Project Summary/Abstract The attainment of both translucency and strength is a vital requirement for ceramic restorative materials. Unfortunately, these properties are often mutually exclusive. Porcelain-based and glass-ceramic materials have higher translucency but lower strength, and are thus susceptible to premature failure. Zirconia-based ceramics are stronger and tougher but have poor translucency. There is therefore an urgent need to develop translucent and strong ceramics for the next generation of better-performing restorative materials. Accordingly, the long-term goal of this project is to develop esthetic, strong, and abrasion-resistant nanocrystalline yttria- stabilized tetragonal zirconia polycrystals (Y-TZP) for dental and biomedical applications. The overall objectives in this application are: (1) optimize the translucency and strength of nanocrystalline Y-TZP via compositional and microstructural tailoring; and (2) elucidate microstructure-mechanical properties of Y-TZP at the nano and microscale levels. To our knowledge, this proposal is the first to systematically address these questions. The central hypothesis is that nanocrystalline Y-TZP exhibits improved translucency, strength and reduced abrasiveness relative to its microcrystalline counterparts. This hypothesis is formulated on the basis of preliminary results produced in the applicants? laboratories. To test this hypothesis, we will pursue 3 specific aims: (1) Optimize nanostructured Y-TZP for translucency and strength; (2) Elucidate the dependence of translucency, strength degradation and toughness on Y-TZP microstructure; and (3) Determine resistance to fatigue and wear of nanostructured Y-TZP using a mouth-motion simulator. The approach is innovative because it departs from the status quo by developing a new form of nanocrystalline Y-TZP with improved translucency and fracture resistance and reduced abrasiveness using novel processing methodologies. The proposed research is significant because it extends clinical indications for zirconia to the esthetic zone and promises minimally invasive treatments. Such an approach will prolong prosthetic lifetimes and preserve tooth structure, thus reducing money and time spent correcting premature failures. As an adjunct benefit, the development of nanocrystalline Y-TZP will provide a model system for establishing a broader correlation between mechanical properties and grain size, thus extending classical fracture mechanics laws into the nanoscale domain.