The extraction method is one approach to the evaluation of the cytotoxicity of dental materials.However, the method of extraction differs with the testing standard.The objective of the present study was to clarify the efficiency of three different methods of obtaining extracts from prosthodontic materials for crown and bridge use.These methods were the static and dynamic extraction methods and extraction by heating.Extracts used were DMEM tissue culture medium alone or DMEM supplemented with either 10V/V% fetal bevine serum or distilled water.Cells used were L-929 cells from mouse subcutaneous tissues or early passage cultured cells derived from human gingiva.Viability of cells was evaluated by neutral red and MTT assays.The experimental process was repeated five times.Static extraction and extraction by heating did not provide consistent data for the materials tested, while dynamic extraction allowed assessment of the cytotoxicity of such materials as Ni-Cr alloy and cold-curing resin.The extract obtained in tissue culture medium supplemented with serum had higher sensitivity than the other two kinds of extracts in expressing the cytotoxicity of materials, in particular those of Ni-Cr alloy and cold-curing resin.Repetition of extraction five times was useful in examining the sequential change of cytotoxicity.Early passage cultured cells derived from human gingiva were less sensitive to the materials tested.There were no differences in cytotoxicity on the basis of either cell type used or assay method used.These findings demonstrate that different cytotoxicity values are obtained under different extraction conditions, and that extraction methods are useful in the evaluation of the cytotoxicity of materials tested.