| All-ceramic materials have been successfully used for dental restorations for about twenty years. The main functions of the restorative ceramics are esthetics and mechanical properties. However, most of the present all-ceramic materials do not meet both needs. For esthetics purpose, various porcelains and glass-ceramics are used. They exhibit natural tooth colors and translucency, but exhibit low or moderate strength and toughness which are lower than or close to that of dentin and enamel. For core-ceramic materials, they exhibit significantly higher strength and toughness than the above, but are generally too opaque and need to be combined with veneers. In addition, the mechanical properties remains low when compared to metallic materials, which makes such materials sensitive to manufacturing flaws and stress concentrations. Thus there was a need for new materials combining both esthetics and high strength and toughness.Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is a kind of widely used biomaterial for nearly 20 years in orthopedic field such as ball head of total hip replacement. Because of its excellent mechanical properties especially high fracture toughness obtained from stress induced tetragonal to monolithic phase transformation mechanism, a lot of experts started to do some research on Y-TZP as all-ceramic dental materials. From then on, many new dental materials concerns on TZP blooming, such as In-ceram zirconia from VITA company, Cercon System from DEGUSSA company, or glass ceramics toughened by partial stabilized zirconia etc. At present, in our country, systematic study on 3Y-TZP as dental materials was rare. As part of a NNSF research, the aim of the current study is to apply 3Y-TZP as dental all-ceramic bridges material for its excellent mechanical properties and good biocompatibility as well as color similar to natural teeth.With the development of nano-technique, nano-sized powder of ceramics has come into being. The first part of this study is to compare nano-sized powder with micron-sized powder of 3Y-TZP in sintering and mechanical properties and microstructure as well as phase composition. By Archimedes technique, the sinter abilities were estimated : specimens from nano-sized powder of 3Y-TZP could be sintered at about 1500 C which is lower than specimens from micron-sized powder of the same material by or so 100 C. And to specimens from nano-sized powder, the three points flexural strength was 921.7+44.2Mpa, fracture toughness was 10.2 + 1.6 Mpam 1/2, both were higher than that of specimens from micron-sized powder .In order to make the surface conditioning easier, to lower the sintering temperature, and to shape the personal contour of crown by slip-casting method, additives of glassy phase was taken into consideration. Small amount of glass was added to keep original high strength and toughness, at the same time to improve its properties. Three kinds of glass system with different thermal expansion coefficient were compared. Separately they were B-Al-Si glass system, Mg-Al-Si glass system and Na-Al-Si glass system. In the end, 3Y-TZP/5%G1 composite got the best results in comprehensive properties. The value of its three points flexural strength is 627+39.4MPa, and its fracture toughness (SENB method) is 6.7+ 1.1Mpam1/2. SEM, XRD aparatus were used to analyze their microstructure and crystal phase composition. The results were: the grain of 3Y-TZP/5%G1 composite was fine and distributed evenly with low pore rate and t-m phase transformation was attribute to its strength.The match of the two materials is important to strength of prostheses in clinic. From the results we found that the thermal expansion coefficient of inner framework 3Y-TZP and 3Y-TZP/5%G1 composite was similar. TEC of inner framework material was little higher than that of the outer composite material. Tolerance tothermal impact temperature was over 200 C.By sandwich method, shear bond strength of interface between 3Y-TZP and 3Y-TZP/5%G1 was 58.2Mpa if sintered at 1440 C for 40 min...
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