Fixed Restorations E-Book

Irena Sailer

• Herausgeber: Quintessence Publishing
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 730

Veröffentlichungsjahr: 2021

Beschreibung

In Fixed Restorations: A Clinical Guide to the Selection of Materials and Fabrication Technology, the authors Irena Sailer, Vincent Fehmer, and Bjarni Pjetursson have created a timely and comprehensive guide to modern reconstructive dentistry. The book is divided into four parts: basic information regarding materials and production processes, step-by-step clinical procedures with extensive case presentations, long-term outcomes, and management of complications. With over 2000 clinical images and diagrams, backed up with the scientific evidence for recommendations, the best practice for tooth- and implant-supported fixed restorations is clearly described. The vast clinical and technical knowledge and experience of the authors has resulted in a unique textbook that will aid in decision making regarding material selection and procedures for all patients in need of fixed restorations.

Leseprobe

Irena Sailer | Vincent Fehmer | Bjarni Pjetursson

FIXED RESTORATIONS

Irena Sailer | Vincent Fehmer | Bjarni Pjetursson

FIXED RESTORATIONS

A CLINICAL GUIDE TO THE SELECTION OF MATERIALS AND FABRICATION TECHNOLOGY

A CIP record for this book is available from the British Library.ISBN: 978-3-86867-563-4

Quintessenz Verlags-GmbH Quintessence Publishing Co Ltd

Ifenpfad 2–4 Grafton Road, New Malden

12107 Berlin Surrey KT3 3AB

Germany United Kingdom

www.quintessence-publishing.comwww.quintessence-publishing.com

Copyright © 2021 Quintessenz Verlags-GmbHAll 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, or otherwise, without prior written permission of the publisher.

Editing: Anya Hastwell, Elizabeth Ducker, Quintessence Publishing Co Ltd, London, UKLayout and Production: Ina Steinbrück Quintessenz Verlags-GmbH, Berlin, Germany

Dedication

“To our families and mentors who inspired us”

Irena, Vincent, and Bjarni

Forewords

I must admit that the request from Irena Sailer, Vincent Fehmer, and Bjarni Pjetursson to write a foreword for their new book entitled “Fixed Restorations” surprised me. My first thought was: Do we need a book about fixed restorations in this day and age?

On second thoughts, I rapidly changed my mind. They are right. It is necessary and even urgent to publish such a book at this juncture. In many discussions with colleagues, I have noticed how little we know about the incredible product developments in fixed restorations in recent years, and the controversies surrounding the issue. Many protocols and elements have changed in this area of dentistry. It seems essential that the dental community have an overview and guidelines of the current state of the art. A multitude of different materials is available in fixed restorations. Also, the manufacturing techniques for fixed restorations have made fundamental developmental changes, which need to be fully understood.

The practicing clinician should also have a strong foundational knowledge of all the various materials and manufacturing techniques in fixed restorations. But, hand on heart, is this requirement possible? Only during their formal education years do clinicians learn the ability to obtain profound knowledge of the composition and availability of the different materials in fixed restorations; their advantages and disadvantages; their various fields of application; and the various manufacturing techniques. The combined elements of official tutoring, available literature, communication, and controlled hands-on experience allow the clinician to formulate opinions about the gold standards of restorative treatment. Considering the last decades of dentistry, it is apparent that a clinician will never be in the position of always being up to date in the fields of new materials and new manufacturing techniques of fixed restorations. During a clinician’s entire professional life, development of these new techniques and materials is too rapid and intensive to remain fully informed.

Therefore, nowadays, more than ever, the clinician must build a team with his or her laboratory technician. The laboratory technician is the individual who works with dental components daily, gaining a deep understanding of the advantages and disadvantages of different materials. Laboratory technicians hold casts in their hand or look at models on the screen daily; they see the chipping, the fractures, and the problems of the different materials used for fixed restorations as they are utilized and produced. They can formulate opinions on suitability and functionality better than anyone else. The wise and ethically motivated dental clinician and researcher needs to lend an ear to the incredible experience and understanding of laboratory technicians.

Irena Sailer, Vincent Fehmer, and Bjarni Pjetursson choose this innovative approach in their book by selecting authors with different backgrounds. Irena Sailer and Bjarni Pjetursson are both incredible clinicians and researchers. Still, they knew and understood that for such a book project to succeed an exceptional laboratory technician’s contribution and input would be required. They found it in Vincent Fehmer. They together have the complete knowledge and experience to create such a mammoth undertaking. I can see with my own eyes what thorough and intense discussion they must have had during the writing of this book. They knew that one of them would never be able to finish such a project. The only way to succeed was to form a team with three exceptional characters.

In the fall of 2019, I had the pleasure to be invited to the wedding of Irena and Vincent. Bjarni was the chosen best man. At the fantastic evening party, all attendees could feel the unique energy between the three of them. They have more than just friendship. There is energy, emotion, and pleasure between them. These characteristics are necessary to build an incredible team to create a unique project like this book.

Dear lovely readers, you now have this book in your hands. I am convinced that you will feel the energy and the enthusiasm of the team behind it while reading. The sparks of fixed restoration will also fly in your mind.

Prof Dr Markus Hürzeler

Today’s progress in dentistry is extremely rapid regarding the development of new materials and techniques for treating patients in need of fixed restorations. It is easy for clinicians to lose oversight of the myriad of materials available and the technical methods to process them and thus to feel left behind this rapid but fascinating progress. In addition, scientific journals in the field are filled with articles on new material categories, new material compositions, and new techniques and methods for material processing. It is becoming increasingly difficult for clinicians to master the problem of which material is best for which indication in clinical practice. With this book, the authors Irena Sailer, Vincent Fehmer, and Bjarni Pjetursson have compiled clinically relevant and useful recommendations on where and how to apply the optimal dental materials in a given clinical situation. It clearly represents the current best practice for decision making regarding material selection in patients in need of fixed restorations. I expect this book to help seasoned clinicians, trainees in dental schools, as well as students in postgraduate programs to provide better care for their patients.

Divided into four parts, the book covers basic information regarding materials and the overall production processes in the first part, and the clinical procedures step-by-step in the second part. The broad illustration with excellent pictures helps the reader to understand the connection between the initial diagnosis, the patient’s needs, the careful identification of indications, and the optimal choice of the best suitable materials, coupled with the state-of-the-art manufacturing technique. The discussion of the clinical challenges occurring around dental restorations would not be complete without the third Part detailing the important issues of long-term outcomes, and the final Part describing the management of complications. Thanks to their years of experience in clinical dentistry and their careers as clinical researchers, the authors excellently combine clinical judgment with the scientific evidence for the recommendations on best practice for fixed restorations. In the light of today’s important role of dental implants to support and improve the desired clinical outcomes, this book deals with materials to restore natural teeth as well as dental implants.

In summary, the authors are to be congratulated for having compiled a guide for the dental community to enable better health care in this era of rapid technical and scientific development in the field of dental restorative materials and their application in clinical practice.

Prof Dr Dr h c Christoph Hämmerle

For decades, restorative dentistry has been dominated by mechanistic therapeutic concepts and simple material sciences aspects. However, in more recent years, these concepts were severely challenged and replaced by biologically oriented treatment concepts. “To maintain, rather than to extract a tooth” became the paradigm for restorative dentistry. In this respect, the placement of implants became a concept to replace missing teeth rather than to replace teeth. The teeth experienced a renaissance in their significance and priority in the concept of total patient care and maintaining the dentition for a lifetime.

