Objective: To compare cytotoxicity of an at-home tooth whitener in two mouse fibroblast cell lines and primary cultures of human gingival fibroblasts. Methods: L929 (ATCC CCL1) and 3T3-L1 (ATCC CCL 92.1) fibroblasts were from American Type Culture Collection (Rockville, MD), and human gingival fibroblasts were obtained from primary cultures of gingival tissues obtained from a healthy female. The cells were cultured in Eagle's MEM, supplemented with fetal bovine serum, non-essential amino acids, L-glutamine, penicillin, streptomycin and amphotericin B. An at-home whitener containing 10% carbamide peroxide was evaluated for cytotoxicity at doses of 0, 5, 25, 50, 100 and 500 µg/mL using L929, 3T3-L1 and human gingival fibroblasts. Culture media served as the negative control, and phenol was included as the positive controls. Cells were seeded in 96-well plates, incubated at 37^oC for 24 hours, treated at the specified doses, and then evaluated for cytotoxicity after 24 hours using the MTT tetrazolium assay. The 50% inhibitory dose (ID50) was calculated using the absorbance data. The experiment was conducted using six cultures in each group. Results: The results showed a dose-related cytotoxicity of the whitener in all three cell types, and the cultures at the dose of 500 µg/mL were abolished. The ID50 values were comparable between the groups of L929 (68 µg/mL) and human gingival fibroblasts (75 µg/mL). 3T3-L1 cells showed a higher ID50 (42 µg/mL), indicating that this cell line is more sensitive to the cytotoxicity of peroxide-containing whiteners than L929 and human gingival cells. Conclusion: L929 cells appear to be more appropriate than the 3T3-L1 fibroblasts for estimating the cytotoxic potential of peroxide-containing whiteners.

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