Esthetic problems with metal-ceramic restorations (opacity, inadvertent display of the metal, graying of the soft tissues surrounding the restoration) have led to the introduction of a number of all-ceramic (non-metallic) alternative in the past ten years. However, these ceramic materials are not as strong as the metal-ceramic restorations they are intended to replace. This has continued to limited the applications of all-ceramic dental prostheses (primarily to single tooth anterior restorations) due to their unacceptable clinical failure rate (mechanical fracture). The primary objective of this research is to study and apply advanced ceramic processing technology to the fabrication of all-ceramic dental restorations. Significant new scientific data on surface diffusional processes in alumina and many other basic science areas will result. The application of this technology will be directed toward the fabrication of a real-world end product, a net-shape ceramic (minimal firing shrinkage). It is expected that the developed material will be significantly stronger than currently available all-ceramic systems. Coacervated colloidal processing will be used for powder processing to obtain greenware of uniform packing density, pore structure, and distribution of second phase sintering agents. The process being proposed leads to a net-shape ceramic composite consisting of 60-70 volume percent of a continuous ceramic framework and 30-40 percent of a continuous second phase (e.g., polymer, glass, ceramic). It is expected that an interlocking of the two continuous, three dimensional microstructures will provide significant toughening of the material. This should result in an all-ceramic material that has widespread application as a crown and bridge material, providing improved strength, esthetics and biocompatibility. The development of this novel process and material will be accomplished through the systematic application of ceramic processing technology. Initially, alumina will be used as the model ceramic system. The ceramic matrix will be developed through the evaluation of factors that affect surface diffusion and interparticle necking (e.g., dopants, particle size, coordination number,and sintering time and temperature). Specimens will be sintered in a dilatometer, and a functional balance between the shrinkage and strength will be achieved. The introduction of second phase ceramics to achieve the desired alumina matrix will also be studied. These second phase materials will be incorporated by imbibing sols (e.g., Zirconia, Alumina) into the formed greenware and through colloidal coprocessing of powders (e.g., Zirconia, Alumina). The porosity of the greenware and sintered alumina matrix will be studied with BET analysis. Emphasis will be placed on optimizing the mechanical properties (modulus of rupture) of the primary alumina matrix while minimizing the shrinkage.
