A study of the hardening mechanisms and microstructural characteristics of an improved dental amalgam
Abstract
Dispersalloy dental amalgam has been developed in the last twelve years and displays a significant decrease in creep rate and an increased resistance to corrosion. The manufacturer claims that the decreased creep rate results from a dispersion hardening mechanism employed in this radically new amalgam. The product consists of a spherical copper-silver eutectic phase added to a fine-cut amalgam alloy. The ratio of eutectic spheres to fine-cut alloy is approximately 1:2 by weight. Unlike other dispersion hardened alloy systems however. Dispersalloy's tensile strength is somewhat less than for many fine-cut amalgams. All mechanical and microstructural testing indicates that the system is solution hardened by a distributed copper concentration within the y, matrix phase. Analysis determined that a 3-5 weight percent copper concentration in the Ag3Sn particles is the source of the copper solute atoms. In addition, the copper-silver eutectic spheres, present in the amalgam microstructure, act as sinks to tin atoms liberated by the Ag3Sn-mercury reaction initiated during trituration (mixing). Formation of a tin-rich shell about the eutectic spheres is beneficial because the tin is then unable to form the deleterious Y2 phase. It is this phase which is most corrosive and leads to early failure of the amalgam restoration. Finally, particles observed by some dental researchers upon the polished copper-silver spheres, within the amalgam microstructure, were confirmed to be the result of polishing contamination. The particles are not inherent to the Dispersalloy metallurgy.
Degree
Ph. D.
Thesis Department
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OpenAccess.
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