Abstract :
Objectives.
The aim of this study was to determine the relationship between the tin content in the γ1 phase of dental amalgam and the kinetics of mercury dissolution.
Methods.
The tested materials were the same eleven commercial amalgams used by Mahler et al. (1994) to study mercury evaporation, which contained from 0.13% to 2.49% Sn in the γ1. In one set of tests, specimens were stabilized in air before exposure to synthetic saliva for three 24 h sampling periods. In another set of tests, they were exposed for 2 h immediately after wet-grinding. Solutions were analyzed for mercury by atomic absorption spectrophotometry. The results were analyzed by ANOVA and Tukey tests (p < 0.05).
Results.
For air-stabilized specimens, the 24 h Hg loss was independent of the tin content in γ1, for 0.92 to 2.49% Sn. The loss was higher for amalgams containing 0.13% and 0.32% Sn. For abraded specimens, the 2 h Hg loss decreased with increasing tin content in γ1. It is proposed that tin oxide growth is initially controlled by diffusion of tin to the γ1/tin oxide interface, the rate of which increases with increasing Sn content in γ1. Later the growth becomes controlled by the electric field across the oxide. Mecury release rate, controlled by diffusion through the oxide, is inversely proportional to the oxide thickness and initially lower for high Sn content in γ1. For a steady state oxide thickness, tin diffusion and tin content in γ1 no longer affect mercury dissolution. When tin oxide film dissolves, a minimum tin content is required to maintain a barrier against mercury dissolution.
Significance.
The results show the importance of rapid formation of a surface oxide to minimize mercury dissolution. The theoretical analysis provides a quantitative model for explanation of the effects of tin content and time.
