Surface chemistry of a high-copper dental amalgam.

In amalgam, mercury is intended to take the form of stable intermetallic compounds. Any mercury leakage must therefore come from free mercury not involved in such compounds. Thus, a knowledge of the exact surface chemistry of dental amalgam is necessary if this phenomenon is to be understood. From XPS and EDS analyses, a model of the surface chemistry of amalgam is proposed which fully characterizes all the phases that are present. The data show the surface to have a composition different from that of the bulk, being comprised of a hydrocarbon deposit and adsorbed water covering the intermetallic phase gamma2 (Sn(6-8)Hg), tin (iv) oxide, and mercury in a free state. After amalgamation, the amount of mercury at the surface decreases with time and eventually attains a constant concentration, where it is all involved in the gamma2 phase, leaving no free mercury. A model is proposed for the surface of amalgam and the changes in this model with time.