Characterization of Low and High Copper Amalgam Alloys and the Effects of Mixing Time on their Properties

Part 2. Microscopic observations

Abstract

Effects of mixing time on the microstructure of several low and high copper amalgams were observed. An apparent relationship was found between the microstructure, especially enclosed porosities, and physical properties reported previously¹⁾. In regard to the mixing time, a greater influence was observed with either lathe-cut or high copper than spherical or low copper, with respect to the particle shape and copper content of the alloys. Sufficient mixing is required for lathe-cut high copper alloys.
However, differences in the mixing characteristics were often observed even with alloys having similar particle shape or composition. This may be due to the dissimilar surface characteristics of alloy particles, causing the differences in affinity with mercury. Prolonged mixing to eliminate the porosities in the set amalgam may cause the poor results, such as remarkably shortened working time and increase in shrinkage during setting.
The mixing time of an amalgam alloy should be estimated on both technological and practical bases.