RECONFIRMATION OF THE EXISTENCE OF DELTA(2) IN DENTAL AMALGAMS

The similar to 90 degrees C endotherm peak in the thermogram of a conv entional dental amalgam is due to two overlapping peritectic transitio ns involving SnHg-delta(2) and HgAgSn-gamma(1), respectively. The aim of the present study is to separate these two events and thus confirm that the delta(2) phase is indeed a part of an amalgam microstructure. The materials used in this study were: sample 1, gamma(1) + 1 wt % Sn ; sample 2, gamma(1) + 2 wt % Sn; sample 3, gamma(1) + 3 wt % Sn; and sample 4, a commercial conventional amalgam with 48 wt % Hg. In powder form, they were exposed to 1 wt % NaCl solution at 37 degrees C for u p to 45 days. At 15 day intervals, samples were withdrawn from the sol ution, washed, dried and then characterized by the differential scanni ng calorimetry (DSC) technique. Corrosion of Sn from ternary gamma(1) matrix and intergranular delta(2) in respective materials during their exposure to the NaCl solution led to the following: (a) a progressive increase in gamma(1) --> beta(1) transition temperature in samples 1 and 2; (b) a gradual decrease in delta(2) peak and its disappearance i n sample 2; and (c) in samples 3 and 4, initial splitting of the simil ar to 90 degrees C peak into two distinct endotherms associated with d elta(2) and gamma(1), respectively. Continued corrosion of the last tw o materials produced further changes in delta(2) and gamma(1) in a man ner similar to that seen in samples 1 and 2. On the basis of these obs ervations, we have concluded that the similar to 90 degrees C endother m is a valid indicator of the existence of the delta(2) phase in denta l amalgams.