| For some reasons, up to now, the alloys containing noble metals for porcelain restoration have little application in China, but the demands become more and more intensive with the increase of the living level of people. Therefore, we have developed a precious ceramic alloy system, Au-Pd-Ag alloy, especially designed for PFM fixed partial denture. The principal elements of alloy were Au 70.7wt% Pd 11.8wt% Ag 13.9wt% Sn0.5wt% In 3.0wt% Zn 0.1wt%Ge and Ru. The properties of the alloy are as follows: (1) The alloy has nontoxic metallic elements which satisfy the required biological conditions. (2) Compared with ISO standard, the alloy has enough mechanical properties. (3) With addition of noble metals, the alloy has good corrosive resistance and steady chemical property. (4) It has the approximate thermal expansion coefficient with VITA95 porcelain system and can form a good bonding. (5) The low cost makes it available to public application in China. In this paper a new surface treatment method was also developed to improve the bonding strength between porcelain and alloy.The alloy was prepared through melting gold, silver, palladium, tin, indium, ruthenium, zinc, germanium in the high frequency induction furnace protected by argon and then deaerating the crude alloy at vacuum. The mechanical properties of the alloy were tested by computerized electronic testing machine. The mechanical properties of system meet the ISO standard of Metal-ceramic dental restorative system. The as-cast microstructure of the alloy consists of equiaxial grains of the solid solution (Ag-Pd-rich phase) and the eutectic in grain boundary (Au-rich phase).In this paper the biocompatibility of the precious ceramic alloy was assessed elementarily by three different tests which included cytotoxicitytest ( MTT assay ) , haemolysis test and mucous membrane irritation test (Hamster's pouch). All the tests were performed in accordance with the ISO's or Chinese standards. The results indicate that the alloy has no toxicity to human body and no harm to health. Hardness, corrosion resistance and microstructure of the selected Au-Pd-Ag alloy were measured and observed after different heating processes: as-cast, 980/30min, 400/30min and the complete simulated porcelain firing cycle. The results showed that heat treatment did affect hardness of Au-Pd-Ag alloy. Differences in hardness and corrosion behavior exhibited by the alloy are related to compositional and microstructural changes. But the nobility has more important effect on corrosion resistance.The effect of pre-oxidation with different holding-time of the Au-Pd-Ag alloy on the resulting bonding strength between the alloy and VITA ceramic has been studied using metallography, SEM , XRD ,and three-point bending test. The results indicated that the pre-oxidation improved the bonding strength of alloy-ceramic, the maximum was reached after lOmin pre-oxidation process. The oxide were mainly composed of AgO and InO. At different temperature points (1001 200 , 300 , 400 U 500 ) , the thermal expansion coefficient of the alloy is closed to that of the porcelain. The thermal expansion coefficient a 2-600r= 18.468 X 10"6/ and A a porcelain-alloy > 2X 10"6/, but after slow-cooling process, the difference between the thermal expansion coefficient A a porceiain. a^y <1 X 10"6/ and could meet the clinical demand.A new surface treatment technique was developed to prepare nano-scale TiO2 and SiO2 film on the substrate surface by sol-gel method. XRD and SEM were used to study the surface composition, microstructure and surface morphology of the films and the results of three point bending test showed that the new method could improve the bonding strength significantly.In this paper thermocycling and surface finishing or cold working were examined for their effects on marginal adaptation of metal ceramic casting. The thermocycling of metal ceramic restoration after surface finishing resulted in increased marginal openings, and most of the loss of marginal fitness occurred during the pr...
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