayn (S-S I ) , a nd more contouredl ip 1 week later IS-Sm). M odifications Of the final objective can,be easilya nd:'o ~ jec t ,ve ly discussectusing '~ bebre : cmda fte r"' , photoqroph«;prini~ olthe .rncckup, w hich qre presentedjothe patient (S-S n,'S:Sq). ln the present case; th is'approach revealed th ai the pati ~ntexpeded softer, more rounded shapes. Toothpreparations were gU ided by the silicon indexes. The left central incisor hod to be prepared more extensiv:ely because Of its rnore facial position (5-8p). Tooth reduction .wos minimal on other teeth , Immediqtefinal views end srn ile ()-8q to ~'S s) ,show the,objective modifications cornporedio the diagnostiC mcck-up..Correspondinq-snuotion after 3yeorsof clinicolservice (5-Si) : N ote the'stability and health of the soft tissue. SCltisfac;tion and absolute integration of the, res'tora t ion~ are evident in the patient's smileand face ' (S~S r) ", ," , ' ' .' "

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I NITIAL T REAT M ENT PL A N N ING AN D D IA GN OST IC ApPROACH

Mock-up for demanding patients

sta ins to characterize the interdenta l area a nd

The mock-up methods presented in Figs 5 -7 a nd 5-8 are very simple and time efficient.

a liqui d g laz ing resin to soften the surface [Fig s 5 -9f to 5-9i ). The brown interdenta l staining increases tooth indi vidua lity ("separati on " effec t) ,

Some elementar y steps, however, can

be

a nd the soft g lossy surface of the g laze im-

added to this bas ic technique to improve the pa tient's co mfo rt and help him o r her envisio n the fina l g oa l. Figure 5 -9 first seems to describe a trad itiona l di rect mock-up (Figs 5 -9a to 5 -ge), but it co uld be eas ily enha nced w ith lig ht-curing

proves the surface reflect ivity and patient's comfo rt. The same "tricks" ca n be appli ed to fabricate highl y attractive pro visional resto ratio ns (see Fig 6-26) .

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FIGURE 5-9: ENHANCED DIRECT MOCK-UP. Four BPRs have been plann ed fo r the maxillary incisors of this patient The regular moc k-up protocol is applied first: block-out of pal atal undercuts and interdental spaces with sticky wa x, insulatio n o f teeth and soft tissues w ith a ge nerous layer of Vaseline (5 -9a ), load ing of acr ylic resin into the silicon inde x (5-9b), a nd place ment over the teeth w ith finger pressure until curing is co mplete (5-9c). The mock-up is left in place and the thin laye r of excess resin is removed with a sca lpel by incising the g ingival sulcus (5-9 d , 5-ge). The mock-up IS first characterized by infiltrating the con nectio n area w ith brow n lig ht-curing stains [Kolor Plus, Kerr) to provid e the effect of indiv idual teeth (5-9f) Followinq curing of the interd ental sta ining , the mock-up is gla zed w ith a low viscosily resin (Skin G laze , A naxd ent) a nd lig ht-cured . Complementary curing through a layer of glycerin jelly (5-9 g ) is required to o btain a pe rfect g loss (5-9 h). The moc k-up ca n be retrieved only at this stag e; ge ntle use of a sca ler releases the acrylic resin (5-9i) , The mock-up is thin and delicate a nd can be g iven to the pat ienl in a film bo x [5-9 il.

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FiGURE 5-9 (CONT(NuEDj. The' pa tient h;'s bee ~ instructed to insert and remove the template using herJingernai ls " t5-9k~ 5,91) , The' mcc k-iiphcs.helped to define ,new forms: symmetry cind de creosedcrownwld thz'heiqh t r,0tios (com,pare 5~9rri end 5 -9n); as we ll as improved relationship wit h lhelips (co mpare 5-90 and ,S-9p ) and f ace and personality of the pa tient (compare 5 -9q and 5 -9r) , The patient is satisfied , but some c h anges ~ere' discussed and transferred to the final BPRs . Several, prints of the mock-up were presented' to the pa tient and used.to specify these changes , ,(5 -9 s), Cor responding final clinicc l view wit h the defin itive BPRs(5;9t). Ot her views of this ca se can be found in Fig s '6-18 and 8-10: " " .. .

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II\JITIAL T REAT ME NT PL A N N ING A N D DIAGNOSTIC ApPRO A CH

Extremely dema ndi ng pa tients can be co nfused by the insufficient esthetic qua lity of the trad itio nal mock-up , even in its enha nced form. They are una ble to o b jectively eva luate the template unless more tran slucent, slrotilied acry lics are

high probabi lity of reestabl ishing the patient's co nfidence. This aspect of ~he relatio nship is

used . Here, preliminary tooth preparations and impressio ns are best ind icated for the fabr ication of an elabo rate template using, fo r instance, a sandwich techniq ue (Fig 5-10).118 Such diagnostic co mmitment may seem exaggerated ; how ever, it offers maxi mum predictab ility of the treatment outcome, resulting in a

muc h mo re costly to miss the esthetic target and have to do the final ce ramic w o rk over agai n. Instead , the addi tiona l effo rt gi ven to the d iagnosti c template provides pred ictability and assura nce to the dental technic ia n w hen fa bricat-

price less w hen co mpared to the possib le conseq uences o f inad eq ua tely defined treat ment ob jectives. As a ma tter of fact, it w o uld be

ing the final ce ra mic pieces.

FIGURE 5-10 : INDIRECT DIAGNOSTIC TEMPLATE FOR AI"-J EXTREMELY DEMANDING PATIENT. Recovery o f esthetics and function of a nterior teeth was the driving force for placing BPRs in this pa tient (5-1Oa; see also Fig 4 -6). Because the co nventional di rect mock-up did not satisfy the pa tient, prelimina ry tooth preparations and impressions (5-10 b; clini cal situatio n just befo re takin g final impressio ns) were carried out to fab rica te an indirect template reprod ucing the exact shape of the diagnos tic w axup (5 -1Oc] Ac rylic ma teria ls w ith d ifferent translucency (ena mellike an d denlinlike] w ere used in a sandw ich technique (5 -1Od) i .1 8 Due to incompa tib le insertio n axe s, the template w as d ivid ed into Ihree seg ments (5-1Oe) These provisio nal restoration s w ere pla ced two -by-two using a clear provisiona l luting cement (see Fig 6 -28 ). The three ac rylic paris w ere Ihen co nnected a nd locked into position by adding liq uid resin in the pa latal embrasures. (Fig ures 5- 1Oa and 5- 1Ob are repri nted fro m Mag ne a nd Douglas19 wi th permi ssio n.)

212

I N D I R E C T D I · A G N O S TI C T E M P LA T E.. '

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FIGURE5-10 (CONTINUED). The pa tient's satisfaction and confidence were established through this indi rect diagnostic template, as seen in the 'patient's smile (5- 1Of, 5 -.10g; compare '5- 1Of wi th the baseline photograph overlay) and face (5- 1Oh] . Because tooth prepa rations did not require modi fications, the fina l po rcelain restorations could be fabricated w ithout additional cli nica l steps, and the intact origi nal Single dies w ere used (5 -lOi; see Fig s 7 -] to 7-7 for fab rication of master models). Final view s follovJing def initive insertion of BPRs( 5: 1O] to 5 -1 0 1) . O ther views of this case are presented in Fig 4-6. (Fi gure 5-1 OJ is reprinted from Magne and Douqlcs " wi th permission.)

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INI TI AL T REATM ENT P LANN ING A ND D IAGNOSTI C A p PROAC H

BPRs combined with traditional full-coverage crowns

ra mic restorati ons are produced first, de fini-

It is not uncommon to encou nter situatio ns in w hich preexisting full-coverage crowns must be

tively bo nded , and combined with acry lic provisio na ls o n teeth requiring full cove rage (Figs 5 -11 k to 5 -1 10).

p laced in combina tio n w ith BPRs o n nei gh bo ring [o r a ntag o nistic) teeth. Figure 5- 1 1 depicts

3. Restorative phose II. About 2 to 4 w eeks

a d ifficult case requiring a tradit io nal po rcela infused-to-metal (PFM) cro wn on one ce ntra l incisor an d a porcela in veneer on the other. It w o uld be diffi cu lt for the de ntal techn ician to fabricate these different type s of restoration simulta neo usly. The c ha lleng e lies in the fact that the esthetic integ ratio n of a BPR is high ly related to the underlying substrate, ad hesive cementatio n, a nd hydra tion condi tio ns. O n the o ther hand , the final esthetic o utco me o f a PFM

2 . Restorative phose I. Definitive ad hesive ce-

later (the estimated time required for sta bilization of color/ hyd ra tio n of teeth w ith bonde d restora tio ns), a separa te imp ress io n is ta ken for replacement of the rema ining acrylic crowns by defini tive trad itiona l cro wn s (either PFM o r a llcera mic). Shad e selection an d pho togr ap hs should be repeated at this stage. In this way, the ce ram ist ca n accurately reprod uce the a lread y "integ ra ted " adh esive restora tio ns [Fig s 5 -1 1p a nd 5 -1 1q ).

crown (or o ther kind of o paq ue, metal-free cemented crown ) is o nly minima lly influenced by the tooth, the under lying cement, o r hyd ra tio n co nd itio ns. A spec ia l seq uence must be adopted to facilitate the ce ra mist's work.

For the case in Fig 5- 1 1, inversion o r simplifica tio n o f this seq uence [ie, by proceed ing to a sing le imp ress io n a nd simultaneous fa brication of definitive restoratio ns on bo th ce ntral incisors) would have resulted in a n unpred icta ble

1 . Diagnostic phose. Ina ppro priate crowns are elimina ted and repla ced wi th direct pro visio n-

esthetic o utco me due to the d iffere nt integration modes o f PFM crowns and BPRs.

a ls (Fig 5 -1 1c) using , fo r insta nce, prefa brica ted resin shells; the trad itional acrylic mockup is then carried o ut o ve r preexi sting restorati o ns a nd teeth (Fig s 5- 1 1d to 5- 1 1 j).

FIG URE 5-11 : COMBINED PFM CROWN AND BPR s. This pa tient (5-1 1aJ presents w ith a n ope n gol d crow n on the rig ht la teral inciso r a nd a n o ld resin crow n on the left centra l incisor (5-1 1b). A fter remova l of the latter, a di rect provisio na l acrylic was placed ; removal o f Ihe open crown did not req uire provisio na lizal ion [5-1 1c). Two po rcela in veneers w ere planned fo r the right centra l a nd lateral inciso rs, a nd a PFM crow n for the left central inciso r. N ew vo lumes, includin g longer central inciso rs, w ere caref ully designed by the wax up (5 -1 1d ). The final trea tment ob jective w as tested in vivo by the fa brication of a tradi tional mock-up (5-1 1e to 5- 1 1j; sa me techniq ue as in Figs 5-7 a nd 58) A thick layer of Vaseline was p reviously a pplied to the teeth to avoi d ad hesio n betwee n the acrylic mock-up a nd the preexisting oc rvlic resto ration (5-1 1e)

216

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FIGURE 5-11 (CONTINUED), Fo llowing th~ pa tient's approval of the mock-up (5-11 i, 5-11, j), the rig ht central a nd latera l incisors w ere p rep o redfo r BPRs, (5- 1 1k), im med ia tely folJ()wed by fina l impressio \ls, The ceram ist fa bri cate d the two fina l,BPRs a long w ith a "sandwich" acrylic prov isional for the leficen tral incisor (5, 1,111"T he nex t -sessio n co nsisted.o] the try-in a nd fincil od heslveploceinentol the cera mic restor a tions a nd provisiona l cernenro tlo n o f the a crylic c rown; note the interd enta l' b lock trian gl e between the ce niraliricisors (5- 1 1m). Tw owee ks lorer, the soft tissues have matured (5' 11 n; no te perfect closing oli nterdentc l space), a nd the n ew ly design ed smile a lrea dy b lend s wi th the pa tient's face (5- 11 0 ), The PFM .crown o n the left ce ntral incisor w a s fa br ica ted o nly a t thi s fina l stage (5-1 1 p]. fo llow ' ing a seco nd impression , Wi th this pa rticular seq uence , the dental technic io nwos o ble.to fa bri ca te '0 PFM that closely resemb les the pree xisting BPRs (5 - 1 1q) , '

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INITIAL TREATMENT PLANNING AND DIAGNOSTIC ApPROACH

Special considerations related to orthodontic therapy

depicts a case

of

severe Class II division 1

malocclusion (dental and skeletal) treated by combined

orthodontic/orthognathic

surgery

Incisal edge wear develops in a specific pat-

(Figs 5-12b and 5-12cl. In the presurgical

tern related to the tooth position and long axis.

stage, space analysis required extraction

of

of a

When BPRs are planned subsequently to ortho-

mandibular incisor and stripping

dontic movements, the orthodontist should po-

maxillary teeth. The patient was referred only

sition teeth ideally, according to their main axis

at the end

(see Fig 2-2cL crown emergence, and gingi-

12d to 5-12f). Crown shape and length still

val contour. Preexisting wear facets and incisal

appeared inappropriate, as illustrated by the

edge configuration must be ignored at this

inverted incisal line (Figs 5-1 2g to 5-1 2iL but

stage.

this problem is easily corrected with the future

of this

extensive treatment (Figs 5-

restorations. Most important, tooth

of

anterior

positions

this approach, the dental com-

and gingival contours were favorable and al-

position may appear esthetically displeasing

lowed a traditional additive diagnostic proce-

(immediately following orthodontic treatment)

dure. Two consecutive mock-ups were required

because incisal edges no longer conform to

to reach a satisfactory situation (Figs 5-1 2j to

the newly designed occlusal plane and smile.

5-1 2ql, which was subsequently reproduced in

This is normal and will be resolved subse-

the form

As a result

of four

BPRs (Figs 5-1 2r to 5-1 2y).

quently by restorative procedures. Figure 5-1 2

FIGURE 5-12: APPLICATION OF BPRs FOLLOWING COMBII"lED ORTHODONTICjORTHOGNATHIC SURGERY. The patient originally presented with a Class II division 1 malocclusion, clearly apparent in her face and smile (512a). The extraction of a mandibular incisor and stripping of maxillary anterior teeth preceded orthognathic surgery. The releradiograph clearly demonstrates the presurgical skeletal defect and marked overjet (5-1 2b) Adequate skeletal and dental relationships were obtained lollowinq a bilateral sagittal split osteotomy (5-12c). Intraoral views taken after removal of the orthodontic appliance reveal adequate tooth position and favorable periodontal architecture; tooth forms, however, suffer from the stripping of proximal surfaces [5-1 2d to 5- 12f) The configuration of incisal edges was inadequate (reversed) as compared to the lip line and smile (5-12g to 5-1 2i) A first waxup and its corresponding mock-up were carried out to restore a cohesive incisal edge line (5-1 2j to 5-121) The patient was pleased but still requested longer incisors (5-1 2m, 5-12n). A new template was fabricated and resulted in a harmonious relationship between the lower lip and incisal edges (5-120, 5-12p); the patient was completely satisfied. The final incisal edge elongation was approximately 3 mm; this objective is now well defined (5-12q, bottoml; compare to the first waxup (5-12q, center) and initial situation (5-12q, top) (Figures 5-12h, 5-12j, 5-121, 5-120, and 5-12q are reprinted from Belser et al 20 with permission)

220

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FIGURE 5-12 (CONTINUED). Tooth .preporotions iu~tbeforetaki~g final impressions (5-12r). Firialintraoral.views of BPRs demonstrate the -restored coronolvolume and length (5-1 2s to 5-12u) that exccilvreproduce the diagnostic template. Therefore, the patient w as not surprised to feel the comfortable harmony of the new ly designed incisal edges ~ ' w ith her lower lip (5-12v, 5- 12w).As often.seen in such cases, tra nsformation Of the smile also results in significant ' changes in hairslyle(5-12 x, 5-12y) . The before/after bloc k-ond-whne reproductions help to understand the cohesive force of t he incisa l edge and lower lip conformiiy ' ( 5~ 1 2 z , 5-12()a). O ther aspects of .this case m e found in Figs ' 6-25 a nd,Fig 7-10 . (F igure 5-12w is repri nted from Belser et al 2C w ith permission.) ." .' '. '.

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I

INITIAL TREATMENT PLAI\INING AND DIAGNOSTIC ApPROACH

SUMMARY OF DIAGNOSTIC APPROACHES In all cases, the first stage involves redefinition

envisioned therapeutic objective only after pre-

of the desired tooth morphology (waxup) and

liminary preparation of the teeth. The subse-

of the

surrounding soft tissues on the

quent mock-up will act as a provisional. If the

study cast. In a second phase, the diagnostic

first preparations were only preliminary (as in

effort is evaluated in vivo. Three clinical situa-

Fig 5-81, they must be corrected before the final

eventually

tions can be distinguished (Fig

5-13):

impression (Fig

5-13, middle column, dotted

frame).

1. The tooth volume has to be redefined via augmentation (see Figs 5-7 and 5-9). This situation is the most frequent and provides the op-

3. The patient requests a more sophisticated template (Fig 5-10). In these complex preoper-

tion to fabricate a diagnostic acrylic template

ative situations, it appears justified to fabricate

directly in the potienl's mouth [onto unpreoored

transient restorations in the dental laboratory

teeth) using self-curing acrylic resin applied in a

after obtaining a precise impression. If the

silicon matrix.

preparations prove adequate, the same impression can subsequently be used for the pro-

of

2. The tooth volume has to be redefined via reduction/displacement (see Fig 5-8). This situ-

duction

ation is rather exceptional and offers the possi-

and a new impression taken (Fig

bility

224

of

a diagnostic in vivo evaluation of the

the master casts. If the first prepara-

tions were preliminary, they must be corrected column, dotted frames).

5-13, right

.'

Aug ment Fina l·Volume

Reduce Fina l Volume

Fabricate Ind irect Template

Waxup

Waxup

Waxup

Intra o ra l mock-up

Preliminary too th ' .prepara tio

Preliminary tooth preparatio

.. . . ... .. ..

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Final tooth prepara tion"

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. Impression

Intraoral mock-up (= provlsio nols] .

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Fi~OI impression (+, di rect provisio nols

.. ..

:.,' .. : Final tooth preparation

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Final restoration

(+ di rect provislo nols)

~

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FIGURE 5-13: SUMMARYOF POSSIBLE TREATMENT SEQUENCES. . \ .v.

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I

INITI AL TREATMENT P LAN NING AN D DI AGN OST IC A p PROA CH

C LINIC A L PHOTOGRAPHY O nly a limited number

of

the a fo rementio ned

ob jec tives would be possible wi thout the use of adequa te clin ical pho tog ra phy equ ipmen t. As the say ing goes, "A picture pain ts a thousand words," a nd that powerful princip le must be used to optimize co mmunicatio n. A n idea l situa tion is crea ted w hen bo th the o pera tory and the la boratory are using similar equi p ment, es-

The most important feat ure of the bod y, w hether tra d itional o r numeric , is the a bility to read flash on the film/ sensor pla ne of the ca mera and to set the pro per fla sh intensity for co rrect ex posure . This essential feature is ca lled "thro ug h the lens" (Til ).

pecia lly in the case of so-ca lled telede ntistry, ie, w hen the la bora tory is located in a nather bui ld-

The lens

ing , c ity, o r sta te . In this situa tion , photogra phic

An adeq uate focal length fo r clin ica l dentistry

slides, w hen taken appro priately, w ill save the pa tient a number of visits to the laboratory. C a mera bod y, lens, and flash system are criti-

seems to be 105 mm, w hic h a llow s for an o ptimal working distan ce and minima l image disto rtio n. The lens must o ffe r a 1: 1 magnification

ca l eleme nts to be cons idered (Fig 5 - 14 ).

ra tio , w hich ca n be ea sily inc reased to 1: 1.5 w ith an add itio na l close-up lens. M ax imum focus depth is o bta ined by selec ting a mini-

The camera

body

mum aperture o f f2 2 to f3 2 . A 2 x teleconverter can be a ttached to o bta in a 1:3 repro-

The bod y mig ht be the least sig nifica nt part of the system. Sing le-lens reflex ca meras (SLR) can

duction ratio . In this case, the aperture must be

be either nume ric (SLR di gi ta l) o r lrc d itio no l (SLR 35 mm). M odern 35-mm ca meras feature

focus dep th is expected . SO lTl e 105-mm lenses ca n be used a lone lie . w ithout additiona l

a built-in motor d rive (auto ma tic odvon co] . au-

lenses) for pa tient port ra its. Fo r this spec ific sit-

tom at ic film loadin g , a nd a uto ma tic ASA setring , w hich elimina tes ma ny erro rs usua lly

ua tio n, f2 .8 a perture is selected , g iving a soft a mb ience (thro ug h the reduced focus depth)

made by the novic e. In ei ther d igital o r con-

a nd ena bling the use

ventional SLR camera s, it is recomme nded to

of the

inc reased (eg, to f 16 L and a red uctio n in

of the

po int ligh t in spite

increased working d istan ce .

use a mode of exposure w ith p rior ity to the a pe rture (d ia p hra g m). This w ill ena ble manual selec tio n o f different f-sto ps to gene ra te d ifferent focus de pth.

FIGURE 5-14: STANDARD PHOTOGRAPHIC EQUIPMENT RECOMME NDED FOR ESTHETIC DE NTISTRY. The system consists of a traditional body [SLR 35 mm ), a dual-point light [TILcompliant), and a 105-mm macrolens (5-14a). This SLR digital body (5-14b; FinePix S1Pro, Fuji) can be used with th e same lens and fl ash system illustrated in 514a. II is equipped with a 6-million-pixe!-capable charge-coupled device and includes a regular viewfinder (arrowhead) and [iquid crystal display screen. Reg ular film is replaced by memory cards, which provide immediate data access (5-14c).

226

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I

The

INITI AL T REATM ENT PL ANN ING A ND DI A GN OSTI C A p PROAC H

flash system

two different purposes. The following general principles must be known (Fig 5-14e) :

Dua l-po int light systems (see Fig 5-1 4 a ) represent an idea l co mpromise to simultaneou sly pro-

• Th e poi nt light is a three-dimensional light that generates shadows, optim ally revealing texture, sha pe, and con tour; it is best used for a n-

vide adequate di stributio n of light , yet a llow fine three-dim ensional reproductio n of tooth vol-

terior intraora l views, smile, face , and casts (in-

ume (Fig 5- 14d) .

clud ing laboratory w o rks). The flash must be compliant w ith the TIL ca m-

• The ring lig ht generates a d iffuse a nd shad owless light that hides no part of the sub ject (Fig 5-14e); it is best used for surgery, po ste-

era, wh ich co ntrols exp osu re. Typical lig hting for macrophotogra phy includes either point lig ht or ring light. These two lig ht so urces present fundamental d ifferences a nd are used for

rior intrao ral mirror pictures, and pa thology photography.

D U AL -P OI NT

"'.

L I G H T

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5-14d

FIGURE 5-14 (CONTINUED) : IDEAL LIGHT SOURCE-RING LIGHT VERSUS DUAL-POINT LIGHT. This view results from the co mbination of a vertical dual-point light, a 10 5-mm lens, a nd an additional close-up lens, provid ing a 1: 1.5 magnification ratio 15-14d ); flash reflections enhance the three-di mensional nature of the tooth by outlining the mesial transition line angles (dotted areas), yet providinq adequate perception of surface texture (circled). Compara tive views (5- 14 e): note the flatness of image s produced with ring light as compared to that generated by dual-point light.

228

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I

INITI AL TRE ATMENT PL ANNING AND DIAGNOSTIC ApPRO A CH

SHADE DOCUMENTATION It is not the a im of this section to cover the extensive top ic of color in dentistry but simply to provide the reade r w ith some principles that may generate significan t improvements.

pies w ill remain unchan ged . These principles are di scussed in a rational approach using currently ava ilab le tools, ie, d igital photographs, shade ta bs, a nd a shade -map pi ng sheet.

First, al l dental la borato ries should includ e a w o rkplace that ca n be used for the documentation of shade (Fig 5 -15) . A lthoug h it seems

Principle 1: Use multiple light sources

primari ly necessary for the denta l laboratory [see Fi g 5- 1b }, some cases ca n be solved w hen adeq uate shade documentation is performed by the dentist a lone, espec ia lly w hen the denta l la boratory is in a nother city o r state. As discussed in Chapter 2 , colo r is not the ma jor element of esthetic success in a resto ratio n. For decades, choosing co lor has remain ed a sub jective process. The future surely lies in the automation of shade selection through multifunctional innovative tools, including di gital ca meras and color data recording. W hile the tools may evolve, some basic princi-

For each pati ent, the o pe rator (either the de ntist o r technician ) should try to understan d a nd document color (tooth-light inleroctions], rather than select the shade . This ideally impli es using var io us lightin g co nd itio ns (Fig 5-16L eg , dayligh t, art ificial light , and flash from digita l cameras. It is important to take into account the lig hting in the pa tient's daily env ironment. Shade selection should a lso be made under the same type of ligh t source. This a pp roac h may aid in avoid ing effec ts of metame rism.

FIGURE 5-15 : SHADE DOCUMENTATION WORKPLACE IN A DENTAL LABORATORY. Th is "patient's place" includes a d isinfecting device, co mmercial shade gUide , selection sheet, custom shade tabs, an artificia l ring light, a nd examina tion g loves (O ral DeSi gn Ce nter, Montreux, SWitzerland). FIGURE 5-16: FIRST PRINCIPLE FOR SHADE DOCUMENTATION. Metamerism implies that ceramics a nd teeth ca n match under one light condition but not under other light sources. By this token, de tailed understandin g of shade must be accomplished wi th more than one lig ht source. Na tural da ylight seems idea l but varies according to atmospheric conditions.

230

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I

INITIAL TREATMENT PLANNING AND DIAGNOSTIC ApPROACH

Principle 2: Acquire experience with a given shade-guide and porcelain system

Principle 3: Use a reference tooth and generate functional shade documents accordingly

The shade-guide system might be the least im-

Shade documents must not only provide gen-

portant element in shade selection. Interestingly,

eral data on the basic tooth shade (eg, data

the Vita Lumin Vacuum shade guide (Vita],

from the shade guide] but also more detailed

which is still universally recognized and has

information that shows individual characteristics

been faithfu lly and successfully referred to by

of

most porcelain brands, seems to present major

tralateral or antagonistic tooth (Figs 5-17a to 5-

defects. For instance, within the same hue (A

17c].

8,

C

an intact reference tooth, usually the con-

or DL there is a simultaneous and nonlin-

ear variation

of the

two other color dimensions

(chroma and value]. As for many other choices

Skilled operators can routinely gather this informalion by:

in high-end dental technology, the following reality must be emphasized:

1 . Taking

photographs while selected

tabs

from the commercial shade gUide are held The experience acquired with a given porcelain system and its corresponding shade gUide is more important than the real choice and characteristics

of the

system itself.

edge to edge with reference teeth (Figs 517d to 5-17g]. 2. Completing a shade-mapping sheet with reference to custom shade tabs for specific porcelain masses (Figs 5-17h to 5-17jl. Digild imaging can facilitate these steps.

