The effect of ageing on the creep and compressive strength of high copper content amalgams

Corrosion of non-gamma 2-amalgams

Eight different dental amalgams were studied in an in vitro corrosion test. Cylindrical test specimens were stored in weak lactic acid solutions at different pH for 1 month. The concentrations of mercury and copper in the solutions were measured and corrosion depths estimated. The results indicated that more copper was released from non-gamma 2-amalgams compared with conventional ones. The amounts of copper from these amalgams were not directly correlated to the concentration in the alloys. Mercury was released in much lower amounts than copper for all amalgams and seemed to originate from the gamma 1-phase. A low pH promoted the corrosion.

Corrosion of amalgams

The release of copper, mercury, silver, tin or zinc from conventional, dispersed phase and spherical high copper content amalgams immersed in artificial saliva solutions for periods up to 30 d has been measured using nuclear tracer techniques. During initial corrosion, i.e. within a few hours substantial amounts of mercury were found to be present in particulate matter in the three types of amalgams. The release of particulate matter was pronounced for the dispersed phase type of amalgam. After about 30 electrochemical corrosion was found to be the predominant process for release of various corrosion products. Zinc was demonstrated to be the major corrosion product released to the artificial saliva solutions from conventional as well as dispersed phase amalgams. Due to low radioactivity levels silver and tin could not be quantitatively assayed. However, the upper limits of silver and tin in the artificial saliva solutions referring to exposure periods up to 30 d were estimated to 0.1 microgram and 25 microgram respectively. The chemical state of the various corrosion products has been evaluated. The deposition of CuCl2 X 3 Cu(OH)2 on the surfaces of copper rich amalgams was observed according to X-ray diffraction analysis.