MERCURY VAPORIZATION FROM AMALGAMS WITH VARIED ALLOY COMPOSITIONS

The fact that mercury is released from dental amalgam restorations aft er abrasion provides a source of continued controversy over the safe u se of this material. Studies have shown that the amount and rate of me rcury release vary for different amalgam products. The objective of th is study was to determine how alloy composition affects mercury vapori zation from experimental amalgams with similar alloy particle size and shape and percent residual mercury. An hypothesis to be tested was th at mercury release is dependent upon the concentration of tin in the s ilver-mercury matrix phase of the amalgam. Seven spherical amalgam all oys (two low-copper and five high-copper) were made by a dental manufa cturer (Tokuriki Honten, Japan). Trituration conditions were adjusted so that all set amalgams had the same residual Hg (47.3%). ADA-type am algam cylinders were aged for 14 days at 37 degrees C, then lightly we t-abraded on #600 silicon carbide, dried, and placed into a tube throu gh which air was blown at a rate of 750 mL/min. Mercury vaporization w as monitored with a gold film analyzer (Jerome 411) for 30 min. Total Hg release was determined by integration. We analyzed polished specime ns via electron microprobe to determine composition, volume fraction o f silver-mercury matrix (gamma(1)), and amount of tin in the gamma(1). The results showed a strong negative correlation (r(2) = 0.941) betwe en the log of total mercury released and the amount of tin in the gamm a(1). The effect of alloy composition, specifically the presence or ab sence of zinc in the amalgam, could not be definitively determined. It is concluded that the tin content in the gamma(1) matrix is the prima ry determinant of Hg vaporization from amalgam. biocompatible material s.