FIGURE 5-17: SHADE DOCUMENTS AND POSITION OF SHADE TABS. General and detailed shade information can be recorded with photographs [slides or digital files) 15-17a to 5-17i) This patient requires a porcelain veneer on the right central incisor (5-17a). The logical reference tooth is the intact left central incisor, which displays numerous characteristics (5-17b, 5-17c] Intraoral phototographs of shade tabs must include general views (5-17d] and closer shots (5-17e, 5-17f) Above all, shade tabs must be positioned to receive the same amount of light as reference teeth during the photograph. By this token, shade tabs should not be placed side by side with natural teeth (because of the frontal shift between teeth and shade gUide); only the edge-to-edge position is recommended because teeth and shade tabs are on the same plane, parallel to the plane of the camera body and film, and at the same distance from the camera flash system (5-17g) The cervical parts of shade tabs are often more saturated and must be omitted; they should never be juxtaposed against the incisal edge of the reference tooth.

232

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S HAbE TAB S , A N D TEE TH ED GE - T 0 - E D G E

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5

I

INIT IA L T REATM ENT PLA NNING A ND D IAGNO STI C A p PROA CH

of

A bove a ll, sha d e documen ts must conform to

order to place the correct amount

the stratification technique and porcelain sys-

shade in the ceramic buildup (see Fig 7 -1 1).

masking

tem used so that they can be continuously referred to during the ceram ic w o rk. The same

Shade documentati on should not be done at the

d oc umenta tio n must be ' repeated at the try-in

end

stag e w hen ad justments are required . When

dration commonly occurs during de ntal treat-

of

a regular clinical session. Tooth de hy-

bonded ce ram ic restora tions wi ll be p laced o n

ments and will generate brighter shades. By the

stained teeth, it is reco mmend ed that shade

same token, during shade documentation itself,

documentati on fol low tooth prepara tion; the

photographs must be taken intermittently to

stained to oth substrate must be id entified in

a llow rehydratio n of teeth by the patient 's sa liva.

FIGURE 5-1 7 (CONTINUED) . The ca mera was tilted cervica lly to prevent flash reflectio ns at the level o f the incisal edge (5- 17 h). The resulting high-mag nification view of the reference tooth constitutes a map for the a pplica tio n of specific porce lain masses such as opa lescent enamels, incisals, and stains; this picture is w or th a thousand words (517 i). A print of this image (instant digi tal shot] ca n be used to generate a shade-mapping sheet that specifies the co rrespondin g porce lain masses (5-1 7jl .

234

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5 I

INITI AL TRE ATMENT PL ANNIN G A N D DI A GNO STI C ApPR O ACH

References 1. Magne P, M ogne M , Belser U The dio gnostic template A key element to the comprehensive esthetic treatment concept Int J Periodonlics Restorotive Dent 19 9 6 · 16: 560-5 69. ' 2 . Rieder C E The role of operatory a nd la bora tory personnel in pa lient esthetic consultations. Dent C lin North Am 19 89 ;33275-284 3 . M ag ne P, Magne M, Belser U. Restoura tion des dents anterieures. Rev Mens Suisse O do ntoslornclol 19 9 3 · 10 3 : ' 31 8-3 24. 4 . Raetzke PB. Co vering localiz ed areas of rool exposure employing the "envelope" technique. J Periodontol 19 85 ; 56 39 7-40 2 . 5 . Bruno JF. Co nnective tissue graft techniq ue assuring w ide root coverage . Int J Periodontics Restorative Dent 1994 · 141 2 7-13 7 . ' 6 . Buonocore MG. A simple method of increasing the adhesion of acrylic filling ma terials to enamel surfaces. J Dent Res 19 55;3 4 :84 9-8 5 3 . 7 . Fradeani M . Six-year follow-up w ith Empress veneers. Int J Periodontics Restorative Dent 19 9 8; 18 :2 16-225 . 8. Peumans M, Va n Meerbeek B, Lambrechts P, VuylstekeWau ters M , Vanherle G . Five-year clinica l performance of porcelain veneers. Q uintessence Int 19 9 8;2 9 :2 1 1- 2 2 1. 9 . Friedman MJ A 15-year review of porcelai n veneer failure-A clinician's observations. Co mpend Co nlin Educ Dent 19 9 8 ; 19 :6 25-6 36 . 10 . Dumfahrt H. Porcelain laminate veneers. A retrospective evaluation after 1 to 10 years of service: Pa rt II-Cl inical results. IntJ Pro sthodont 20 00 ; 13 :9-1 8 .

1 1. Li n CP, Douglas W H o Structure-property relations and crock resistonce at the bovine dentin-enomel junction. J Dent Res 19 94;73 : 10 72 - 10 78. 12 . Garber D. Porcelain laminate veneers: Ten years later. Part I: Tooth preporotion. J Esthet Dent 19 9 3;5 :56-62 . 13 . N attress BR, Youngson CC , Potterson Cj, M ortin DM, Rolph JP. An in vilro ossessment of tooth prepara lion for porcelain veneer restora lions. J Dent 19 9 5 ;2 3 : 16 5- 170 . 14 M agne M , Douglas W H oPorcelain veneers Dentin bonding optimization and biomimetic recovery o f the crow n J Prosthodont 19 9 9 ; 12 : 11 1-1 21. 15 Magne P, Douglas W H oAdditive conlour of porcela in veneers: A key element in enamel preservalion , ad hesion a nd esthetic for the ag ing dentition. J Adhesive Dent 19 9 9 ; 1.81 -9 1. 16. M agne P, M agne M , Belser U. Natural a nd restorative ora l esthetics. Part I: Rationale and basic strategies for successful esthelic rehabilitations. J Esthet Dent 19 9 3 -5: 161 -173 ' 17. Rieder C EoUse of provisional restorations 10 develop a nd achieve esthetic expectations. IntJ Period ontics Restorative Dent 1989 ;9 : 122-1 39 . 18. M agne M , Magne P. Schlusselelemente eines umfassenden asthetischen Behand lungskonzeptes Dent Labor 19 9 9;47 5 45-55 5. 19 . Magne P, Douglas W H oRationaliz a tion of esthestic restorative dentistry based on biomimetics. J Esthet Dent 19 9 9 · 11 :5- 15 ' 20 . Belser U, Magne P, Magne M . Ce ramic laminate veneers: Co ntinuous evolution of indications. J Esthet Dent 19 9 7 ·9 : ' 19 7-207.

,

236

•

CHAPTER

6

TOOTH PREPARATION, IMPRESSION, AND PROVI S10 NALI ZATI 0 N

W ith the understa nding

of

too th crow n bio mec hanics a nd the prog ress

of

dentin ad hesives, bonded ce ra mic restorati ons present an extended spectrum of indi cati o ns for an terior teeth. To prevent short-term fail ures, the new g enera tio ns

of

" porcela in veneers" require accurate knowled ge o f the

stress dis tribu tion w ithin the too th-resto ration compl ex . The optima l pre paratio n de sign an d finish line ca n vary accordin g to the initia l cl inica l situa tio n, shape, and arran gement of intact hardlissues. Becau se tooth preparatio n/ impression , and provisio naliza tio n usually occur du ring the sa me cl inica l session, final imp ressions a nd fa brica tion of provisio nals are discussed in this chapter as we ll.

6

I TOOTH

PREPA RATI ON , IMP RESSI O N , AND P ROVI SI ONALIZATION

GENERAL CONSIDERATIONS When adequate di c q nosfic steps have been strictly applied , practica l restoro tive procedures can beg in w ith maximum confidence and pred ictability. The fina l ob jective be ing w elldefined, the active thera peutic effo rt ca n now

This leads to maximum preserva tion of remaining sound, mineralized t is ~ ue d uring tooth prepara tio n a nd, co nsequently, to a very co nservative a pproac h (Fig 6- 1).

foc us o n the techn ical procedures for tooth preparation.

A minimum a mount o f prepara tio n geometry,

The prepara tio n design for bo nded porcelain restorations (BPRs) should Simultaneously allow optima l margina l ad a ptati o n of the final restoration and reflect an utm ost respect fo r the hard tissue morphology.

ing the fina l bondi ng procedure . The lo ng-term preservat io n of the integri ty of ~h e tooth-resto ration co mplex also implies the need for a sufficient and homogeneous cerami c thickness to provide the restoration with some intrinsic mecha nica l resistance.

BPRs must be differentiated from traditi onal cemented crowns, especially regardi ng retention and resistance fo rm. The ad hesive proper ties and physicochem ica l characteristics of the luting composites al low the tooth-restoration interface to be sub jected to substantia l stresses . From this view po int, the geo metric a nd mechan ical parame ters o f the tooth prep aration are o f secondary impo rta nce .

how ever, is still requi red to facilita te pla cemen t a nd positioning of the cerami c workpiece dur-

This c ha pter wi ll systema tically review tissue reduc tion, margin co nfig ura tio n and local izatio n, and fundame ntal aspects related to w ra pping and incisa l overlapping , a nd w ill add ress peculiar situatio ns such as thin versus thick teeth, preexisting restorations, d iastemata, etc.

FIGURE 6-1: BPRs FOLLOWING 5 YEARS OF SUCCESSFUL CLINICAL SERVICE. Initial view of previo usly crownfractured incisors (6-1a) Only a pellicle o f ename l wa s removed (6-1 b, 6- 1c). Period ontal surgery was not required despite severe hard tissue breakdown and very sho rt clini ca l crow ns. Detai led view s of the master cast (6-1d to 61f) Co rrespo nd ing cerami c restoratio ns fabricated w ith a co mbinatio n o f feldspa thic porcelain , hydrotherma l low-fusing g loss, a nd a refractory d ie techniq ue (6-1 g to 6-1 il. The inci sal ed ge extends more than 5 mm o n fhe left ce ntra l inciso r. There is very little prima ry sta bi lity of the restoration s; the long-term success essentia lly relies o n ad hesio n. C linical results mo re than 5 years o tter placeme nt (6-1i, 6- 1k]. The ac id-etch technique w as used w ith a n enamel ad hesive a nd a photopo ly merizi ng restorative co mpo site (minipar ticle hybrid ] as the luting agent [resto ra tio ns w ere bond ed o nly to enamel beca use no effic ient de ntin ad hesives w ere avai lable a t the time o f place ment). The restorations a re suppo rting sig nifica nt protrusive g Uida nce . The 5-yea r fol low -up revea ls a favorabl e soft tissue respon se (6-11) . The restorati ons show exce llent margin al ada ptatio n a nd sea l, colo r sta bility, a nd smoo th surfaces. There is no recurrent ca ries o r cera mic crock s (6-1 m]. (F ig ure 6 -1a is reprin ted from M ag ne et a ll w ith pe rmission)

240

_....;.~---------!y :i----------==-~

r

~

6 I

T OOTH P REPARATI ON , I MP RESSI ON , A ND PROVISI ONALI ZATI O N

TISSUE REDUCTION Basic principles Early tooth preparation fechniques fo r BPRs unfortunately did not pro mote op lima l preservatio n of enamel . Reduction burs w ith ca lib rated d iamond rings w ere proposed to cut ena mel, a nd de pth co ntrol was based o n the preexisting tooth surface (Fig 6-2) . Whe n the initia l ena mel w as a lready thin, redu ction based o n such depth cuts led to ma jor dent in exp osures. As expl a ined in C hap ter 5 , the veneer sho uld a im to resto re the o rig inal vol ume of the tooth,2.3 especia lly in cases of thin initia l ename l.

Therefor e, a diagn ostic wa xup restoring the o rig inal vol ume of the tooth sho uld be used as a reference for tooth redu ction [Fig 6-3). This ba sic pri nciple will save a sig nificant amoun t of so und tissue, not on ly ena mel, but al so the critical dentinoenamel junction . The simp lest and most important tool for ena mel reduction is a w ell-ada pted, horizon tally sectione d silicon inde x fro m the w ax up (Fig 6-3).

FIGURE 6-2 : BURS FOR INITIAL FACIAL REDUCTION . Schema tic d raw ing o f the incisa l view o f hori zonta l cross-sections of central incisors (P = pa latal , F = facia l). (Top) Ca librat ion burs w ith d iamond rings are not recommended beca use they cut accord ing to preexisting tooth surface a nd vo lume Excessive a mount of enamel is red uced (red dotfed line), risking dentin expo sure (white arrowheads), especially at the level of the transitio n line a ng les of age d teeth. (Bottom) Use of trad itional burs (slig htly ta pered , round-ended ) in co njunction w ith silicon indexes of the additive w axup w ill a llow econom ic reduction of ename l and minimize de ntin exposure beca use cutting (red dotted line) is made according to aug mented tra nsition line ang les (white arrowhea ds) and expanded crown volume. FIGURE 6-3 : MAXIMUM CONSERVATION OF THIN FACIAL ENAMEL. Initial view s show short central inciso rs with preexisting co mposites a nd thin ena mel (6-30 10 6-3 c). Sig nifica nt spac e is initia lly present fo r the future restoration [6 -3 b, as indica ted by the horizo ntal ly sectioned silico n index from the additive wa xup) and wi ll allo w extremely co nservative too th preparation . The prepar ation technique includes the reali zation of interdental a nd facial gro oves (63d , 6 -3e) fo llowed by facial red uctio n (6-3f). Final BPRs di splay marked transition line a ng les and uniform thickness [6-3g 10 6 -3;). C linica l service is now more than 7 years, as illustrated in Fig 4 -8 . The d iag nostic approach is presented in Fig 5-5 and cera mic stratificat ion in Fig 7-9. (Figure 6-3i is reprinted from M ag ne" w ith permission)

242

.-r,.; ,

.-;==:.-j

t-. .-

6 I

TOOTH PREP AR ATION, I M PRESS IO N, AND PR O VISIONALIZ ATI ON

Recommended sequential procedure The step-by-step preparation is shown in Fig 6 4 . As is the case for realization of the mock-up, a rig id an d accura te matrix must be obtained by sub jec ting the silicon materia l to press ure during setting (see Fig s 5-71and 5 -7m ).

1. Initial control with the silicon index. Before reducing the ena mel, placement of the facial index reveals areas of the tooth surface that w ill req uire o nly minimum prepara tio n (typica lly the proximal crests and transition lines) [Fig 6 -40) .

2 . Axial reduction I: Interdental preparation. Ax ia l reduction necessitates the use of three d ifferent d iameters of ta pered , round-ended burs c .cssico llv des iq ned fo r traditi on al fixed prosthodon tics. Recommended burs are 85 6 L0 14, 856L-O 16 , a nd 856 L-020 [Bra sseler) o r D6 , 235, a nd 237 (Intensiv). The smallestdiam eter bur is used first to cut the proximal red uction grooves (Figs 6-4 b a nd 6-4c) . This step can be significantly enhanced by the use of osci llating instruments (see Fig 6-9).

3 . Placement of a deflection cord. The aim of slig htly defl ecting the gin gi va is not to produc e an introsulcular margin but to improve ViSibility d uring prepara tio n of the parag ing iva l margin . A special low-trauma techn ique is used for placement (6-4d). Additi onal d eta ils reg ard ing interde nta l and cerv ica l preparalio n are giv en in the next sectio n ("Marg in co nfiguratio n and loca lization ").

4 . Axial reduction II: Facial grooves. The med ium-diame ter bur is used to crea te facial reduc tion g rooves [Fig s 6-4e a nd 6-4f). Three vertical grooves are recom mended o n central incisors and ca nines, tw o grooves on la tera l incisors. The depth of each groove is individ ua lly con trolled using the silicon qu ide (Fig 6 4g) . The preexisting surface of the tooth must be ignored; o nly the surface of the silico n index should be used to check the depth cuts .

FIGURE 6-4 : RATIONAL TOOTH PREPARATION PROCEDURE . The initial control w ith the silico n index shows a lready ava ila ble space for the future restoration (6-4 a) . Tooth preparation starts with part ia l interdental penetration (6-4b, 6-4cJ, follow ed by placement of a deflection co rd. The bima nual insertion technique is used to avo id trauma to the so ft tissues: the co rd is stabil ized w ith a periodontal probe on the site of insertion, whi le a spatula is used to posi tio n the co rd in the sulcus [6-4d) . Facial dep th cuts a re then prepa red w ith a larger bur [6 -4 e). They a re bare ly visible beca use of the minimum sacrif ice of sound tissues (6-4f). Each g roove is ind ivid ually co ntro lled w ith the silico n matrix (64g) . So me aspec ts of the preexisting surface w ill be almo st untouched , eg, the facioprox imal transition line ang les a t the d ista l surface of the right central incisor. The larg est bur is used for axi al reduction (6-4h l, w hich prevents the formation of w avy surfaces resulting from repenetratio n into the depth cuts. The con trol of axia l reductio n reveals that proximal crests a re al most untouched, a llow ing maximum preserva tion o f ena mel (6-4i). The incisa l-edge clearance is co ntro lled w ith a pa latal index [6-4 j], follow ed by de finitio n of the pa latal finish line lie, a sligh tly concave butt margin) wi th a large round d ia mo nd bur (ie, 801 -016 or 801-02 3 , Brasseler) (6-4 k). It is extrernelv impor tant to round off al l sharp edges, which ca n be ac complished using soft flexib le dis ks (6-41 ]. Final view of the prepara tions af ter remova l of the de flection cord shows clea n paraging iva l marg ins (6-4 m) M eSially, margin s remai n within preexisting co mposites, w hereas d istally, the marg in has to be extended more palatally due to enamel deminera lization . Preparatory steps a nd po stope rative view s of this case ca n be found in Fig 4-7 .

244

6

I T O OTH

P REPA RATI ON , I M PRESSIO N , A ND PR OV ISI O NA LIZ AT IO N

5 . Axial reduction 11/: Gross preparation . The g ross wi th a tration wavy space

axial reduc tio n is p refera bly realized larger bur (Fig 6-4h ) to prevent repeneinto the g roo ves. In this simple w ay, surfaces ca n be avoided . A unifo rm of 0. 5 to 0 .7 mm should be ge nerated

by this method (Fig 6-4i L ultimately p rod ucing the same thickness o f ce ramic a t the p rox imal a nd axial levels.

6 . Control of incisal reduction. The pal atal half o f the silico n index is final ly used to check the incisa l clear ance [Fig 6-4 j). A t lea st 1.5 mm is

cie nt clearance for the ce ramic, smoo th co nto urs, absence of undercut) an d the final impressio ns will sig nifica ntly facilitate the w o rk of the dental ceram ist, lead ing to minimal use of d ie spacer a nd thus red ucin q the risk o f postbo nd ing cracks. 1.5.6 It is impo rtant to co ntrol the space avai lable at different horizontal levels of the preparation (from cer vical to incisal); this ca n be easily acco mp lished by sectioning the silic on ind ex acco rd ing to the "notebook method " (Fig 6-5 1, w hic h c reates a bound multilayer index .

requ ired.

7 . Palatal wrap and incisal preparation. Establishment of the pala ta l fini sh line is usua lly the last step of tooth preparat ion (Fig 6 -4 k). Ad d itio nal detail s regard ing incisal and pa lata l prepara tio n are g iven in the section "W ra pping a nd overlapping."

8 . Finishing. It is essentia l to p rod uce prepara,.'

tions w itho ut sharp a ng les, cons ide ring that the improved qua lity of both the preparat ions [suffi-

The basic elements of tooth preparati on are presented in Fig 6-6. A last co ntrol of the preparati on must incl ud e care ful exa mina tio n of the insertio n path of the future restora tio n a nd verifi cati on of the abse nce of undercuts, especi a lly in cas es w here the p roximal margin s extend further pa latally (see Fig 6-20). Speci fic situations reg ard ing margin local izalion and confi guralion are d iscussed in the follow ing section .

FIGURE 6-5: THE NOTEBOOK FACIAL SILICON INDEX . The tradit ional silico n index is cured under 4 a tm in a pressure po t, then sectio ned horizo ntally. The differenl loyers ore still bound on one side of the index (right) . The matrix can be open ed like a book to visualize the entire aspect of the reduction , from the inci sal edg e to the most cervica l part (left] FIGURE 6-6 : BASIC ELEMENTS OF TOOTH PREPARATION . This sc hematic view shows that axial reduction ca n vary betwee n more tha n 0 .7 mm incisally (see Fig 6-4 i) a nd a bout 0.5 mm cer vical ly. Incisal clea ra nce must be at leasl 1.5 mm bUI can extend up 10 5 10 7 mm in fraclured teeth (see C ha pter 4 , type IliA ). FIGURE 6-7 : ZENITH OF THE GINGIVAL MARGIN . Placement of the marg in d uring too th prepara tion must take into ac count the most apica l po int of the gi ng iva l co ntour, w hich lies di stal to the main tooth axis (leftj.8 Symmetric scallop ing does not appear nalura l (righ t]

246

:.. .--.. . . -------.. .

------- ------------------./:4!;"!:i~'··-··=::..~

i/!~ ." (

6

I

TOOTH PREPARATI ON , I M PRESS IO N , Ai\JD PR OV IS IO NALIZAT IO N

M AR G IN C O NFI G URATION AND LOCALI ZATI ON Cervical and proximal margins In the ce rvica l a nd proxima l areas, the crea tio n o f a lig ht cha mfer w ithout internal line angles is universally acce pted . Such a finish line w ill a llow a maxim um p reserva tio n of enam el a nd w ill therefo re a lso prevent marginal rn'crolc o kc q e ." Fo r optima l esthelic results, it is recomm ended tha t the sca llo ped co ntour of the g ingi va be respec ted (Fig 6-7; see also 6-4 m). Insertio n of a thin de flection cord (Gi ng ibra id Oa o r 1a , Va nR) facil itates this task by underlining the ind ividual g ing ival perimeter [see Fig 6-4 d ). The dep th cuts ar e kep t a t a consistent d istance to the co rd , opproximo telv 0. 5 mm, lead ing to a para gin gi va l mar gin . Intra sulcu lar margi ns ar e reco mmended only w hen clos ing a diastema or interdental tria ng le to al low the den ta l tech nicia n to crea te a progressive emergen ce profi le (see Fig 6 -2 1 ).9

The a mount of interdenta l penetra tio n depend s o n the type of interdenta l co ntact [Fig 6-8 ). Lig ht contacts ca n be removed by co nservative ly extend ing the prepara tion limit (Fig 6- 8 , left]. With a larg e contact surfac e, how ever, it is recommended that the surfac e be stripped to create accessib le margi ns wi thout excessive penetration (Fi g 6-8, right) . Except fo r two peculiar situ o tio ns that requ ire extensive interdental penet ration (w ra pp ing of o ld C lass 3 restora tio ns a nd reduction of d iastemata / interd enta l triangl es; see Fig 6 -20), it is best to avo id useless sac rifice of proxima l tooth substa nce. Sig nifica nt prog ress for interde ntal pre para tion w as made w ith the inrro d uction of so nic oscillating preparatio n techniqu es (So nicflex/ Sonicsys, KaVo) (Fig 6 -9).

FIGURE 6-8 : DEFINITION OF IN TERDENTA L PENETR ATIO N. The interdenta l marg in (red arrowheads) can extend beyond a ligh l con tact poin l w ithoul sig nifica nt sac rifice o f tooth subsla nce (left). On Ihe o ther hand , it is recom mend ed tha t the prepara tio n not be extended beyond a large proxima l co ntact surface (center) beca use of the sign ifica nt amo unt o f enamel Ihat must be cut and the associa led risks o f den lin exposure (white arrowheads). Instead , marg in loca tio n can be kept con serva tive, provided that the co ntac t surface is stripped (right), facilila ting accurate reprodu clio n du ring impression taking. In a ll ca ses, a "ce ramic-to-cera mic" contact poinl will be recovered w hen the restore tions are placed. FIGURE 6-9: OSCILLATING INSTRUMENTS AND THEIR ADVANTAGES OVER ROTARY INSTRUMENTS. Os cilla ting inslruments include an a ir-driven so nic ha nd piece (top) an d va rious tips w ith a "half-bur" sha pe featuring a flat nonworking surface (6 -90 ) Ty pica l instruments are the to rpedo-sha ped (left) a nd hemispheric (right) tips.

248

6

I T OOTH

P REPARATI ON , IMP RESSION, A ND PROVISION ALI ZATION

Due to their nonrotar y action and half-bur sha pe (Figs 6 -9 a nd 6 - 10L osedla ting tips al low rap id a nd minima lly invasive prep aration. M arg in definiti on is significa ntly enha nced and poses no risk to intact neigh boring tooth surfac es. Such tools are very useful in cases of excessive crowd ing. Especia lly w hen used o n large interdental contact surfaces a nd ove rlap-

p ing teeth, sonic tips allow a more conservative proxima l prepa ration as co mpared to burs (Fi g s 6 -9 b). Another indi cation for osci llatin g preparati on is the need for subg ing iva l marg ins, w hich ca n be finished precisely w ithout da mag ing the soft tissues.

FIGURE 6-9 [CONTINUED) . A sig nifica nt amount of tissue ca n be saved wh en the interdental prepar atio n is achieved w ith the to rpedo-sha ped tip because its cross sectio n conforms exactly to the desig n of the marg in (6-9 b , left). Even w hen the thinnest traditi on al cylind rica l bur is used instead (6-9 b , right). there is a high risk of overpreparat io n and den tin exposure (while arrowheods), in add itio n to the risk o f da mag ing the neighborin g tooth (block arrowheads). FIGURE 6-10 : PREPARATION WITH OSCILLATING INSTRUMENTS IN A STANDARD CASE. The righ~ central inciso r had been frac tured , a nd both central incisors w ill be veneered (see prepa ratory and dia g nostic steps of this case in Fig s 5 -6 a nd 5 -7). Extremely thin trad itiona l burs ca n be used to begin the interde ntal prep arati o n; special care must be taken reg , use of a metalli c matrix) to protect the neigh borin g tooth (6 -1 0 0). Final de finitio n of the marg in is ac hieved w ith a n oscillating torped o-sha ped instru ment (6- 1Obi. In this spec ific situatio n, the task was facilitated by a comp osite restoration o n the lateral inciso r that co uld be strip ped at the mesia l aspect (6- 1Oc; co mposite restoration detail ed in Fig 5-6) The proxima l margi n is sharp and accessib le (6- 1Od ). Following placement of a def lection cord and the realization of dep th g rooves d riven by the silicon index (6- 1Oe], axia l preparati o n is achieved wi th trad itional burs (6-1Of) to ge nerate a uniform space o f about 0 .7 to 0. 8 mm (6-1Og). Sonic tips w ere used agai n after the incisal reduc tion: the hemispheric tip is idea l to round a nd so ften the conto ur o f the marg in a t the tra nsition between the ax iop roximal w a ll a nd pa latoincisal edg e (6-1Oh; 6- 10 j, arrowhead] . All prepared surfaces feature soft co ntours a nd w ere kept wi thin ena mel excep t for the fractured area of the rig ht ce ntra l inciso r (6-1Oi, 6-1Oil. There seems to be a reduced space for the restoration o n the right centra l incisor in Figs 6-1Og a nd 6 -10 i due to the more cervical cross-sectio n plan a nd different viewin g a ng le

250

6

I T O OTH

PREP AR ATION , I MPRE SSI ON , A N D PR OVI SIONALI ZATION

Wrapping and overlapping

As early as the late

19 8 0 s, a p hotoelostic

study by H ighton et a lii revealed the imporThe systematic c rea tion of an inci sal and inter-

tance of an inc isa l/i nterd ental ove rla p tha t ap-

pr o ximal w ra p aro und is appli ed in pr a cti c e by

peared to pr o vide the cera m ic w ith a sup e rior

the majority o f cl inic ia ns and ha s been rec e ntly

intrinsic resistan ce due to be tter stress d istribu-

of

the b iom echanica l inte-

tio n in the restoratio n itse lf. A d d itiona l sc ientific

g ra tio n o f ve ne e rs. The ex ten t of w ra p p ing is

ev idence suggests that the typ e of incisal fini sh

d epend en t o n the init ial situa tion (eg , preexi st-

line to be used is a func tio n

ing c ro wn fracture) and the pr osthetic o b jec tive

of incisal overlop." :"

o p tim iz ed in v iew

(eg , if ma jor modifi cation of fo rm o r cl o sure dia stema ta

is planned,

a

ma ximum

of

wrap-

of typ e

Sinc e the indicati on s for

BPRs ha ve been suc cessfully ex te nd ed to the treatment

of c rown -frac tured

incisors and worn

anterior den titions (se e Chapter

around is imperative).

and amount

4),31 0.14 - 18

new

issues have ari sen co nc e rning the design o f Practi cally speaking, the establi shment of in-

such restorati on s. The exte nt o f to oth sub sta nc e

terpro x imal

o ffe rs

los s must be c on sidered becau se it w ill sig nifi-

od vontoqes": it faci litates the esthe tic

ca ntly infl ue nc e the lo c atio n of the pa la ta l fini sh

many

of

and

incisa l w ra p around

the BPR in the inc isa l zone, it e n-

line (Fig 6- 1 1). Differen t pa ttern s o f stress ore

ha nc es the liber ty o f the den ta l c e ra mist w ith

e xpected o n the p a latal margi n o f the ve ne e r

respect to form and emergen ce profile o f the

depending o n the or ig ina l leve l

restoratio n, and , most important, it faci lita tes

line (eg , moderate fracture through the palatal

the pl acement of the fina l restorati on (eg , sta -

co nc a v ity versus exten sive fracture thro ug h the

bilizati on o f the BPRs and easy access to a ll

tubercule

d ef inition

of the

of

the fra cture

cingu lum) .

marg ins du ring bonding).

