Influence of Alloy Composition on the Hardening of Silver--Tin Dental Amalgam

The reactions of Hg with Ag--Sn alloys with compositions spanning the phase fields beta , ( beta + gamma ), gamma , and ( gamma + Sn) were examined. The nature and morphology of the reaction products formed on bulk specimens of the alloys were examined. The progress and characteristics of the reactions that occur during hardening of amalgams prepared from powders of these alloys were monitored using a high-sensitivity dilatometer. These results were correlated with direct observations on the development of the microstructures. The reaction of Hg with the beta -phase alloy occurred rapidly and resulted in a very marked and rapid expansion during the initial stages of hardening. gamma -phase alloys reacted more slowly and contracted markedly during hardening. The behavior of amalgams made from alloys with compositions lying between these two extremes appeared to be explicable in terms of the characteristics of the separate phases from which they were constituted. 12 ref.--AA