Calorimetric studies of Ag-Sn-Cu dental amalgam alloy powders and their amalgams

Differential scanning calorimetry (DSC) technique has been used to examine the reaction sequence in dental amalgam alloy powders of (1) Ag-Cu-Sn lathe-cut particles (single composition type in dentistry terminology), (2) mixture of lathe-cut Ag-Sn-low Cu and spherical particles of Ag-Cu eutectic composition (admix type) and (3) their amalgams, i.e. alloys of liquid Hg and these dental amalgam alloy powders. All the peaks in the DSC curves have been identified and discussed. DSC curves of single composition-type powders showed as many as six distinct peaks, whereas admix-type powders showed only four peaks. Quite interestingly, amalgam of single composition powders exhibited only three peaks, whereas amalgam of admix type displayed four distinct peaks. The noticeable differences of peak positions in the DSC curves of the amalgam powders and their amalgams and the associated chemical reactions have been explained. DSC curves of the alloy powders and their amalgams studied at four different heating rates have showed peak shifting and the variation of change of enthalpy (Delta H) as well with the heating rates (v (h)). The peak temperatures and the heat evolved and absorbed of all the peaks have been determined with the help of built-in software available in the DSC unit.