Since all dental restorative materials are foreign substances, their potential for producing adverse health effects is determined by their relative toxicity and bioavailability, as well as by host susceptibility. Adverse health effects to dental restoratives may be local in the oral cavity or systemic, depending on the ability of released components to enter the body and, if so, on their rate of absorption. The medical scientific community is now in general agreement that patients with dental amalgam fillings are chronically exposed to mercury, that the average daily absorption of mercury from dental amalgam is from 3 to 17 micrograms per day, and that the amalgam mercury absorption averages 1.25-6.5 times the average mercury absorption from dietary sources (World Health Organization, 1991). The health significance of this chronic mercury exposure is now being investigated by several medical research groups.