FIGU RE 6-11 : DIFFERENTIAL MARGIN LOCATIO N FORMODERATE OR SEVERE PREEXISTING CO RONAL FRACTURE S. Possible locations of the palatal fracture line (arrowheads): in the area of th e palatal concavity for th e moderate fracture (left), and in the area of th e tubercule convexity for the severe fracture (right). Stress distribution in the future restoration margin may differ depending on the area of fracture FIG URE 6-1 20: TANG EN TI AL TE N SILE STRESSES ON THE PALATAL CERAM IC MARGIN (M AXILLARY INCISO RS) . Orig inal contours and finite element mesh developed for the optimization of BPRs itoo}." The position of the palatal margin is indicated for different initial situations: 11 to 14 (minimum loss of incisal structure), F1 and F2 (moderate loss consequent to fracture or wear), and F3 and F4 (severe loss consequent 10 fracture). The facial aspect of the veneer is the same for all d esiqn s . The location of the palatal margin is the same for 14 and F2 . The horizontal and vertica l displacements are fixed a t the cut plane of the root (mesh dia gram, arrows). The incisal load (50 N ) is located approxima tely 1.5 mm below the incisal edge . G enercilly speaking, elevated tensile stresses are found at margins located near the palatal fossa (more explanations in 6-1 2b )

252

Mode rate preexisting fracture

J.

'

Severe preexisti ng fracture

6

I

TOOTH PREPARATION, IMPRESSION, AND PROVISIONALIZATION

Considering the high tensile stresses that may

concavity is not recommended because it cre-

be generated in the palatal concavity during

ates a thin extension

funclional loading (Fig 6-12; see also Fig 1-

maximum tensile stresses.

5L

19

of ceramic

in an area

of

one must question whether the palatal

of

"mini-chamfer," which is frequently prepared,20

Extension

should not be replaced occasionally by a sim-

concavity often results from an extended proxi-

pler finish line, such as a butt margin. The use

mal preparation, which tends to give the lami-

of a

nate veneer a design close to that

butt margin actually provides the margin

of

palatal margins too far into the

of a

three-

of porcelain, marginal extension of

quarter crown (Fig 6-13, left] 21 For this reason,

ceramic (as with a palatal chamfer). Figure 6-

a mini-chamfer or a butt margin is recom-

12b shows how changes in the palatal margin

mended in order to avoid the palatal concavity

the restoration with a strong bulk instead

of creating

a thin

design as well as the extension

of

bonded

ce-

in the case

of extensive

interdental preparation,

(Fig 6-1 3, right).

ramic restorations influence the stress distribution during extreme functional loading. The restoration

of moderately fractured

and severely

2. For moderate crown fractures (incisal one third) or severe wear, the palatal finish line is

of maximum

fractured incisors is considered. These results

often localized in the zone

can be summarized as follows:

stresses (Fig 6-12b, F1 and F2). In these situations, a butt margin limits the extension

1.

For maximum remaining tooth substance, the

stress pattern along the palatal surface is barely influenced by the finish line

of the

ceramic, thus reducing the amount

tensile

of the

of stress at

the restoration interface.

BPRs (Fig 6-

12b, left column). Considerable differences are

Worn teeth present the same dilemma os teeth

detected, however, when comparing stresses at

with moderate fracture: the incisal line crosses

the level

of

the restoration margin. Limited in-

the crilical zone

of the

palatal concavity. Here

cisal overlaps (butt margin or mini-chamfer) pro-

again, a butt margin IF1) permits minimum ex-

tected the restoration margin from harmful ten-

tension

sile stresses in the palatal concavity. The use

of

a long chamfer that extends into the palatal

of

the preparation into the concavity,

while the mini-chamfer (F2) places the restora-

lion rnorqin in an area

of higher

stress.

FIGURE 6-1 2b: MODIFIED VON MISES STRESS DISTRIBUTION THROUGHOUT THE BUCCOLINGUAL SECTION OF RESTORED INCISORS. The thick dotted arrows show the location and direction of load. The thin white arrows show the margin location 1m) (Left column, 11 to 14) Margin location is very favorable for 11 and 12, less favorable for 13, and detrimental for 14. Stresses in the palatal concavity are well above 100 MPa only for 14 [see 6-120). [Right column, F1 to F4) Margin location is not ideal but acceptable for F1 and detrimental for F2. Stresses in the palatal concavity are well above 100 MPa for F2 (see 6-120) Margin location and overall design of F3 and F4 are very favorable; the tooth-restoration interface and the restoration itself are not subjected to elevated stresses (see 6-120).

254

Equiva lent mod ified Von Mises (M Pal

.,'

, ,.

6

I

TOOTH PREPARATION, IMPRESSION, AND PROVISIONALIZATION

One should exercise caution when designing an enamel butt margin. This situation may present longitudinally sectioned enamel rods, which may have a negative effect on the subsequent adhesion to enamel. 22 The orientation

of enamel

prisms is illustrated in Fig 6-14. The situation appears most critical in the incisal

Andreasen et al 16 and yielded great ultimate crown strength. The finite element mesh was used to reproduce this situation and calculate the stress distribution (Fig 6-15). The composite provides a favorable effect, simultaneously allowing the decrease of stresses in the palatal concavity (stress redistribution into the more flexible composite] and relocating the margin of the veneer into the "safe" incisal area. How-

area, where enamel prisms are sectioned at a low angle of 30 degrees. A mini-chamfer (intermediate between 12 and 13) can be recom-

ever, such buildups must be carefully consid-

mended in this situation, because it will section

ered because thick layers

enamel rods at an angle close to 90 degrees

been proven to induce the development of postbonding flaws. 1 5 .6 Rebonding of the frac-

and stay reasonably distant from the concavity. For fractured teeth, a horizontal butt margin is adequate because a horizontal finish line will generally section the enamel prisms obliquely

of

composite have

tured tooth fragment, when possible, is certainly indicated since it has been proven to

at an angle greater than 50 degrees.

give good results when supplemented with a veneer. 15 In fact, this treatment modality seems

Another way to avoid the palatal concavity in

appropriate prior to placement of a laminate veneer because of uniform thermal expansion

fractured teeth would be to make a composite buildup designed as a "stress breaker." This modality was studied in a load-to-failuretest by

and the absence of hygroscopic expansion in the rebonded tooth fragment.

FIGURE 6-13: DILEMMA OF EXTENSIVE INTERDENTAL PREPARATIOI"JS. (Left) Maximum penetration of the interdental space often leads the clinician to extend the incisal overlap during tooth preparation. The resulting veneer unfavorably involves the palatal concavity. (Middle) Clinical photograph of veneers featuring the problematic design illustrated on the left. The accelerated degradation of the margins and short-term fai lure of the ceramics appeared at the level of the long palatal chamfer on the left central incisor. (Right) Maximum interdental preparation is compatible with the avoidance of the palatal concavity and the realization of a butt incisal overlap. Such a design is especially recommended for closure of interdental spaces due to gingival recession as well as for the total wrapping of preexisting Class 3 composites when indicated (see Figs 6-19 and 6-20).10 FIGURE 6-14: ORIENTATION OF ENAMEL PRISMS AS DETERMII'.IED ON AN INTACT TOOTH SECTION. Prism orientation is indicated (in degrees) based on measurements made at the possible locations of the morqin." FIGURE 6-15: STRESS DISTRIBUTION THROUGHOUT A FRACTURED INCISOR RESTORED WITH A VENEER ON TOP OF A COMPOSITE BUILDUP (F 1cp]. The thick dotted arrow shows the location and direction of load. The thin white arrows show the margin location. The stresses in the palatal concavity are redistributed into the more flexible composite The margin of the veneer (m1) is relocated in the "safe" incisal area.

256

6

I T OOT H PR EPARATIO N,

I MPR ESSI ON, A ND PROV ISIO NA LI ZAT ION

3 . For severe crown fracture (incisa l two thirds), the pa la ta l margins are sub jec ted to low tensile fo rces beca use they are located in the low stress area of the c ingu lum [see Fig 6 -12b, F3 a nd F4) . The la tter, w ith its smooth convexity, ca n be co mb ined either wi th a butt marg in or a mini-chamfer w ithou t ge nera ting harmful stresses .

po rcela in. Interesting ly, the to oth-resto ratio n interface is not sub jected to stresses more har mful than those fou nd in other resto ra tive de sig ns. COincidenta lly, for pa tients w ith crow n fra ctures in w ho m BPRs w ere p laced o n both cen tra l inciso rs (Fig s 6 -1, 6-3 , and 6-10), the pa latal marg in on one inci sor w as pla ced be low the pa la ta l co ncavity a nd the o ther w a s p laced

Surp riSing ly, severe fra ctures IF3 to F4 ) p resent

above it (Fig 6 -16) . This d esign , resulting from

c hara cteristics less com plex than those fo und in

the differential preexi sting loss

moderate fra ctures. The restoratio n itself shows

vo ra b le in view of scientific d a ta d isc ussed

lowered stresses in the pa latal conca vity be-

w ithin this sectio n.

ca use

of stress

red istribut ion in the b ulk

of

tissue, is fa-

of the

FIGURE 6-16 : IDEAL LE VEL OF PALATAL MARGINS . View s o f pre pared ce ntral inci sors (top, patient from Fig 6-10) a nd BPRs o n master cast (bottom). The left ce ntral inci so r is an F3-lype BPR . The BPR on the rig ht centra l incisor has a n intermed ia te de sig n betwee n 12 and 13 . The marg in o f bo th BPRs (arrow s) cou ld be placed outside the fossa (red translucent ova!). Note that the "cera mic-to-cera mic" interdenta l cont ac t poin t has been resto red .

258

---------~,..::/ '.

.-_---_....

_------ ~~

6 I

TOOTH PRE PARATI O N , IMPRESSI O N , A N D PR OVI SI ONALIZATI ON

PECUL IAR SITUAT IO NS Thin versus thick teeth

tomi c features

of teeth

to be restored (thic k ve r-

sus thin, flat versus co ncave) is imp erati ve to the Teeth restored with por celain ve neers are ab le to mimic the beha vior

of

d esign optimizati on

of BPRs.

inta c t teeth w ith simi-

lar stress dis trib utio n pa tterns. Fro m the p rev ious sec tio n, it is und erstood that stresses are

Existing Class 4 defects

hig hly cor re lat ed to shape (co nvex ve rsus conca ve) a nd com pos itio n (eg , e na mel-de ntin dis tribution

and restorati ve materia l thickness).

of

Extensive loss

of tooth

structure (lar g e C lass 4

defects] can be restored by mea ns

of the

lam i-

surface , it is not surpri sing that the stress at the

nate ve nee r a lo ne (Fi g 6-18 , simpl ified a pproach) .3.1o.J2,i6 A p re p ros the tic co mp o site

pa la ta l ce ra mic mar gi n is correla ted w ith the

buildup resto ratio n w ill not co ntribute to an in-

Due to the co ntra sting a na to my

stress

of ~ h e

the palat al

intact inc iso r at the correspo nd ing

crease in the ullirn o te streng th

of

the tooth

loca tio n lie . high in the pala ta l conc av ity and

resto ra tion comp lex" but could be considered

low at the tube rcl e).

a positive resilient compo nent."

In this ap-

proach, a preexisting Class 4 restorat ion a nThese anatomi c fact or s ca n vary from tooth to

chored by a para pulpal p in or intrar a dicul ar

tooth and patient to patient, and it con be an -

screw can be used as a sup p lementar y pre-

ticipated that extremely thin teeth w ill be sub-

p ros thetic resto ratio n.

[ectcd to more ben d ing stresses com pa red to thic k teeth. Tw o anato mic types are re p rese nted

Ho w ever, lar g e bul ks

of composite

under po r-

6-17: a thin flat tooth, w hic h obviou sly

ce lai n venee r restora tio ns sho uld be avoided

requires a substa ntia l incisa l clearance to gen-

because the re is still significa nt con c ern about

in Fig

era te a certa in bulk

of

inc isa l po rcelain, an d a

thick cur ved incisor that requires only minimum inci sa l red uctio n. Careful observa tio n

of a na-

the ad d itive effec ts of the c uring con trac lion and high therma l ex pa nsio n pos ite resins.1,5,6

of

cer tai n com-

FIGURE 6-17 : VARIABLE INCISAL CLEARANCE ACCORDING TO ANATOMIC TYPE . To create an o ptima l thickness of inci sal po rcelain (line o f asterisks), the inci sa l edge of a thin fla t tooth must be reduced more than 1 5 mm. The intrinsic resistance of the laminate w ill be enha nced w ithout sub jecting the pa lata l margi n to detrimental stresses (slig ht palatal co ncavity) In a thick curved tooth, a similar bulk o f incisa l po rcelai n is often compa tible w ith less tha n 1.5 mm of incisal clearan ce . Extensive incisal reductio n a nd cha mfering are not reco mmended o n such a tooth beca use it would pla ce the pa latal marg ins a t the level of high tensile stresses from the deep fossa .

260

,

Thin flat tooth

:

\

"

Thick curved tooth

. .....

. . ...... ..::.\

\,

\

\

FIGURE 6-18 : LARGE PREEXISTING CLASS 4 COMPOSITES . Both central incisors present large C loss.4 co rnpos- . ' }tes (6-18a) that wereremoved immediately prior to tooth preparation (6-1'8b). The li nol prepara tions show the extent of themesial interdentOi defects; dotted areas delineate exposed dentin thatwas sealedwithadentin bondi ng agen t prior to linol impressions (6-1 8c, solidrnostercostl. The correspondi ng porcelain restora tions present a bulky mesial asped but do not involve the remaining palatal surface (6-1 Sd]. Postoperative view r()lIowi ngi n~er tjo n of BPRs.on the four incisors (6- 18e), O ther views of this case can be round in Fig 8 ~ 10. , . -

'\

'

6

I T OOTH PR EPA RATIO N,

I M PRESSIO N, A ND PRO VISION ALIZ ATI ON

Existing Class 3 restorations

the luting composite a nd the extremes o f therma l c ha nges. Pro blems related to thermal

Veneering teeth w ith preex isting Closs 3 composi te restoration s addresses again the problem of interdental penet ration and positioning of the marg ins. The safety of interdental wrap-

stresses ca n ge t worse in the presence 3 composites (Fig 6 -19).

ping ca n be cla imed beca use the most important mecha nical eve nts in incisors appear w ithin the bucco lingual pla ne .24 .25

of

Class

A numeric study determ ined that partial or total wrapping of preexisting co mposite restoratio ns is ind icated to minimize thermal stresses. 26

Stresses and stra ins within the crown seem to

In medium and lo ng interdenta l wraparounds, part of the pree xisting com posite bulk is re-

be minimally affected by interdental preparation s. Ho w ever, mechani cal loadin g is no t the

placed by the extension of the ceramic , w hich red uce s the influence of the nearby expa nd-

o nly source o f stress. Add itio na l factors must be considered, suc h as the curing contractio n of

ing/ co ntracting composite restoration [Fig 619 c).

FIGURE 6- 19 : TWO·DIMENSIONAL FINITE ELEMENT A NALYSIS O F THERMAL STRESSES IN THE PRESENCE OF CLASS 3 COMPOSITES . The numeric model w a s ge nerated from a horizon tal section at mid-height of the crown (619 a , Jeft). Due to symmetry, o nly the mesial hal f o f the sectio n w as used. Tw o-d imensio na l FE model (6 - 19 0, center; M enta t software, MSC Software). The margin loca tio n of eac h veneer (short [S], med ium [M], lo ng [L]) is indi ca ted o n the model [6 -19 a , right). First principa l stresses (ps 1) in the med ium-wr a p veneer sub jected to thermal cha nges alo ne (6- 19 b). The w hite area represents the o rig ina l sha pe at 3rC (ba seline). Defo rmatio n due to tempera ture changes (6 0 °C a nd 5 °C) w as magnified by a facto r of 500 . N egative va lues of stress appear in dark g ray a nd delineate the area of comp ressive stresses. Lig ht gra y area s ind ica te tensile stresses. A "bend ing effect" ca n be o bserved (dotted arrows indicate relative di splacement of the restorati ve margin) : a g iven thermal load shows o pposite effects on the restoration surface and the interface, creati ng pure co mpressive stresses on one side of the restoration w hile generati ng pure tensile stresses on the other side. Simulatio n of nega tive thermal stress (SOC ) for the short-wrap and long-wr a p veneers (6-19c) . Deforma tio n of the tooth-resto ratio n co mplex is magnified by a factor of 400 . The light gra y surface a nd dotted lines show the original shape of the too th-restoration co mplex at 3r C Deformati on is less uniform w ith the sho rt-w ra p veneer: the bulk of the composite restoratio n crea tes a contracting pole (arrows) and induces bend ing of the venee r. Deformation is more uniform (few er bending moments) in the long-w rap veneer becau se of the sma ller vol ume of con tracting composite. Scanning electron microscope (SEM) view of a hori zo ntal tooth sectio n at the junction between the facial cerami c venee r and a C lass 3 co mposite 16-19d) 25 A temperature-ind uced ceram ic crac k is found at the restoration margi n in a situatio n simila r to the short-w ra p veneer, whi ch correlated wi th the locat ion of maximum stresses found in the FE mode l ab ove . (Figures 6-19a to 6- 19d are repri nted fro m Magne and Dougla s26 w ith permission )

262

, Thelmal stress a lo ne (medium wrap! .'

',

'

.

Thermal stress alone (Y Cj

6

I

TOOTH PREPAR ATI O N , IM PRE SSI O N , A ND PR OV IS IO NA LI ZAT IO N

Overall perform a nces of different de grees of interdenta l w raparound de sig ns can be evaluated in light of pra ctical and cl inical par am eters. The short-w rap veneer co rresponds to a trad itio na l a nd co nserva tive p roximal ve neer prep ara tion that stays fa c ia l to the co ntact. This often precl udes the need for provisio na lizati on , but ultimately leaves the tooth-restoratio n interface visible. La tely, p repara tio ns extended into the co ntac t area have become popular-they hide the marg in and provid e a posit ive seat for preci se insertion Y In lig ht of these clinica l ad va nta ges and know ing the negative influence of the intact bulk of preexisling interdental com posites on thermal stress distribution [Fig 6-1 9 d J, avoidance of shortwra p veneer s is recommended . Practiti oners and dental tec hnic ia ns, however, should know that long-wra p veneers ar e d ifficult to fabri cate and man ipulate, as a result of the extensio n of cera mic, de lica te insertio n axis, a nd mar gin definitio n. C linica lly, a typ ica l error in extending proxi mal prepara tio ns is use o f a deep c ha mfer (Fig 6- 1ge, far right ). A mini-cha mfer o r butt inc isa l covera g e is recommended instea d . A safe method for interdental and in-

c isal tooth preparation is to kee p the main axi s of the bur (o r osc illating tip) o bliq ue o r ho rizontal (Fig 6-19f). W rong preparatio n desig n often results from a sing le ve rtica l instrument axis (6 -1 9 g) . M aximum w ra paro und is absolutely indi ca ted w hen maj or c ha nges of fo rm o r closures of d iastema ta (or interd enta l triang les) are planned , provid ing that an ad equate margin (marked interdental cha mfer) and ceramic thickness are ac hieved . In other situati on s, a partia l w raparo und (medium wrap) may be the best comprom ise between stress di suibutio n, esthetics, and clinica l practicality w hen placing porcelain veneers o n teeth restored w ith Cla ss 3 co mposi tes. In this situation , preexisting restorations must be carefull y exam ined for their qua lity and eve ntual ly be replaced . Replacement of C lass 3 co mposites is possible w ithout a ffecting the facial a spect of a preexisting BPR . A pa latal a ccess cavity must be used and co mb ined wi th adequate bonding to the ceramic (see Fig 9-6) .25

FIGURE 6-19 (CONTINUED) : O PTIM IZATI ON O F WRAPAROUND DESIGN IN THE PR ES EN CE OF A PREEXISTING C LASS 3 COMPOSITE . White dashed arrows show the level of incisal prepara tion . Gray dashed arrows show the level of interdental prepara tion. A bsence of interdental penetration (6- 1ge , for le ft) is not recommended due to limited esthetics a nd negafive thermal eHects o f intact remainin g co mposite (see Fig 6-19d)26 Partia l w ra pping (61g e, left center) seems to oHer a favora ble co mpromise for both esthetics a nd thermal stresses. Total w rapping (61g e, right center) might be indica ted a nd is advantageo us w hen combined w ith a butt incisal margin . Extensive chamfering into the pa la tal co ncavity [6 -1g e, for right) must be avo ided due to functional stresses [see also Fig 6-13 , center) and beca use it o ften genera tes on acute incisal edge (black arrowhead). Even thoug h facial axial preparati on ca n be ac hieved w ith the bur ali gned pa rallel to the tooth long axis, adequate interdental and incisal cutting is ac hieved w ith a horizontal stroke (6-1 9f) . W hen this technique is omilted and a only vertical axis is used, risks of chamfering and overprepar ing the palatal surface are obvious [6-19g)

264

No wrapp ing

Partial w rapping

Tota l wrapping w ith "butt"

Total w rapping with chamfer

6 I T O OT H P REPA RATI O N , I M PRESS IO N, A N D PR O V ISIO NA LI ZAT IO N

Preparations for closure or reduction of diastemata or interdental black triangles

req uire meticulo us study o f the inser tio n ax is

of

the future lam ina te venee r. It is therefore recommend ed tha t d iag nostic prepara tio ns be carried o ut o n the initia l models.

Cas es in w hich d iastemata or interdenta l blo ck tria ng les are to be close d req uire on extend ed

In the case of a red uced periodontium, a hor-

interp roxima l prepara tio n, w hich, in turn, al-

izonta l path of insertion is requ ired to preserve the co ronal tooth structure despite a red uced d ia meter of the tooth in the ce rvica l ar ea (Figs 6-20c to 6-20e).10

lows the ceramist to pro d uce a progressive emerg ence of the interdental extensio n [Figs 6 2 0 0 a nd 6-20b). These very speci fic situations

FIGURE 6-2 0 : TOOTH PREPARATION FOR DIA STEMA CLO SURE . C losures of interdental triang les o r d iastemata are ra re situations in w hich maximum pe netratio n of the proximal surface is req uired to a llow the de ntal technicia n to ge nerate interdenta l mini-w ings wi th a prog ressive pro file that co mpensates for the loss of soft tissue or abnormal tooth positio n (6-20a) . Typical aspec t o f the co rrespond ing BPR; the mini-w ings, w hich form a prec ise line ang le (marked in red), are made w ith a po rcelai n of a hig her chro ma to prevent the illusion of a bulky tooth (6-20 b). Teeth a re o ften larger in the incisal area (6-20 c, I) co mpared to the ce rvica l area (C). Maximum proximal penetra tio n must be co mbined w ith a palatal butt margi n beca use it w ill allo w a horizonta l insertion pa th o f the veneer (6-2 0 c). The na tura l di vergence of axia l wa lls ca n be ma intai ned , which logica lly leads to maxi mum preservatio n of enamel (6-2 0 d; addi tiona l views of this case ca n be found in Fig 4 -5). When maximum proxima l penetratio n is combined w ith a pa lata l chamfer, it w ill o nly a llow a n ob liq ue insertion pa th of the veneer (6-20e) The natural div ergence of axial w a lls cannot be maintain ed , w hich logically leads to more invasive tooth prepara tion a nd increased risk of ax ial dentin exposure co mpared to 6-20c (Figure 6-2 0 b is repr inted from Belser et a l l o wi th permission .)

266

- - - - - - - c - - - - - - - - - - - - - - - - - - - -- - - - -

Horizontal insertion path

Oblique insertio n path

Compa tible wit h divergence

Co nvergence re,quired

-

6 I

T O OT H PREPARAT ION, IMPRESSION, AND P ROVI SI O NALIZAT ION

of interdental triangl es loss of pap illae) requir es the

Clos ure

(subseq uent to

same princip le the as discussed for di astemata . Fig ure 6 -21 shows a n additional requi rement for the subtle

complex case, closure of the space w as first visualized w ith the diagnostic mock-up and then follo wed by a ppropriate tooth prepara tion . Due to the o rig ina l prominence of these teeth,

clos ing o f a ny kind of interdentol space : to prod uce a g rad ua lly progressive emergence pro-

extensive dentin ex pos ures co uld no t be a vo ided , w hich required the use of an immedi-

file, the g ing iva l marg in must be placed into the

ate dentin bo ndi ng technique , desc ribed on fol-

ging ival sulcus. Such an approach w as a pp lied in the case shown in Fi g 6 -22 . Fo r this

lowi ng pages .

