Relief formation in polished amalgam surfaces.

The relief produced in the surface of dental amalgam as a result of polishing was studied by scanning electron microscopy in traditional low-copper amalgams, high-copper dispersant-type amalgams, and high-copper single-composition amalgams. Specimens were polished metallographically in two planes at right angles to each other. Micrographs were taken of the edge between the planes; the profile of one of the polished planes could be traced and the microstructural phases recognized. The traced lines were analyzed by a computer that calculated the mean levels of the phases and the mean deviation (roughness) of all the phases along the scanned distance. Recesses were seen in the surface of the gamma-2 phase. The gamma-1 phase attained the highest level, protruding above the phases of the alloy particles. The results indicate that well-polished amalgam surfaces have a structural relief that contributes to the roughness and limits the degree of smoothness that can be obtained in an amalgam surface.