The main purpose of this research is to develop ceramics for use as posterior restorations as alternatives to dental amalgam. Currently, porcelain inlays are fabricated from porcelains that provide long lasting esthetics and are being used as alternatives to dental amalgam. However, their acceptance is limited by low fracture toughness and fracture is the major cause of failure which limits their clinical acceptance. A second problem is poor marginal fits due to shrinkage during sintering. Although expensive processing equipment is available, the approach taken here is to develop superior ceramics that can be processed by simple technology for lower cost. The first project involves the study of silicate glasses that can be plasticized by hydration in a steam autoclave. Previous researchers have demonstrated that stable, tougher and even flexible glasses result by incorporation of water into the silicate glass structure. The second project is to continue research on the transformation toughening of leucite porcelains by stabilizing the high temperature form of leucite with cesium. Funds for this project have been supplemented by a Senior Fellowship Award. Leucite porcelains are the most widely used type of dental porcelain. The third study involves the processing of mullite by near net shape methods to produce tough mullite-ZrO2 composites. This will be done by the controlled oxidation of zirconium and aluminum alloys which results in a volume expansion to compensate for the sintering shrinkage. A fourth study involves the development of advanced calcium aluminate macro-defect-free cements for use as direct restorative materials. This study investigates the new chemically bonded ceramics developed for industrial applications; some of these materials exceed the strength of currently used direct restorative materials. The composition of these experimental cements are analogous to the structure of dental enamel containing hydrated ceramics with small amounts of polymer within the structure.
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