Gamma-1 to beta-1 phase transformation in retrieved clinical amalgam restorations

A number of important reactions occur in clinical amalgam restorations. This investigation examined the extent of the gamma-1 to beta-1 transformation in a variety of amalgam restorations retrieved from clinical trials. Sixteen restorations of five brands of low Cu amalgams, 28 restorations of four brands of high Cu blended amalgams, and eight restorations of three brands of high Cu single particle amalgams were studied. The extent of the gamma-1 to beta-1 transformation was determined by the ratio of the integrated intensity of the 002 beta-1 peak to the 330 gamma-1 peak in x-ray diffraction patterns. These values were correlated with age, marginal deterioration grade, and residual Hg content. Restorations consistently contained more beta-1 than comparable laboratory controls. Blended high Cu amalgams generally contained more beta-1, which was correlated with better marginal grades. Beta-1 content was inversely related to residual Hg content. No other associations could be established. A model of the complex interactions between corrosion and transformations was developed.