Amalgamation mechanism in dental amalgam alloys

Abstract

Model experiments to explore the amalgation mechanism in conventional Ag₃Sn and high copper single-composition dental alloys have been conducted by rotating alloy roda in liquid mercury at different speeds and for different durations. After removing the rod from the mercury, the vacuum volatilization technique was used to accelerate the supersaturation of dissolved elements in the liquid mercury. The surface and sectional scanning electron microscope (SEM) views give direct evidence for new amalgamation mechanism in high copper dental alloys. The amalgamation reaction begins with the selective dissolution of the Ag₃Sn phase in mercury, tin gettering to the crumbled-off Cu₃Sn phase, heterogeneous nucleation of the Cu₆Sn₅ phase on the seed of the crumbled-off Cu₃Sn phase and was followed by the nucleation of the Ag₂Hg₃ phase. The unexplained phenomena, the formation of the γ-2 phase (Sn_7-8Hg) in higher content of mercury and the nonexistence of the γ-2 phase in higher content of copper alloys such as Sybralloy, were clearly understood by applying the new model.