X-ray diffraction and SEM/EDS analyses of phases in new dental amalgams

The superior clinical performance of several dental amalgams which contain high Cu concentrations and little or no gamma 2 has stimulated the introduction of a number of new amalgam alloys. This investigation sought to study the nature of the phases present in eight commercial systems after trituration. Samples were powdered for X-ray diffraction phase analysis or were polished for SEM/EDS analysis. These methods were complementary since they permitted positive identification of the phases and their distribution and composition, respectively. The matrix phase of all systems was gamma 1 (Ag-Hg). Cu6Sn5 was found as the major Sn-rich amalgamation product. The Cu6Sn5 phase forms reaction zones around th Cu-rich particles with morphological variations from system to system. All amalgams contained the gamma (Ag3Sn) phase, but it was microstructurally distinct only in two particle systems. Small amounts of the gamma 2 (Sn-Hg) phase were found in three systems. These results suggest that there are important microstructural variations in the new Cu-rich systems which could eventually result in variations in clinical performance.