Determination of Mercury in Dental Hard Tissue: An in Vitro Study

The purpose of this study was to determine the levels of mercury in hard tissue from dental amalgam fillings under in vitro conditions. Methods and Results: The study included 30 human teeth that were extracted for various clinical reasons. The teeth were stored in a physiological solution until they were used. The teeth were divided into 3 experimental groups: Group 1 (n=10) – occlusal surface cavity preparation (class I according to Black); Group 2 (n=10) – proximal-occlusal surface cavity preparation (class II); and Group 3 (n=10) – mesio-occlusal-distal [MOD] surface cavity preparation. Each of these groups was divided into 2 subgroups: subgroup 1 (n=5) – amalgam fillings were not polished, and subgroup 2 (n=5) amalgam fillings were polished. The teeth were filled with amalgam, and those in subgroups 2 were polished after 24 hours. The amount of mercury released from the amalgam fillings was determined 9 months after the teeth were filled. Before chemical analysis, the teeth were irrigated 4 times over a period of 10 minutes in an ultrasonic bath. From each tooth, 250mg of the powder was mineralized with royal water (HCl+HNO3 in a ratio of 1:3) in a microwave oven, for 54 minutes. After mineralization, the samples were filtered and analyzed with inductively coupled plasma optical emission spectrometry. The average mercury level after polishing the amalgam filling was significantly smaller (P=0.032) only in Group 1. The average mercury levels in the 3 groups revealed significant differences between both the unpolished samples (one-way ANOVA F = 69.54, P < 0.001) and the polished samples (one-way ANOVA F = 110.54, P < 0.001). Group 3 with MOD surface cavity preparation was characterized by the highest mercury levels. Conclusion: The teeth with an MOD amalgam restoration are characterized by the highest mercury levels. The more mercury is released from unpolished amalgam fillings than from polished amalgam fillings in teeth with occlusal surface cavity preparation (class I according to Black).