FIGURE 6-21 : INTRASULCULAR MARGIN FOR OPTIMAL INTERDENTAL CLOSURE. Intrasulcular margin s (center) not only a llow for op tima l interdental closure bul a lso for an improved emergence profil e co mpared 10 suprag ingiva l margi ns (right) . The gingival fiber apparatus is not affected by such modification of the interdental design w hen a n intrasulcular margin is used,28 and long-term esthetic success ca n be established, FIGURE 6-2 2 : COMBINED INDICATIONS FOR BPRs-CLOSURE OF INTERDENTAL TRIANGLE. Initial treatment of this ca se included graft-type interventions (detailed in Fig 5-4) follo wed by fab rica tion of study ca sts (6-22a) . Porcelain veneers w ere proposed to the pat ient to compe nsate for tooth agi ng, cracking, chipping, a nd thinning of enamel, as w ell as to reduce the interdenta l black triangle between the centra l incisors. Because of the o rig inal pro minence of bo th incisors, it w as not possible to proceed to an add itive w ax up, a nd a very limited amo unt of w ax w as added to the mode l to recreate adequate crown co nto urs (6-22 b). A simple acrylic mock-up was ac hieved (6 -22c to 6 -2 2 e) to al low the pa tient to envisio n the trea tment o b jective. Comparative views before and after appli cation of the mockup w ere shown and exp lained to the patie nt (6-22f, 6 -22g), w ho immedia tely accepted the treatment proposal, It w as decided to mai nta in the preexisting metal-ceramic crow n on the right latera l incisor, Tradit io na l tooth prepara tio n procedures included the realization of dep th grooves (6-22 h) followed by facial axial red uction, w hich was care fully con trolled using a notebook-type silicon index (6-22i , 6 -22 jl .

268

. ,'

..

6

I

T O OT H PR EPAR ATI O N , IMPRE SSI ON , AN D PRO VI SIONALIZAT I ON

IM ME DIATE DENTIN BO NDI N G Despite a ma jor effo rt to confine the preparation to the e na mel shell, pecu liar situa tio ns such as initial ly prom inent o r ma lal ign ed teeth [Fig 6-22 ) may still involve dee per pre paratio ns reaching dentin. W henever a substa ntia l a mo unt of dentin has been exposed by the preparati o n, loca l applicati o n of a dentin bo ndi ng ag ent (DBA ) is reco mmended. C linica lly, two method s may be a ppl ied to pro mote de ntin ad hesio n w hen ploci nq indi rec t bonded restorati ons. The first a nd co nventio na l approa ch consis ts of delay ing ap plicat ion of the DBA (eg , acid etching fol lowed by the app lication of the primer liquid a nd the bonding resin) until the la st treatment stage, w he n proc eed ing to luting the veneer. To avo id incomplete sea ting of the restorati on , it is usua lly reco mmended that the adhesive resin be kep t uncured w hen p lac ing the veneer. It is assumed that the pressure of the luting co mpo site durinq sea ting of the vene er may c rea te a col -

la pse of deminerali zed den tin (col lag en fibers) and subseq uently a ffect the adhesive interface co hesive ness 2 4 ,29,3o More recen tly, an o rigi na l approa c h w as proposed to o p timize DBA a polica tio n . 24.3 1-33 I Beca use the DBA appears to have a superior po tentia l for adhesion wh en applied to freshly prepared denti n, its app lica tio n is recommended immed iately after the co mpletion of tooth prepara tio n, before the final impressio n. A cli nica l ad vantage is that this precautio nary measure seals and protects the pulp-dentin o rga n and, by the sa me token, prevents sensitivity and bacterial leakage duri ng the prov isional pha se. The use of a filled adhesive resin [eg , Optibo nd FL, Kerr) mig ht facilitate this procedure , w hic h w ill be expla ined in C ha pter 8 (see Figs 8-1 1 a nd 8-12 ).

FIGURE 6-22 (CONTINUED) : IMMEDIATE DENTIN BONDING PRECED ING FINAL IM PRESSIO N S. Because of the proximity of the preexisting metal-ceramic crow n, safe finishing of tooth prepar a tio ns ca n o nly be ac hieved w ith oscil lating di a mo nd tips, w hich a re a lso useful to generate smooth a nd low-trauma intrasulcular marg ins (6-2 2k). Extended den tin exposures result from the nonadd itive w axup; immedi ate de ntin bo nd ing must be carried o ut, starting w ith etching o f the sclerotic ce rvical de ntin (35% phosphoric ac id), w hich req uires an extended etching time of 30 seconds (6-2 21 ). The remaining dentin is etched for only 15 seco nds [6-2 2 m) After rinsing a nd evacua tio n of excess water, a hyd ro philic monomer (primer) is a pplied with a gentle brushing motion [6 -2 2n) followed by suctio n of the excess solvent (6 -2 20; note the resin-saturated dentin with g lossy appeara nce). Fin ally, a thin coat of filled ad hesive resin (O ptibo nd FL) is applied and cured . Use of a periodo ntal probe a llows accurate and ca reful placement 16-2 2p). Excess ad hesive resin must be removed from the dentin a nd ena mel margin s w ith fine-grai n diamond burs (cervica lly) o r oscillating tips linterdenta lly) a t low speed 16 -2 2q ; see 6 -22 z). To avo id interaction w ith the impression ma terial, the surface of the c d hesive layer must be devo id of the oxyg en inhibition layer; add itional curing af ter covering the adhesive w ith g lycerin jelly is recommended . N ew def lectio n cord s have been placed fo r the fina l impressio n; note the intrasulcular margin at the mesial aspect of bo th centra l inciso rs (6-2 2 r)

270

,\ , '

v, "

'\,'

6

I

T O O T H PR EPARA TION , I M PRESSI O N, A ND PROV ISIO NA L IZAT IO N

Addi tio nal curing of the DBA through a layer of glyce rin jelly is recommended to remove the oxyge n inhibiti on layer and prevent interac tio n of the dentin adh esive wi th the impression materia l (especiall y polyethers ). W hen gingival margin s are in dent in, a marked chamfer is recommended to provide adeq uate marg in definition a nd enough spac e for the ad hesive and overly ing restorati on (Fig 6-

2 2 z ). Magn ifica tio n gla sses help to accurately place the ad hesive an d remove exce ss resin from the marg in . Furth er ad hesio n of the luting agen t to the preexisting ad hesive layer must be promoted by surface roug hening with a bur or microsandblasting plus dry ing wi th alcoh ol just before luting [see Figs 8-6b and 8- 12b).24

FIGURE 6-22 (CONTIN UED). The intrasulcular margin s al lowed the use of interdental mini-wi ngs to close the interdenta l black triangle 16-2 2s, 6 -22 t) . Ceramic o f a hig her chroma wa s used in the interdental and cervica l area (622u, 6-22v) Simulation of the root por tion is a lso possible wi th porce lain venee rs and was essential to the esthetic outcome of this case (6-22 w) . The befo re/ after views emphasize the esthetic a nd functional rejuvena tion of the smile thro ugh restora tio n of the enamellike shell, w hich enhance s color, crow n shope, and length (6 -22 x, 6 -22y).

272

DE N TI N

MARG IN

FIGURE 6-22 (CONTINUED): CONDITIONING OF DENTIN MARGINS. Schem¢tiC cross-sectional views of g ing ival dentin marg ins (D) wi thd~ flecti o n cord in place (ye l lo~A/ ). IE) Residual ena mel. Immedi ate d entin bondi ng is not possible in the presence of a traditional light chamfer (6-22 z, left center) beca use the adhesive .Iayer (Adh) tends to pull over the marg in, creating a feather-edg e finish line and insu fficient. marg in definition. Immedi ate dentin bonding ca n be easily carried out in the presence of a marked chamfer (6-22z, right centerlbecause ap plication of the ad hesive ca n be confined to the prepared surface and leaves sufficient space for the restora tion. For optimal margin definitian, the resin can be removed about 0.5 mm from the dentin perimeter w ith fine-groin d iamonds (6-2 2z, for right; see 6-22q) . In this lost case, the dentin bondi ng age nt must be rea pplied to the prepa ration margi n w ithout preliminary curing [ust before the final placement of the restoralion.

6

I

T OOTH PRE PARATION, IMPRES SI ON , AND PR OVI SIONALIZ ATION

DEFINITIVE IMPRES SION S Becau se o f the accessib le margins [usua lly fa-

Accura te re productio n of the surround ing sof t tis-

vora ble for BPRs), final impressio ns do not p re-

sues in the final imp ressio ns is impera tive, a s it

sent a maj or c ha lleng e . Preci se to o th p repara-

w ill help the ce ra mist to optimize tooth sha pe

tio ns and

g ing iva l

a nd contours. A s is the case w hen placi ng

tissues, in co mb ina tion w ith a "o ne-ste p, double-mix" impre ssion techni que 34-36 (Fig 6 -2 3 1,

finish lines, a low -traum a ging ival deflection method is essentia I.36.38 The use of deflection

w ill p rovid e appropriate re production o f the

co rds ldevo id of ad rena lin impreg na tio n) in-

p reparatio ns a nd surro unding tissues.

duc es the least cl inica l damag e to the per i-

adeq ua tely cond itio ned

odo nta l tissues compared to other

rnelhods."

A d d itio n silico ne material s (polyvi ny l siloxo nes]

The p reexisting cord (used d uring tooth prepa-

are reco mmend ed due to thei r bro ad ly recog-

ratio n) is removed and repla ced w ith a new

nized ela stici ty and resista nce to teari ng ; they

an d d efi nitive pa c king (Fi g s 6 -2 3 b to 6 -2 3 h). A

a lso p rovide a ccuracy for multiple po urs, w hic h

syste ma tic approa c h using two co rds is recomrnendec ."?

will be essentia l in the fabr icati on of a d eq ua te master ca sts (see Fig s 7 -3 to 7 -6 ].9,3537

, :; -2 ~::J

r

.

FIGURE 6-23: CONDITIONING OF THE GINGIVA FOR THE ONE-STEP, DOUBLE-MIX IMPRESSION TECHNIQUE . C linica l view lo llowin q de finitive tooth prepa rations: crevicular fluid co nta mina tes the prep arati on margi ns (6-230 , arrowheads). High-qua lity impressio ns are possib le w hen a co mpressio n co rd [here, surgica l suture 2-0) is placed to seal the bottom of the sulcus. Individ ual co mpression cords a re placed , one per tooth from the mesial to the distal aspect (6-2 3b to 6-2 3e). The second co rd is placed over the co mpressio n co rd ; it is larger but a lso more superficia l (here, G ingibra id Oa , Va n R). Use o f two instruments (bimanua l techniq ue w ith a periodonta l probe and a spa tula) facil itates the insertion w ith low forces (6-23f) . The packing must rema in in place a nd be a llow ed to absorb moi sture fo r a bout 5 minutes to generale some expa nsion of the superficial cord (6-23 g) Excess mo isture is eliminated jusl prio r to ta king the impression. The deflection co rd can be placed co ntinuously on several teelh (6-2 3 h).

274

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I

TO OTH PREPAR ATION, I MPRESSI O N, A N D P ROVI SIONALIZ ATION

Gingival deflection

One-step, double-mix impression

A co mpression co rd of sma ll di a meter [surg ica l suture 2-0 or Ging ibrai d Oa, Va nR) is first plac ed in the bottom of the sulcus. This cord w ill remain in plac e dur ing impression ta king, thus "sea ling" the sulcus a nd limiting the flow o f

In the o ne-step , double-mix imp ression tech­ nique , the defl ectio n co rd is removed , immedi­

crevic ular fluid . A more supe rfici a l deflec tio n co rd (G ing ib ra id Oa or 1a, Va nR) is then inserted in the entra nce of the sulcus w ith the bi man ual tech nique (Fig 6­ 23 f). A sing le co rd ca n be used for multiple prepara tio ns (Fig 6-2 3 h). When immedi ate denl in bo nd ing has been app lied , the inhib i­ tion layer must be removed from the surface of the adh esive layer to avo id interaction wi th the imp ressio n ma teria l; gentle rub b ing w ith pumice o r add itio na l lig ht curing after co vering the adh esive w ith glycerin jelly (air blocking) mig ht be requ ired .

ately follow ed by in jection o f a light-body im­ pressio n ma teria l into the sulcus a nd insertio n of the tray loaded w ith a more visco us materia l (Figs 6 -23 i to 6 -23 q ). Due to the visco elastic behav io r of gin gi va l tissues, they rema in de­ flected a fter removal o f the co rd (Fig 6 -23 rL w hich al lows pe netration of the ligh t-bod y im­ pression material into the sulcus, slightly be­ yo nd the prepara tio n margin s (Fig s 6 -23s to 6 ­ 2 3 u). Either comme rcial o r ind ividua l trays can be ada pted to the tech nique. Indi vidual trays, how ever, offer more accurate intrao ral posi­ tionin g , require less heavy-bo dy material , and fac ilitate fabricat ion of the master cast in the la bo ra to ry.

G ing iva l defl ection must be car ried o ut at

least 5 to 10 minutes prio r to impression ta k­

ing to a llow the de flection cord to expa nd by

w a ter sorptio n.

FIGURE 6-23 (CONTINUED) : ONE-STEP, DOUBLE-MIX IMPRESSION TECHNIQUE. Schema tic view of the clinica l situa tio n w ith do uble co rd pa cking [6 -2 3 i). During impress io n taking , seq uences 1, 2 , and 3 (Fig 6 -2 3i l are carried o ut rapidly. The def lectio n co rd is removed , and a fluid impression material (blue) is immed iately injected into the sul­ cus. The entire prepara tio n is covered w ith the lig ht-body ma teria l a nd d irectly fo llowed by the insertion of the tray, w hic h has been loaded w ith a more viscous material (purple). The co rrespond ing "dy na mic" clinical seq uence is de­ scribed in Figs 6 -2 3 k to 6-2 3q . The sa me operato r ca n simulta neously remove the deflectio n co rd and inject the light­ body materia l (6-2 3 k to 6-2 3 n). Insertion of the tray is precede d by gentle a ir blow inq of the low-viscosity materia l (6 -23 0) . The entire proce d ure is carried o ut w ith lip retractors in plac e (6 -2 3 p , 6 -23 q ). The purpose of this technique a nd the viscoelasticity of the soft tissu es are illustrated by the clinica l view iust fo llowin g retrieva l o f the tray : the g in­ g iva is still w ell deflected and the co mpression co rd maintai ns a dry sulcus (6-2 3 r) . The impression demo nstrates ac­ curale reproduction o f prepa rations, ma rg ins, a nd a bsence of blood (6 -23s, 6 -2 3 t). M agn ified view of the impres­ sio n cross sectio n aro und the left central inciso r (6 -2 3 u) Provisional restorations o f this case ca n be seen in Fig 6 -28 . (Pa tient treated in co lla bo ration w ith Dr N . Pera kis, University o f G eneva )

276

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6

I T O OT H

PREPA RAT IO N, IM PRESSI O N , AND PR OVISION ALI ZATI ON

DIRECT PROVISIONALS AND PROVISIONAL BONDING Fabrication techniques Provisional venee rs ca n be fabri cat ed in the sa me w ay as the di agnostic mock-up, ie, using a rigid silico ne matrix loaded with self-curing acrylic resin and a pplied to the prep aratio ns until curing is co mplete. Use of co mposi te material s or stiff resins is not recommended beca use they are too brittle. Sta ndard self-curing acrylics , w ith their elas­ tic ity and favora ble ha nd ling pro perties, are optimal materials to be used as provisional s. There are variou s ways to make provisiona l ve­ neers that involve different fabri cation times a nd esthetic outcomes . The more sophisticated

methods require the co mbined use of dentinlike a nd ena mellike acr ylic resins (Fig 6 -24) . The Widely recogni zed Vita shade gUide ca n be used to seled the righ t dentin core materia l (eg , N ew Outline, dentin, Anaxd ent). Enamellike acrylics must not have specifi c shade s; glassy tran spar ent (eg, New Outline, Tra nspa Clear ) and milky translucent resins (eg, N ew O utline, Med ium Va lue) can be co mbine d to ac hieve dif­ ferent incisal effeds. Whatever technique is used, it always star ts with abund ant a pplicatio n of Vaseline onto the prepara tions, neig hbo ring teeth, and g ing iva . Three a pplica lion modes of the resin w ill be exp lained: o ne step , single mix (o ne sing le resin); o ne step, double mix (tra ns­ par ent + dentin) ; two steps, do uble mix (dentin corel cut back + translucent).

FIGURE 6-24: BASIC ACRYLIC MATERIALS REQUIRED FOR ESTHETIC PROVISIONAL RESTORATIONS . Highly es­ thetic provisio na l restorations can be achieved using den tinlike core material (left) and incisa l resins (center, right) (New O utline). Various aspecls of the inci sal edge are obtain ed by mixing different rati os of transpar ent a nd translucent in­ cisal materials: 50% :50% for an average tooth, 70%: 30 % for a young tra nsparent incisal edge. The dentinlike resin co re features standardi zed colo rs based on the Vita shade guide.

FIGURE 6-25: MULTIPLE PROVISIONAL VENEERS FABRICATED WITH A ONE-STEP, DOUBLE-MIX TECHNIQUE . C linica l view immed iately folloWing preparation a nd final impression of the fo ur moxillcr y inciso rs [6-25a) A very light layer of self-curing translucen t/tra nsparent mixture is a pplied to the silicon index (6-25b) . The uncured resin is then cove red with dentinlike material (6-25 c). and the ind ex is immediately press ed over the preparatio ns; the ope r­ atory field is then coo led by rinsing. Because thin veneers ca n be def ormed by premature elimina tio n of the silico n ind ex, the index is removed o nly a fter curing is co mplete (6-25d ). The splinted restoration s a re easi ly unlocked w ith a sca ler inserted at the proximo ] surface. Final view of the provisio nal a fter g ross excess removal a nd g laZing (6-25e, 6-25f).

280

Core resin

Transparent

Tra nsluce nt

(Vita shades)

(glassy)

(milky)

ONE

S T E P

f

DO U BLE

M ,I' X,

6

I

T O OT H P REPAR ATION , I MP RESSIO N , AND PROV ISIONA L IZAT ION

One step, single mix. This is the trad itiona l and

One step, double mix (Fi g 6 -25 ). A sma ll

shortest method . A sing le amo unt of co re acrylic

am oun t o f a tro nsluce nt/ fro r- spcre n' mixture is

resin is mixed , loaded to the silico n index, and pressed ove r the teeth. The powder co ntent can co nsist o f 10 0 % d entinlike resin (for d iscolored

first po ured into the inci sal edge of the silicon

index. It is immedi ately completed with a sec­

ond mixture o f dentinlike materia l a nd pressed

teeth] o r includ e 10 % o f tran sparent resin for a

over the teeth . This o ne-step method is simple

a nd not time-co nsuming a nd ca n crea te provi­

more natura l o utcome. This method a lw ays re­ sults in a resto ration w ith uniform shade and opacity. How ever, minor touch-ups such as ad­ d itional stai ning a nd glazing ca n produ ce a fa­

vo ra ble esthetic o utco me (see Fig 6 -28 ).

siona ls w ith a tra nslucency that g rad ua lly in­

c reases toward the inc isal edge .

FIGURE 6-25 (CONTINUED): SPOT-ETCH PROVISIONAL BOI'IDING. Each abutment loo th is subjected to ena mel spo t etching [6 -2 5 g ), then rinsed a nd d ried . The prepara tio ns are then coa ted w ith photopo lymerizing unfilled resin (6-25 hl, w hich is cured on ly a fter the sea ting o f the provisio nal (6 -2 5 il. The final situa tion shows exce llent primary sta­ bility due to com bined splinting a nd bo nd ing (6-25 jl. These provisio na ls reprod uce the add itive w axup w ith high fi­ delity; tooth shop e and incisa l co ntours co nform much better to the so il tissues a nd lip line (6-25kl than at the beg in­ ning of treatment (inset) Final views a nd other aspects of this case are found in Fig s 5-12 a nd Fig 7-10 .

282

6 I

T O OTH P REPARATION, IMPRESSION, AND PROVIS ION ALI ZAT ION

Two steps, double mix (Figs 6-26 and 6-27). A uniform mixture of de ntin is app lied to the sil­

icon ind ex, wh ic h is pressed over the prepa­ ratio ns until curing is compl ete . The inc isal edge is then cut back to reprod uce the natural morph ology of den tin. Photopo lymerizing co l­ ora nts ca n be applied to the d entin co re to simulate incisa l c harac teristics (cra ze lines, w hite spo ts, etc). The silicon ind ex is then load ed aga in, this time w ith a translucent/ tra nsparent mixture, a nd p ressed over the char­ ac terized dentin co re. This techni que co rre­ spo nds to the intra oral applica tio n of a la bo­

ratory sa ndwich techniq ue4 1.42 a nd ca n result in highly soph istica ted p rovisio na ls.

Glazing

Due to their extreme frag ility, p rovisio na l ve­

neers should not be mechan ica lly pol ished . A

light-curing g lazi ng resin ca n be used instead

[Skin Gla ze, Ana xde nt) . For multip le co n­

nected restoratio ns, the g lazing resin ca n be

mixed wi th brow n co lorants to infiltrate the

co nnectio n areas (proximal and inc isal embra ­

sures; Figs 6 -26m a nd 6 -26 nl, opticall y sepa­

ra ting the co nnected restorat ions a nd enhanc­

ing the esthetic outcome .

Most g lazi ng resins have a darkening effect

that must be a nticipa ted at the time of shad e

selectio n. For insta nce, a dentin shade A 2 w ill bec ome A3 after g laz ing .

FIGURE 6 -26 : PROVISIONAL VENEERS M ADE WITH A SANDWICH TECHN IQUE . Tooth preparations, neighb or­ ing teeth, a nd soft tissues have been iso lated w ith Vaseline (6 -26 a). The silico n ind ex is first load ed w ith d entin resin based o n Vita shade-g uide selectio n (6-26b, 6-26c ) a nd pressed over the prepa rations until curing is co mplete (6 ­ 26d) . A reas that w ill be cut back are marked w ith a penc il (6-26e). A d ia mond bur is used at low speed (w ithout w ater spray ) to sha pe the incisal edge into a n a natomic dentin co re (6 -26 f). Incisal embrasures ca n be acc urately co nto ured w ith a brasive d isks (6-26 g ) and a sca lpel. W hite spots a nd craze lines ca n be pa inted o nto this dentin co re using photopolymerizing stains [not show n). A fter the surface of the cut-back resin is w et w ith liqui d monomer, the silico n index is loaded w ith a tra nsparent/tra nslucent mixture (6-26h, 6-26i ) a nd pressed over the preexisting de ntin co re until curing is co mplete (6-26il Both veneers a re kept co nnected 10 enhance primary stabi lity. A fter g ross excess remova l, the connection area can be sculpted w ith a sca lpel to create a thin sulcus (6-26 k). The restora tion is finally retrieved for finishing (6 -26 11

284

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-

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-

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S T E PS,

-

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STAINING

GLAZING

FIGURE 6-26"(CONTINUED): FINISHING. A mixture of g laZing resin and brown stains is used to slightly infiltrate the 'connectio n sulcus (6-26m, 6-26n j. After po lymerization, the outer surface is coated wi th .pure glazing resin (Skin Glaze) and cured (6-26 0 to 6-26q). A last curing must be car ried out throug h a layer of glycerin jelly (6-26r) to pre­ vent formation of an inhibit ion layer and ensure perfect curing of the glazed surface. Final integ ratio n of the provi­ siona l veneers is shown in 6-26s to 6-26v. Note how the brown interdental colorants mask the connect ion area and provide the illusion of ind ivid ua l teeth (6-26t). The sandwich acrylic prov isionals integrate well w ith the gingiva and lips (6-26u, 6~26vL w hich wi ll ensure a co mfortable tra nsitio n for the pa tient. FIGURE 6-27: INCISAL CHARACTERISTICS OF SANDWICH PROVISIONALS. The veneers on the central incisors have been fabricated in a two-step, double-mix sandwich techniq ue. Interarch relationships allowed the prov isional to be extended above the pala tal prepara tion rnorqi n' (arrowhead), which enha nced the primary stability and locking of the restorations (6-27 0 , provisional sectioned to show pa latal margins) . Distinct effects have been obtained (6-27 b, 627c) as a result of the con trast of opacity be tween the dentin and incisal shades (see Fig 2-8) but a lso because of the marked ana tomy of the underlying simulated de ntin core that shows several individual lobes. No photopolymer­ izing stains were used in this case. .

6

I T OOT H PREP A RATI ON,

I M PRESSIO N, A ND PRO VISION ALIZ ATION

Provisional bonding and locking After spo t etching of the ena mel, the prov isio na l luting is car ried out w ith unfilled adhes ive resin tha t is light cured throug h the restorations (see Figs 6-25g to 6 -25i ). Spot-etch bonding, how ever, must be avoi ded when extensive dent in exposures have al­ ready been coa ted with a den tin bonding agent, due to the possib le interac tions be­

Additiona l stab ility and definitive locking can be obtained by adding excess liqu id resin to the pa lata l surfaces (see Fig 6 -2 7 a ) and pa latal emb rasures. Splinting multiple restora tions can significantly enhance the primary stability of the provisiona l restorat io n. Optimal stability and locking can be obtained w hen the provisi o na l is left in the mouth during a ll sta g es of fabri cati o n (no retrieva l) and fini shing.

twee n the den tin bondi ng agen t and the pro­ visio na l bond ing resin. In these cases, the resto rat io n can be secured first w ith clear provisio na l ceme nt [TempBond Clear, Kerr) (Fig 6 -28 ).

6·28b

FIGURE 6-28 : PROVISIONAL BONDING WITH CLEAR LIGHT-CURING CEMENT. TempBond C lear is a two-co m­ po nent, slig htly tooth-colo red, tra nslucent cement (6-28a , 6 -2 8 b] It is self-cure cap a ble but can al so be light-cured, w hich should improve hardness and retention. Clini cal view of provi siona l veneers just before elimination of excess cement (6 -28 c). This provisio nal was fab rica ted w ith a one-step , single -m ix technique a nd characteri zed by sta ining the embrasures and g laZing (see Figs 6 -261to 6 -26 r). The tra nslucent provisio nal cement ca n ensure a favorable es­ thetic o utco me despite the minimal thickness and relative tra nslucency of the provisional veneers (6-2 8d , 6 -2 8e). Too th prepar ations and final impressio n of this case ca n be found in Fig 6 -23 .

288

6

I

TO OTH PREP ARATION , IMPRE SSION, AN D PR OVI SION ALI ZATION

17 Wa lls AW . The use of c d hesivelv retained all-porcelain ve­

References 1. Magne P, Kwon KR, Belser U, Hodges JS, Douglas W H C rack prope nsity of porcela in lamina te veneers: A simu­ lated o pera tory evaluation. J Prosthet Dent 1999;8 1:

327-334. 2. M ag ne P, Doug las W H. Add itive contour o f porcelain ve­ neers: A key element in enamel preservation, ad hesion and esthetic for the ag ing dentition. J Ad hesive Dent

1999; 1:81-91 . 3. Mag ne P, Perroud R, Hodges JS, Belser UC Cl inica l per­ forma nce of novel-design porcelai n veneers for the recov­ ery o f co ronal volume a nd length . Inl J Periodon tics Resto r­ ative Dent 2000;20:441 -457.

