Development And Performance Evaluation Of The Precious Metal Dental Casting Alloys

With the increase of the living level and sanitarian consciousness of human beings, therequirement for the quality of dental material become more and more rigorous. Precious metaldental casting alloys are selected broadly in dentistry for their chemical stablility, feasiblemechanical performance and favorable biocompatibility. However, most of our precious metaldental casting alloys reply on import which are more expensive. Therefore, six precious metalcasting alloys have been developed. On the basis of the tarnish-resistance study of the sixalloys, we have selected two typical alloys: Ag-30Au-15Pd-10Cu and Ag-12Au-23Pd-9Cu.The microstructure, corrosion, cytotoxicity and mechnical properties of these two alloys areinvestigated by means of SEM, EDS, XRD, potentiodynamic polarization and MTT. Theresults have shown that: (1) The two alloys have not contained toxic metallic elements such as:Ni, Cd, Be etc, and have not had cytotoxicity; (2) Both the two alloys consist of twophases. one is a Ag-Pd-rich fcc solid solution (a₁) and the other is a Cu-rich fcc solid solution(a₂). The element Au is evenly distributed throughout the two phases; (3) The as-castmicrostructure of the first alloy consists of equiaxed grains of the solid solution (a₁) and asmall amount of the lamellar eutectic (a₁+a₂), and the as-cast microstructure of the secondalloy consists of lamellar eutectic structure (a₁+a₂) and a small amount of solid solution (a₁);(4)Both the corrosion- and tarnish-resistance of the alloys accord with the nationalstandard. Compared with the imported alloys, the two alloys have better corrosion-resistanceand the mechanical properties of Ag-30Au-15Pd-10Cu alloy reaches to that of type-Ⅲ alloy,the hardnesses of the two alloys are lower which lessen the abrasion of natural tooth and havebetter polishability; (5) After immersed in the Fusayam artificial saliva for 24 hours, thealloys are all under passive state. It is sggested that this phenomenon is due to the selectivedissolving of copper atoms from the alloys sunk in the siliva, which makes the alloys' surfaceenriched with Au, Pd, Ag atoms. The development of these two alloys will be beneficial tothe science and technology of dental materials.