Objectives: Previously, we have examined the estrogenic activity of the components of dental sealants by a reporter gene assay, and found that a hydrophobic monomer, bisphenol A dimethacrylate, was associated with the estrogenicity shown by commercial products (Tarumi et al., J Dent Res, 79[11]:1838-1843, 2000). However, the estrogenicity of the constituents of composites has not yet been fully elucidated. The purpose of this study was to assess the estrogenic activity of various monomers and additives for resin composites by the reporter gene assay. Methods: Six monomers, three photostabilizers, three photoinitiators, two inhibitors and eight co-initiators were tested. Each chemical was dissolved in dimethyl sulfoxide (DMSO), and diluted with a phenol-red-free D-MEM. Human embryonic kidney fibroblast cell 293T were transiently transfected with both luciferase reporter plasmid containing estrogen responsive element (ERE) and expression vector for human estrogen receptor alpha, and incubated with the samples for 24 hr. Relative luciferase activity of each sample to estradiol 17-beta was calculated and compared with the results for 0.1% DMSO as a negative control (Student-t test). The dependence of the activity on ERE for estrogenic chemicals was confirmed using control reporter plasmid without ERE. Results: One photostabilizer (2-hydroxy-4-methoxy-benzophenone, HMBP), two photoinitiators (2,2-dimethoxy-2-phenyl-acetophenone, DMPA and Benzil, BL), and one inhibitor (2,6-di-tert-butyl-p-cresol, BHT) showed significant estrogenic activity (p<0.05). On the contrary, no resin monomers exhibited the estrogenicity. The minimum estrogenic concentrations were 1 µM for HMBP, 1 µM for DMPA, 10 µM for BL and 50 µM for BHT, respectively. Conclusions: Among 22 components for composites, four additives showed ERE-dependent estrogenic activity. HMBP frequently used for commercial composites were included in the four estrogenic compounds, and it is suggested that estrogenic effects of composites containing HMBP should be further evaluated.

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