The periodontal aspects of abutment teeth and final restorations receive great attention when restoring a mutilated dentition. It was realized that oral diseases, with the exception of trauma and malignancies, represent opportunistic infections that have to be successfully treated before restorations can be incorporated. The principle of “never building a house on sand, but rather on a solid foundation” was introduced and consequently implemented in restorative dentistry. This, in turn, meant that periodontal and endodontic treatment had to be successfully completed prior to prosthetic rehabilitation.

At the same time, tremendous progress was made in developing dental materials that were able to mimic the natural dentition in terms of esthetics and function. These techniques require highly skilled laboratory technicians and profound knowledge of dental materials in order to be applied in clinical work.

It is evident that a modern textbook on restorative dentistry has to be based on the biologic principles discussed above. While a plethora of texts address single aspects of prosthetic restorations, there are only a few textbooks that present a comprehensive view on the entire field of oral rehabilitation. Moreover, only occasionally do we encounter a textbook with a clear biologic background. The present text is such an exceptionally rare documentation of a biologically based treatment philosophy. The numerous case documentations are testament to the feasibility of individually optimal restorations centering on the patient’s needs rather than on idealistic and hardly affordable concepts.

Irena Sailer, Vincent Fehmer, and Bjarni Pjetursson are a trio that has successfully established international recognition in the field of oral rehabilitation. They have worked together for over 10 years and are well known from their annual Icelandic Education Weeks. These have been very successful 1-week events with an international attendance of enthusiastic participants. Both Irena Sailer and Bjarni Pjetursson are clinically highly competent and skilled clinicians. They unite the fields of Periodontology and Restorative Dentistry in a unique way. Vincent Fehmer is a well-known master dental technician who completes the trio and contributes to the technical aspects of restorative dentistry. It is fortunate indeed that this trio has taken the time to provide the profession with such a unique textbook on all modern aspects of restorative dentistry.

Prof Dr Dr Niklaus P Lang

Authors

Prof Dr Irena Sailer, Prof Dr med dent, Hon Prof (U Aarhus)

Chair, Division of Fixed Prosthodontics and Biomaterials, University of Geneva, Geneva, Switzerland

Honorary Skou Professor, University of Aarhus, Aarhus, Denmark

Adjunct Associate Professor, Department of Preventive and Restorative Sciences, School of Dental Medicine, University of Pennsylvania, PA, USA

MDT Vincent Fehmer

MDT, Division of Fixed Prosthodontics and Biomaterials, Clinic of Dental Medicine, University of Geneva, Geneva, Switzerland

Prof Dr Bjarni E Pjetursson, Prof Dr med dent, DDS, MAS Perio, PhD

Professor and Chairman, Department of Reconstructive Dentistry, and Dean, Faculty of Odontology, University of Iceland, Reykjavík, Iceland Invited Professor, Division of Fixed Prosthodontics and Biomaterials, University of Geneva, Geneva, Switzerland

Co-author

Prof Dr Jens Fischer, Prof Dr med dent, Dr rer nat

Division of Biomaterials and Technology, Clinic for Reconstructive Dentistry, University Center for Dental Medicine UZB, University of Basel, Basel, Switzerland

Prof Dr Irena Sailer, Hon Prof (U Aarhus)

Prof Dr Irena Sailer received her Dr med dent degree from the University of Tübingen, Germany (1997/1998). She received an Assistant Professorship at the Clinic of Fixed and Removable Prosthodontics and Dental Material Sciences, Zurich, Switzerland (2003), where from 2010 she was an Associate Professor. In 2007, Prof Dr Sailer was a Visiting Scholar at the Department of Biomaterials and Biomimetics, Dental College, New York University, NY, USA. Since 2009 she has held an Adjunct Associate Professorship at the Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania, PA, USA (Head: Prof Dr MB Blatz).

Prof Dr Sailer is Head of the Division of Fixed Prosthodontics and Biomaterials at the University of Geneva, Switzerland. In 2019, she received an Honorary Skou Professorship at Aarhus University, Denmark. She is a Specialist for Prosthodontics (Swiss Society for Reconstructive Dentistry), and holds a Certificate of focused activities in Dental Implantology (WBA) of the Swiss Society for Dentistry. She is a member of the Board of Directors of the European Association of Osseointegration (EAO), Vice President of the European Academy of Esthetic Dentistry (EAED), member of the Swiss Society of Reconstructive Dentistry, the Education Committee of the International Team for Implantology (ITI), and the Greater New York Academy of Prosthodontics (GNYAP), and Editor-in-Chief of the International Journal of Prosthodontics. She is widely published and holds several patents on esthetic coatings of dental/medical devices, and on a digital dental splint.

MDT Vincent Fehmer

MDT Vincent Fehmer received his dental technical education and degree in Stuttgart, Germany, in 2002. From 2002 to 2003 he performed fellowships in the UK and the USA in Oral Design certified dental technical laboratories. From 2003 to 2009 he worked at an Oral Design certified laboratory in Berlin, Germany, at Zahntechnik Mehrhof. In 2009 he received his MDT qualification in Germany. From 2009 to 2014 he was the chief dental technician at the Clinic for Fixed and Removable Prosthodontics in Zurich, Switzerland. Since 2015 he has been dental technician at the Clinic for Fixed Prothodontics and Biomaterials in Geneva, Switzerland, and runs his own laboratory in Lausanne, Switzerland.

MDT Fehmer is a Fellow of the International Team for Implantology, an Active member of the European Academy of Esthetic Dentistry (EAED), and a member of the Oral Design group, the European Association of Dental Technology (EADT), and German Society of Esthetic Dentistry (Deutsche Gesellschaft für Ästhetische Zahnheilkunde, DGÄZ). He is active as a speaker at a national and international Level. MDT Fehmer has received honors including the prize for the Best Master Program of the Year (Berlin, Germany). He has published numerous articles within the field of fixed prothodontics and digital dental technology. He also serves as reviewer for several international journals and is a section editor for the International Journal of Prosthodontics.

Prof Dr Bjarni E Pjetursson, DDS, MAS Perio, PhD

Prof Dr Bjarni Pjetursson received his DDS from the University of Iceland in 1990. From 1990 to 2000 he worked as a general dentist in his private clinic in Iceland. In 2000 he started his postgraduate training in Periodontology and Implant Dentistry at the University of Bern, Switzerland. He received his specialist certificate (EFP & SSP) and Masters of Advanced Studies in Periodontology and Doctorate in Dentistry from the Faculty of Medicine, University of Bern. From 2003 to 2005 he did his postgraduate training in Prosthodontics at the University of Bern. From 2005 he was Assistant Professor and Senior Lecturer at the Department of Periodontology and Fixed Prosthodontics, University of Bern, and from 2009 to 2014 the Dean of the Faculty of Odontology, University of Iceland.