4 . M agne P. Mega brasion: A conservative strategy for the a nterior de ntition. Pract Period ontics Aesthet Dent

199 7;

9: 389-395 . 5. Barghi N , Berry TG. Post-bonding crack formation in po r­ cela in veneers. J Esthet Dent

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6. Magne P, Versluis A, Douglas W H . Effect of luting com­ posite shrinkage and thermal loads on the stress di stribu­ tion in parcela in lamina te veneers. J Prosthet Dent 1999 ;

81 :335-344. 7. Lacy AM, W oda C , Du W , W a ta na be L In vitro mi­ croleakage at the g ingival margin of po rcelain and resin veneers. J Prosthet Dent 1992; 67 :7-10.

neers during the management of fractured and worn ante­ rior teeth: Part 1. C linica l technique Br Dent J 1995 ; 17 8:

333 - 336 . 18 W a lls AVV. The use of odhesivelv retained all-po rcelain ve­ neers during the manage ment o f fractured and wo rn ante­ rio r teeth Part 2 C linica l results after 5 years of follow-up Br DentJ 1995;178 :337-340

19. Mag ne P, Versluis A, Douglas WH. Rationa lization o f in­ cisor sha pe: Experimental-numerical a nalysis. J Prosthet Dent 1999 ;81 :34 5-355 .

20. Garber DA Porcela in laminate veneers: Ten years later. Part I Tooth prepara tion. J Esthet Dent 1993 ;5:57-61 . 2 1. EI-Sherif M , Jaco b R. The cera mic reverse three-quarter crown for a nterior teeth: Preparat ion desiq n. J Prosthet Dent 1989 ;61 :4-6 .

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1999; 19 :54 3-553 . 24 . Magne P, Doug las W H Porcelain veneers: Dentin bond­ ing optimiza tion and biomimetic recovery J Prosthodont 1999;12 111- 12 1

of the crown. Int

8. Stein RS, Kuwa ta M. A de ntist a nd a de ntal technologi st

25. M ag ne P, Doug las W H. Cumulative effects of successive

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9 . M agne P, M og ne M , Belser UC The esthetic w id th in fixed prosthodon tics J Prosthodont 1999;8:106- 118.

10. Belser UC, Magne P, Mag ne M . Ceramic laminate ve­ neers: Co ntinuous evolution o f indications. J Esthet Dent

1997 ;9 :197- 207 . 1 1. Highton R, Ca puto AA , Matyas J. A photoelastic study of stress o n porceloin laminate prepa rotions. J Prosthet Dent

1987;58: 157-161. 12. M og ne P, Douglas W H. Design optimiza tion a nd evolu­ tion o f bonded ceramics for the an terior dentition : A finite­ element anal ysis. Quint essence Int 1999 ;30661-672.

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14. M ag ne P, M agne M, Belser U. N atura l a nd restorative ora l esthetics. Part \I: EsthetiC treatment moda lities. J Esthet Dent 1993; 5 :239-246 .

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16. A ndreasen FM , Flugge E, Daugaar djensen J, M unks­ ga ard EC Treatment o f crow n fractured incisors w ith lam­ inate veneer restorations: An experi mental study. Endod Dent Traumatol 1992;8:30-35 .

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1997;78 :545-549 . 28 . Kop p FR. Esthetic princi ples for full crown restoratio ns. Part II: Provisionalizati on . J Esthet Dent 1993;5 25 8-264 . 29 . Dietschi D, M ag ne P, Holz j. Bonded to tooth ceramic restorations: In vitro evaluation of the efficiency and fa ilure mode of !wo modern adh esives. Rev Mens Suisse O do n­ toslomatol 1995 ;105:299-305 .

30 . Dietschi D, Herzfeld D. In-vitro evaluation o f marginal and internal ada pta tion of class II resin co mposite restorations oher thermal a nd occlusal stressinq , Eur J O ral Sci 199 8;

106 :1033-1042. 31 . Berlschinger C , Paul Sj, LUlhy H, Scharer P Dual ap plica­ tion o f dentin bondi ng agents: Its effect on the bo nd streng th. Am J Dent 1996 ;9 :115-11 9 .

32 . Paul SJ, Scha rer P. The dual bond ing technique A modi­ fied method to improve od hesive luting procedures. Inl J Periodo nlics Restorative Dent 1997;17:5 36- 545. 3 3 . Pa ul Sj. Adhesive Luting Procedures. Berlin: Qu intessence,

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TOOTH PREPARATION, IMPRESSION, AND PROVISIONALIZATION

34. Johnson GH, Craig RG. Accuracy of addition silicones as a function of technique. J Prosthet Dent 1986;55: 197-203. 35 Tian AH, Whang SB, Tian AH, Sarkissian R. Clinically ori­

I

6

39 Azzi R, Tsao TF, Carranza FA, Kenney EB. Comparative study of gingival retraction methods. J Prosthet Dent 1983; 50:561-565. 40. Nemetz H, Donovan T, Landesman H. Exposing the gin­

ented evaluation of the accuracy of commonly used im­ pression materials J Prosthel Denl 1986;56:4-8

gival margin: A systematic approach for the cantral of hemorrhage. J Prosthet Dent 1984;51647-651.

36. Magne P, Magne M, Belser U. Impressio ns and esthetic

41 Magne P, Magne M, Belser U. The diagnostic template:

rehabilitation: The preparatory work, clinical procedures and materials Schweiz Monatsschr Za hnmed 1995;

A key element to the comprehensive esthetic treatment con­ cept. Int J Periodontics Restorative Dent 1996; 16:

105.1302-1316. 37 Tuit CM, Rosen M, Cohen J. Becker PJ Effect of impres­

560-569. 42 Magne M, Magne P Schlusselelemente eines um fas­

sion technique and multiple pours on accuracy af stone models. J Dent Assoc South Afr 1991 ;46 5 15-5 18.

senden asthetischen Behandlungskonzeptes

Dent Labor

1999;47:545-555

38 l.oe HL, SilnessJS Tissue reactions to string packs used in fixed restorations J Prosthet Dent 1963; 13:318-323

291

"',

'. v ,

CHAPTER

7

LABORATORY PROCEDURES

A plethora of method s have been proposed fo r fab rica ting bonded porce­ la in restorat ions. This cha pter add resses fabricati on of the ma ster casts, a s well as the cor respo nd ing choice

of restorati ve

materia ls a nd techni q ue .

During this final treatment pha se , effo rt essentially focuses o n the rep ro­ d uction of a de sig n tha t has been a lready tested a nd approved by the pa­ tient du ring the di a gnostic pha se . Patient, clin ician , and ceramist w ill in­ tera ct for a last clin ica l trial o f the de finitive restorations befo re procee d ing to the final luting proced ure, w hich ellen completes this clin ica l sessio n.

7 1 L AB ORATO RY PRO CEDUR ES

CH OICE OF RESTORATIVE MATERIAL AND TECHNIQUE Composite versus ceramic

Ceramics: Which one?

A numbe r of systems using so-ca lled revolutio n­

The d iscuss io n a bove is ba sed on the use

ary com po site technolo gies have been mar­

di tiona l feldspathi c

keted in a n a ttempt to red uce la borato ry ex­ penses. However, the use of cera mics, instead

toughe r but a lso more so phistica ted ce ram ics, such as In-Cera m Spine l! [Vita ]' Procera [N o bel

o f compos ite resins, has proved its efficiency in the way patients ca n pe rce ive a nterior restora­

Biocare), or Em press (Ivoclarl, is questionable. In a cl inica l trial about lo ng-spa n incisa l edg e

tions, as demonstrated in a clini cal study by M eijering et ol. ' C eramic is a lso the most bio­

reconstruction using feldspathi c BPRs,8 the w o rst failur e was an ac cidental chi ppin g that oc­

mimetic materia l w hen it comes to replacemen t o f signi fican t a mo unts of tooth substance, pro b­

curred during a traumati c bite after 1 yea r o f clini cal service . The veneer w as poli shed a nd

a bly because of its abi lity to simulate and re­ store cro wn rig id ity.v Due to their high thermal

no further complications occurred (the veneer has been in cli nical service more than 9 years ).

expa nsio n a nd elasticity, co mpo site veneers are

In the same study, 12% of teeth dis played crack­

not able to achieve this goal 4 a nd seem to yield unfavorabl e esthetic s, unstab le marg ina l in­ tegri ty, a nd decreased survival rate .5 - 7 O n the

ing , w hich could justify the use

o ther hand , even tradit ional po rcela ins such as bas ic feldspa thic materia ls are able to co mpen­ sate for structura l tooth w ea kness. W hen used in the fo rm of bo nded veneers, they can contribute to the recovery of crow n bio mecha nics, even fo r nonvital inc lsors. :'

of tra­

porce la in . The use o f

of

toug her ce­

ramics. The possible o rig ins of these po stbon d­ ing cracks , how ever, can be identified (eg, error in tooth prepara tio n, as in Fig 7 - 1, o r in­ sufficient cleanin g of the inner po rcela in surface after hyd rofluo ric acid etch ing , as explain ed in Fig 8-3d ) and mig ht not be related to the inher­ ent toug hness of the materi a l. In a ny case , it must be de termined to w ha t extent cracking should be considered a fa ilure (Fig 7-1 ). C racking is a n unavoida ble phenome non in the agi ng o f brittle layered material s. In enamel, crack ing is a natural protective pro­ cess ag ain st tensile stresses.9 •10 Most intact teeth d isplay numero us enam el cracks.

FIGURE 7-1: THREE-YEAR FOLLOW-UP OF PALATALLY CRACKED VENEER. Baseline facial view of po rcelain ve­ neers (7- 1o }. Pa la tal cracki ng oc curred 2 w eeks after placement [7 -1b) d ue to a n erro r in toot h preparation (see Fig 6-13, ce nter) N o crack evol utio n is de tected after more than 3 years [7-1c). The restoration is still in clinic a l service more than 7 years la ter.

294

7

I

LABORAT ORY PROCEDURES

of

The crucia l rol e is playe d by the dentinoenam el

W ea r prope rties

[unctio n acting as a "c rack stopper" d ue to its spec ific architecture and co llagen fiber ar­ ronqernent. '? The sa me can be sa id about

most co ntesta ble ospect.":" Adeq uately fired feld spath ic po rcela ins, however, con show sig­

cracked feldspath ic BPRs: as lo ng as the bond between too th and restoration ca n survive, the

de ntal cera mics are the ir

nificantly less abrasio n com pared to aluminou s porce la in and noncrysta lline low-fusing g lass. 19

for six c racked teeth in the a fo rementio ned

In addition , porcelain veneers might no t be the so urce of sig nifica nt ena mel w ear problem s be­ ca use of the co nserva tive nature of the trea t­

studv." Fig ure 7-1 suppo rts

ment: the palatal and functiona l side o f the

restorat ion w ill be preserved , as w as the case this point, showing a n ear ly failur e of a veneer that cracke d on a pa la ta l surface a fter 2 weeks of cl inica l ser­

vice. This problem did not prevent the too th­ restorati on co mplex from co ntinuing to serve optima lly more than 5 years later. A basic mis­ take in tooth preparation (excess ive invasio n of the palata l surface w ith a long cha mfer) proved to be the cau se of this relativ e fai lure. II

tooth is o ften preserved and left intact. This as­ sumptio n is consi stent w ith the fact that most clinica l eva luations on porcela in venee rs and BPRs7.8,2o-24 ha ve not revea led sig nifica nt w ear problems.

Choice of fabrication technique

C rack propensity ca n be minimized by ( I)

Ceramic fired over refractor y die is the oldest"

"soft" preparations (no shar p an gl es), (2) suf­ ficie nt thickness of the ce ra mic material ,12.13

a nd most Wides pread method for fabricatin g a

(3) adeq uate wrap ping an d de sign of the restoration ,11,14.15 a nd (4) thoro ugh cleaning of the inner porcela in surface follow ing hydroflu­ or ic acid etching (see Fig 8-3 ).

porc elain piece . The main adva ntages techniq ue are as follow s:

of

this

• No specia l equipmen t is required . • Extremely sophi sticated effects of color and tran slucency ca n be o bta ined thro ugh a full­ thickness layering technique [Fig 7-1a ).

It is important to remember that ultima te tensile streng th o f ceramics used in the porcelai n-fused­

• Tradi tiona l feldspathic porcelains ca n be used;

to-metal (PFM) technique is 2 to 3 limes higher co mpared to that of natural enamel (see Table

w hen combin ed w ith hyd rofluoric acid etching a nd silaniz a tio n, they show extremely reliable

1-1) .

bonding to resins."

FIGURE 7-2: FELDSPATHIC PORCELAIN VENEERS FIRED OVER REFRACTORY DIES. These veneers are fabricated by layering leldspcthic porcelain over an improved refractory material. M arginal fidelity can be excellent, as illus­ trated by th e repositioning of the restoration on its original intact stone die.

296

7

I L AB OR AT OR Y PR O CE DUR ES

These advanta ges are also found in the plat­ inum foil technique , wh ich is the closes t al ter­ nat ive to the refra ctor y d ie techni que but re­ q uires less effo rt in cos t ma king . In add itio n, da ta from the early 1990S 27-29 repeatedly showed the superio r marginal fid el ity of plat­ inum foil veneers. These results have lost their releva nce since the introduc tion of improved refractor y material s leg , Ducera-Lay, Ducera ) and use of smaller indi vidua l dies .30.3J M i­ crosa ndb lasting wi th 25- to 50-~ m g loss pear ls is now used to remove the investm ent material from the completed vene ers, which also al­ low ed sig nifica nt improvements in margin al closure of refra ctor y-derived restorat io ns that can easily a pp roa ch 20 to 4 0 ~m (Fig 7-2) .32 The platinum foil technique suffers from the fact tha t cos ts must be prepared by trimming of the gingiva l part of the stone model . Newer meth­ ods w ith refractory d ies a llow the g ing iva l stone to be maintained [see section on "M os­ ter cos ts in the refrac tory di e techniqu e" ), w hic h is a maj o r element to qui d e the stra tifi­ ca tion a nd elabora tion of fine ceramic co n­ to urs a nd emergence profile. O ther techni qu es that have been proposed for fa bricati on of BPRs are di scussed below.

Cast glass-ceramic restorations (Dicor, C a ulk/ Dentsply) w ere first introduced for all-ceramic crow ns. The materia l exhib its interesting physi­ ca l and chemica l properties." but the high fab­ ricotion costs and restricted esthetics have lim­ ited further develo pment of this system.

298

Pressed cetamic" leg Authenti c , Ce ramay; Empress, Ivoclar ) offers tw o elabo rat io n modal­ ities: the reinfo rced pressed porcelain is used to fabricate ei ther o n entire restoration o r o nly a core . This latter option a llows esthetic improve­ men ts and ch ar a cterization by addit ion a l cera mic firing. Esth etic characterizat ion , how­ ever, remains very limited co mpared to the full­ thickness laye ring that ca n be app lied w ith the refractory d ie techni que.

Slip costuiq" (In-C era m Spinell , Vito Zahnfab­ rikl ca n generate restora tio ns wi~h high er intrin­ sic streng th compared to other systems . The basic method w as o rig inally marketed for full crowns and la ter adopted to BPRs w ith the use of spi nel [M gA IP 4) instead of a lumino. Due to the high crystallin e co ntent of this materia l, tra­ ditiona l hyd rofluoric acid etchi ng is not effec­ tive . Resin bond ing to In-C eram alumino , for in­ stance, requir es tribochemical silica coa ting o r use of a special resin monome r."

Machined ceramics (Cerec, Sirona ; C elay, Mikronal, even tho ug h original ly designed for chairside use, have become popular for la bo­ ratory use a lso. BPRs mode from machin ed ce­ ramic suffer fro m shad e uniform ity and rather simp listic anatomy, unless additi onal porce lain firings are carried out.

I

LABORATORY PROCEDU RES

7

MAS TER CAS TS IN THE REFRACTORY DIE TEC HN IQ UE

Add ition silico ne impression materia ls are ideal for the refracto ry di e technique : they are elastic, resistant to tearing , and , above a ll, they al low accurate multiple po urs, w hich is essentia l to the fabricati on of master costs .":" A sequence fo r fabri catio n of master casts is exp lained in Fig 7­ 3. This techniq ue is a var iatio n of other proto­ cols pro posed by Sheets a nd Taniguchi 30 and C hiche and Pinault .3 1 The prod uction of qual ity refractor y BPRs can be rela ted to the use of multiple cas ts resulting fro m three co nsec utive po urs of the sa me fina l impressio n, ea c h cast being used for on ly o ne preci se purpose (Fig 7- 3 ). M ultipurpose casts a re not indi cated beca use each use w o uld re­ sult in prog ressive d eterio rat ion .

First pour: Single dies A very accura te produ ction seq uence must be respected and is summar ized in Fig 7-4 .

they must be care fully han dled becau se they are the most accurate reproduction of the prepara tio n. M arg ins are immedi ately trimmed , marked w ith a red penc il, a nd co ated w ith cy a noac ryla te hardener (M ar g id ur, Benzer Dental ). Further trimming must be per formed to repr odu ce a root form w ith tw o ant irotat ion groove s (Figs 7 -4a a nd 7-4b). These o rig ina l d ies must be kept unto uched be­ ca use they w ill be used to verify the fina l fit of the restoratio ns (co ntro l di es).

Refractory dies. The co ntrol d ies are immed i­ ately duplica ted using high-quali ty la borato ry silicones (eg, Deg ufo rm, Deg ussa) (Fig 7-4a ). Tw o sets of rep licas are po ured in stone . O ne set is co ated w ith die spa cer 1 mm short of the margin and then duplicated to generate a set of refractory di es (eg , Ducera-Lay, Ducera ). The other set of replicated stone dies w ill be used in the fa bricat ion of the soft tissue model . The re­ fractory d ies w ill also integrate the soft tissue cast but need additiona l preparato ry steps.

Stone dies. Sing le di es a re made of vacuum­ mixed improved stone (eg, w hite Fujirock. G C) ;

299

', ' \

.\.

"

MA S T. E R 1st pour

2 nd pour

3rd pour

Indi vidual ' d ies

Sol id model

Soft tissue model

,

Trimmed to simulate root w ith a ntirotation g roo~es

,

Mul tiple sets , Orig inal (stone) . • Stone replica : .• .Retractory replica .~

..

Final control of seating and mar'gi nal fit (original die) '

l Mounted in articulator w ith antago nist . :.... ; : : ... .

..

Occlusal a nd proximal . adj ustments

Die stone replica .' repositioned into impression

, Hard stone gingiva :+- rem ovable and . inferchcn q eoble d ies (stone refractory)

..

...•~ Ce ramic layering . . and finishing

\.

,I

FIGURE 7 -3: SUMMARY OF SEQUE~CEFORTHE: FABRICATION OF CASJS-C0f'.l?E.CUTIVEPO~RS OF THE FINAL IMPRESSION.. One set of casts is used for a single purpose; as ind icated a t the .bottom{blacko rrows}: Stone and refractory replicas of individuoldles are required to generate the soft tissue mode l {dotted arrows).Details o f the fa brication of each cast are presented in' follOWi ng fig ures . FIGURE 7-4 : SEQUENCE FOR SiNGLE DIE FABRiCATION AND DUPLICATION. Desiqn.o nd configu ration of the original hard stone die include a conical root shape,a ndtw o latera l slots. .I hellrst step is to produce a hi gh-precision . silicon mold of this die (d uplicating impression 1): A r eplica is poured using the same hard stone (stone replica 1L and die space r is ap plied 1. mm short of the marg in {red area}; a h i gh~preci si on silicon mold of lhestonereplico w ith the die space r is prod uced (duplicating impressi on 2 ). Two sets of di e~ are ultimately genef()ted : one set in rehoctorv material poured in d uplicating irn pressjon 2 · end ' bne set in' hard stone '(stone replica 2) 'pbured i.n duplic ating im­ pression 1 (7-4a). The second stone replica d oes not include the die spacer and will be. repositioned . into -theorlq i­ na l impression for fab rication of the soH'tissue model (see Fig 7 -6a): ' . . .

M U L TID I, E

T Ee H ' N

QU

E'

7

I LA BORATORY PR OCEDU RES

Refrac to ry di es must underg o the followi ng

Second pour: Solid cast

prepara tory steps: 1. M argi ns are marked w ith a specia l pe ncil that is resistant to firing. 2 . A dehyd ra tion firing is car ried o ut (1 , 1OO°C fo r 5 minutes) . 3. A co ating of fine-gra in po rcela in pa ste (con­ necting layer) is applied 1 mm apica l to the margi ns an d fired (9 7 0 °C fo r 1 minute). Step 3 ca n be repeated until a smoo th, even surface is ach ieved . The fine-g rain co nnecting po rcela in leg , C o nnector Ducera -La y, Ducera ) is an essentia l ing red ient for the fina l fit of the restorations; it ac ts bo th as a sea ler o f the re­ fractory surfac e a nd as a n adhesive (ancho red to the di e) tow ard whi ch the firing shrinkag e sho uld occur. For larg e teeth, the root po rtio n o f refracto ry dies can be shortened slig htly, be­ ca use experience has indi cated that the smal ler the di e, the better the marg inal fit.

I'

Tedi o us trimming is avo id ed beca use al l sets of d ies (includ ing refracto ries) have an identi­ ca l root portion , w hic h co nstitutes the exact replica of the o rig ina l sing le di es.

The same extra-hard sto ne is used for the pou r­ ing of a full arch. This cast must be trimmed a nd mounted in an art iculator (Fig 7 -5). Beca use the sol id cast represents a g ood ref­ erence for interdenta l relationships, it w ill be used for the fina l check o f the oc clusio n (intra­ and interarch co ntac t po ints). The use of a mounting ta ble a llow ing arb itrar y hinge axis tra nsfer on a semiad justa ble ar ticula­ tor (eg , Pa lla dent) is reco rrrnended. '? Follo w ing this method , accurate stab iliza tion can be ex­ pected . Numero us errors ca n be genera ted dur­ ing the mounting of maxillary casts with a face­ bow " : as a result, the face-bow yie lds no profitable improvement of occlusa l accura cy. Posterior teeth must have adequate occl usa l re­ lationships, a llowing the mandi bular cast to be positio ned in max imum intercuspation w ithout regi stration material . A soft silico n bite sho uld be used on ly in case of unstab le positio n; it is important to real ize, however, that vertica l erro r at the oc clusal p la ne and at the co ndy le of an ar ticulator ca n be generated w hen recording ma teria l is present.

FIGURE 7-4 (CONTINUED). Example of precision silicon mold in a plastic ring (inset). Tw o diffe rent molds have been used to ge nera te stone replicas o f the orig ina l d ies {left} a nd a refractory set {right}. Marg ins of the refractory dies have been ma rked w ith a refractory pencil, followed by a dehyd ration firing at 1, 1OO°C. A connecting porcela in paste has been applied over the entire preparation plus 1 mm ap ica l to the margi ns {arrowheads}; it produces a glossy surfac e followin g firing at 9 7 0°C. Each set of dies features the same config uratio n and desig n (root form wit h an­ tirotation g rooves) (7-4 b).

302

,

I N

,

'

'.,

,

,

D I V I D U A L'

DI E S

"

' " ,

7

I L A BO RATO RY P ROC EDU RES

Third pour: Soft tissue cast To generate this cast, stone rep licas of or igina l individ ual di es are carefully repositioned into the impression , sta b ilized [Fig 7-6a L a nd iso­ lated . Stone is po ured arou nd the dies , result­ ing in a ca st ba se w ith a ccura te g ing iva l co n­ tours and artificia l a lveoli conforming to the o rig inal shape of the dies (Fig 7-6b). The mo jo r ad vantage of this cast is tha t stone dies an d refractor y di es can be inserted a nd inter-

SO L I D

cha nged , due to the identica l design of their root portions , w hich have the same an tirotati on grooves [Fig 7-6c) . This cast is mai nly used d uring the ceramic layerin g proce ss and ca n be mounted in an ar tic ula tor as a g ross g uid e for occl usio n. The soft tissue cast should not be considered p recise and , therefore , sho uld not be used for fine occlusa l cdjustrnents . Fo r fab­ rica tio n of multip le veneers , sto ne d ies rep li­ ca ting the w ax up can be inserted to qu ide the a p plica tio n of po rce lain [Fig 7-7 ).

C A S T

FIGURE 7-5: SOLID CAST. This o ne-piece ca st is the o nly o ne thot must be mounted in the ar ticulator (7-50, 7 -5b) . The sto ne g ing iva ca n be trimmed a round the a butment teeth to ensure the seating of the final restorations [not illus­ trated) . FIGURE 7-6 : FABRICATION OF THE SOFT TISSUE CAST. Sto ne die s are repositioned in the impression, stabilized w ith pi ns and sticky w ax (7-60), and finally isolated and sealed wi th a thin layer of wa x (using a hot electric spatula , not shown]. The first a mount of stone is poured arou nd the die s, the cast ba se be ing poured in a seco nd step afte r removal of the pins. The soft tissue cast includes standardized alveolar sockets (7-6b]. The antirotation grooves of in­ dividual dies are reprodu ced and a llow fine positioning of either stone di es (0), refractory di es (b), or di es reprod uc­ ing the w ax up (e) (7-6 c). FIGURE 7-7: ADVANTAGE OF INTERCHANGEABLE DIES FOR FABRICATI ON OF MULTIPLE VENEERS. A silico n matrix is used to rep roduce the d iag nostic w axup o n the stone d ies of the soft tissue cast (7-70 , 7-7b) . The sa me cast ca n be load ed w ith the refractory dies (7-7c). Wa xed d ies can be inserted selectively during ceramic stratifica tion to g Uide elaboration of pro xima l surfaces and to respect the particu lar dime nsions of ea ch tooth .

304

S 0

F T

T I S S UE

CA S T

7

I

LABOR ATOR Y P ROC ED U RES

CERAMIC LAYERING AND FINISHING Ela borate stratifica tion methods have been pro­ posed by the most di stingui shed ce ra mists aro und the world . Fo r cli nicia ns, under standing the principles of ceram ic layer ing wil l result in an improved eva luatio n and app recia tion of the ce ramic w o rkpiece. Una ttainable goa ls

The method presented here is a rational and di­ dacti c adaptati on of the dentino enam el laye r­ ing fou nd in na ture; it is based o n the use of a feldspathi c por celain (Creation , Klema) and can be used ei ther for veneering metal-cerami c core s o r for direct appl icati o n on refract ory di es

a nd unrealistic co rrectio ns a re often reque sted by cl inicia ns w ith insuffici ent dental techn ique aw aren ess. O n the other hand , those w ho have developed the ir co mprehension of ce­ ramic stratificati on w ill directly benefit from this know ledge by (l ) improving the w ay they han­ dle the ce ra mic pi eces and (2) strengthening their ow n intraoral layering techni ques w hile using freehan d co mpo site restoration s.

[veneers, inlays, and on lays). It Simply consists of two to three co nsecutive firings follow ed by g laZing (F ig 7-8 ): (1 ) the opa que de ntin firing (o ptio na l, on ly for staine d o r fractured teeth); (2) the dentino enamel core firing; and (3) the "ena mel skin" firing. Finishing and mechani cal poli shing w ill also be d iscussed . A typi ca l firing sched ule is g iven in Ta ble 7 -1 (loca ted a t the end of this sectio n).

FIGURE 7-8: STEP-BY-STEP CERAMIC STRATIFICATION . Preop erative a nd immedia te postoperative views (7-8a, 7-8b) o f a pa tient w ith mixed indica tio ns for BPRs (types liB, IIC, a nd IliA). The first ba ke wi ll ge nera te an op aq ue dentin co re o n the fractured tooth (7-8c to 7-8e ) It is foll ow ed by the applica tion of a core of regular dentins (7-8f) and more translucent incisal enamels (7-8g) . Modified dentins are infiltrated to simulate inner charac teristics of the in­ cisal edge (7 -8 h). A n inner translucent enamel skin cov ers this buildup (7-8 i, 7-8il , a nd then the seco nd bake ca n be carri ed out (7-8 k; note the shrinkage of crown volu me).

