Microstructure of dental amalgam.

Numerous studies have been done in the past to identify the phases present in dental amalgam. Both metallographic and X-ray diffraction techniques have been used.-' Most researchers now presume that dental amalgam consists mainly of three phases. The original particle is an alloy of Ag, Sn, Cu, and sometimes Zn; the major portion is the compound Ag3Sn, which is often referred to as Py. After amalgamation, a portion of the original particle is left; in addition, an Ag2Hg3 (,yi) phase and a Sn-Hg (Y2) phase form. Schmitt' and Wing2 have described the Py and yi phases in the microstructure. However, the 72 phase has not been identified metallographically, except by pointing out voids where apparently a phase was present. Other phases have been proposed, but their existence has not been established. Although Cu may be present in the alloy in a proportion as high as 6 per cent, this element has not been identified in the structure. Wing2 and Crowell' both have postulated that a dark or gray etch-resistant area which appears in the alloy particles may be a Cu-Sn phase. Since the polishing methods which have been used in the past are not consistent, we developed a standard procedure for metallographic polishing which does not erode the 7Y2 areas. In addition, an etching solution was developed which reveals all the phases in amalgam without etching out the more reactive phases. After examination of various microstructures, a typical microstructure was defined. Then the three major phases were identified in the structure. Further work in this area will depend on a more positive identification of the phases and of the elements present.