Presently he is a Professor and Chairman of the Department of Reconstructive Dentistry, University of Iceland, and a Titular Professor at the Division of Fixed Prosthodontics and Biomaterials at the University of Geneva, Switzerland. Prof Dr Pjetursson is a board member of EAO, an ITI Fellow, Associate Editor of the International Journal of Prosthodontics, and member of the editorial board of Clinical Oral Implants Research. He has published extensively in and given over 700 lectures in 50 countries around the world. His research interests are clinical studies in implant dentistry and evidenced-based evaluation of different treatment modalities in implant and prosthetic dentistry.

Contributors

PD Dr G Benic

Lugano, Switzerland

PD Dr A Bindel

Zurich, Switzerland

Dr F Brandenberg

Lucerne, Switzerland

Dr D Büchi

Chur, Switzerland

Dr F Burkhardt

Geneva, Switzerland

Dr U Calderon

Geneva, Switzerland

Prof Dr Dr J Fischer

Basel, Switzerland

DT W Gebhard

Zurich, Switzerland

Dr P Grohmann

Berikon, Switzerland

Prof Dr R Jung

Zurich, Switzerland

Dr N Kalberer

Geneva, Switzerland

Dr D Karasan

Geneva, Switzerland

Prof Dr H Lee

Pusan, South Korea

Dr J Legaz Barrionuevo

Geneva, Switzerland

Dr L Marchand

Geneva, Switzerland

PD Dr S Mühlemann

Zurich, Switzerland

DT C Piskin

Lausanne, Switzerland

Dr J Pitta

Geneva, Switzerland

Dr C Riera

Geneva, Switzerland

Dr M Strasding

Geneva, Switzerland

DT B Thiévent

Zurich, Switzerland

Prof Dr D Thoma

Zurich, Switzerland

Dr E van Dooren

Antwerp, Belgium

PD Dr A Zembic

Winterthur, Switzerland

Contents

Forewords

Authors

Contributors

Part I Basics

1.1 Current restorative materials

Jens Fischer

1.1.1 Introduction

1.1.2 Requirements for restorative materials

1.1.3 Overview of current materials for fixed restorations

1.1.4 Conclusions

1.1.5 References

1.2 Patient-related factors for material selection

1.2.1 Introduction

1.2.2 Patient demands

1.2.3 Esthetic requirements

1.2.4 Amount and quality of tooth substance

1.2.5 Amount and quality of soft tissues

1.2.6 Occlusal and functional requirements

1.2.7 Conclusions

1.2.8 References

1.3 Technical factors

1.3.1 Introduction

1.3.2 Conventional vs computer-aided manufacturing techniques

1.3.3 Optical factors influencing the material selection

1.3.4 Monolithic and veneered restorations

1.3.5 Conclusions

1.3.6 References

1.4 Diagnostics

1.4.1 Introduction

1.4.2 Esthetic parameters to be evaluated: step-by-step checklist

1.4.3 Time points for diagnostics, diagnostic tools

1.4.4 Conventional procedures

1.4.5 Digital procedures

1.4.6 Augmented reality in dentistry

1.4.7 Diagnostics for fixed implant-supported restorations, surgical stents

1.4.8 Conclusions

1.4.9 References

1.5 Decision-making criteria for replacing the missing tooth

1.5.1 Introduction

1.5.2 An evidence-based approach to treatment planning

1.5.3 Factor 1 – The patient’s perception

1.5.4 Factor 2 – The estimated longevity of the restorations

1.5.5 Factor 3 – The neighboring teeth

1.5.6 Factor 4 – The evaluation of the tooth gap

1.5.7 Factor 5 – The complexity of implant placement

1.5.8 Factor 6 – Assessment of risk factors

1.5.9 Factor 7 – Multiple risk factors

1.5.10 Conclusions

1.5.11 References

1.6 Tooth preparation: current concepts for material selection

1.6.1 Introduction

1.6.2 Minimally invasive preparation techniques

1.6.3 Defect-oriented preparation techniques for posterior teeth: onlays, overlay-veneers, and partial crowns

1.6.4 Conventional crown and fixed dental prosthesis (FDP) preparation technique: the universal tooth preparation

1.6.5 Virtual diagnostics and guided tooth preparation

1.6.6 Resin-bonded fixed dental prosthesis (RBFDP) preparation

1.6.7 Conclusions

1.6.8 References

1.7 Provisional restorations

1.7.1 Introduction

1.7.2 Direct provisionals

1.7.3 Eggshell provisionals

1.7.4 CAD/CAM provisionals

1.7.5 Conclusions

1.7.6 References

1.8 Impression techniques

1.8.1 Introduction

1.8.2 Biological width

1.8.3 Methods for temporary tissue retraction

1.8.4 Conventional impressions

1.8.5 Optical impressions

1.8.6 Conclusion

1.8.7 References

1.9 Material-related cementation procedu res

1.9.1 Introduction

1.9.2 Adhesive cementation of silica-based ceramics (feldspathic ceramics, glass-ceramics)

1.9.3 Adhesive cementation of oxide ceramics (zirconia)

1.9.4 Adhesive cementation of hybrid materials (resin-nano ceramic, resin-infiltrated ceramic network)

1.9.5 Universal silanes/primers and universal resin cements

1.9.6 Conclusions

1.9.7 References

1.10 Fixation of implant-supported restorations

1.10.1 Introduction

1.10.2 Cemented implant restorations

1.10.3 Screw-retained implant restorations

1.10.4 Screw-retained versus cemented

1.10.5 Conclusions

1.10.6 References

1.11 The titanium-base abutment concept

1.11.1 Introduction

1.11.2 Traditional implant restorations supported by stock/customized abutments

1.11.3 Monolithic implant restorations supported by titanium-base abutments

1.11.4 Factors for predictable outcomes: adhesive cementation of monolithic ceramics to titanium-base abutments

1.11.5 Conclusions

1.11.6 References

1.12 Material selection flowcharts

Material selection for tooth-supported single-unit restorations

Material selection for tooth-supported multiple-unit restorations

Material selection for implant-supported restorations

1.13 Cementation flowcharts

Cementation flowchart for metal-ceramic restorations

Cementation flowchart for zirconia restorations

Adhesive cementation flowchart for lithium disilicate restorations

Adhesive cementation flowchart for feldspathic ceramic veneers

Cementation flowchart for posts

Cementation flowchart for extraoral cementation (eg, in laboratory)

Part II Clinical procedures step-by-step

2.1 Minimally invasive restorations (veneers)

2.1.1 Anterior regions: Additional veneers after trauma (two maxillary central incisors)

2.1.2 Anterior regions: Anterior veneer after trauma (single maxillary central incisor)

2.1.3 Anterior regions: Traditional veneers for restoration of amelogenesis imperfecta six maxillary anterior teeth)

2.1.4 Anterior & posterior regions: Traditional and palatal veneers after deep bite and orthodontic pretreatment (six maxillary anterior teeth)

2.1.5 Anterior & posterior regions: Traditional veneers after undetected celiac disease (10 veneers – maxillary premolar to premolar)

2.1.6 Anterior & posterior regions: Traditional veneers with the application of augmented reality (10 veneers – maxillary premolar to premolar)

2.1.7 Anterior & posterior regions: Traditional veneers with the application of augmented reality and orthodontic pretreatment (six maxillary anterior teeth)

