The effect of recasting on corrosion of a silver–palladium alloy

Objectives. Noble and semi-noble dental casting alloys are often reused by recasting. The aim of this study was to determine if repeated casting has a detrimental effect on the corrosion behavior of a silver-based dental alloy. Methods. A commercial Ag–Pd–Cu–Au alloy was cast and four times recast. Electrochemical tests were performed to determine the effects of recasting on the polarization parameters and the corrosion current density in artificial saliva. Changes in hardness, chemical composition and microstructure were determined. Results. Recasting had little effect on the shape of the polarization curves, but the corrosion current density dramatically increased after the fifth cast. Hardness increased with recasting and the microstructure showed grain growth. Increased subgrain formation was found for the fifth cast. The elemental map showed decreased surface concentration of Au for the fifth cast. The bulk concentrations of Au, Ag and Pd remained constant, but the copper and zinc contents slightly decreased and the content of impurities increased. Significance. Recasting of an Ag–Pd–Cu–Au alloy initially had little effect on the corrosion susceptibility in artificial saliva, but a severe degradation of properties was observed after the fifth cast. The results indicate that a dental alloy of this type can be safely recast only a small number of times.