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Tarnishing of gold and silver alloy dental restorations in service is caused mainly by the formation of sulfide films. Since the reactions are electrochemical in nature, electrochemical techniques can be used to examine them. In this study, a practical test of the susceptibility to sulfide tarnishing was designed, based on coulometry at constant potential in an aqueous sodium-sulfide solution. The effects of temperature, potential, and time were examined. The index of susceptibility was defined as the anodic charge per square centimeter of the surface in 0.01 M Na2S at 37°C and 0.0 V saturated calomel electrode (SCE). The solution must be deaerated to prevent the loss of S2− ions, and the test procedure must ensure reproducible surface conditions and avoidance of spontaneous sulfidation. A series of dental alloys was evaluated using a test period of 1.5 h. The results showed good agreement with reported clinical data.
dental materials, sulfur, tarnishing, electrochemical corrosion, gold alloys, silver alloys, corrosion tests, coulometers, implant materials
Associate professor of Metallurgy, Georgia Institute of Technology, Atlanta, GA