2.1.8 Anterior & posterior regions: 360-degree and occlusal veneers with a single implant restoration (seven mandibular teeth and posterior implant)

2.1.9 Complex situations: Full-mouth rehabilitation with traditional veneers and overlays

2.1.10 Complex situations: Additional veneers and implant restorations (maxillary premolar to premolar)

2.2 Minimally invasive restorations (resin-bonded fixed dental prostheses [RBFDPs])

2.2.1 Anterior regions: Failing central incisor after many years of periodontal treatment

2.2.2 Anterior regions: Congenitally missing lateral incisor (RBFDP after orthodontic pretreatment)

2.2.3 Anterior regions: Congenitally missing lateral incisors (RBFDP after orthodontic pretreatment)

2.2.4 Anterior regions: Full-mouth rehabilitation with congenitally missing teeth (RBFDPs, veneers, and overlays after orthodontic treatment)

2.2.5 Complex situations: RBFDP and additional veneer in combination with orthodontic pretreatment

2.3 Defect-oriented restorations

2.3.1 Posterior regions: Defect-oriented partial crowns and overlay in posterior regions

2.3.2 Posterior regions: Defect-oriented overlays in posterior regions

2.3.3 Posterior regions: Defect-oriented restoration of endodontically treated posterior tooth

2.3.4 Posterior regions: Defect-oriented restorations (direct computer-aided composite build-up)

2.4 Conventional single crowns (SCs)

2.4.1 Anterior regions: Anterior SC with non-discolored abutment tooth

2.4.2 Anterior regions: Anterior SCs with discolored abutment teeth

2.4.3 Posterior regions: Posterior SC with non-discolored abutment tooth

2.4.4 Posterior regions: Posterior SC with a discolored abutment tooth

2.4.5 Complex situations: Conventional SCs and fixed dental prostheses (FDPs)

2.4.6 Complex situations: SCs in combination with an implant

2.5 Tooth-supported all-ceramic single crowns (SCs), fixed dental prostheses (FDPs), and a removable telescopic restoration

2.5.1 Anterior regions: Full-mouth rehabilitation

2.5.2 Posterior regions: Tooth-supported, all-ceramic three-unit fixed dental prosthesis (FDP)

2.5.3 Posterior regions: The 3D-printed prototype

2.6 Implant-supported single crowns (SCs)

2.6.1 Anterior regions: Anterior implant- supported SC with GBR

2.6.2 Anterior regions: Anterior implant- supported SC with GBR

2.6.3 Anterior regions: Anterior implant- supported SC

2.6.4 Posterior regions: Posterior implant- supported SC with GBR

2.6.5 Posterior regions: Posterior implant- supported SC with GBR

2.6.6 Posterior regions: Posterior implant- supported SC and optical impression

2.6.7 Complex situations: Tooth- and implant-supported all-ceramic SCs and fixed dental prostheses (FDPs)

2.7 Implant-supported restorations

2.7.1 Anterior regions: Implant-supported four-unit fixed dental prosthesis (FDP)

2.7.2 Posterior regions: Implant-supported three-unit fixed dental prosthesis (FDP)

2.7.3 Posterior regions: Implant-supported fixed dental prosthesis with mesial cantilever (FDP)

2.7.4 Posterior regions: Implant-supported fixed dental prostheses (FDPs)

2.7.5 Complex situations: Full-arch implant-supported fixed restoration with pink ceramics (FDP)

2.8 Maintenance

2.8.1 Intraoral direct repair of an existing restoration

2.8.2 Maintaining an existing restoration

2.8.3 CAD/CAM-fabricated Michigan splint

Part III Long-term outcomes of fixed restorations

3.1 Introduction

3.2 Tooth-supported veneers

3.3 Tooth-supported inlays and onlays

3.4 Tooth-supported SCs

3.5 Endocrowns

3.6 Tooth-supported conventional multiple-unit FDPs

3.7 Tooth-supported cantilever FDPs

3.8 Resin-bonded fixed dental prostheses (RBFDPs)

3.9 Implant-supported SCs

3.10 Implant-supported FDPs

3.11 Implant-supported cantilever FDPs 693

3.12 Combined tooth-implant-supported FDPs

3.13 References

Part IV Avoiding and managing complications

4.1 Introduction

4.2 Success of tooth- and implant-supported restorations

4.3 Tooth-supported restorations

4.4 Implant-supported restorations

4.5 References

PART I

BASICS

CHAPTER 1

Current restorative materials

Jens Fischer

1.1.1 Introduction

In this chapter:

■ Requirements for restorative materials

■ Overview of current materials for fixed restorations

■ Conclusions

In the past, material selection in fixed prosthodontics was mainly based on metal-ceramics and on a few all-ceramic alternatives. Metal-ceramic restorations were selected in clinical situations with need for high stability (eg, in the posterior region or in the case of multiple-unit fixed dental prostheses), whereas all-ceramic restorations were recommended in single tooth replacement with high esthetic demands, especially in the anterior region. These materials were traditionally processed by manual fabrication technologies such as casting, pressing, or layering1,2. Restorative dentistry with all-ceramic restorations has suffered from a prolonged learning curve. Several of the early systems disappeared shortly after being introduced due to an unacceptable number of mechanical failures3.

Nowadays, clinicians and technicians can choose from a wide range of reliable materials. Digital technologies such as intraoral optical scans and computer-aided design/computer-aided manufacturing (CAD/CAM) procedures have opened up new treatment pathways in fixed prosthodontics. New digital fabrication workflows were defined and in parallel advanced materials were developed and adjusted to the specific requirements of numerically controlled processing such as high-strength ceramics and composites. In these digital workflows, the restorations are fabricated by means of computer-aided milling from prefabricated blanks, increasingly replacing conventional manual processing.

The different materials available today exhibit differences in properties, influencing the esthetics and the long-term performance of the restorations. As multiple alternatives exist for each clinical situation, it is more difficult to select the most appropriate material for the respective clinical situation today than in the past4–6. As a consequence of the transformation in present technology, selection of the restorative material requires understanding of the interaction between material properties and clinical performance7.

After an introduction to the requirements for restorative materials and the behavior of the different material classes used in dentistry, this Chapter will provide an overview of the current material options for fixed restorations and their clinically relevant properties, indications, and limitations.

1.1.2 Requirements for restorative materials

In the oral cavity, restorative materials have to meet three requirements: biocompatibility, longevity, and esthetics.

Biocompatibility

The term biocompatibility implies that the material shall do no harm to the living tissues, achieved through chemical and biological inertness8. As every material potentially dilutes or degrades depending on the environment, the extent of decomposition, and the quality and amount of released substances determine the degree of biological complications. A possible host response might be localized or systemic toxicity, hypersensitivity, or genotoxicity9. The restriction to biocompatible components strongly limits the room for the development of new materials.

Due to the strict regulations for medical devices, manufacturers have to prove biocompatibility of their materials. International standards help the choosing of the appropriate tests and in interpreting the results. Tests must be done with every novel material prior to approval. Biological tests are employed in a sequence, ending up with animal tests9. Furthermore, manufacturers of medical devices are forced by law to perform a systematic post market surveillance of the materials and devices. Measures have to be taken to minimize risk and unexpected side effects must be notified to the authorities. Fortunately, it can be concluded that biological and immunological adverse reactions attributed to dental materials are rare and the reported adverse effects are acceptable9.

