GALVANIC CORROSION AND CYTOTOXIC EFFECTS OF AMALGAM AND GALLIUM ALLOYS COUPLED TO TITANIUM

The aim of this study was to examine and compare the galvanic corrosio n of a conventional, a dispersed high-copper, and a palladium-enriched spherical high-copper amalgam and a gallium alloy coupled to titanium in saline and cell culture solutions, and to evaluate the effects of the couples on cultured cells. The potentials and charge transfers bet ween amalgams and titanium were measured by electrochemical corrosion methods. Cytotoxicity of the couples; as indicated by the uptake of ne utral red vital stain, was determined in 24-h direct contact human gin gival fibroblast cell cultures. Results of this study indicated that b efore connecting the high-copper amalgams to titanium, the amalgams ex hibited more positive potentials which resulted in initial negative ch arge transfers, i.e. corrosion of titanium, However, this initial corr osion appeared to cause titanium to passivate, and a shift in galvanic currents to positive charge transfers, i.e. corrosion of the amalgam samples. Lower galvanic currents were measured for the amalgam-titaniu m couples as compared to the gallium alloy-titanium couple. Coupling t he conventional or the palladium-enriched high-copper amalgams to tita nium did not significantly affect the uptake of neutral red as compare d to cells not exposed to any test alloy. However, significant cytotox ic effects were observed when the dispersed type high-copper amalgam a nd the gallium alloy were coupled to titanium. Even though the corrosi on currents measured for these couples were less than gold alloys coup led to amalgam, these results suggest there is the potential for relea sed galvanic corrosion products to become cytotoxic. These data warran t further investigations into the effects of coupling amalgam and gall ium alloys to titanium in the oral environment.