Minimizing The Hg-Exposure During Amalgam Removal In Vitro L. Kremers, T. Bruggey*, R. Hickel (Dept. Of Operative Dentistry, University Of Munich) In the present in vitro study the question had to be observed, how procedures could be improved to minimize Hg-releasing during amalgam removal. The influence of different parameters was tested (high speed handpieces vs. turbine, rotation speeds, suction capacity, preparation instruments).   Further the isolation of rubberdam against released Hg was tested under different conditions (material: vinyl vs. latex, thickness, age of storing).   In a preparation training set 140 mod amalgam fillings were removed under permanent water cooling, measuring the Hg-exposure with an atomic absorption spectrophotometer. For each parameter test 10 – 15 amalgam fillings were measured. The isolation of rubberdam was explored by measuring the Hg-diffusion ratio after placement of fresh triturated amalgam. 280 rubberdam sheets (different qualities, latex and non-latex matrials) were tested, 10 – 30 for each tested group.   The results show, that a suction ratio of 220 l/min produced a significantly lower Hg-exposure (93 µg/m³) than a low suction ratio of 120 ml/min (735 µg/m³). Regarding the rotation speed, the tested hand pieces produced significantly lower Hg-exposure (31 – 82 µg/m³) than a turbine (622 µg/m³). The test of different preparation instruments showed significantly lower Hg-exposure using diamond burs (82 – 461 µg/m³) (Komet 835 314 010) in comparison to the new carbide burs (108 – 1213 µg/m³) (Komet H 34 L 314 012). Regarding the isolation, the latex rubberdam showed a significantly lower Hg-diffusion ratio (3,6 – 4,1 µg/m³) than vinyl products (6,2- 18,6 µg/m³). A proportional dependence between the thickness of latex rubberdam and its isolation (thin rubberdam: 0,15 mm, 6,9 Hg µg/m³; special heavy rubberdam : 0,37 mm, 1,8 Hg µg/m³) was found. Aging of latex rubberdam (10 years stored) raised the diffusion ratio (3,0 – 16,2 Hg µg/m³).   It has to be considered, that slow speed preparation with diamond burs (normal grit) and high volume suction produces minimal Hg-evaporation.   The use of rubberdam is recommended, latex rubberdam should be prefered. Medium quality offers a sufficient Hg-diffusion isolation. The rubberdam should not be stored over time.