Dynamic thermal expansion and scanning calorimetry of mercury phases in dental amalgams

Abstract

Thermomechanical analysis, TMA, was used to evaluate the linear thermal expansion coefficient,α, of four different types of dental amalgams: Conventional lathe-cut alloy, conventional spheralloy, high copper dispersalloy and high copper ternary alloy. Dynamic thermal expansion studies showed an interesting contraction behaviour around 85 °C for conventional amalgams and 105 °C for high copper amalgams which coincided with the endotherms produced by differential scanning calorimetry, DSC, and was attributed to the existence of theγ 2 andγ 1 phases, respectively. Pure single phases were prepared and characterized by DSC at 210 °C forγ 2 and 120 °C forγ 1. When theγ 2 was enriched with mercury, the decomposition endotherm showed gradual shift to lower temperatures and reached 85 °C. The value of the linear coefficient of thermal expansion ranged between 15 and 35 ppm/°C for all the investigated brands.Thermomechanical analysis has confirmed previous results achieved by DSC in characterizing mercury-containing phases in dental amalgams.