Stress protein assay for the evaluation of cytotoxicity of dental amalgam.

To evaluate the cytotoxicity of mercury in dental amalgams, a stress protein assay was performed and the results were compared with the cytotoxicity evaluated by a neutral red uptake assay. The induction of a major stress protein, hsp70, was analyzed at levels of mRNA, synthesis and accumulation in human HeLa cells treated with extracts from amalgam, metal mercury and mercuric chloride. Mercuric chloride induced an increase in the synthesis of hsp70 at concentrations of mercury half those used for the neutral red uptake assay. The extracts from dental amalgam and metal mercury induced an increase in hsp70 mRNA at concentrations of mercury half those causing the inhibition of neutral red uptake into cells. Furthermore, the extracts from dental amalgam or metal mercury increased the synthesis of hsp70 and inhibited the uptake of dye at concentrations of mercury 1/10-1/50 lower than those at which mercuric chloride acted. These results suggest that the stress protein assay is more sensitive than the conventional neutral red assay for the evaluation of the cytotoxicity of mercury in dental amalgams and that the methods used in the preparation of metal solutions seem to be critical to the evaluation of cytotoxicity of dental materials.