Mercury vapour exposure during dental student training in amalgam removal

Background: Amalgam that is used for dental fillings contains approximately 50% elemental mercury. During dental student training, amalgam is often removed by drilling without the use of water spray and suction, which are protective measures in preventing mercury aerosol. In this study we measured mercury vapor levels in ambient air during amalgam removal as is typically performed in dental training. Methods: Mercury vapor levels in ambient air were measured in a dental school laboratory during removal of amalgam fillings from artificial teeth set into a dental jaw simulator. Mercury vapor was measured under three conditions (25 measurements each): with the simultaneous use of water spray and suction, with the use of suction only, and with the use of neither suction nor water spray. These three conditions are all used during dental student training. Results were compared to Alberta occupational exposure limits for mercury vapor in order to assess potential occupational risk to students. Analysis of variance testing was used to compare data obtained under the three conditions. Results: When water spray and suction were used, mercury vapor levels ranged from 4.0 to 19.0 mu g/m(3) (arithmetic mean = 8.0 mu g/m(3)); when suction only was used, mercury vapor levels ranged from 14.0 to 999.0 (999.0 mu g/m(3) represents the high limit detection of the Jerome analyzer) (arithmetic mean = 141.0 mu g/m(3)); when neither suction nor water was used, the vapor levels ranged from 34.0 to 796.0 mu g/m(3) (arithmetic mean = 214.0 mu g/m(3)). Conclusions: The Alberta Occupational Health and Safety threshold limit value for mercury vapor over an eight-hour time-weighted period is 25.0 mu g/m(3). The absolute ceiling for mercury vapor, not to be exceeded at any time, is 125.0 mu g/m(3). When both water spray and suction were used, mercury vapor levels were consistently below this threshold. When suction without water spray was used, mercury vapor levels exceeded the safety threshold 8% of the time. When neither water spray nor suction was used, 36% of the mercury vapor readings exceeded the absolute ceiling value. To maximize safety, dental schools should train students to remove amalgam only while using water spray and high volume suction. Alternatively, students should use appropriate occupational hygiene personal protective equipment during amalgam removals.