Recent developments in alloys for dental amalgams: their properties and proper use.

Since the development more than ten years ago of a new type of amalgam alloy that will react with mercury without forming the unfavourable gamma2 (Sn7-8Hg) phase, several new alloy brands with a similar reaction pattern have been presented. This new generation of amalgam alloy is called non-gamma2 alloy as distinct from the conventional alloys. Three of the new alloys studied contain approximately three volume percent gamma2 and should be classified as modified concentional amalgams. The non-gamma2 amalgams may be characterized in the following way: (1) instead of gamma2 they contain a reaction product of copper and tin (Cu6Sn5), the so-called eta1 phase. (2) They are significantly more resistant to corrosion than the conventional amalgams but do in time produce sufficient solid corrosion products to seal the micro-fissures between filling and cavity walls. (3) When corroding, they do not release metallic mercury, and the solid corrosion products formed and precipitated on the free surface of the fillings seem relatively little resistant to the organic acids of the plaque. (4) Most of them have relatively low creep and tensile strength, but high compressive strength. (5) Clinically the non-gamma2 amalgams are remarkable for superior marginal integrity and, seemingly, also for improved persistence of surface lustre.