306

BASELINE

OPAQUE DENTIN

DENTIN BUILDUP

INCISAL WALL

INNER ENAMEL SKIN

,----'-----~--'----'--------=------'-=-'____,

r'---=--------'--'-'------~~-~___,

BAKE

INTERNAL STAINING

BAKE 2

,--~'------~--=---=----'----~___,

r:

C UT BACK . OF , BA KE 2

BAK E 3 ·

ENAMEL STAINS / BAKE .2 '

OUTER EN AM EL SK IN

G LAZE A ND POLISH .

SAN D BLASTED DI E ,

(

.' ,

FIGURE 7-8 (CONTINUED) . A slig ht cu tback (7-81) should 'a llow a pplication of superficial ena mel sta ins followed by low-tern perc ture .(80 0 °C) fixation bake (7-8m) . The final volume of .the .resforotioncon be ac curately obtained throug h the opplicc tion of a t hin enamel skin V8n) and its subsequent firing(7-80), Glozing and mecha nical polish­ ing o re comb inedto ob tain. the final surface texture and gloss (7-8pl : The refractory mote rio l is removed by mi­ , croso ndblosnnq only-otter completion of' surfac e finishirigprocedures .!7-8q). ,N ofe the we l,l -define~ vertica l lobes (7-$r, 7-8s), nafura l emergence, architecture, and g loss of the fac ial ·surfac e ,(7:8t). Because of the rationa l dentin buildup (opaque plu s regular dentins), no transiti.on ca n be seen betWeen the tooth-suppor ted part of the restoration a nd the freestanding porcelain .inciso l edge (7-8u). The ultimate esthetic inteqrc tiono! the BPR is possible only in the presence of adeq uate g ingivol contour (note perfeCt distal gi ng ival seam)'and favorable periodo ntal response (7-8vl. Diagnostic and preparato ry steps of this case are' illustrated in Figs 5-6 a nd 5-7,' tooth preparation a ~d provisional­ iz()tion in Fi gs 6-10 and 6-26 . ' Cl

.v..

7

I L AB O RATO RY

P ROC ED U R ES

Fi gures 7 -9 a to

7-9c show the postopera tive

a nd tooth prep arati on views, respectively, of a case developed with the stratifica tio n principles deta iled in the follow ing para gra phs.

Unless a special preliminary opaque build up is req uired (as mention ed a bove), stratifica tion

Opaque dentin buildup

ca n normall y start w ith the a pplicatio n of den tin pow d ers using the base shade d entin (usually several shades wi th hig her chroma in the ce rvi­

Tw o typical situalions require the use of modifi ed o paq ue dentin : stained teeth (see section o n "Masking effects") a nd fractured incisa l edges. In the la tter, the lack of sufficient supporting nat­

ural dentin must be co mpe nsated by a speci a l

build up of opaq ue dentin that reprodu ces a sim­ ilar outline for a ll preparati ons (Figs 7-9d to 7­

9 f). The abse nce of opaq ue dentin w ould result in increased lig ht ab sorpti on at the level of the miss ing natural dentin. Similarly, w ith stained tooth preparations, the absence of a thin, modi­ fied opaque dentin liner w o uld result in insuffi­ cien t masking a bility of the veneers . High er­ va lue dentin can be used fo r this purpose:

I '

Dentin buildup

ca l area a nd high er va lue in the inci sal area ]. A full-size tooth is built in dentin using the palatal silico n ind ex of the w axup as a mold

(Figs 7 -9 g a nd 7-9 h).

Cutback

This basic form is then redu ced , especi al ly a t

the incisal and proxim oinci sal level, to g ener­

a te space fo r other po w ders (Fig 7 -9 i). The cut­

ba ck dentin should reprodu ce the incisal dentin

co re described in Fig 1-2 . For ce ntral incisors,

this architecture typica lly include s three basi c

vertica l lobes, o r mamelons. The w ax up is co n­

sta ntly used as a reference (in the form of a pa latal silicon index) for the placement of the different masses.

FIGURE 7·9: STEP-BY-STEP CERAMIC LAYERING. * Final view of the case that will be deve loped and the initial tooth prepara tions (7-9a to 7-9 c; the black-and-w hite a nalog piclure is presented to a llow a better percep tion of the final brightness a nd va lue) All of the layering w ill be performed on the soft tissue ca sl; refraclory dies have a lready been dehyd rated, coated with the connecting porcelain , and fired (7-9 d ). In fractured teeth, the first increments are made w ith opaque dentin pow de rs to restore the missing dentin (7-ge ); they are immedi ately fired (7-9 f). The tooth is then fully built w ith dentin powders (7-9 g , 7-9h ) The volume is reduced incisally and proximally by crea ting co ncave sur­ faces (7-9i ). Both views in 7-ge a nd 7 -9i are d irected dow n to the incisal edge to improve perception of the rela­ tio nship be tween the build up and the silico n index. (Figure 7-9 a is reprinted from Magne 4 2 w ith permissio n.) * Some ceramic powd ers hove been artificia lly sto ined 10 allow beHer perception of the buildup technique. Pink enamels; yellow = modified dentins; unstained = shaded ena mels and enamel skin.

31 0

= regular

denlins; blue

= incisal

\.'

,

\

\ .",

,

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"",'

BAsEL! N E

OPAQUE DE ~rfIN

BAKE

".' .

D.ENTIN BUILDUP

r--"--'-'---'----'----'----'-----'-~-----'--__.r-----'----

----'-----'--'-'--___,

, C UTBACK

7

I L AB OR AT ORY

PR OCE D URE S

Enamel incisal wall Two d istinct "ho rns " of pure enam el are placed a t the mesia l and di stal aspects of the inci sal edge (Figs 7-9 j an d 7-9k). Their exact loca tio n

o us interna l effects w ithin the inci sal edg e are c rea ted by the ba la nced a pplica tion o f fluores­ cent and nonfluorescent stains (Fi gs 7-9 p to 7­ 9 r). Fluorescent sta ins w ill ge nera te high-val ue area s leg, ide al for highli ghting dentin mamel­ oris], w hereas nonfluorescent stains tend to re­ d uce va lue [Fig 7-9 r). These distinct internal

a nd length are gUide d by the palatal silicon index (Fig 7-91 ). These mesial a nd d istal inci sal horns define the pal atal inci sal w a ll resulting from the pla cement of o ther vertica l enamel in­ crements (Figs 7-9m and 7-9n). The lifelike ap­ pearan ce o f this w a ll is achi eved by al ternating enam el powders with var ious translucencies and chroma . Fully tra nsparent inc isal ce ra mic ca n be mixed wi th the or ig inal ename l pow­ ders to g enerate a wi de rang e of va lues. Shaded ena mel pow ders ca n a lso be used . The incisal w a ll must be slightly oversized (ap­

Th e characterized d entin wal l is still thin (Fig s 7­ 9 s a nd 7 -9t). The next step is the a pp lica tion of

proximately 0 .5 mm longer and w ider than the silico n ind ex] to anticipate the firing shrinkage.

a n inner ename l shell; the entire faci al surface is cov ered with a co mbin ation of other tra nslu­

Dentin characterization The inci sa l w a ll is used as a substrate fo r the in­ filtration of de ntin powd ers that have bee n modi fied wi th intensive stains (F ig 7-9 0 ). Vari-

characteristics and effeds must be defined ac­ curately using a sl ide of a n intact reference tooth . The sa me procedure is a pplied to the pal ata l surface .

Enamel covering and first bake

ce nt and o pa lescent pow ders specia lly de ­ signed to simulate shaded ena mel. The cervical third , midd le third, and incisa l third of the facia l surface are covered separately. Special cervi­ ca l tra nsparent ena mels are applied first (Fig 7­ 9 u), followed by the definitio n of a central " belt" covering the mid d le third (Fig 7 -9v).

FIGURE 7-9 (CONTINUED) . The inci sa l w a ll is de fined first by the placement of mesial and di stal increments or in­ c isa l horns (7-9 j, 7-9 k). Their initial leng th co nforms to the silicon index (7-9 1) Vertical increments of ename l w ith var­ ious translucencies and chro ma are used to build the rest of the w a ll, the final length of wh ich should be a pproxi­ mately 0 .5 mm oversized (7-9m, 7-9n). The w a ll is then infiltrated w ith tinted dentins (yellow ish area in 7-9 0) to prod uce special internal effects of the incisal edg e (dentin mamelons) These dentins are modified w ith fluorescent reg, In N ova , C reation) a nd nonfluorescenf stains leg , Ma ke Up, C reatio n); both types of sta in have a w ide range of col ­ o rs (7-9p) Blac k light emphasizes the d ifferent behavior of each type (7-9q) . Even dar k In N ova co lors ca n feature a go od suppo rt of brig htness by fluorescence, w hile brig ht Make Up stains ca n a ppea r black under luminescent con­ d itio ns (7-9 r). The charac terized incisal laminate must be kept thin (7-9s) The same steps are app lied to the pa latal surface (7-9t). A preliminary enamel covering (inner skin) is app lied using shaded enamels (7-9 u to 7-9 w ) The tooth must be oversized to compe nsate fo r subsequent firing shrinkage .

312

IN CI SA,L WA LL

,., ....

I'N TE RNA LS TAIN IN G .

.. \.

J , INN ER EN A'MEL' SK·IN

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,',

.

"

.

\,

.

.

7

I L A BO RAT O RY

PROC EDUR ES

Different combina tio ns of shaded ena mels are used accord ing to the type of tooth (dar k vers us brig ht), but they are a lw ays applied a lternately in tiny vertica l increments (Fig 7-9 v). Specia l blue translucent enamel pow ders ca n be a pplied a t the proximo incisa l level w hen req uired . Fina lly, the remain ing incisa l wi ndow is covered w ith enamel pow ders that ca n integrate some o pa lescence (Fi g 7 -9w ). The subseq uent fil-in g (seco nd ba ke in the fabricati on o f fractured teeth) is ca rried o ut a nd should reveal three chara cteristic area s wi th w ell-defined va lues: hig h-va lue midd le third, ave rage-va lue ce rvica l third , a nd low -va lue incisa l third [Figs 7 -9 x a nd 7-9 y). This d istrlbution of va lues is found in 60% to 7 0 % of natural teeth (see Figs 2- 1Oc to 2- 1Oe).

Characterized enamel skin and firing At this sta ge, vo lumes 'sho uld be slig htly underbuilt [Fig 7 -9x ). It mig ht be necessary to cut ba ck the surface slig htly to leave a thin and unifo rm space fo r the a pplicatio n of the outer enamel skin (F ig 7-9z ). The appli ca tio n of this lost layer is usually prece ded by the introd uc-

tion of ename l characteristics, eg, in the form of white spots and craze lines (Fig 7 -9aa ). A low-temperature firing (800°C) all ow s the fixatio n of these stai ns before the fina l covering w ith the outer tra nslucent enamel skin. Here a ga in, d ifferent po wders must be used alternately in vertica l inc rements (F igs 7 -9 b b a nd 7 -9 cc). Translu cent/tran sparent o pa lescent enamels are indi cated a t this stage . Because this layer is thin, o nly minor firing shrinkag e w ill oc cur, al lowin g fine co ntrol of the ultimate shope a nd vol ume. The la st firing revea ls the interna l staining a nd structure of the buildup (F igs 7 -9dd and 7 -gee).

Contouring Beca use most spec ia l effec ts leg , stained de ntin, ena mel characteristics) have been embedd ed w ithin the previous layers, surface g rinding can be perfo rmed w ithout a lteratio n of these essentia l characteristics. The fina l co ntouring is fac ilita ted w hen the landmarks of c rown shope are mar ked w ith a pencil (Figs 79 ff and 7 -9 g g ). Cre sts and transitio n line a ng les ca n be either softened o r accentuated wi th d ia mond burs.

FI GURE 7-9 (CONTINUED) . The bake sho uld gene ra te a tooth w ith reduced vol ume, featuring a ll internal effects a nd dentin charac teristics (7-9 x). The palatal view revea ls the low-va lue incisal edge and the uniform opaque dentins underneath (7 -9 y). The first enamel skin must be slig htly undersized (7 -9z) to allow fo r its characteriza tion and subseq uent coverage . G rind ing is often necessar y to increa se space at the proximoincisa l level (7-9 z, arrowheads) . Tiny w hite spots a nd craze lines can be pa inted o n the red uced surface [7-9 00 ). N ote these effects especia lly a t the d istal incisal edge of the left central incisor (7 -9 aa , arrowhead) After a low -temperature firing, these stains are fina lly covered w ith the outer ename l skin (7-9 bb) The fina l sha pe of the tooth must be a lta ined (7-9cc) Following the last firing , the main tooth shape should be al most de finitive (7-9dd , 7-gee).

314

' \

., - ----'----'----'--'-'-'----'-- - - '---'--

---'--

-

';'

, ,

BAKE 2 ----,

(

,

SLiG HT CUTBACK OF BAKE 2

-,

ENAMEL 'STAIN S/B AKE 2'

, o'UTER ,ENAMEL SKIN

.------------'----~

(

"

r - - - ' - -- --

(

BAKE 3 ' ---'----------,

7

I LA BORATORY PROC EDURES

Adequate surface mo rpho logy must be ac hieved, espec ia lly vertical develo pmenta l lobes , before elaboration of the surface texture. Tiny horizontal develop mental g rooves should be prod uced (when required) on ly at the last stag e, someli mes even a fter g laz ing . Any type o f co ntouring should be car ried o ut w ith relatively new diamond instruments. Ceramists must be aware of the possible pro blems related to the use of old burs: diamond particles being sheared off not o nly ca use premature w ear of the bur but may also increase smear ing of the meta llic binde r onto the po rcela in surface . The smear ing o f nickel o n ce ramic substra tes has been dernonslroted ." As a consequence , new d ia mo nd burs characterized by a pure d iamo nd cutting surface w itho ut metallic binder between crystals have been propo sed but are still under development ."

intraora l pol ishing of po rcelain ca n eq ual o r su rpass the smoothness of glazed porcela in. Today, it is recog nized that improved esthelic results are o bta ined by po llshinq ." However, the deg ree of success of any polishing technique is still dependent upon a wel l-condensed po rcelain a nd adeq uate firing conditions, because poros ity in the porcelain is not co mpletely eliminated by pol ishing as it is in natural glaze firing .53 Therefo re, the combined use of g lazi ng a nd pol ishing ca n be ad vocated to improve bo th esthetic and surface characteristics. Mecha nica l pol ishing usually beg ins w ith d iamond-si licon w heels (Figs 7-9hh and 7-9ii), fol-

pared to the gold standard gi ven by the orig ina l glaze . Some authors initia lly demonstrated the superio r smoothness of g lazed porcela in.44.45

lowed by ove rg lazing (w i ~ h ad d ition of gl az ing liquid) or autog lazing, knowing that overglazing usually softens the surface texture . Hig hly reflective surface s are finally achieved w ith pum ic e and cal ci um carbona te (Sig ol in , Thom pson Siegel). Ca lcium carbo na te is a common abrasive materia l used in dentifrice. It is softer and finer tha n pumice a nd allow s exce llent finishing of the porcelain surface . It is used w ith brushes a nd felt tips [Fig 7-9 iil a t d ifferent rotating speeds : long-ha ir brushes used at relatively high speeds are ide al to finish smooth surfaces a nd co nvexi ties, w hereas short-hair

O thers, however, favo r mecha nica l polish ing 4&-49 Haywood et a 150 .5 1 even co ncluded that

brush es used at low speed are best to fin ish wavy surface s an d co ncavities.

Glazing and surface finishing A number of mechani cal pol ishing techniq ues are descr ibed in the literature and w ere com-

316

,

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G LAZ E AND PO LISH

~-----=- ---'"

\

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,-- -~-- ---------- -.,

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FIGURE 7-9 (CONTlNl:JED) . Tra nsition li nea ng l~~, lobes, a nd ' s u pe r fic i~ f g' roo~es ~ re marked w ith; pencil to assist the optimization of surloce ~orpho logy and contours ( 7~9ff; inset, black-and-white ana log), .I heporcelo jri restorations must remain on the refrac tory dies durlnqmechomcol contouring and finishing (7-9gg) , Silicon-d iamond wheels, felt tips, a nd diam ond paste ca n be used for preliminary finishing (7-9 hhj, Fociol.view of the veneers before g lazing (7 9i i), AMer glazing , a compact peor-s haped.felt tip and pumice can be used (7-9jj ), The final gloss (7-9 kk, 7-9 11 ) is obtained w ith brushes a nd calcium carbonate 'a brasive,

7

I

LA BORATORY PROCEDURES

At this stag e of the procedure , the restorati on is stili attached to the refracto ry d ie (Figs 7 -9 kk and 7-911 ]. The di e should be removed by sa ndbla sting (w ith 50-~ m g loss beads) on ly a fter co mpletion of surface finishing procedure s. M echa nica l polis hing requires the physica l suppo rt of the underly ing investment material , a nd premature removal w ould result in high risks for fracture w hile handli ng the ce ramic piece . The sa nd blasted porcelain w o rkpieces (Fig 7-9mm) ca n be repositioned o n the stone d ies (Fig 79 nnl, but fina l control of proximal co ntacts is ide a lly achieved with the solid cost. The clin ical try-in sho uld not revea l need for major co rrectio ns, especi a lly w hen ap pro priate

diagnostic steps have been acco mplished . Because at this stag e the restoratio n is no longer physicall y suppo rted by the di e, any corr ectio n firing s must be carried o ut o nly w ith low -fusing ceram ics (eg, Duceram-LFC, Ducera) . N o correction s were required for the case in Fig 7 -9 . Final views show adequate o pacity of the ceramic core due to the use of o paq ue dentin (Fig s 7-9 00 a nd 7-9 pp). The righ t a mo unt of luminescence wa s obtained as we ll (Fig 7-9qq ) beca use fluorescent stains were adequa tely integ rated into the buildup . The final touch is gi ven by the characteristics a nd interna l sta ining of the ena mel skin, w hich simulates the o pa lescence and na tura l imper fec tion s of ena mel (Fi g 7-9 rr) .

Table 7-1 Exa mple of firing schedu le Idle' 1°C)

Heat rate 1°C/min]

Hi-temp (0C)

Dry (min)

Hi-temp hold (min)

Die dehydration Connecto r peste

575 300

55 55

1,100 970

9 4

5 1

620

969

Denlin Colora nt fixation Enamel skin

300 403 300

130 80 130

960 800 950

9 2 3

0 0 0

620 620 620

959 800 949

C lozlnq, wi lh vacuum G lozing, no vacuum

300 300

55 130

950 930

1 9

0 0

620

949

Corrections, low fusing G la·z ing, low fusing

300 300

55 55

660 645

3 3

0.5 0.5

380

Vacuum start (0C) -

-

Vacuum stop (0C) -

-

659 -

FIGURE 7-9 (CONTINUED). Final view of the restorations oher removal o f the refractory material (7-9 mm). Because the soft tissue cost is not acc urate for oc clusa l relatio nships, reposition ing of the veneers on to the original stone dies might not be possi ble (7-9nn, arrowhead show inq inco mplete seating o f the restorati on ). The solid cast must be used instead . Both direct lig ht a nd tra nsillumination (7-900, 7-9pp) show the successful wo rk of the ceramist: the full incisal bulk of the po rcelain does not di ffer from the tooth-supported cervica l pa rt of the restoration, and it is impossible to di stingu ish these two areas de spite the very different underlying substrate (note view of tooth prepara tio n inset at 7-9 00 ). (Fig ures 7-900 to 7-9 qq are reprinted fro m M ag ne a nd M ag ne 54 w ith permissio n.)

318

DIE 'SAN DBLASTED'

'"

,

.,'.,

FIGURE 7-9 (CONTINUED) . A black 'light used to evaluate the lluorescence reveals 0 balanc ed use of the various ', pigments (7-9qq).Use of lipstick can rncketeeth appear brighter a nd emphasizes enamel chara cteristics V9 rr). Fina l ' genera l views s ho~ satisfactory' integration w ith mand ibular teeth (7 9 5S to 7-9 uu).'Deta iled views ofdiag nostic steps for this case can be found in Fig, 5-5, tooth prepara tion in. Fig 6-3, a nd follow'up view s in Fig 4-8.

7

I LAB ORATORY PROCEDURES

SPECIAL EFFECTS Shape effects As mention ed in C ha pter 5 (und er "D iagnosti c w c xup" ], spec ia l features of the facial surface arc hitecture ca n be used to create the illusion of a shorter tooth or a wide r tooth. These effects must be integ ra ted into the initial d iagnostic wa xup . Figure 7 -10 depicts a case in whi ch crow n length had to be substa ntia lly increa sed to conform to the lower lip co nto ur and restore the co hesio n of the smile . Hor izontal segmentation of the facial surface a nd externa l posi-

tion ing of the mesial a nd di stal transition line a ng les w ere used to ma ke the teeth a ppear sho rter than they rea lly are. The o pposite effect [to make the tooth a ppear longer) w o uld have been obtained by flattenin g the faci a l surface and bring ing the tran sitio n line a ng les closer to the cen ter of the tooth. Schematic illustration of the po ssib le o ptical a lteratio ns of tooth shape is g iven in Fig s 7 - 1Og to 7 - 1Oi. O ther useful tricks for spec ia l effec ts can be found in cla ssic wo rks published by lombcrd r" and Golostein.:"

FIGURE 7- 10 : SPECIAL EFFECTS COMPENSATING FOR TOOTH LENGTH AND WIDTH . The pa tient presented after co mbined orthognath ic/orth odont ic treatment (see Fig 5- 12) . The initia l situation reveals worn incisors and an inverted smile line (7-100]. Sig nifica nt increase of inci sor leng th was planned , c llowinq the recovery of a po sitive incisal curve co nformi ng to the lip co ntour (7-1 Ob) To compen sate for the exce ssive length of the central inciso rs, the fac ia l surface of the po rcelai n restorati on w as d ivided into severa l horizontal seg ments representing different planes (7- 10c) . Postopera tive intrao ra l views (7- 1Od to 7- 1Of). The light from the ca mera flash system ca n reflect only one segment at a time 17-1 Oe, lines and arrows indi cate a t least three seg ments), gi ving the illusion of a sho rter tooth . The theo retic exp lanatio n of such a n illusion is g iven in 7-1 Og . [Figu res 7- 1Od a nd 7 - 1Oe are reprinted from Belser el al 55 w ith permission .)

322

\

..

x.

" T ,O ,O

LARGE "

" TOO

LON · G "

FIGURE7-10(CONTINUEDj . I, II, a nd 111 ,represent the different ho rizo nta l segments

~f

the facial surface (7- 1Og ). l A tooth that a ppear s "too larg e ! (or'~too short") can be corrected by .bri nging the transition line a ng les cioser to the .. center of the tooth a nd f lattening the f acia l surface to ob tai n a la rge cenlrol.seqrnent (7- 10 g , left). A tooth that a ppears "too long " (or "too narrow ") is c orrected by bringing the transition line a ngle s closer to the prox irnc l-surfoceond d ivid ing the facia l surface into a t least three d istinct segme nts (7 -10 g , right). The ceritrol inciso rs in 7 -1Oh (top) are the same wi dth. The image w as d ig itally mod ified by slig htly.moving the mesia l crests, d ista lly fo r ther ig ht centra l inci sor and mesia lly for the left centra l incisor; as a result, the left central incisor now appears w ider and closer (7- 1Oh, botlom) .When the transitio n line a ngles are ma inta ined , va ria tio ns in the proxima l shape are not likely to generate majo r cha nges in the ap pare nt wi dth of the crow n (7-1Oil ; this principle is 'used fo r the clo sure of di astemata and ca n ' . becorribined w ith other effeCts, the interdental extension of po rcelai n be ill g made of a more satura ted rootlike po rce" lo in (7-1Oi, redd ish o reos] (see a lso Fig 4 -5): .

DIASTEMA

C LOS U R E

7

I LABORATORY

PROCEDUR ES

Masking effects

proach is recom mended : the d iscolored substra te is mainta ined , and masking is o btained

Selective intrinsic masking. Followi ng tooth

by integ rating a certai n degree of o pacity into the ceramic w orkpiece . The refractory di e technique offers the possib ility of incorpo ratin g a thin an d loca lized layer of opaque cera mic w ithin the first laye r of the restoration . Ceramics

prepara tion, residua l b leaching-res istan t discol oration of enam el and dentin may impair the final optica l integra tio n of the cerami c w o rkpiece . Different method s have bee n pro posed to mask discolored ar ea s of the tooth substrate d uring the proce ss of veneering . Supe rficia l a nd loca lized de fects (eg , white enamel spo ts ) ca n be removed mechani ca lly du ring tooth p repar a tion. Undercuts a nd de ntin exposures related to the mechanica l eradication of the sta ined area can be immediately treated with a bon d ing agent (and app lication o f composite) to reestab lish a n adequa te contour of the pre parati on. This a pproa ch, how ever, remain s restrictive d ue to the limited masking ab ility of current co mposites. Furth ermore, thick layers of bo nding agent o r co mposite sho uld not be app lied [see next section o n "C o nfig ura tio n of the cera mic w o rkpiece" ). In these cases, a s wel l as for extensive discol o ration (Fig 7-11), another conse rvative ap-

have a grea ter ab ility to mask than do resins. As illustrated in Fig 7- 1 1c, the ceram ist proceed s to selective ap plicatio n of a n o paque cera mic liner; it sho uld never cover the entire prepared su rface unless req uired by the extent of d iscoloration. It is particularly important to limit the ar ea of opaq ue line r w hen the tooth presents unstained cervic a l and margina l surfac es; intraora l views (Fig 7-1 1b) are used as to pog raphi c maps to localize the stained area s. In this w ay, the final veneers (Fig 7- 1 1e) w ill behave op tically like reg ular veneers, especia lly in their relatio nship w ith the margin a l g ing iva (o ptima l lig ht red istrib utio n, no o paque "wh ite lines"), and simulta neo usly feature localized o paque zone s masking on ly the sta ined are a s of the teeth.

FIGURE 7- 11: SELECTIVE INTRINS IC MAS KING. The patient o rig ina lly presented w ith a genera lized dyspla sia of enamel and preexisting full-coverage crown s o n maxillar y anterior teeth. Follow ing a co mp lex preparatory phase (see Fig 4- 12 ), seco nd-ge neration provisional crowns w ere placed on the moxillorv teeth, a nd mandibular incisors a nd pre molars were prepared for bo nded cera mics (7-1 1a J Severa l intraora l view s of the prepared surfaces w ere taken, including photog rap hs w ith a custom shade gUide corresponding to the resid ual sta ining (7 -1 1b). These slides w ere used by the cera mist as to pogr a phic maps to place d istinct patches of o paque liner onto the refracto ry dies (7-1 1c). Translucent pow ders w ere used ce rvica lly a nd incisally because these area s w ere not sign ificantly stained (7-1 1d). The inner surface of the fina l veneers d isplays a limited and intrinsic opaque zone (7-1 1e, arrowheads). C linica l situation just before try-in (7-1 1fl. Veneers w ere tried in alternately to control the masking effect (7-1 1g, 7-11 h); a neutra l, translucent g lycerin ielly ca n be used as a try-in paste.