On the other hand it is unrealistic to assume that absolute material inertness is attainable and biological behavior is definitely predictable by means of biological tests10. Hence, the biocompatibility of dental materials must always be weighed against their benefit11. Controlled clinical trials are currently still the best way to assess the clinical response to materials. But even these tests have significant limitations. Therefore, practice-based research networks and practitioner databases are increasingly considered as a valuable alternative10.

Longevity

The long-term success of a restoration mainly depends on its mechanical performance. From the technical side the success of a restoration can be controlled by the durability of the material, the nature of the design, the quality of the processing, and the effectiveness of the finishing.

Material

The mechanical behavior of dental materials is mainly characterized by elasticity, flexural strength, fracture toughness, and hardness. These properties are basically given by the type and strength of the bondings between the atoms.

Elasticity is the ability of the material to resume its initial shape after loading, measured in GPa (= 103 N/mm2). Stressing a material beyond its limit of elasticity leads to plastic deformation, a permanent distortion. Brittle materials such as ceramics only show minimal or no plasticity, which means they fracture very soon after reaching the limit of elasticity. The stress where fracture occurs is the flexural strength, measured in MPa (= N/mm2). The resistance against crack growth is called fracture toughness, measured in MPa√m.

Elasticity, flexural strength, and fracture toughness are bulk properties. Hardness in contrast is a surface property, which is defined as the resistance to localized deformation induced by mechanical indentation or abrasion. Harder materials therefore show less risk of surface damage. Flexural strength and hardness are correlated to a certain extent.

The main risk for mechanical failure of restorations are flaws at the surface, which might act as a starting point for microcracks. In case of tensile loading, a microcrack opens and stress develops at the tip of the crack. Stress which exceeds the strength of the material leads to crack propagation. Under cyclic loading − such as mastication − crack growth happens in a micrometer scale. But over time the crack grows significantly. Finally, catastrophic failure occurs when the residual cross-section is too small to withstand the load.

It is important to understand the fracture mechanisms of the different materials. In metals the crack tip is rounded out by plastic flow and thus the risk of fracture is significantly reduced (Fig 1-1-1). In ceramics plastic flow is not possible due to the covalent bonds. The crack tip remains sharp and crack growth is a significantly higher risk than in metals. That is the reason for the well-known brittle behavior of ceramics. To increase strength and in particular toughness, strengthening mechanisms on the microscopic level to impede crack propagation are employed. In brittle materials this might be achieved by internal compression or by particles, which act as obstacles against crack growth (Fig 1-1-2). The objective of such strengthening mechanisms is to stop crack growth or at least to hamper it, like a hurdler who is not as fast as a sprinter.

Figs 1-1-1 Schematic representation of crack propagation in materials. (a) Plastic material (eg, metals). (b) Brittle material (eg, ceramics).

Fig 1-1-2 Schematic representation of crack propagation in particle-reinforced materials under tensile stress (red arrows). When the crack tip strikes a particle, crack propagation is impeded, or at least decelerated.

The term durability includes not only the mechanical characteristics specified above but resistance to wear and aging as well. The degradation of the materials by wear and aging depends on the mechanical properties and also on the susceptibility to the oral environment including humidity, temperature, and loading characteristics. Water for instance may attack the material’s bonds especially at phase boundaries or microcracks, thus promoting degradation.

Design

Several mistakes can be made when designing a restoration. Insufficient dimensioning in crown walls or connectors of fixed dental prostheses is one reason for failures. Instructions of the manufacturers have to be strictly followed. Further, sharp edges increase the risk of failure due to an uncontrolled stress development (Fig 1-1-3). And finally, restorations made by materials, which require a thermal treatment should be designed with an even wall thickness as far as possible to get a homogeneous stress distribution during cooling. That applies especially for veneering ceramics, which must be layered in a uniform thickness and adequately supported by the framework both for metal-ceramic and all-ceramic bilayers.

Figs 1-1-3a to 1-1-3d Insufficient thickness of the crown and sharp edges of the preparation caused fracture of the restoration. (a) Restoration on tooth 47 after cementation. (b) Radiograph after cementation. The insufficient occlusal thickness of the restoration and the sharp edge of the distal preparation are obvious. (c) Fracture of the restoration after 1 year in function. (d) Analysis of wall thickness on the basis of the CAD design.

Processing

A shaping process always requires machining, a thermal treatment such as sintering or pressing or a polymerization process. If not processed properly, defects might be created in the material, thus reducing the strength of the restoration (Fig 1-1-4). The manufacturer’s instructions must be meticulously followed.

Figs 1-1-4a to 1-1-4c Fractured zirconia framework 42 x x 32. (a) Framework after sintering, fracture occurred between 41 and 31. (b) Light microscopy image of the fractured area. The area was cut in the white state in order to separate the two pontics. Thus a crack was initiated, which was not sealed during sintering. (c) Scanning electron microscopy (SEM) of the fractured surface after sintering. The formation of grains at the surface indicates that the fracture occurred before sintering.

Finishing

Materials, if machined, sintered, pressed, or polymerized, must be finished with material specific tools and appropriate speed, feed, and pressure of the tools to avoid damage at the surface. For ceramics, as an alternative a glaze firing (a heat treatment without additional application of glaze) or glazing (a heat treatment with additional application of glaze) can be performed (Fig 1-1-5). However, if the restoration is not handled in a way appropriate to the material, it might occur that subsurface damage is not sufficiently eliminated by the finishing procedure and residual flaws potentially act as an origin for microcracks.

Figs 1-1-5a to 1-1-5d Schematic representation of the effect of polishing, glaze firing, or glazing on the surface quality. (a) Microcracks at the surface after processing. (b) Surface after polishing. (c) Surface after glaze firing. (d) Surface after glazing.

Esthetics

Materials for restoring teeth have to mimic the esthetic appearance of the tooth itself. The tooth is a complex structure of a dentin core, providing the color of the tooth, and a more translucent enamel layer. The replacement of dental hard tissue by a dental material needs to balance color, translucency, refraction and reflection, opalescence, and fluorescence. Some materials show a blending quality, also named the “chameleon effect.” These requirements strongly restrict the choice of materials to ceramics and resins. As a compromise metals may be used when covered by tooth-colored veneers.

Color

Coloring of resins and ceramics is obtained by using inorganic pigments, mostly metal oxides (Fig 1-1-6).

Fig 1-1-6 Pigments used to produce the appropriate shades.

Translucency

When there is no light absorption and no optical obstacle in the material, light passes through a material like a windowpane without being scattered. This effect is called translucency (Fig 1-1-7).

Figs 1-1-7a and 1-1-7b Translucency of different ceramic shades. (a) Dentin layer. (b) Enamel layer.

Refraction and reflection

When light passes through an interface and enters a different material, eg, from air to glass, the direction of light propagation is changed, which is called refraction. Depending on the incidence angle, light might also be completely reflected as if hitting a mirror (Fig 1-1-8). These effects lead to a scattering of the light. Interfaces in a material (ie, particles incorporated for strengthening) add to the optical properties by scattering the light as well (Fig 1-1-9).

