A study of alternative metal particle structures and mixtures for dental amalgams based on mercury additions

The perception that mercury in dental amalgam is toxic to the human organism has prompted worldwide efforts by the scientific community to develop alternative amalgam-like materials that utilize little or no mercury. In this investigation, an attempt is made to develop a new dental alloy system by adding liquid mercury to silver-coated Ag4Sn intermetallic particles in lesser amounts than are used in conventional amalgam alloys. An effort to precipitate the important eta-prime (Cu6Sn5) phase was made by adding pure Cu and Sn powders to the alloy formulation during trituration. Tytin a popular Ag-Sn-Cu single-composition, spray-atomized conventional dental alloy was used as the control to obtain baseline data for comparisons of microstructures and mechanical properties. Amalgamation of the coated particles with mercury, with or without the addition of Cu and Sn powders, mostly produced specimens with chemically non-coherent microstructures that were relatively weak in compression. These results were due, in part, to mercury's inability to chemically wet the Ag-coated particles and Cu and Sn powders because of naturally occurring surface oxide films. The strongest specimens tested had silver dendritic coatings, resulting in compression strength values up to 40% of the control's. Their higher strength is attributed to mechanical interlocking at the particle/matrix interfaces.