The objective of this project is to improve high copper dental amalgams by studying (1) amalgamation kinetics and (2) amalgam structure and properties. In the kinetics research, radioisotope techniques are being used to study dissolution rates of high copper aloys into mercury. These techniques will also be used to measure the growth rate of the amalgam matrix phase, gamma-one, in alloys with several different compositions. In the amalgam structure and property research, compressive strength and ADA creep are being measured in a variety of amalgams aged for up to one year at 37-degrees C. In addition, mechanical property data on high copper amalgams are being correlated to data on the volume fractions and grain sizes of the phases present in these amalgams. Microstructural changes occurring during creep deformation are being followed with a recently installed scanning electron microscope. This microscope and the attached x-ray analysis equipment have already yielded significant information about creep and fracture in amalgam. Extensive microstructural analysis of two phenomena associated with creep, grain boundary sliding and a newly discovered "needle" phase, are being conducted. Work is also proceding on a "chewing machine" which will be desinged to produce in vitro marginal fracture of amalgam restorations. Examination of these marginal fractures using the scanning electron microscope should lead to increased understanding of the relation between creep deformation and marginal fracture.