Fig 1-1-8 Reflection of light at the ceramic surface. Depending on the surface roughness and the incidence angle, reflection is more or less pronounced.

Figs 1-1-9a to 1-1-9f Refraction of light in a glass-ceramic (Vita Suprinity PC) before and after crystallization. (a and b) Schematic representation of light refraction. In the glassy state (a) the material is translucent. Light passes through the material without being refracted. After crystallization (b) light is scattered at the interfaces between glass matrix and crystals. The light is partially refracted and the material thus appears whitish. The surface is slightly etched with hydrofluoric acid to demonstrate the transition from the glassy state to the typical microstructure of glass-ceramic characterized by a glass matrix and incorporated crystals. (c and d) Microstructure before (c) and after (d) crystallization. (e and f) Appearance before (e) and after (f) crystallization.

Diffraction and opalescence

At obstacles smaller than the wavelength, the light will be refracted and scattered in all directions. By diffraction white light is split into the spectral colors. The short blue wavelength will be more deflected than the long red one. If the light source is behind the observer, mainly the blue light is seen; if the light source is behind the object mainly yellow and red colors are seen (Fig 1-1-10). The effect is visible in the sky: small water drops scatter the light. If the sun is in front of us, we mainly see yellow and red light; if the sun is behind us, we can see the azure blue sky.

Figs 1-1-10 Opalescence of a dental ceramic.

Fluorescence

The teeth glow when illuminated with ultraviolet light. Electrons are stimulated by the ultraviolet light and give off the energy by emitting visible light (Fig 1-1-11). Materials for esthetic restorations must show a similar effect. The name originates from the mineral fluorite, where this effect was first observed.

Fig 1-1-11 Fluorescence of a dental ceramic.

Blending quality

Blending quality (“chameleon effect”) is the perception that color differences between esthetic dental materials and dental hard tissues appear smaller when the materials are viewed side-by-side than would be expected when viewed in isolation12.

1.1.3 Overview of current materials for fixed restorations

Modern restorative systems may roughly be classified into composites, silicate ceramics, and zirconia. The application of metal-ceramics is still very common but decreasing.

Composites

A composition material – abbreviated to composite – is a material composed of at least two constituent materials with differing physical and/or chemical properties. In dentistry the term composite is − as a general linguistic usage − restricted to materials composed of polymers and ceramics. By coupling ceramic and resin the advantageous properties of both materials are combined: the elasticity of resin counteracts the brittleness of ceramic and the tendency of resin to wear is counteracted by the wear-resistant ceramic. Composites are provided in blanks either made out of a polymer matrix reinforced with ceramic particles (particle-filled polymer) or out of a ceramic network infiltrated with polymer (polymer-infiltrated ceramic). They are both indicated for restoring teeth or implants chairside in one session by CAD/CAM technology. Of course, they may also be processed in a dental laboratory. Both materials show an excellent milling accuracy and edge stability, as well as a significantly reduced processing time compared to ceramic materials.

Particle-filled polymer

The polymer of this material group is mainly composed of dimethacrylates such as bisphenol A-glycidyl methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and triethylene glycol dimethacrylate (TEGDMA) (Fig 1-1-12). The resin matrix is filled with ceramic particles (Fig 1-1-13). The basic structure is close to composite filling material with a ceramic filler content of about 50% by volume or 80% by mass13. Due to their low mechanical strength, most materials are available in blanks for single-unit use only, yet in different shades. The main indication for the particle-filled polymers are posterior tooth-borne single-unit restorations like inlays, onlays, overlays, and partial crowns. Some products are released for fixed dental prostheses up to three units (eg, Ambarino High-Class, creamed, Marburg, Germany) and even up to five units (eg, LuxaCam, DMG, Hamburg, Germany) or for implant-supported full arch fixed/removable prostheses (eg, Crystal Ultra/Trilor, digital dental, Scottsdale, AZ). Some manufacturers also recommend the fabrication of anterior tooth-borne restorations like veneers, however, as the esthetic result does not reach the outcomes of silicate ceramics, the particle-filled polymers cannot be recommended for highly demanding esthetic situations. Esthetic improvement can be achieved by “veneering” the particle-filled polymer restorations with filling composites; however, their main application remains for the fabrication of monolithic single-unit restorations.

Fig 1-1-12 Chemical structures of Bis-GMA, UDMA, and TEGDMA.

Fig 1-1-13 Microstructure of particle-filled polymer. The surface is slightly etched with hydrofluoric acid to better illustrate the microstructure composed of resin matrix and glass particles.

The fillers are mainly silica or quartz, as well as barium- or strontium-containing silica glasses providing radiopacity, and sometimes ytterbium fluoride, which shows a slight release of fluoride. The particles are incorporated in order to reinforce the material and to scatter the light, thus supporting a tooth-like appearance of the restoration.

For Lava Ultimate (3M ESPE, Seefeld, Germany) the indication “single crown” is excluded due to frequent problems with debonding. In a clinical trial with this material on zirconia abutments an extreme rate of debonding of 80% in the first year was observed14. It is unclear whether the high debonding rate is transferable to other composite materials. In any case the bonding procedure has to be carefully observed and manufacturer recommendations should be followed15. Particle-filled polymers need to be adhesively cemented to the tooth substrate. To increase the surface area and thereby the bond strength, the bonding area must be airborne-particle abraded according to the manufacturer’s recommendations. Chemical bonding is obtained by a primer containing methacrylates and silane, where the methacrylates bond to the polymer matrix and the silane to the ceramic fillers (Fig 1-1-14).

Fig 1-1-14 Chemical structure of silanes and their intermediate bonding to polymer and ceramic surfaces.

Polymer-infiltrated ceramic

The main component of this type of composite is a sintered porous ceramic network, which is infiltrated by polymer (Fig 1-1-15). There is only one product available (Vita Enamic, Vita Zahnfabrik, Bad Säckingen, Germany). The composition is 86% by mass of a fine-grained ceramic and 14% by mass of a mixture from UDMA and TEGDMA. The manufacturer recommends the material for all single tooth restorations as well as implant-supported crowns. The strengthening mechanism in this material is again the use of phase boundaries between polymer and ceramic to stop or deviate cracks. Furthermore, cracks are dissipated and thereby lose energy (Fig 1-1-16).

Fig 1-1-15 Microstructure of a polymer-infiltrated ceramic.

Figs 1-1-16a and 1-1-16b Crack development originating from an indentation. (a) In polymer-infiltrated ceramic the crack is dissipated due to multiple phase boundaries. (b) In feldspar ceramic the crack runs straight through the material.

Polymer-infiltrated ceramic restorations need to be adhesively cemented to the underlying tooth substrate or abutment. The material provides excellent bond strength similar to ceramics due to a micro-retentive etch pattern when etched with hydrofluoric acid (Fig 1-1-17); however, silane should be applied to the intaglio surface of the restoration to improve bond strength16–18.

Fig 1-1-17 Etch pattern of polymer-infiltrated ceramic (60 sec with 5% hydrofluoric acid).

Silicate ceramics

The ceramic materials routinely used in restorative dentistry today encompass feldspar ceramics and lithiumsilicate glass-ceramics.

