Viscoelastic Modeling Aided Experimental Optimization toward Fracture-Resistant Porcelain-Veneered Zirconia and Lithium Disilicate Restorations

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Project Summary/Abstract Dental crowns and bridges are usually constructed by applying an esthetic porcelain veneer to a strong core. Ceramic core materials, such as zirconia and lithium disilicate, are currently favored for their ease of fabrication and for their strength. While porcelain chipping and fractures are observed in all types of veneered dental prostheses, they are particularly prevalent in porcelain-veneered zirconia. The high chipping/fracture rate is due predominantly to residual stresses introduced by the high-temperature veneering process. However, comprehensive knowledge of key material, design, and processing parameters that govern residual stresses remains obscure. The long-term goal of this project is to improve the fracture resistance of porcelain-veneered prostheses through the reduction of deleterious residual tensile stresses, in conjunction with superior design of a graded veneer/core interface. Accordingly, the overall objectives in this application are to develop a rigorous viscoelastic graded finite element method to guide the design of next-generation fracture-resistant porcelain- veneered ceramic prostheses, and to use clinically relevant fracture mechanics test methods to validate finite element model predictions. The central hypothesis is that the incidence of chipping and fracture of porcelain- veneered ceramics can be reduced to the levels seen in porcelain-fused-to-metal prostheses, through the optimization of material, design, and processing parameters. This hypothesis is formulated on the basis of preliminary results produced in the applicants' laboratories. To test this hypothesis, we will pursue two specific aims: (1) Develop a rigorous viscoelastic graded finite element model, and use this model to optimize the residual stress profile in anatomically-correct porcelain-veneered prostheses through the tailoring of material, design, and processing parameters. Validate model predictions against direct measurement using the Vickers microindentation method; (2) Experimentally quantify resistance to veneer chipping and fracture of porcelain- veneered prostheses with optimal material, design, and processing parameters relative to their bilayer counterparts and a commercial porcelain-fused-to-metal restoration, using edge-chipping methodology and mouth-motion fatigue testing. The approach is innovative because it departs from the status quo by developing a novel viscoelastic graded finite element method and utilizing this model to design continuously graded veneer/core interfaces. The proposed research is significant because it vertically advances the understanding of how stress profiles in all-ceramic prostheses can be tailored for better fracture resistance. Ultimately, such knowledge will bring us closer to a solution of a pervasive clinical problem—chipping, delamination and fracture of porcelain veneered prostheses—leading to reduced morbidity of dental prostheses and cost of replacement to the public.