Indirect Cytotoxicity Of An In-Office Bleaching Agent

Objectives: To evaluate the trans-enamel and trans-dentinal cytotoxic effects caused by a bleaching agent with 35% of hydrogen peroxide (H₂O₂) (Whiteness-HP, FGM, Brazil) to cultured MDPC-23 odontoblast-like cells after different periods of application on enamel surface. Methods: Enamel/dentin discs were individually adapted to artificial pulp chambers. The following groups were evaluated: G1 – control group (no treatment); G2 and G3 – 1 or 3 applications of a 35% H₂O₂ gel for 15 min., respectively; G4 and G5 – 1 or 3 applications of a 35% H₂O₂ gel for 5 min., respectively. Cell metabolism was evaluated (MTT assay) after application of the extracts (culture medium plus bleaching gel components that diffused through the enamel/dentin discs) for 60 min. on the previously cultured cells and the data was submitted to statistical analysis (Kruskal-Wallis/Mann-Whitney; a=0.05). Results: The reduction of cell metabolism observed in G2 and G3 was 0.3% and 30.4%, respectively. In G4 and G5 the cell metabolism increased by 18.3% and 6.3%, respectively. Considering G1 (control group) as 100% of cell metabolism, statistical difference was observed only between G1 and G3 (p<0.05). Time and frequency of application of the bleaching agent with 35% H₂O₂ used in this in vitro study was directly related to the metabolism of the MDPC-23 cells. Conclusion: The bleaching agent with 35% of H₂O₂ applied for 45 min. on enamel caused moderate indirect cytotoxicity to the cultured cells. On the other hand, the same dental product increased the MDPC-23 cell metabolism when applied for 5 min.