The full potential of esthetic ceramic-based restorations cannot yet be realized. Shaping-induced damage, exacerbated by fatigue damage during normal chewing, dramatically reduces their initial strength. Since residual strengths fall to values close to occlusal forces, it is not surprising that clinical success of molar crowns has been disappointing. All-ceramic posterior bridges with acceptable success rates over 5-10 years remain a dream. Survival of the crowns is a complex set of interactions between material, fabrication, design, and service variables. In Phase I, our team developed fundamental understanding in damage initiation and accumulation in materials recommended for posterior dental crowns. The influence of microstructure, fatigue and machining parameters on damage have been characterized in monolithic materials. By layering these materials, the conflicting demands for strength and esthetics can be met. Through rational design, the inevitable damage can be managed, yielding a damage tolerant structure which can withstand microcracks within a layer without sacrificing the structural integrity of the system. The overall objective of our revised proposal is to develop a fundamental understanding of damage initiation and accumulation in all-ceramic dental crowns as a function of materials, crown design, and fabrication variables. Our overall approach to meeting this objective is to progress systematically from simple flat-layer structures in normal axial loading toward crown geometries in complex loading, working with clinically-relevant materials at all stages. Ultimately, crowns on extracted teeth mounted in a pseudo bone-PDL system will be subjected to typical cyclic occlusal loading in a wet environment. Our """"""""deliverables"""""""" are (1) a design specification guiding development of new materials and (2) fundamental understanding of damage initation, propagation, and accumulation, culminating in a robust model for predicting clinical behavior of combinations of new materials, tooth preparation design, and crown design. With these outcomes, it will be possible for the first time to use basic materials properties to accurately predict application-based performance of new materials. Investigation to accomplish these goals are organized in four projects: (1) Damage Modes and Failure Mechanisms, (2) Complex Loading, Crown Geometry, and Performance, (3) Novel Joining Methods and Interfacial Fracture Mechanics, and (4) Fatigue Performance of Layered Ceramic Crowns on Teeth. The scientific effort will be complemented and supported by two cores: (1) Statistics and Data Analysis Core and (2) Integration and Administration Core.
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