[Influence of surface condition upon the cytotoxicity of copper-gold alloy (in vitro) (author's transl)].

Cellular responses to dental alloy may be easily influenced by surface condition of the alloy. From this point of view, the author had a plan to analyse the mechanism of cytotoxic phenomenon of gold-copper alloys, 91% Au-9% Cu, 83% Au-17% Cu, 75% Au-25% Cu, 58% Au-42% Cu, 50% Au-50% Cu, 25% Au-75% Cu, 20% Au-80% Cu, 15% Au-85% Cu, 10% Au-90% Cu, pure gold and pure copper. Test piece of the alloys was heated and treated with solutions of 2% HCl or absolute methanol. The cytotoxicity of the test piece was observed by means of tissue culture, in vitro. There is no cytotoxic action in the cases of pure gold and higher carat alloys than 58% Au-42% Cu alloy, but mild toxicity in lower carat alloys than 50% Au-50% Cu alloy. On the contorary, in the test piece heated and treated with 2% HCl solution, mild cytotoxicity is recognized in the cases of 83% Au-17% Cu and 75% Au-25% Cu alloy. Cellular damage was very severe in the case of lower carat alloys than 50% Au-50% Cu alloy. In the test piece heated and treated with absolute methanol, pure gold, 91% AU-9% Cu and 83% Au-17% Cu alloys have no cytotoxicity, but strong cytotoxicity in the lower carat alloys than 75% Au-25% Cu alloy. Discoloration of the test piece heated and treated with the solution of 2% HCl or methanol, was measured with JIS Colour Chart. Same discoloration was observed in the cases of pure copper, lower carat alloys that 25% Au-75% Cu of the control group, lower carat alloys than 58 Au-42% Cu of 2% HCl treatment group and lower carat alloys than 58% Au-42% Cu of methanol treatment group. From these findings, the discoloration of the alloys caused by heating may be produced by the formation of thin copper-rich-film at the surface of test piece. It is revealed that the cytotoxicity of Au-Cu alloy may be caused by the formation of copper-rich-film at the surface of Au-Cu alloy.