The Cytotoxic and Apoptotic-necrotic Effects of Whitening Materials on Human Gingival Fibroblasts

Background and Aim: Carbamide peroxide (CP) and low concentrations of hydrogen peroxide (H2O2) have been used as bleaching agents for discolored vital teeth. Long-term exposure to these whitening materials (WMs) may cause irritation and ulceration of the gingiva and other oral soft tissues. The aim of this study was to investigate cytotoxicity and mechanisms of the cytotoxic effects of these WMs on human gingival fibroblasts (HGFs). Materials and Methods: HGFs were exposed to whitening materials with various dosages ranging from 0.001 to 10 mmol/L and then they were processed for analyzing MTT and DNA fragmentation. In addition, possible mechanism of the whitening-material-mediated cytotoxicity was investigated through flow cytometric analysis. Results: The exposure of human gingival fibroblasts (HGFs) to H2O2 and CP in vitro inhibited cell growth in a dose-dependent manner (p<0.001 and p<0.001 at 24hours (h), respectively). Cytotoxicity was found to occur due to H2O2-induced chelation of calcium as shown by control experiments with the calcium chelator (p<0.001). Addition of a competitive inhibitor of nitric oxide synthase modulated H2O2-induced cytotoxicity (p<0.001). Conclusion: The results of the present study indicate that these WMs show toxic effects on HGFs, in vitro. Apoptosis was the main form of cell death due to these WMs and their effects were evaluated via several mechanisms. The direct bleaching procedure that cures these materials in situ should be used cautiously.