Small crystalline particles are used to reinforce the material, analogue to the particle reinforcement in composites. When the particles are created by crystallization of a glass in a well-defined temperature profile, the term glass-ceramic is used for these materials. These particles support the optical properties of silicate ceramics. The light may pass through the glassy phase and refraction will occur at the phase boundaries between glass phase and crystalline phase (cf. Fig 1-1-9). The more crystals are present the more phase boundaries are effective and the material gets more and more white and opaque, because the light is more and more reflected.

Feldspar ceramics

Feldspars are a group of minerals composed of alkaline oxides, alkaline earth oxides, alumina, and silicate. Feldspar-based ceramics have the most tooth-resembling optical properties compared to other dental materials and lead to high esthetic outcomes.

As the mechanical stability of these ceramics is rather low, their indication is limited to single tooth restorations. For sufficient stability during clinical function, feldspathic ceramic restorations have to be adhesively cemented to enamel and, thereby, are reinforced. Hydrofluoric acid etching provides a microretentive etch pattern, which after silanization offers sufficient bond strength16. The main application for the feldspathic CAD/CAM blanks is the chairside fabrication of single-unit restorations like veneers, inlays, onlays, and partial crowns.

The results of a systematic review showed that early feldspathic single crowns exhibit significantly lower survival rates than other all-ceramic crown types, especially when manually layered19. However, in the beginning of the 1990s, a feldspathic CAD/CAM material (VITABLOCS Mark II, Vita Zahnfabrik) was developed in line with the CEREC system (Dentsply Sirona, York, PA, USA), which is still on the market, successful, and unchanged over three decades.

Some of the current feldspathic materials are reinforced by leucite, a feldspathoid (IPS Empress, Ivoclar Vivadent, Schaan Liechtenstein; Paradigm C, 3M ESPE, Seefeld, Germany)20,21, others (VITABLOCS Mark II, VITABLOCS Triluxe forte, VITABLOCS RealLife, Vita Zahnfabrik) by sanidine and anorthoclase, minerals of the feldspar group as well as nepheline, a feldspathoid22. These particles develop during the production process. Feldspar ceramic is also available for press technology.

Lithium-silicate glass-ceramics

It is well known from household items that glass-ceramic is a very strong and durable material. The idea was to adapt the material for dental application21. The glass-ceramic is based on a lithium-silicate glass, which is rather weak and therefore machinable. Via thermal treatment the glass partially crystallizes. The crystals act as particle reinforcement and increase strength while mimicking the optical properties of tooth substance (reflection, scattering of light)21.

Two types of glass-ceramics were developed over the years. In the first material (IPS e.max, Ivoclar Vivadent, Schaan, Liechtenstein) lithium-disilicate (Li2[Si2O5]) is the main crystalline phase. In a further development, the main crystalline phase was changed to lithium-metasilicate (Li2[SiO3]) and zirconia was added in an amount of 10 weight%, solved in the glass phase23 for the purpose of strengthening it (Celtra Duo, Dentsply Sirona; Vita Suprinity PC, Vita Zahnfabrik). The crystals are much smaller compared to lithium-disilicate (Fig 1-1-18), resulting in better wear properties when opposing human enamel24.

Figs 1-1-18a and 1-1-18b Microstructure of glass-ceramics. (a) Lithium-disilicate (IPS e.max CAD). (b) Lithium-metasilicate (Suprinity PC).

In general, glass-ceramics may be milled in the fully crystallized state (eg, Celtra Duo) or in the glass state and crystallized subsequently (eg, IPS e.max CAD, Vita Suprinity PC). As the crystallization process does not influence the dimension of the work piece, the fit of the restoration is not affected by the thermal process.

Lithium-silicate glass-ceramic is also offered for the fabrication of restorations by press technology (eg, IPS e.max Press, Ivoclar Vivadent; Celtra Press, Dentsply Sirona; Vita Ambria, Vita Zahnfabrik). The respective composition is adjusted to the press process and therefore slightly different from the machinable variant.

Today, the lithium-silicate glass-ceramics are mostly applied in the monolithic state, without additional veneering ceramic or with only a very small amount of veneering ceramic in facial areas. With this, the risk for chipping of the veneering ceramic is reduced. Recent investigations have demonstrated very favorable clinical outcomes of the monolithic lithium-disilicate tooth- and implant-supported single-unit restorations, and also of lithium-disilicate resin-bonded prostheses19,25,26. However, multiple-unit lithium-silicate fixed dental prostheses exhibited pronounced failure rates due to catastrophic fracture. Therefore, the indication for fixed dental prostheses is limited27.

Zirconia

Zirconia, the strongest tooth-colored ceramic, was adapted to the requirements of dental application in line with the evolution of the CAD/CAM technology28. Zirconia is the oxide of zirconium (ZrO2). Zr and O form a strong chemical bond, resulting in a high flexural strength, exceeding the strength of any other tooth-colored ceramic. Zirconia cannot be processed with conventional procedures like layering or pressing. Zirconia was processed in the densely sintered stage in the beginning, yet, the milling of this hard, tough ceramic was very time-consuming and associated with excessive tool wear. The development of the zirconia white-stage milling out of pre-sintered blanks with subsequent sintering to full density using the direct ceramic machining (DCM) procedure29 enabled its large-scale application in dentistry. To compensate the sintering shrinkage, restorations must be milled so as to be considerably oversized, in the range of 20%.

Zirconia shows three different crystal modifications. At room temperature zirconia has a monoclinic structure. Heating zirconia leads to a phase transition from monoclinic to tetragonal structure at 1170°C. And finally, above 2370°C a cubic structure is stable (Fig 1-1-19). Replacing 3 mol% of ZrO2 by Y2O3 stabilizes the tetragonal phase down to room temperature due to oxygen voids in the crystal lattice and the larger atomic radius of Y compared to Zr. The abbreviation of this material is 3Y-TZP (TZP stands for “tetragonal zirconia polycrystals”). The tetragonal phase of this material is metastable and only occurs when the grain size of zirconia is less than 1 µm30. When energy is brought into the material the phase transition to the monoclinic structure is triggered, even at room temperature. This phenomenon is used to reinforce zirconia: the phase transition from tetragonal to monoclinic (t 🡢 m) is associated with a volume increase of about 4–5%. Microcracks under tensile stress lead to stress concentration at the crack tip. In this area, the mechanical energy is sufficient to provoke the t 🡢 m phase transition. For the phase transition only a slight movement of the atoms in the crystal lattice is necessary (Fig 1-1-19). The increase in volume associated with the phase transition leads to an intrinsic compressive stress at the crack tip, opposing the external tensile stress and thus increasing the materials strength. This effect is not reversible. When the monoclinic phase is established, the strengthening mechanism in this area is consumed; like a match, once lit it cannot be lit again.

Figs 1-1-19a to 1-1-19c Crystal structures of zirconia. (a) Cubic. (b) Tetragonal. (c) Monoclinic.

As zirconia is a polycrystalline ceramic without a noteworthy glassy phase, multiple phase boundaries are present. Further, the refractive indices of the tetragonal and the monoclinic phase differ as a function of the direction of the light incidence. That is the reason why 3Y-TZP has an opaque whitish appearance. 3Y-TZP, therefore, is solely used either as abutment material for implants or framework material for fixed restorations, which for esthetic reasons has to be masked with veneering ceramic.

