Electrochemical properties of copper and gold containing dental amalgams

Summary 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 γ 2 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 conventional amalgams although current densities were less. After ageing for I month the – 250 mV peak associated with γ 2 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 ‐250 mV (γ 2 ) peak after 1 week and current densities were I0 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 > 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 γ 2 phase the resulting AuSn 4 apparently corrodes in an analogous fashion. However, since distribution of AuSn 4 may be different from γ 2 , i.e. not continuous, the effect of corrosion on its mechanical properties may be different.