A method of determining the corrosive properties of dental amalgams.

The purpose of this study was to determine the corrosive properties of 5 dental amalgams, using a modified rotating disk electrode method described by Van der Merwe, De Wet and Mc Crindle (1991). Ten cylindrical specimens of each amalgams were prepared according to the ISO guidelines. The amount of gamma-2 present was determined by the method employed by Sarkar and Greener (1972), while the corrosion rates were calculated from the Tafel slopes of the polarisation diagrams. All data were analysed statistically. Results showed that at day one Silvalloy contained the most gamma-2, followed by Amalgaphase (previous formulation) and Amalgaphase (new formulation). Dispersalloy and Amalga Sphere contained no gamma-2 at day one. At day nine none of the amalgams tested contained gamma-2 phase. The corrosion rates of the different groups of amalgam varied significantly (p < 0.01) as tested by ANOVA. The spherical amalgam, Amalga Sphere, showed a better corrosion resistance (p < 0.01) than the other amalgams. The method used for evaluating the corrosive properties of dental amalgam proved to be precise, rapid and simple.