High copper dental amalgams: comparative study of the structure and the in vitro corrosion resistance

A dental amalgam made from a lathe-cut powder with a high copper content was characterized with respect to its microstructure by means of scanning electron microscopy techniques. A comparison was made between the in vitro corrosion resistance of this relatively new high copper amalgam, a dispersion-type amalgam and a ‘single composition alloy’ amalgam. The effect of toothbrushing was included to avoid the superficial accumulation of corrosion products. Electrochemical data on the behaviour of the three types of high copper amalgams examined were collected by tracing anodic polarization curves and by measuring the polarization resistance. After immersion in synthetic saliva for 30 days, the amalgam made from the lathe-cut powder with high copper content and the dispersion-type amalgam showed preferential attack on the copper-rich phases, while the γ1 phase appeared only slightly altered; corrosion products rich in tin and chlorine were detected. The ‘single composition alloy’ corroded to a lesser extent.