Factors Affecting the Fracture Strength and Fatigue Resistance of Molar Crowns Produced Using a Zirconia-based System by Mohammed Hani Zahran A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Dentistry University of Toronto © Copyright by Mohammed Hani Zahran (2013) Factors Affecting the Fracture Strength and Fatigue Resistance of Molar Crowns Produced Using a Zirconia-based System Mohammed Hani Zahran Doctor of Philosophy Graduate Department of Dentistry University of Toronto 2013 Zirconium-oxide ceramic was introduced as a potential restorative material for posterior teeth due to its superior mechanical properties. However, zirconia is opaque and needs to be masked with an esthetic veneer. Short-term clinical studies showed a high rate of veneer chipping/delamination for zirconia-based posterior crowns. This may be attributed to either inferior strength of the veneering porcelain or weakness in the zirconia-veneer bond. The aims of this in-vitro project were to analyze some of the factors that can influence the performance of zirconia-based molar crowns and to characterize the zirconia-veneer interface. The project consisted of four parts. The first part aimed to evaluate the effect of total thickness, core thickness and veneering technique on fracture mode and strength of zirconia-porcelain specimens of simple geometry. Results indicated that all three variables significantly affected mean fracture load, while only two (total thickness and core thickness) affected fracture mode. The second part aimed to assess the effect of core design and thickness on fatigue resistance, fracture strength and fracture mode/extent of zirconia-based molar crowns. Results indicated that core thickness, but not core design, had a significant effect on ii fracture strength. The anatomically-shaped core design reduced the size of the veneering porcelain fracture. In the third part, the effect of core design and two different CAD-CAM-produced veneering materials on fatigue resistance, fracture load and fracture mode of zirconia- based molar crowns was examined. Results indicated that the veneering material, but not core design, had a significant effect on fracture load and mode. The fourth part aimed to characterize the zirconia-porcelain interface using modern surface analysis techniques (Time of Flight Secondary Ion Mass Spectrometry (ToF- SIMS) and X-ray Photoelectron Spectroscopy (XPS)). Results indicated chemical changes of zirconium along the interface. In conclusion, improving the strength of the veneering layer by using pressed veneering porcelain can enhance performance of posterior zirconia-based crowns in comparison to manual build-up technique. Furthermore, fusing a CAD-CAM-produced veneering layer to the underlying zirconia core is a promising technique that can augment veneering porcelain strength and enhance zirconia-porcelain bond. Modifying core design, crown thickness and core thickness can improve performance of zirconia-based molar crowns. iii Dedication iv Acknowledgement Praise and gratitude to ALLAH, Almighty, without whose gracious help it would have been impossible to accomplish this work. First and foremost, I would like to express my gratitude to my supervisor, Prof. Omar El-Mowafy, whose expertise, understanding, time and patience, added considerably to my graduate experience. I appreciate his support, advice, guidance and mentorship throughout my master and doctorate journey, which lasted more than 8 years. Special thanks to my co-supervisor, Prof. Asbjorn Jokstad, for his expertise, understanding, patience, professionalism and mentorship during my clinical training at the Faculty. His insight and guidance contributed significantly to this project. Also, I wish to thank my other thesis advisory committee members, Dr. Laura Tam and Dr. Amin Rizkalla for the time they provided throughout this project. Dr. Tam’s valuable and thorough comments and suggestions helped significantly in improving the quality of this finished product. Without Dr. Rizkalla’s expertise in the field of engineering and his appreciated effort in performing some of the mechanical testing at his lab, this project would not be possible. Specials thanks also go to my family for the support they provided through my entire life, and very special thanks go to my wife, love and best friend, Dania, and my sons, Abdullah, Ibrahim and Yousuf. Without their love, encouragement, on-going support and sacrifices throughout this process, I would not have finished my graduate program. A special welcome goes to the new member of our family, Abdulelah, who was hidding for the last 9 months and joined us just after defending my dissertation. In conclusion, I recognize that this research would not have been possible without the financial support of the King Abdulaziz University, Saudi Arabia. This support is duly acknowledged. v Table of Contents Chapter 1: Introduction and Literature Review ...................................................................... 1 1.1. Introduction ...................................................................................................................................................... 2 1.2. Dental Ceramics Classification .................................................................................................................. 3 1.3. Indications for All-Ceramic Restorations ............................................................................................. 4 1.4. Fracture of All-Ceramics Materials and Restorations ..................................................................... 4 1.5. Fatigue Process in Ceramics Materials and Restorations .............................................................. 5 1.5.1. Factors Affecting the Fracture and Fatigue of Ceramic Restorations ....................................... 7 1.5.2. Improving the Strength of Ceramic Material .................................................................................... 12 1.5.3. Laboratory Testing of the Performance of the Ceramic Materials and Restorations ...... 13 1.5.4. Methods for Testing the Effect of Fatigue on Ceramic Materials and Restorations ......... 14 1.5.5. Simulating the Clinical Situation in the Fatigue Testing .............................................................. 18 1.6. Survival Rates of All-Ceramic Crowns .................................................................................................. 19 1.7. Zirconium Oxide Ceramics ........................................................................................................................ 20 Chapter 2: Rationale and Objectives .................................................................................... 27 Chapter 3: Manuscript 1 ....................................................................................................... 29 Effect of total thickness, core thickness and veneering porcelain application technique on fracture of zirconia/porcelain combinations ............................................................................................ 30 Chapter 4: Manuscript 2 ....................................................................................................... 58 Effect of core thickness and design on fracture strength and fatigue resistance of zirconia-based crowns ........................................................................................................................................ 59 Chapter 5: Manuscript 3 ....................................................................................................... 96 Effect of core design and veneering material on fracture strength and fatigue resistance of zirconia molar crowns ................................................................................................................................... 97 Chapter 6: Manuscript 4 ..................................................................................................... 129 Characterization of the interface between zirconia and veneering porcelain .......................... 130 vi Chapter 7: Summary and Clinical Relevance ..................................................................... 155 Appendices ......................................................................................................................... 159 Reference ............................................................................................................................ 197 vii List of Tables (Table 3.1) Composition and some properties of materials used for core and veneering porcelain. ...................................................................................................................... 44 (Table 3.2) Firing program for materials used in the study. ................................................. 45 (Table 3.3) Experimental groups according to core thickness (mm), total thickness (mm) and veneering porcelain. ............................................................................................... 46 (Table 3.4) Fracture load (N) data for all groups. ................................................................. 47 (Table 3.5) Factorial ANOVA .............................................................................................. 48 (Table 3.6) The effect of different independent variables on fracture load (N). .................. 49 (Table 3.7) Incidence of different types of fracture mode for all groups. ............................ 50 (Table 3.8) Effect of different