Most veneering ceramics are based on feldspathic ceramics. For the veneering procedure, the feldspathic ceramic powders have to be mixed with modeling liquid by the dental technician in order to become ceramic slurries. Differently colored slurries are then manually applied to the restoration framework according to the desired shade and the respective optical properties, 20–40% oversized. Subsequently, the veneering ceramics are sintered onto the framework in a furnace, thereby shrinking to the desired dimension. The sintering procedure is performed under vacuum to remove the air captured in the ceramic slurry. Despite the vacuum the air cannot be fully eliminated. Smaller voids of some micrometers in diameter do not equal any risk but may contribute to the optical properties of the ceramic by reflection and scattering of light.

However, numerous studies have reported problems with the zirconia veneering ceramic, ranging from superficial chipping to fractures of larger pieces like, eg, entire cusp tips31–33. Despite all scientific efforts to further improve the strength of the veneering ceramics, their bond to the zirconia substrate and the firing regime during the veneering process, chipping remains to be the major technical complication of veneered zirconia restorations33.

More recently, new variations of zirconia were developed exhibiting tooth-like color and more translucency, allowing for the monolithic application of zirconia for single- and multiple-unit restorations28. These new types of zirconia have a higher amount of yttria. An increasing yttria content leads to the stabilization of the cubic phase. The cubic structure is isotropic, which means that whatever the light’s angle of incidence, the refractive angle is always the same. Therefore, the higher the amount of yttria, the higher the translucency (Fig 1-1-20). These recently developed zirconia types can be applied almost without veneering ceramic or just monolithic, even in esthetically demanding situations. However, with an increasing amount of cubic crystals the strengthening mechanism by phase transition under stress is increasingly lessened and the flexural strength is reduced (Fig 1-1-21).

Fig 1-1-20a to 1-1-20c Translucency of 3Y-, 4Y-, and 5Y-TZP.

Fig 1-1-21 Flexural strength and corresponding translucency of 3Y-, 4Y-, and 5Y-TZP.

Typically, the zirconia qualities are classified by their yttria content of 3, 4, or 5 mol%, termed as 3Y-TZP, 4Y-TZP, or 5Y-TZP.

The same shade and translucency of the zirconia offered by different manufacturers may exhibit different mechanical stability. Hence, the indications and dimensions of the monolithic zirconia restorations must be carefully considered, and manufacturer recommendations should be followed when selecting a material for a specific indication and designing the appropriate restoration. Furthermore, the details on the applied zirconia type, its shade, and manufacturer should be documented in the patient’s record.

Clinical studies on monolithic zirconia restorations are scarce, and the observation periods rather short. More research with longer observation periods is needed to elaborate the indications and limitations and the effect on the stomatognathic system of this recent type of all-ceramic restorations.

As a side note, it may be hypothesized that the clinical success of zirconia has stimulated the rapid development of the digital technologies and CAD/CAM procedures.

Metal-ceramics

Metal frameworks veneered with feldspathic ceramics are a long existing, well-documented material combination for single- and multiple-unit fixed dental prostheses on teeth and implants19,32,33. The composition of the veneering ceramics is very near to the veneering ceramics for zirconia, based on natural or synthetic feldspathic raw materials. However, the coefficient of thermal expansion has to match that of the underlying metal. It has been evaluated empirically that the coefficient of thermal expansion of the veneering ceramic should be one unit below that of the metal. In that case the metal is shrinking a little more during cooling and puts the ceramic under pressure. Thereby, detrimental tensile stress is avoided in the ceramic area.

Metals provide elasticity. Thus, the layered veneer is protected against tensile stress from underneath during mastication. The success story of metal-ceramic restorations is based on this phenomenon. In the beginning of the 1960s it was the first time that esthetic fixed restorations were achievable by veneering a metal framework with a tailored ceramic. From then on metal-ceramics were the gold standard for fixed restorations. However, the importance of this technique significantly decreased with the progress in all-ceramic restorations using zirconia instead of alloys as framework material. Due to the increasing demand for esthetic, biocompatible, and metal-free restorations by patients, all-ceramic and composite materials are increasingly used and will replace metal-ceramic restorations in the near future.

The metal substructures of metal-ceramic restorations are fabricated from different alloys by casting, milling, or selective laser melting. While casting is possible with all types of alloys, milling and laser melting is only economical with base metal alloys. The advantage of metals is their plastic behavior under stress. While in high-strength composite and ceramics cracks might grow under tensile load due to stress concentration at the crack tip, in metals a crack tip is rounded under stress due to plastic deformation (cf. Fig 1-1-1). Thus the stress intensity is reduced. This is why metals have a much higher fracture toughness compared to ceramics or high-strength resins.

The starting point for the metal-ceramic technique was a high-gold alloy, based on the binary system gold-platinum with a gold content of approximately 70–80% by weight. Over the years, as gold and platinum prices rose, different types of precious metal alloys were developed for economic reasons. These were precious metal alloys mainly based on a considerable amount of palladium, replacing gold as well as alloys based on the binary systems palladium-copper or palladium-silver with only low or even no gold and no platinum content. Further, base metal alloys such as cobalt-chromium alloys and chromium-nickel alloys were developed.

The traditional way to process precious and base metal alloys is casting, applying the lost-wax technique. A wax model of the framework is modeled manually, embedded in a refractory embedding compound, and burnt out, resulting in a hollow shape according to the desired framework. Molten alloy is cast into the hollow. After solidifying of the alloy, the casting object is divested, cleaned, and further processed.

Base metal alloys, such as cobalt-chromium alloys, have recently become a valid alternative to the gold-reduced and palladium-based varieties. They suffered from some technical disadvantages in the past, as casting of these metals is difficult. Their indications in daily clinical practice were very limited for this reason. Yet, CAD/CAM technology enabled the processing of the base metal alloys by allowing for computer-aided milling of industrially fabricated blanks, as well as additive manufacturing by selective laser melting technology.

With all types of metal-ceramics, the dark color of the metals has to be esthetically improved with veneering ceramics, adapted to the material properties of the respective metal alloy. Until today, the veneering procedure for the metal-based types of restorations is mostly performed by manual layering of veneering ceramic34,35. Some veneering ceramics can also be applied by the pressing technique, a veneering process that is not widely used, however.

It may be very challenging to achieve perfect esthetics with metal-ceramics, since the underlying framework is dark and the space for transforming its color into a natural tooth-resembling appearance with veneering ceramic is limited. Dental technicians need to develop pronounced skills and high experience levels for excellent esthetics with metal-ceramics.

1.1.4 Conclusions

Material properties determine the indications for the respective materials. Metal-ceramics will increasingly be replaced by composites and all-ceramic solutions. Composites play a certain role in single tooth restorations. The trend today is toward all-ceramic restorations due to their high esthetics and biocompatibility. For multiple-unit restorations, the material selection portfolio is rather limited. Of all-ceramic options, only zirconia demonstrates sufficient mechanical stability for this indication.

For the practitioner it is important to choose the right material. Table 1-1-1 gives an overview of selected non-metallic material options, their indications, and recommended cementation protocols to facilitate the choice.

Table 1-1-1 Classification, indications, and cementation protocols for selected metal-free restorative materials according to the manufacturers’ instructions

1.1.5 References

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