The electrochemical properties of dental amalgam

The effects of variations in composition and processing on the open‐circuit electrode potentials measured as a function of time of amalgams made from silver–tin, silver–tin–copper, silver–tin–zinc, and silver–tin–copper–zinc alloys have been determined at 37°C in distilled water, in saline solution, as well as in acetate and citrate solutions buffered to pH values of 3, 7, and 10. The electrochemical potentials of the alloys measured as a function of time in neutral acetate solutions show anodic polarization from an initial cathodic potential value of approximately 0.1 v with respect to the standard hydrogen electrode to a constant potential level depending upon alloy composition. In neutral acetate solution the potential–time curves of silver–tin amalgams with 7:5 mercury to alloy ratio show a rapid anodic polarization from an initial anodic potential value of 0.28 v to a minimum value of 0.05 v at approximately 1 hr followed by a potential reversal to a plateau value of 0.40 v. For 7:5 amalgams in neutral acetate solutions increases in both the trituration time and in the severity of processing deformation cause a small increase in initial potential, with a decrease in anodic polarization, while an increase in amalgam age lowers both the initial potential value and the longer‐time potential plateau. Increasing the mercury content of the amalgam to a 2:1 ratio decreases the rate of potential reversal from the minimum, whereas decreasing the ratio to 4:5 decreases the amount of depolarization from the minimum value. The effects of copper and zinc additions to silver–tin alloys are mixed. In neutral acetate solution the 7:5 ratio amalgams from silver–tin–copper alloys show anodic polarization from the same initial value as the silver–tin amalgams, followed by a region of decreased polarization. Both silver–tin–zinc and silver–tin–copper–zinc alloys exhibit a much higher initial anodic potential (0.78 v), and following the achievement of the potential plateau have a slow anodic polarization to the long‐time potential value shown by silver–tin amalgam. Three commercial alloy amalgams were studied in neutral acetate solution. The two amalgams containing zinc have a potential behavior similar to that of the experimental zinc‐containing amalgam; the non‐zinc amalgam shows a rapid anodic polarization from an initial anodic potential value of 0.24 v, a minimum at 1 hr, and a reversal to the long‐time potential values of 0.40 v shown by the zinc‐containing amalgam.