Electrochemical properties of copper and gold containing dental amalgams

Alloying or admixing of a dental amalgam alloy with an element or alloy which has a higher affinity for tin offers a means for eliminating the corrosion prone gamma2 phase. Accordingly, the corrosion behaviour of non-conventional amalgams containing Cu and Au were investigated by anodic polarization studies in Ringer's solution. The Cu containing amalgams were produced by admixing Cu-Hg (copper amalgam) with conventional amalgam in the ratios of 0-5:1 and 1:1. A 10 w/o Au in Ag-3-Sn was used as the gold amalgam alloy. The anodic polarization profile of the 0-5:1 Cu admixed was similar in shape to admixed conventional amalgams although current densities were less. After ageing for 1 month the minus 250 mV peak associated with gamma2 disappeared and the current density decreased by ten fold. After 2 months the current density decreased by one hundred fold. The anodic polarization of the 1:1 Cu admixed amalgams did not display the minus 250 mV (gamma2) peak after 1 week and current densities were 10-3 below that of conventional amalgams. The behaviour of these interesting amalgams is rationalized on the basis of the ease of formation of Cu-Sn intermetallics where Cu/Sn larger than or equal to 3. The anodic polarization profile of 10 w/o Au containing amalgam essentially is that of conventional amalgam and does not change drastically after 6 months. Although the Au may reduce or eliminate the gamma2 phase the resulting AuSn4 apparently corrodes in an analogous fashion. However, since distribution of AuSn4 may be different from gamma2, i.e. not continuous, the effect of corrosion on its mechanical properties may be different.