Composition of clinically aged amalgam restorations

Twenty-five amalgam restorations ranging in age from two to 25 years were obtained from five subjects. An electron microprobe was used to analyze the specimens for bulk elemental composition and phase composition, and the volume fractions of phases were determined by point-counting on back-scattered electron micrographs. Twenty-one of the specimens were conventional, low-copper amalgams, and the remaining four were high-copper amalgams. The bulk elemental compositions showed little variation from newly prepared amalgams except for the presence of a small amount of chloride and other contaminants. The compositions of the phases were essentially the same as is found in new amalgams, except that there was considerable internal amalgamation of gamma particles. The distribution of phases in the clinically aged amalgams was quite different from that of new amalgams. The low-copper amalgams had decreased amounts of gamma, gamma-1, and gamma-2 phases and increased beta-1 and tin-chloride. The high-copper admixed amalgams had decreased gamma, increased beta-1, and enlarged reaction rings (gamma-1 and eta′).