326

.v , , v':

'.\'

7

I LA BO RAT O RY

PR OC ED URES

W hen the selective intrinsic masking concept is fol low ed, the porc elain restorat io n inherently masks the discoloration, w hich is noticea ble a t the try-in stag e (Fig 7 -1 1h). The ma in advantage is that regular tran slucent co mposites ca n be used for luting (there is no need fo r opaq ue or nontran sparent luting agents). Selective intrinsic masking con trasts w ith other techniqu es used to hide discoloration . O ne common method ignores the discoloration until the final luting of the restoratio n; the ceramic being devoid of marked opa city, a n opaque liqui d resin must be pa inted at the inner surface of the cera mic wo rkpiec e . The result is unpred ictable beca use these orga nic o paq ue liners ca nnot be cured before the restoration is seated [preliminary curing w ould risk a ltering the fit of the restora tio n). As a result, the final thickness and extent of the pa inted resin is too var ia ble . W hen required, the porcela in should 'integ rate a n intrinsic opaque liner to co mpe nsate for residua l di scoloration of the tooth, a nd the use o f opaq ue luting resins shou ld be avoide d . Use of opa q ue luting ag ents co uld be responsib le for w hite lines a t the restora-

When trealing teeth for unsu ccessful p reliminary bleachin g, any bon ding procedures must be delayed for a t least 2 to 4 w eeks after the end of bleac hing because oxygen remnants ca n inhibit the bo nd strength. N igh tguard vital bleac hing beneath existing porcela in restorations is a lways po ssib le a nd vo luo ble-": it mig ht not c hange the col or of the po rcelain, but it ca n enha nce the apparent col or of the teeth in the event of recurrent disco lorati on.

Preventive masking of nonvital teeth. N o nvital teeth are characterized by their unstab le color. How ever, because BPRs can be placed w ithout inva di ng the pa lata l surface (see Fig 4-7), interna l bleaching is possib le on pulpless teeth w ith existing po rcela in veneers. A preventive approac h a nticipa tes the po tentia l relaps e by ap p lying a uniform and mode rate o pa q ue liner to the ce ramic workpiece a t the time of fa bricat io n. To obta in uniform results when Sim ultaneously veneering vita l and nonvital teeth, the same stratifica tion technique (includ ing the opa que liner) should be ap plied to a ll teeth.

tion marg ins, unnecessary uniform op acity of the ce ra mic w orkp iece, and unfavora ble light d istribution with the surrounding soft tissues .

FIGURE 7- 1 1 (CONTINUED). Ma nd ibular restorations are bo nded, but the ac rylic provisionals are still in place on the moxlllo rv a nterior teeth [7-1 1 i); a separate impression w ill be made to fabri cate the final rnoxil lorv crow ns. Desp ite the underlyin g residual discoloration on the mand ibular teeth, the resto ratio ns were bo nded w ith a reg ular tra nslucent compo site. The cera mic integ rates w ell because o f the selective intrinsic masking . No opaq ue liner w as req uired a t the ce rvica l level, o ptimiZing op tica l interactio n wi th the surro und ing tissues (7-1 1 j), Add itiona l view s of this case ca n be found in Fig 4- 12 .

328

7

I LA B O RAT OR Y PR O CE DURE S

CONFIGURATION OF THE CERAMIC WORKP IECE The structura l performan ce of brittle dental ma-

most unc racked spe c imens ha d a fa ci al rati o

terials ca nnot be d irectly correla ted to their

greater tha n this va lue . The C ER/C PR ra tio ap-

streng th volues."? Standard ceram ic p roperties

pears to have a relevant influence o n the stress

[flexura l streng th, fra cture to ugh ness) are not suf-

d istributi on in po rcela in la minates du e to bo th

fic ient to accoun t for the flaws in a clinica l situ-

the curing co ntrac tio n of the luting co mpos ite

a tio n. Configu ration fa cto rs of the restora tion

and the thermal expa nsio n coeffic ient mismatch

a lso p lay a key role, a nd thic kness might be the

of the two restorati ve material s invol ved.

most relevan t beca use it can be ob jective lv con trolled by the operator (either the dental

These importa nt findin g s are summari ze d in Fig

techn ic ia n or cl inic ia n). As a matter o f fa ct, it is

7-12, w hic h a lso helps in und erstand ing w hic h

ofte n asked w hether there are rational gu ide-

elements can directly affect the CER/ C PR rat io

lines d efining the minimum possi b le thic kness of

an d therefore the crack p ropensity, ie, a luting

an a nterior BPR . At presen t, there are no ma g ic numbers fixing the limit a t w hich the ceramic

200 ~m) and a ce ramic veneer that is too thin [< 600 prn l.

workpiece becomes intrinsicall y too wea k. The

Their co mb ina tion logi cally lead s to the highest

structura l integr ity of

risk of fa ilure (F ig 7-12, D). Direct imp licati on s

the resto ra tio n results

mostly from its bond ing to the tooth substrate.

co mpo site that is too thick (>

ar ise for both the ceramis t and the cl inic ia n:

The theoret ic risk of fa ilure must therefo re include a ll elements of the tooth-restorat ion com p lex, including the luting composi te. The' term

of

• W hen the por celain is meant to reproduce the preex isting con tour of the tooth (with out odd i-

spec ific material

live co ntour), the ceramic must be thinned a nd

p roper ties, ha s been pro po sed to c haracterize

the C ER/CPR ratio is compromised. In this sit-

the structural per forma nce of the g loba l resto ra-

uation , on ly a ve ry p rec ise internal fit of the

tive system.

restoration [< 100 ~ m ) w ill p revent the C ER/

crack pro pensity, instead

CPR ratio from dro p ping below the reco mExpe rimental-numeric tria ls have demo nstrated

mende d va lue of 3.0 (Fig 7-12, B). The im-

that the cra ck propensity of porcelain cou ld be

portance of a controlled an d uniform tooth

related to the respective thickness of luting co mpos ite (CPR) a nd cera mics (CER).12,i3

reduc tion must be po inted o ut because a minimal and homog eneous thickness of ceram ic w ill provide the restoration w ith a favorable

Measuremen ts of ceramic s a nd luting co mpos-

co nfiguration [hig h C ER/C PR ratio). In the

ites were taken at d iffe rent locat io ns o f the

case of w o rn enamel surfa ces, it is essential to

restora tion (fa c ia l, inc isal, proxima l). W hen the

reestabli sh the o rig inal vol ume of the tooth . The

ratio of these va lues [C ER/ C PR) for eac h loca-

use of an addi tive d ia g nostic w axup a nd the

tion was consi dered, sig nifican t di fferences

corre spond ing silico n ma trices is imperol ive in

were obs erved : most crac ked porcela in ve-

this regar d because it increases the po tential

neers exhi bited a faci a l rotio be low 3 .0, wh ile

thickness of ceramic (Fig 7-1 2, A a nd C) .

330

LA BORATORY PROCEDURES

of

I

7

the

composite thic kness a t this lc ccti on.f The im-

restoration , espe cia lly at the facioa xia l level

• It is essential to o bta in a preci se fit

the preparati o n, w hic h often p resents the

proved quality o f bo th the prepara tion s (smooth cont ours, absence of under cuts) and

lowest cerami c thic kness. During la bo ratory

the final imp ressio ns w ill sig nifica ntly faci litate

procedures, the di e spac er should be care-

the work of the ce ra mist, lea d ing to a mini mal

fully app lied to avoi d a n excessive luting

use

of

F A CI AL

of

die space r.

C ER /C P R

RA T I 0

FIGURE 7-12: POSSIBLE RANGE O F RE STORATIVE MATERIAL THICKNESS AND CORRESPONDII\,JG CRACK PROPENSITY. Th e thickn ess of ceramic (C ER ) and composite (CPR) was varied to simulate four clinically relevant cases [A to D). The CER/ CPR ratio [R) is given, alo ng w ith the average thickness of restorati ve materials in parenthesis (in microns). The four tooth preparations are identical, Ve neers A and C are th icker to simulate an add itive contour, whereas veneers Band D we re kept th in to reproduce th e original contour of th e tooth, Lu ting composite th ickness is 100 ~m for A and B, 20 0 ~ m for C and D. Minimu m risks of failure are found for thick veneers (> 6 0 0 ~m ) w ith thin luting composites « 20 0 prn ], a configuration th at maintains a high C ER/C PR ratio (> 3 .0 )

33 1

7

I LAB ORATORY P ROCEDU RES

References

18 . Krejci I, Lutz F, Reimer M . M arg inal adaptation and fit of adhesive cera mic inlays J Dent 19 9 3; 2 139- 46 .

1. M eijering AC, Roeters FJ, M ulder J, C reugers N H . Patients' sa tisfaction w ith di fferent types of veneer restorations. J Denl 19 9 7 ;25 :4 9 3-49 7 .

19 . Mag ne P, O h W S, Pintado MR, Delong R. Wear of ena mel a nd veneering ceramics c lter la bora tory and cha irside finishing procedures. J Prosthet Dent 19 9 9 ;8 2 : 669-679 .

2. M agne P, Douglas W H o Porcelain veneers: Dentin bonding oplimiza lion a nd biomimelic recovery o f Ihe crow n. Int J Prosthodonl 19 9 9 ; 12 : 11 1-12 1.

20 . Ca lamia JR. C linica l eval ua tion of etched porcelain veneers. Am J Denl 19 89 ;2 :9-1 5.

3. Mag ne P, Doug las W H o C umula live effect of successive restorative proced ures on anterior crow n flexure: Inlact versus veneered incisors. Q uintessence Int 2000;315-1 8. 4. Reeh ES, Ross GK . Tooth stiffness w ith composile veneers A strain gaug e and finite element evaluation Dent Mater 1994; 10 :2 47-2 5 2 . 5. Lacy AM , W ad a C, Du W, Wa tana be L. In vitro rnicroleakoge o t the gingiva l marg in of po rcela in and resin veneers. J Prosthet Denl 19 9 2 ;6 7 :7- 10 6 . Kreulen CM, C reugers N H, Mei jering AC. M eto-analysis o f o nterior veneer reslora tions in clinica l stud ies. J Dent 19 9 8 ;26 :3 4 5- 35 3 . 7 . Meijering AC, C reugers N H, Roeters FJ, M ulderJ Survivol of three types of veneer restorations in 0 clinica l trial: A 2 .5 -year interim eva luation. J Dent 19 9 8 ;26 :5 6 3-5 6 8. 8. M agne P, Perroud R, Hodges JS, Belser Uc. C linical performo nce o f novel-design po rcelain veneers for the recovery o f co ronal volume and length. Inl J Periodonlics Restoralive Dent 2000 ;20 :4 4 1- 45 7.

2 1. Peumans M , Va n Meerbeek B, lornbrechts P, VuylstekeWo uters M , Vanherle G. Five-year clinica l performance o f porcela in veneers. Q uintessence Int 19 9 8 ;29 :2 1 1- 2 21 . 22. Fradea ni M . Six-year follow-up with Empress veneers. Inl J Periodontics Restoralive Dent 1998; 18 21 6 - 2 25 . 2 3 . Friedman MJ A 15-year review of porcelain veneer fa ilure: A clin ician 's observatio ns. Compend C onlin Educ Dent 19 9 8 ; 19 :6 25-636. 24 . Dumfahrt H . Porcela in laminole veneers. A retrospective evalua tion oher 1 to 10 yeo rs of service : Pari II- Cli nical results. Inl J Prosthodont 2000 ; 139-1 8 . 25 . Bruce GA. The Herbst method Rec 189 ] ; 1 ] :47-48.

of filling

w ith gloss. Dent

26 . Roulel JF, Soderhol m KJ, Longma te J Effecls of trea tment a nd storoge cond itions on cera mic/composite bond strength. J Denl Res 19 9 5; 74 :3 8 1- 3 8 7. 27 . Sorensen JA, Strutz JM , Avero Sp' M aterdo mini D. M arg inol fide lity and microleakage of porcelain veneers mode by two techniq ues. J Prosthei Dent 19 9 2 ;6 7 : 16-2 2 .

9. M ogn e P, versluls A, Doug las W H o Rationa liza lion o f incisor shope: Experimentol-numerical ana lysis J Prosthet Denl 199 9 ;81 :345-35 5 .

28 . Wall JG , Reisbick M H, Espeleta KG . Ceme nt luting thickness beneath porcelain veneers made on plalinum foil. J Proslhel Dent 19 9 2 ;6 8 448-450.

10. Lin CP, Doug las W H o Structure-property relations and crock resistance a t Ihe bovine dentin-enamel junction. J Dent Res 19 9 4 ;7 3 : 1072- 1078.

29 . Sim C, Ibbelson R. C ompo rison of fil of porcelai n veneers fa bricaled using different lechniques. Int J Prosthodonl 19 9 3 ;6 :36-4 2

1 1. M agn e P, Doug las W H o Desig n optimiza tion and evolu-

30. Sheets CG, Ton iguchi T A rnullidie technique for the fabrication o f po rcelain la mina te veneers. J Prosthet Dent 19 9 3 ;7 0 :29 1- 29 5

tion o f bonded ceramics for the anterior dentition: A finite element a nalysis. Q uinlessence Int 19 9 9 ;30 :66 1- 672 . 12. Magne P, Kwo n KR, Belser UC , HodgesJS, Doug las W H o C rac k p ro pensity o f porcelain lami nale veneers: A simulated operalory eva luation. J Prosthet Denl 19 9 9 ;81 : 327-33 4 . 13 . M ag ne P, Versluis A, Doug las W H o Effect o f luting co mposile shrinkage a nd therrnol loads on the stress di stribution in porcela in la minale veneers. J Proslhel Dent 19 9 9 ; 8 1.335-344. 14 . Highton R, C ap ulo AA, Matyas J A photoelastic study o f stress on porcelain la mina te preparations. J Prosthet Dent 1987 ;5 8 : 15 7-1 6 1. 15. Mogne P, Douglas W Ho Interdental design of porcelain veneers in the presence of co mposiles fillings: Finite element a nalysis of co mposite shrinkoge and thermal stress. IntJ Prosthodonl 2000; 13 : 117 -1 24. 16. De Long R, Sc sik C, Pintado M R, Douglas WHo The wear of enamel w hen opposed by ceramic systems. Dent M ater 19 89 ;5 :266-271. 17 . Seg hi RR, Rosenstiel SF, Bouer P. Ab rasion of human enamel by d ifferenl denial ceramics in vilro. J Dent Res 19 9 1;70: 2 2 1- 2 25 .

332

31 . C hiche GJ, Pi nault A. Esthetics o f A nterior Fixed Prosthodo ntics. C hicago : Qu intessence, 19 94 : 16 9-1 70 . 32 . Scha fer F, [ o rschke I, Meyer G . Marg inal adapta tion o f Ducera m-LFC O D-inlays. In: Komma 0 led). Hydro thermal Dental Ceramic Systems: A N ew C loss o f M a terials. Hana u-W olfgang , Germa ny : Ducera , 19 9 3: 26 . 33 . Adai r PG , G rossman DG. The casta ble cera mic crow n. Inl J Periodontics Restoralive Dent. 1984 ;4 :32-46 . 3 4 . Beham G . IPS-E mpress: Eine neue Keramik-Technolog ie. Ivoclar-Vivadenl Repo rt 1990 ;6: 3-14 . 35 . Sado un M, Deg ra nge M, Heim N. Les ce rorn iq ues dentai res. 2 erne par tie: Les nouvelles cerorn iq ues. J Biomater Dent 1987;3:6 1- 6 9 . 36. Kern M , Strub JR. Bonding to olumina ceramic in restorative denlistry: C linical results over up to 5 years. J Denl 19 9 8 ;26 :24 5-249 37 . Tja n A H, W hang SB, Tjan AH, Sarkissi an R. C linically oriented evaluation of the accuracy o f commonly used impression rncteriols. J Prosthet Dent 19 86 ;5 6 :4 - 8 .

LABORATORY PROCE DURES

38 Tu il CM , Rosen M , Co hen J. Becker Pj. Effect of impression technique a nd multiple pours on acc uracy of slone models J Dent Assoc South Air 1991 ;46: 5 15- 5 18. ~ M ag ne M, Belser uc. The esthetic w idth in fixed prosthodo ntics. J Prosthod ont 1999;8: 106- 118

39 . M ag ne

40 . Lavigne J, Lucchini JP, Spirg i M . Use of a mounting ta ble for arb itrary hinge transfer on a n articulator. Schweiz M onatsschr Za hnheilkd 1979; 89 :125 1- 1256.

41 Bowley JF, Michaels GC, La i TW, Lin PP Relia bility of a facebow Iransfer procedure. J Prosthet Dent 1992;67 : 491 - 49 8. 42 Magne P. M egabrasion: A conservative slralegy for Ihe anterior dentition. Pracl Periodontics Aesthel Dent 1997; 9389- 395 . 43 Borges C FM , Mag ne P, pfender E, He berlein J Diamond burs mad e w ith a new technology. J Prosthet Dent 1999 ; 82:73-79 . 44 PaHerso n CJ. M cLundie AC , Stirrups DR, Taylor W G Efficacy of a po rcelain refinishing syslem in resloring surface finish o lter g rinding w ith fine a nd extra-fine d iamond burs. J Prosthet Dent 1992 ;68 :402 - 406

45 . C ampbell SD. Evaluation of surface roughness a nd polishing techniques for new cera mic materials. J Prosthet Dent 19 89;6 1:56 3- 56 8.

46 G rieve AR, Jeffrey IW , Sharma S]. An evaluation of three methods of polishing po rcela in by co mparison of surface topogra phy w ith the orig inal g loze . Restorative Dent

199 1;7:34- 36 . 47. Sulik W D, Plekavich Ej. Surface finishing of dental porcelain. J Prosthet Dent 19 8 1;46 :2 17-22 1. 48 Klausner LH , C artwright C B, C harbenea u GT Polished versus autoglazed porcelain surfaces. J Prosthet Dent

1982;47: 157-1 6 2.

I 7

49 . Scurria M S, Pow ers JM. Surface roughness of two polished cera mic materia ls. J Prosthet Denl 1994;7 1: 174- 177. 50. Haywood VB, Heymann HO , Kusy RP, W hiiley JQ , And reaus SB. Polishing porcela in veneers: An SEM a nd specula r reflectance a nalysis. Dent M a ter 19 88;4 :

116- 12l. 5 1. Haywood VB, Heymann HO , Scurria MS . Effects of wafer, speed , and experimenta l instrumentation o n finishing and po lishing porcelain inlra-ora lly. Dent Mater 19 89 ;

5: 185-1 88. 52 . Brew er JD, G arlapo DA, Chipps EA, Tedesco LA. C linica l d iscrimination between autoglazed and polished porcela in surfaces. J Prosthet Dent 1990;64 6 31- 6 34 .

53 . Sulik W D, Plekavich Ej. Surface finishing of denta l porcela in. J Proslhel Dent 1981 ;46217-221 . 54 . Mag ne P, Mag ne M. Porcelain veneers at the turn of the millenium: A w indow to biomimetics [ in French]. Real C lin

199 8;9 :329-34 3. 55 . Belser U, Magne P, M agne M . Cerami c laminale veneers: Continuous evolution of indica tions J Esthet Dent 1997;9: 197-207. 56 . Lombardi RE . The principles of visua l perception a nd Iheir cli nical a pplica tion 10 denture esthetics. J Prosthet Dent

1973;29 :358- 382 57. G oldstein RE. Esthetics in Dentistry. Philadelphia : li ppincott, 1976:425-455 . 58 . Haywood VB, Parker M H . N ightguard vita l bleaching beneath existing porcelain veneers: A case repor t. Q uintessence Int 1999; 30 :74 3- 747 .

59 . Kelly JR. Perspective on slrength. Dent Mater 1995 ;11: 10 3-11 0. 60 . Barghi N , Berry TG . Post-bonding crock formalion in porcelain veneers. J Esthet Dent 1997;9:51-54.

333

-

.

,'.

"",

\

CHAPTER

8

TRY-I N AN D ADH ESIVE LUTING PROCEDURES

The structural integr ity of the intact tooth ha s been expla ined in por t by the structure/ pro perty rela tio nship at the d entinoenam el junction [DEJ). Ena mel and dentin a lone do not have outstan d ing mechan ica l properties. Nevertheless, w hen assembled at the DEJ , they ha ve a unique structure that can ensu re optima l functio n and stress tran sfer for a lifetime . The same statement can be cla imed for bo nded porcelain restorat ions, and the DEJ sets the reference for the ce ramic-composite-too th restora tive co mplex . Successful bond ing

of the

ce ramic w o rkpiece ca n be obta ined by the rigor-

o us a pplicatio n o f seq uentia l procedu res including specific cond itioning

of

the surface s involved , ie, the ce ramic surface (etching a nd sila ne a pplica tio n) and the minera lized dental tissues (etching o f the ename l, cond itio ning

of

the den tin). This cha pter addresses in de tail eac h step

of

the luting

pro ced ures. A dd itio no l considerali o ns incl ude the specia l a pproa ch to denti n bo nd ing, the possible effects o f co mpos ite shrinkage, and the cra ck propensity

of po rcela in.

8

I

T RY- IN A N D A D H ESIV E L UT ING P RO C ED U RES

CHOICE OF LUTING C OMPO SITE RESIN As far as the success of final bo nd ing is concerned , it relies on the adeq ua te prepara tio n and co ndi tion ing of the surfaces involved . This

to 90 seconds per surface is sufficient for a nterio r BPRs, whi ch are much thinner than inlays and o nlay s. In co nclusio n:

co nd itio ning should ultimately provide a d urab le bo nd betvveen the substrate (tooth or po rcelain) and the luting composite . The cho ice of the lat-

1. A nterio r BPRs ca n be luted using a reg ular light-cu ring restorati ve composi te provided

ter raises a critica l prob lem: due to their a bility to flow a nd self-po lymerize , d ual-cure material s

that an extended curing mode is ap plied . Traditional light-curing resins offer co nsider-

are mista kenly preferred over the solely lig ht-curing a nd more viscous com posites. No scientific

a ble adva ntages d ue to their ease of manipula tion (unlimited w o rking time, ideal

studies have differentia ted the clin ica l pe rfo rmance of these materials. How ever, none will

co nsistency),2 favo ra ble physicomecha nica I pro perties (hig her filler co ntent), and color stabi lity.4

d isag ree o n the fact that a suffic ient w o rking time is essentia l to the co rrect positio ning of the restoratio n and car eful elimina tion of excess resin. In this regard, d ual-cure cements are subject to con troversy: their self-curing ability is in-

O ne sho uld select a rather neutral com posite (Fig 8-1) permitting lig ht redistri butio n and dee p curing (ie, inc isal-type translu-

versely related to thei r w o rking time a nd their flowa bility renders excess resin removal extremely d ifficult. A nother d ilemma of dual -cure

ce nt), com pa tible w ith the inheren t luminosity of the restorati o n itself (ie, slig htly fluo-

com posites is the co mpro mise betvveen their de-

viscosity o f co mposite resins is inversely re-

gre e

of convers io n a nd

their color instability due

to a mine deqrodo tion .'

rescent ). It is impo rta nt to re membe r that the lated to the ternpero ture." Fine hybrid s ca n become very thick w hen handled in cool ai r-cond itioned

For these

co mb ined

reaso ns,

lig ht-c uring

o pera tory

room s. In this

restorat ive co mposites (fine hybrid s) have been

case , placi ng the composite syring e in a resea la ble bag in a lukewar m w a ter bath w ill

proposed as luting agents even for ce ram ic in-

reduce film thickness.

lays. It w as demo nstrated that d ua l-cure resins had

no advantag es ove r solel y light-curing

products w ith respect to po lvrnerizoti on rete, provided that ea ch proxirno l resto red surface is cured for a t least 120 seco nds (regu lar curing mode]." This luting protocol has been used suc-

2 . In most cl inica l situation s, d ua l-cure luting cements ca n be o mitted because

of

their d iffi-

cult ha ndli ng a nd uncerta in chemi ca l stability [a mine degrada tion ). Indicati o ns for d ual-cure prod ucts remai n limited to ce ra mic

cessfully for mo re than 8 years even in cases of anteri or bo nded po rcelain restoration s (BPRs) w ith extensive incisal edge span s of cera mic. 3

w o rkpieces of extreme fac ia l thickness (> 2 mm) o r to situa tio ns in w hic h the venee rs

Using higher intensity modes (eg , 800 to

severe residua l di scol orat io n).

1,0 0 0 mW / ern "], reduced curing times o f 60

336

have been rendered high ly o paq ue (as for

BLACK LIGHT

DIRECT LIGHT

INDIRECT LIGHT

...

FIGURE 8-1: CURED SAMPLES OF INCISAL COMPOSITES. Beca use of their neutral and tra nslucent nature, incisa l shades of regular ligh t-curing restorative materials can be used as luting agents for anterior BPRs (8- 1o ]. Esthetic properties of the selected materia l ca n be evaluated under black lig ht (8-1 b, featuring two inci sal shades, the o ne on the right be ing insufficiently lurnmescent]. Direct (8- 1c) or transmitted (8-1d) light should also revea l a certain de gree of opalescence . Some ba tches may present numerous a ir vo ids (visible in 8-1c a nd 8- 1d), whic h must be detected beforehan d by pressing a sample of the material between two glass slides (8-1e). A word of caution : So me incisa l shades do not have enough radi opacity, w hich limits the effectiveness of radiogra phs du ring the final check a nd further follOw-up of restored teeth.

8

I

T RY- IN AND ADHESI VE LU T ING PROC EDUR ES

TRY-IN AND PREPARATOR Y STEPS Final insertion of the ceramic piece must be preceded by a meticulous try-in (Fig 8-2) . Follow -

fication of esthetic a ttri butes and to make sure that the d iagnostic template has bee n re-

ing remova l o f the prov isio nal, a soft silico n cu p (Haw e-N eos) an d a light abras ive pa ste are

spected . At no moment should the pat ient be allowed to totally clo se the bite. This co uld

used to clea n the prepared surface s. W hen

ca use fracture.

pro visiona ls have been secured by spot etch ing (see Figs 6 -25 g to 6 -25 iL a sca ler or abrasive disks (at low speed ) must be used to remove the

Lengthy try-in time must be avo ided bec a use de-

ad hesive resin from the spo t-etched area o f the tooth. The followi ng try-in seq uence is recom-

eva luatio n. N o try-in pa ste is required co nsidering that the po rcelain w o rkpiece sho uld feature

mended :

sufficient intrinsic optica l pro perties (see Fig 71 1). Porcelain surfaces co nta mina ted wi th try-in

1. The restorations must first be checked o n their origin al sto ne di e (sea ting a nd marg inal fit).

pro ducts must be car efully clea nsed w ith resin solvents [aceto ne, etha nol , methanol, o r methylene chloride) .6,7

2 . Each restoration is then individua lly placed in

hydr a tion of reference teeth can a lter the colo r

situ to check the adaptatio n w ith a probe . Note that incom plete seating is rarely due to internal fit pro blems but typica lly results from excess provisiona l luting resin th at has acc umulated o n interdental surfaces ing teeth. .

of

neighbor-

3 . A ll restorations are then placed in ad jace nt groups to verify proximal relationships. 4. Once fitted together in situ, the restorations are shown to the patient wi th a mirror for veri-

W hen a refract o ry d ie techniq ue is used , the resto ration sho uld be finished as much as possible before the first try-in because o nly low -fusing cera mics can be used once the refractory die material has been removed . In most cases, the try-in procedure should only co nfirm the di ag nostic templ ate a nd be immed ia tely follow ed by the final luting.

