Investigation of mechanical and biomedical properties of new dental alloy with high content of Au

Abstract

The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. The demands which have to be met when developing a new dental alloy are linked with fulfilling the necessary requirements for making the alloy suitable for use in metal-ceramic restorations. Due to the stress generated by masticatory forces, alloys for dental restorations must have corresponding mechanical properties (yield strength, tensile strength, and elongation), hardness, the coefficient of thermal expansion (CTE), and biocompatibility. Namely dental alloy placed in an oral cavity reacts with the environment and deteriorates. New dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86.9Au-9.9Pt-1.5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The dental alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: a1-phase rich in Au (main phase) and a2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the a1-phase content is about 98,5 wt.% while the content of a2- phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solids temperature of about 1292 K and a liquids temperature of about 1412 K. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Spectral reflectance data from the mirror-polished flat samples of initial Au dental alloy were collected under the CIE standard illuminant D65. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done. According to the results of our research we can conclude that new dental alloy from Zlatarna Celje satisfied all requested standards regarding mechanical properties, hardness and CTE: Rp0.=550 [N/mm2], Rm =610 [N/mm2], A= 9%, 180 HV and CTE (25-600°C) about 14,45×10-6K-1. This new Au dental alloy has a yellow tinge in comparison to conventional Au-Pt-Zn alloys and did not show cytotoxicity when using standard short-term in-vitro assays on an L929 cell. .