Passivation of dental amalgams and mercury release.

Objectives: In this study the rate of dissolution of mercury from two dental amalgams with different compositions and structures was determined in vitro under different oxidation and abrasion conditions, and the results were correlated with the electrochemical characteristics.

Methods: A spherical high copper and a lathe-cut very high-copper amalgam were tested in aerated and deaerated artificial saliva. The electrochemical characteristics were determined by potential-time, anodic polarization, polarization resistance and cathodic stripping measurements. Mercury release tests were performed after either stabilization in the solution, or abrasion using SiC papers or rotary toothbrush, with or without toothpaste. Dissolved mercury was determined by atomic absorption spectrophotometry.

Results: Both amalgams exhibited passivation, the amalgam with the higher copper content passivating spontaneously even when the oxygen content in the solution was minimized. At a higher oxygen content in the solution the rate of mercury release from the amalgams was lower than when the oxygen content was minimized, and decreased further after a pre-exposure. Brushing generally increased the release.

Significance: The results show the importance of the oxidation conditions and passivation characteristics of dental amalgams for mercury release, especially in the transient state after abrasion by chewing or tooth brushing.