FIGURE 8-2 : TRY-IN. Removal of the pro visional s (8-2a ) reveals unfilled resin co vering the internal surfac e of the veneer except for the spot-etched area (8-2b, arrowhead); the unfilled resin must be removed at the correspo nd ing loca tio n on the tooth surface using a sca ler o r abra sive di sks at low speed (8-2c) Tooth prepara tions are then clea ned w ith a soft a brasive paste a nd a rubber cup (8-2d ). The restorati ons must be checked on the stone ca sts, first indlvid uo llv, then in od jocent groups (8-2e to 8-2g) . The same proce d ure is ca rried out in the mouth (8-2h, 8-2 i).

338

8

I TRY-IN AN D A DHESIVE L UTING PROCEDURES

Try-in alw ays results in some kind

of

chemi cal

be carr ied out under rubber dam . Ad d itional in-

the surfac es to be bonded

for mation for final sea ting ca n be found la ter in

an d , thus, a potent ia l red uction of the future bon di ng . C o nsequently, ce ra mic an d enamel surfaces sho uld be systema tica lly condi tio ned a fter try-in. not before .g

this c hapter unde r "Interdenta l adj ustments d uring luting procedu res." The entire bo nd ing process is then pe rformed a fter seg ments of trans-

contaminatio n

of

As fo r a ll ad hesive techni q ues, the definit ive insertio n of the restoration s has to be preceded by o ptima l isola tio n o f the w o rking field w ith rubber dam , o r at least wi th a deflectio n cor d if a pplication of ru bber da m proves extremely di fficult. A last try-in of the la mina te veneer must

parent matrice s and interdental w edges ha ve been pla ced . The latter prec au tio n pro tects neig hbor ing teeth from the etcha nt, facilita tes insertio n of the la mina te veneer to its final position , and ultimately prevents ac cumu lation of excess luting compos ite in the interproxi ma l area .

FIGURE 8-2 [CO N TIN UED): Sea ting of BPRs must be eva luated by try ing the restorations in od joce nt g roups (8-2 j, 8-2 k). Final ad justments, how ever, must be carri ed out a fter placement of rubber dam . The latter is placed over the teeth to be bo nded includ ing o ne add itional tooth o n each side of the co ncerned segmen t; luting of four incisors implies plac ing rubber dam from can ine to ca nine a nd cla mp ing the first premolar (8-2 1). A n o ptimal ope ratory field ca n be obtai ned by placin g one add itio na l cla mp (Ivory #9 o r #2 12) on the first too th to be bonded (8-2 m, solid rectangle; 8-2n); the clam p is moved to the next tooth as cementatio n proceeds (8-2m , dotted rectangles). Each time, the restora tio n is tried aga in for the fina l ad justments (8-20); w ooden w edges a nd a matrix a re then inserted to protect neig hbor ing teeth from cont a mination by chemica ls a nd luting agents [8-2 p). (Patient treated in co llabo ratio n w ith Dr N . Pera kis, University of G eneva ]

340

8

I T RY-IN AN D ADH ESIV E LU TIN G PRO CED U RES

CONDITIONING OF THE CERAMIC SURFACE It is wid ely recogni zed and ba sed o n scientific evidence that a co mb ination of microme chan ico l interlocking (hyd rof luo ric etching ) a nd chem-

Micromechanical interlocking: Hydrofluoric etching

ica l co upling (sila nizatio n) is requir ed to ob tai n the most effective bo nding of feldspathic po rcela ins.9 , I O

A co mmon protocol is to a pply 10% hydroflu oric (HF) acid for 90 seconds (eg, Biod ent InlayKera mik, Dentsply / DeTrey) to the inner surface of the resto ration (Fig 8-3b) . This procedure has to be pe rfor med under strict protective measures co mprising rubber gloves, mask, and protective g losses. .

C areful handling of the restoratio n is req uired duri ng the co nd itio ning step s. Soft sticky w ax can be used to hold the ceram ic workpiece at the tip of a flat instrument (Fig 8-30 1, eg, on old large a malga m co ndenser.

A fter rinsing (Fig 8-3cl, the cera mic resid ue a nd reminera lized salts (Figs 8-3d and 8-3e)11 must be eli minated by pla ci ng the restoration in di stilled w ater, 9 5% a lco ho l, o r aceto ne in o n ultrasonic both fo r 4 to 5 minutes (Figs 83f a nd 8-3g ].

FIGURE 8-3: ETCHING AND CLEANING OF THE CERAMIC WORKPIECE . The cera mic wo rkpiece ca n be easily handled using a flat-ended instrument (eg, Acc u Placer, Hu-Friedy, o r a Iorge a malga m co ndenser) an d sticky wax (83a ) The internal surface of the cera mic is etched w ith 10% hyd rofluo ric ac id for 90 seco nds [8-3 b) a nd rinsed (83c) Even abundant rinsing proves insufficient to clea n the po rcela in, which is offen co nta minated by a w hite residue or de posit (8-3d ; 8-3e , scan ning electron microg ra ph, o rigi nal magnification x l ,200 ) The latter ore selectively removed by plac ing the restorations in a n ultraso nic ba th (in 95% a lco hol, ace tone, o r d istilled wa ter) for 4 to 5 minutes 18-3f , 8-3g ). White resid ues that ore resista nt 10 this proced ure ca n be removed w ith a brush and a lco hol.

342

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C A UTION ! RE SIDUES TO BE RE M O VED

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TR Y-I N AN D A DHE SI VE LU TING PR O CED URE S

Due to the abund ant glassy matrix surro und ing the c rystalline phose . feldspa thic po rcelai ns offe r an ide a l substrate for hyd rof luoric ac id co nd ition ing : di ssol ution of the g lassy matrix ultimately leaves retentive holes a nd tunnels betwe en the acid -resista nt crysta ls (Fig 8-4) . Ultrasonic cleani ng is essen tia l to enlarge and enhance access to these undercuts." Energy d ispersive spectrosco py ana lyses have shown that the crystalline precipitates o n the etched surfaces, w hich are not read ily solub le in w a ter, are the reaction prod ucts of sod ium, pota ssium, cc lciurn. and a luminum. The precipitates remain on the surface after acid a pplica tio n; they can be removed on ly by ultrasonic clea ning , not by rinsinq . " Practitioners must be extremely prude nt when co nd itioning other types of ce ramics. They must be aware that the tensile fracture resistance of the co mposite-ceramic ad hesion zones is co ntrolled primarily by ceramic microstructure and cera mic surface treatment. For insta nce : • HF co nd itioning is una ble to generate a retentive surface on highly crystalline ceramics with poor g lassy co ntent (eg , In-C eram [Vita] o r Procera [N obel Biocare] co re materials) o r pure noncrystalline ceramics (eg Ducera LFC hyl

drothermal g loss [Ducera] ). Add itional steps ore required for some of these products to generate a positive mechanical interlockinq . eg , through the sintering of silica peri cles." • Lithiu m-based hot-pressed ceramics can be efficiently conditioned by both HF conditioning a nd silo nization, wh ereas the bo nd ing of leucite-based hot-pressed ce ramics is dominated by chemica l cou pling alo ne (sila ne) and ca n be Significantly w eakened by acid applicalion ."

Chemical coupling: Silanization To avoid conlo rninotio n. the fina l try-in of the restora tio n (Fig 8-5 b) must always precede hydrofluoric etching (Fi g 8-5c ) and sila niza tio n. Because of the silica co ntent of feldspa thic po rceloin. a c hemical bond ca n be po tentia lly ach ieved between the porcelain and the luting resin. This bond req uires co upling molecules, ie, ym ethacryl oxypropyl trimethoxysilan e, a lso cal led o rga nofunctio nal silanes. They ore typica lly used as adhes ion promoters between ino rganic substrates a nd org an ic poly mers. Silane-treated porcelain o ffers improved w ettability and methacry late g roups that can form a bond with the methacr ylate groups in the resin.

FIGURE 8-4 : SCANNING ELECTRON MICROPHOTOGRAPHS OF FELDSPATHIC PORCELAIN . (Top) High-mag nifica tion view of the po rcela in [C rec tio n, Klema) surface after simula ted removal of investment ma teria l by microsa ndblasting wi th 5 0- ~m g lass beads. The retentive charac ter of this surface is insufficient; no deep undercuts are observed. Origi na l mag nifica tio n x l ,20 0. (Middle) G enera l view of ceramic sa mple for co mparison between microsa ndbla sted and microsandb lasted /etched surfaces. O rig ina l mag nification x 30 0. (Bottom) Po rcelai n surface after etching with 10% hydrof luo ric acid for 90 seconds [Refentionsgel, Biodent ) and ultrasonic cleaning . The surface is highly retentive and show s co nnections ("tunnels") betw een micro porosities (arrowheads) Ori g inal mag nification X 1, 200 .

344

8

I T RY-I N AN D ADHES IVE LU TING

Silani zatio n

of

PROC EDURES

po rcela in is a rather de licate

and sensitive proced ure and must be performed in acco rda nce with scientific a nd established gUidelines l 6 : • Silanes should be p urchased in a nonactive state because in an aqueous environment, activated silanes w ill react w ith themselves and precip itate out of solution. For this reason, dual-co mpo nent sila nes (two-bottle systems, eg , Silicoup, Heraeus Kulzer; Fig 8-5a) are preferred over o ne-bottle produc ts . • Silane solutions co ntain a high volume of solvents (eg, 90% ethyl acetate in Silicoup Bottle Al; inadeq uately sea led or opened conta iners will allow ra pid evaporalion a nd affect the effici ency of the sila ne. In two-bo ttle prod ucts, one bottle con tains an acid (eg, approximately 5% acetic acid in Silico up Bottle A) a nd the other nonhydrolyzed silane [Bottle B) to be activated [hyd rolyzed via the acid). Such a prod uct can be used for 4 weeks following activati on . After drying, the etched ceramic surface is covered w ith 2 to 3 coa ts of the active silane solution (Figs 8-5d and 8-5e). The solvent should be a llowed to eva po rate betwee n layers. • Heat treatment wil l significantly enhance the promoting effect of the silane 8, 17 by conden sing the coup ling molecules o nto the cerami c surface. This step ca n be achieved in 1 minute by placi ng the restoration in a d ry furnace at 10 0 °C [Fig 8-5 f) o r in 2 minutes w ith a hair

346

dryer. It is believed to eliminate w ater and other co nlc rn ino nts." Chemica l co upling to highly cry sta lline ceram ics w ith poor silica content leg , In-Ceram, Proce ra) req uires the assistance o f tribochem ical silica coa ting (Co jet, 3M Espe) to crea te bi nding sites for the silane molecules .

Application of adhesive resin and luting composite Lig ht-curing resins must be prepared in ad vance on a mixing pad and p rotected with a light shield (Fig 8-5g; Viva pad , Vivadent]. The fina l preparat ion of the ceramic surface is obtained by applying o ne coat of adhesive resin to the inner surface of the ce ramic (Figs 8-5 h a nd 85 il, fol lowed by gen tle thinning w ith a ir. A homogeneous bulk of an incisal-type fine hybrid co mposite is then app lied to the ceram ic surface (Figs 8-5j and 8-5k ). Particular attention should be taken to avoid the incorpo ratio n of a ir bubbles between co mpos ite and ceramic. This w o uld create areas of ligh t absorptio n (gray spots), w hich can be visible after ce menta tio n. Use of composites co nd itioned in compules (Fig 8-5j l can prevent these prob lems. The ve neer, loaded wi th the composite, is then stored under the light shield (Fig 8-5 1) while the operator prepares the tooth surface .

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FIGURE S-5: STEP-BY-STEP CONDITIONING OFTHEC'ERAMICSURFACE. Duel-component silane solutions must be " oc tivo tedtr rsttcoufion: some products m,ayreq u i(~ an octivotion delay) and stored in a closed flask'(8-5a).A final , check of the res toration's seating is 'car ried out under rubber dam (8-5 bL which 'must precede surface cond itio ning . ' S~ r face condi tioning includes 90-secondetching w ith hydrofluoric acid (8-5 c) followed by abundan t rinsing and ultrasonic cleaning . The etched ' porcelo tnsurloce rnusl.be dried (facilitated by ap plication df 95% alcohol'follpwed by air drying) before the silanei s applied. Several layers of silane can b e app lied by olter ~ a te ly coa t i ng and a ir drying , the porcelain 18-5d " 8-5el . Comp lete evaporat ion of the solvent and other contaminants is obtained by heat treating 0 the porcelai n workp iece .ot 100 for at least 1 minute, using a hair dryeror a .srno ll portable furnace'(S-5 f; eg, " Coitene DI500) . Fu rth er stepsabsolutelyrequire a mixing pod wi th alightshield (S-5g). The etched' and silcne-treoted porcela in can then be coated with ad hesive resin (8-5h , S-5i1;the excess ad hesive resin ca n be suctioned but not cured . It is immed iately followed by loodinq of the compositer esin (S-5i, s-5 k). T he lood edporceloin 'workpiece ca n be safely stored under the light,shield (S-51) w hile the operator proceeds to co nditioning of the tool hsurlo ce . (Patien t " ' ' . ' treated in collaboration with Dr N. Perokis, University of G eneva :) ,

e

8

I TRY-IN A ND AD HESIVE L UTING PROCEDURES

CO",IDITIONING OF THE TOOTH SURFACE Differen t cl ini ca l situatio ns must be distin gUished .

situation , var ious extrinsic co ntamina nts ca n a lter further adhesion to den tin. As a lready mentioned in C ha pter 6 (unde r "Immed ia te dentin bon d ing"L such a situatio n must be anticipated

Enamel only

a nd solved at the time of tooth preparatio n because al l afo rementio ned pro blems ca n be pre-

W hen 80% to 9 0 % of the prepared surface is located w ithin ena mel, surfac e co nd itio ning is limited to 30-second etching w ith 37% phospho ric ac id (eg, Ultratech , Ultrad entL foll ow ed by rinsing and d ryi ng . O ptima l d ry ing ca n be o bta ined by a ppl y ing o ne d rop of a lco ho l (Without rubbing ) an d a ir d ryi ng the surface .

vented by the immedi ate a pplicat ion and curing of the dentin cdhesive. prio r to ta king the final irn pression. "'? ' This preca ution not only enha nces bo nd ing a nd protection of the pulpdentin com plex but a lso prevents tooth sensitivity during the provisiona l phase. A t the time o f fina l bondi ng of the restoratio n, the surface of the ad hesive must be meticulously clea nsed w ith pumice . Filled ad hesives (eg , O ptibo nd FL, Kerr) ca n be efficien tly "reactivated" by ro ugheni ng wi th a larg e-grain d iamond bur a t low speed'? o r by microsand blasting w ith the finest sa nd (eg , 30-~m COjet sa nd, 3M Espe; Figs 86 a to 8-6c) . The bo nding procedure itself Will, therefore, be limited to ename l co nd itio ning , ie, phospho ric acid etching (F igs 8-6d to 8-6f) and rinsing (Fig 8-6 g L followed by alcohol drying (Figs 8-6 h and 8-6 i) and a pplicatio n of the adhesive resin (Figs 8-6 j to 8-6 1).

Significant dentin exposure If a considerab le area of dentin has been ex· posed du ring tooth preparation, it is suggested that a den tin ad hesive be applied immediately and strictly acco rd ing to the- manufacturer's instructions. A sig nifica nt problem arises when exposed dentin has not been protected and sea led d uring the provisio na l stage, between prepara tio n and fina l insertion of the BPR . In this

348

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RINSING AND A LCOHO L DRY ING

A PPLI CATI O N OF ADHESIV E RE SI N

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FIGURE 8-6: STEP-BY-STEP CONDITIONING OF THE TOOTH SURFACE. This tooth revea led extensive dentin exposures at the time of preparat ion; the entire dentin surface had been sealed immediately before ta king the final impression . As a result, the adhesive layer (Op tibond FLJ, whic h covers an extensive pa rt of the preparation (8-6a, dotted oreal, must be reactivated by surface roughening (8-6b, 8-6c ; microsand blasting w ith Co jet sand a nd M icroetcher [Danville]). The tooth surface ca n be etched w ith phosphoric ac id [8-6d to 8-6f) for 30 seconds to clea nse the adhesive surface and co ndi tion the enamel. The etchanf is elimina ted by abu nda nt rinsing (8-6g); a dry surface can be ob tai ned by applying alcohol via a colton pellet (8-6h; no scrubbing) and allow ing the prepa ration to air d ry (8-6i). The prepara tion is then coa ted wi th ad hesive resin (8-6 j to 8-61). The excess ad hesive resin can be suctioned but not cured . It is immediately followed by insertion of the load ed ceramic w orkpiece (see Fig 8-7).

8

I T RY-I N AN D A DHESIVE LU TING

PR OCEDURE S

PLA C EMEN T O F THE CE RAM IC RES TO RATIO N The first step in the final placement of the resto ra-

floss ing must be avo ided a t this unpol ymerized stag e becau se it co uld either crock, d isplac e,

tion is to apply one coo t o f adhesive resin to the tooth (see Figs 8-6 i to 8-6 1), follow ed by gen tle a ir thinni ng. From that moment o n, the w or king

o r de tac h the porcelai n w o rkp iece from the tooth ; excess composite can be easily chipped

field must be free from intense light (cha irside

o ff w ith a sca lpel fol lowing pol y meriza tion.

la mp o r o thers); prema ture curing o f this coa ting must be prevented , as it w ould precl ude the perfect sea ting of the restora tio n.

The light curing star ts at the pa lata l aspect for

The restora tion is slowl y sea ted wi th gentle finger pressure a lo ng the insertio n ax is (Fi g 8-70) . Gross excess o f composite is eli mina ted w ith the tip o f an explo rer previously loa ded w ith unfilled adh esive resin (Figs 8-7 b and 8-7 c). The

9 0 seco nds (Fig 8-7 jl at g reater tha n 8 5 0 mW / cm2 (eg , O p tilux 501 , Kerr/ Demetron, Crnode w ith 8-mm Turbo+ tip). Intermittent curing must be a pplied to ovo id hea ting of the soft tissues; in this respect, a protective bar rier (eg , O po ldo rn. Ultradent) ca n be placed between

instrument is g Uided in a cutting motion parallel

the rubber da m and the ging iva . Polymerization of the bucca l aspect fol low s for 6 0 sec-

of co mposite

o nds/ intermittently/ a t each interproxima l area .

to the margin to ovoid extrac tio n

of

the marg inal area must be

from the margin al jo int. Digital pressure and excess eliminot ion are a Iterna tely repea ted . Inter-

Polymeri zat ion

denta l w edges a nd matrices are then removed [Figs 8-7d and 8-7 e) to a llow the co mplete a nd

layer of g lycerin ge l (Fig 8-7k; K-YJelly, Joh nson & Joh nso n). Due to oxyg en inhibitio n d uring

pa ss ive sea ting

of

the restorati on. This stage

per fo rmed a fter covering the co mposite w ith a

ca n be obj ec tively ac hieved w hen the finger pressure does not provoke a ny further protru-

poly meriza tion, marg ins poly merized w itho ut g lyce rin gel show a ra pid degradati on co mpared to ai r-blocked rnorqins." G lyc erin is

sio n of co mposite ceme nt at the marg in (Fig 87 f). A clean brush is used to elimina te the lost

w a ter sol uble an d ca n be ea sily rinsed o ff (Fig 8-7 1).

excess

350

of

resin (F igs 8-7g to 8-7 i). Interdental

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I N ITIA L I N SERTI O N AN D GROSS EXCE SS REMOVA L

" REMOVAL O F MATRIC ES AND FINAL INSERTION

FINE EXCE SS REMOVA L

FIGURE 8-7: STEP-BY-STEP INSERTION OF THE'CERAMIC RESTORATION. The resiora tioncan be initially inserted wh ile wedg es andmatrices are in place (to preventlarge 'occumulo fion ol co mposite in the interdental area) a nd be slowly sea ted w ith dig ita l pressure (8-70). Gross excess is removed using o n explore r in a ,'a cutting moti ~ n is used paral lel to the margi n (8~7h " 8-7;). Polymerizo tioQstarts at the pa latal surface for 90 seconds (8-7 i), followed by 60 secondsmesloloc.olly a nd 60' seconds d istofocially (dotted arrows). All marg ins a re then covered with glyce rin gel a nd cured for 30 seconds ( 8~7 k) ; the g lycerin ca n be easily rinsed off ( 8~7 1) before proceeding io finishing (see 8-7m and 8-7ri ). . " " . ., .." , " ' . ". ' " v: , '" ,

in

,

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8

I T RY- IN A N D ADH ESIV E L UT ING PR O CEDUR ES

Excess adh esive resin and co mposite is best removed unde r rubber dam w ith hand instruments (surgica l blade and sca ler; Figs 8-7 m a nd 8-7n). Rotar y instru ments are not recommende d for this purpose beca use they co uld dam ag e the ce ramic margin . W hen multiple restoration s are to be placed , a serial approa c h accord ing to the aforementioned sequence is ad vocated, repeating the process for eac h tooth (try-in/condition ing of the cera mic/prepara tion of the tooth surface/ insertion of the lamin ate veneer]. It is not recommended to pe rfo rm paral lel bo ndi ng proced ures Simulta neously on severa l teeth.

Var ious factors ca n be responsible for the inco mplete seating of a restoration : premature curing of the ad hesive, a cured fragm ent w ithin the luting comp osite, etc. W hen ligh t-curing composites are used , a ll these problems are reversible as long as the light has not been applied; the restoration can be immedi ately removed , dipped in aceto ne, and meticulously cleaned . Resin residues are eliminated from the tooth surface by rubbing wi th a co tton pe llet soa ked in a lco hol . En amel must be reconditioned by etching , wh ereas the ceramic only req uires reappl ication of the sila ne be fore proceedi ng aga in to cernentotion ."

HAND-I N STRUME NT FINI SHING

OCCL USAL ADJUS TM EN TS

FIGURE 8-7 [CONTINUED). W ith the rubber dam stili in place to protect the soft tissu es, excess comp osite and adhesive resin can be eosily chipped off wi th a N o . 12 surgica l blade (8-7m, 8-7n). Final occl usa l adj ustments can be ca rried out w ith fine d iamonds (8-7 0) and silico n points (8-7 p). N ote the fine pa latal surface finish a nd invisible toothrestoration interface (8-7 q).

352

T RY-IN AND ADHE SIV E L UT ING PRO CEDU RES

I

8

FINAL ADJUSTMENTS AND OCCLUSAL CONTROL Under no circumstances should this step be carried o ut before the fina l bond ing o f the porcela in workpiec es, due to a high risk of fra cture. On ce rubbe r dam has bee n removed , the occlusion is immedi ately adjusted , beg inning w ith centric occl usio n [maximal intercuspati on) . Co rrection s are mad e w ith fine-grain d ia mond burs a nd silico n po ints [Figs 8-70 to 8-7q ). A variety o f co mmerc ial kits [ma inly dia mo nd-silico n points) ca n then be used to improve the intrao ral surface fini shing o f th e cera mic .23- 26 It is often specula ted that the roug her surfaces produced by intrao ral pol ishing (compared to intact glazed ce ramic) will generate increased enam el wear ; it appears that dental porc ela ins

of

w hic h is no t relevant for neuromuscular herrn onv." BPR-restored central inci sors w ith in-

c reased pro minence a nd incisal leng th therefore co ntribute to the defini tion o f the idea l occlu sion , w hic h refers to bot h esthetic a nd physiologic ideal s.3o.32 In o ther wo rds, particular emphasis must be add ressed to the ma intenance o r reestabl ishment o f an adeq uate a nd functional a nterio r q uido nce du ring ma ndibular excursio ns (Fig 8-8) reg ardl ess of w hether this q uido nce involves the new lam inate veneer restoro tions.:' There is no scientific basis indi cati ng th at an ideal occlusion ca nnot be obta ined in previ-

ge nerate an abra sive type of w ear, the am o unt of w hich is not related to the type of surface finish (eg , g lazed versus intraorally poli shed )Y-29

ously worn dentitio ns a nd in pat ients w ith oc clusal paraf unctions. W a lls33 demo nstrated tha t

C rea tio n feldspathi c po rce lai n [Klema) p roved

ear ly 199 0 s, a nd fo llowed for mo re than 5

to be less ab rasive and mo re resistant to w ear

years, co mpared favo rably with tra d itio nal po r-

than alu mina porc ela in or hydrothermal g lass, either intraorall y pol ished or with the intact or iginal gl aze .29

celain ve nee rs a nd inlays. This good succe ss rate is empow ered by the minimal ly invasive

BPRs p laced in worn a nd fractured teeth in the

approach, wh ich is a lways comm endabl e in this type o f pati ent.

The functio nal features o f teeth restored w ith BPRs are co nsidered to be identical to those o f intact natural teeth, keepin g in mind that a key element in the developmen t of har mon io us occlusion is the inci sal gUida nce,3o.3 i the stee pness

A summary

of seq uentia l proce d ures for

the lut-

ing o f BPRs is presented in Fig 8-9 a nd can be used as a che cklist.

FIGURE 8-8 (NEXT PAGE): ULTIMATE ESTHETIC AND PHYSIOLOGIC IDEA L. Typica l indica tio n for BPRs , ie, type IIIB, erosio n a nd wea r. Preop era tive (8-8a) a nd immedi a te posto pera tive (8-8 b to 8-8f) views Functional fea tures of resto red teeth follow those of intact natural teeth. Baseline views before treatment (8-8 g , 8-8 h) a nd after placem ent of BPRs cani ne to ca nine (8-8 i, 8-8 jl The success of this reha bilitation lies in the d iagnostic approach and subseq uent esthetic and functional recovery of anterior teeth. (So me patient as in Figs 8-5 to 8-7 . Patient treated in coll a bora tio n with Dr N . Perakis, Unive rsity of Geneva)

353

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T H

R e

E L A

• Try restoration on intact origi nal single d ie • Try adjacent restorations on solid model

• Remove provisionals (sca lerl • C lean prepared surface (cup and ab rasive) • Remove resin from spo t-etched area (scaler or flexible disk)

• Fit restoratio ns tnd ividuo lly in mouth (sea ting)

,, ~ F i t restorations in adjacen t g roups (proximal relc tionships}': • Show the pa tient • Place rubber dam ; fina l check for fit

1. Hydrofluoric acid etching

1. Roughen adhesive

0)

c c

o

• Profect neighboring teeth wit h interdental matrices a nd w edges

• G loves, mask, glo sses

• Microsandb lasl o r use large groin d iamo nd bur at low speed (filled ad hesive only)*

• Apply 10% HF for 90 seco nds

• Rinse inner surface a nd d ry wi th alcohol

• Rinse copiously • Ultraso nic ba th for 4 m inutes (in 95% a lcohol or d istilled wa ter)

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