Mercury Vaporization from Amalgams with Varied Alloy Compositions

The fact that mercury is released from dental amalgam restorations after abrasion provides a source of continued controversy over the safe use of this material. Studies have shown that the amount and rate of mercury release vary for different amalgam products. The objective of this study was to determine how alloy composition affects mercury vaporization from experimental amalgams with similar alloy particle size and shape and percent residual mercury. An hypothesis to be tested was that mercury release is dependent upon the concentration of tin in the silver-mercury matrix phase of the amalgam. Seven spherical amalgam alloys (two low-copper and five high-copper) were made by a dental manufacturer (Tokuriki Honten, Japan). Trituration conditions were adjusted so that all set amalgams had the same residual Hg (47.3%). ADAtype amalgam cylinders were aged for 14 days at 37°C, then lightly wet-abraded on #600 silicon carbide, dried, and placed into a tube through which air was blown at a rate of 750 mL/min. Mercury vaporization was monitored with a gold film analyzer (Jerome 411) for 30 min. Total Hg release was determined by integration. We analyzed polished specimens via electron microprobe to determine composition, volume fraction of silver-mercury matrix (γ 1), and amount of tin in the γ1. The results showed a strong negative correlation (r2 = 0.941) between the log of total mercury released and the amount of tin in the γ1. The effect of alloy composition, specifically the presence or absence of zinc in the amalgam, could not be definitively determined. It is concluded that the tin content in the γ1 matrix is the primary determinant of Hg vaporization from amalgam.