| The distinct properties of ceramics offer great potential for fabricating long-lasting aesthetic dental crowns. Emerging dental CAD/CAM systems provide a powerful technology for effective fabrication of dental restorations. Durability, precision of fit, and affordability are three fundamental requirements. Damage, initially induced during the fabrication process and exacerbated by clinical cyclic loading, compromises the strength of ceramic-based restorations, often leading to an unacceptably high failure rate. The interrelation among the restorative material, design, fabrication and loading plays a critical role in this regard. The overall objective of this dissertation research is to design and produce all ceramic-based, clinical crowns capable of providing typical occlusal functions that meet the clinical specifications.; Machinability study of dental ceramic forms the basis to address the fundamental requirements of establishing a dental CAD/CAM system. The dental ceramics under this investigation includes: Dicor/MGC material with five types of microstructure, MACOR, Mark II, Zirconia and Alumina. Extensive milling and single point scratch tests have been performed. A set of performance indices consisting of cutting force, surface finish and tool wear, are used for the evaluation of machinability. Empirical models are obtained using the method of design of experimentation to quantify the relationship between the machining performance and material microstructures, and machining parameters. Combined with analysis tools, mechanisms of material removal are elucidated. Two process methods, high speed abrasive machining and laser assisted milling, are investigated as complementary approaches for the milling process under investigation.; An effort has been made for developing a CAD/CAM system to fabricate all ceramic dental crowns. The proposed system consists of a laser digitizer, a virtual environment for geometry modeling and tool path generation, NC milling/abrasive process, and a quality control system. Dental crowns have been successfully fabricated from the five types of ceramic material. Fitness is evaluated by scanning the fabricated dental crown to identify fabrication-related errors in dimension and geometry. A systematic approach is established to assess the potential clinical durability through an in-vitro test device developed in this research. The in-vitro test bed, Mouth Motion Simulator, is another major contribution of this research. The machine closely simulates the motions of the human mandible. The availability of such a device makes it possible to perform accelerated tests to investigate clinical failures of dental crowns. |
