Transdentinal cytotoxic effects of different concentrations of hydrogen peroxide

Objective: The aim of this study was to evaluate the transdentinal effects of an bleaching agent with different concentrations of hydrogen peroxide on the immortalized odontoblast-cell line MDPC-23. Methods: Fifty dentin discs (0.5 mm-thick) were obtained from sound human third molars. After determining the permeability of each disc, they were divided into 5 groups (n=10) with equivalent hydraulic conductance (ANOVA, p>0.05), according to the concentration of H₂O₂ in the bleaching agent: 7.5%; 20%; 35% H₂O₂ or 0%. In the fifth group (control) no bleaching agent was applied. Each dentin disc was adapted to a pulp chamber device in such way that the cells were plated (5 x 10⁴ cells/cm²) on its pulpal surface. The bleaching agents were applied on the oclusal surface of the discs for 30 minutes. The metabolism of the MDPC-23 cells that remained attached to the pulpal surface of the discs was evaluated by MTT assay. The data were submitted to Kruskal-Wallis test complemented by Mann-Whitney at the preset level of significance of 5%. The morphology of the cells was assessed under scanning electron microscope (SEM). Results: It was observed that all experimental bleaching agents that presented H₂O₂ caused intense cytotoxic effects to the MDPC-23 cells. The bleaching agents containing 7.5%; 20%; 35%, and 0% H₂O₂ decreased the cell metabolism by 62.65%; 62.28%; 65.69%, and 17.09%, respectively. Regardless the H₂O₂ concentration, several cells detached from the pulpal surface of the dentin disc. The remaining cells presented notable morphological changes compared to the control group. The correlation test determined that the cytotoxic effects of the bleaching agents were not influenced by the permeability of the dentin discs. Conclusion: All concentrations of H₂O₂ incorporated in the bleaching caused transdentinal significant cytotoxic effects to the MDPC-23 cells.