CORROSION OF GALLIUM ALLOYS IN-VIVO

The aim of this work was to study the corrosion of gallium alloys in v ivo. Three gallium alloys were tested: GF alloy, Galley and an experim ental Galn alloy. An amalgam was applied as a control. After ageing fo r a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentur es. Eight sets of the specimens were retrieved after exposure to the o ral cavity for 2-4 months, and another seven were retrieved after 6-9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investi gated, leaving behind holes up to 20 mu m deep. This is consistent wit h the corrosion reported after immersion tests in a solution of 0.1 mo l lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are als o reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the la ck of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did n ot agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of cor rosion on the Galley specimens appeared to be less and on a finer scal e than on specimens of the two other alloys. The depth of corrosion wa s thus shallower than for this alloy. This finding indicates that ther e is room for further improvement of the corrosion resistance by modif ying the microstructures. Less overall corrosion was found for the ama lgam control than for the gallium alloys.