Corrosion Evaluation of Gold-based Dental Alloys

Three commercial gold-based dental alloys and three constant-nobility ternary alloys (Au-Ag-Cu) were evaluated for corrosion using a quantitative test battery. Integration of the current density, in a de-aerated solution of 1 % NaCl along the approximate potential range found in the mouth (-300 m V to +300 m V vs. SCE), yields a quantitative rank ordering of the test alloys. The results are com-bined with prior findings on other commercial alloys to demonstrate the interaction of nobility and microstructure. Nobility determines the overall corrosion resistance for gold-based alloys. However, be-cause of mutual insolubility, alloying with copper induces silver segregation, resulting in a higher corrosion rate at a given nobility. Thus, microstructure has an influence on corrosion, but heat treat-ments are largely ineffective in altering the basic corrosion char-acteristics. The test techniques, in combination with tarnish evalua-tions, provide a quantitative battery for alloy evaluation. The results indicate the combinations of nobility, microstructure, and environ-ment most likely to avoid corrosion difficulties