Can pigments of different natures interfere with the cytotoxicity from in-office bleaching?

Objective: To assess the influence of tooth stained with different colored solutions on the cytotoxicity of a 35% H2O2-bleaching gel. Materials and methods: The established groups were (n = 8): NC– without treatment (negative control); PC– 35% H2O2 (positive control); CO– coffee + 35% H2O2; BT– black tea + 35% H2O2; WI– wine + 35% H2O2; COBTWI– coffee/black tea/wine + 35% H2O2. Standardized enamel/dentin disks were submitted to staining protocols, adapted to artificial pulp chambers, and bleaching was performed. The chromatic alterations (ΔE00, ΔWID) were assessed after bleaching and the extracts (culture medium + diffused gel components) were collected and applied to odontoblast-like cells. The amount of diffused H2O2, cell viability, and oxidative stress were evaluated and data were submitted to ANOVA/Tukey; p < 0.05). Results: Thirty five% H2O2 effectively bleached the stained specimens, regardless of the staining solution used (CO, BT, WI, and COBTWI), and no differences were found among the stained protocols (p > 0.05). All staining protocols reduced H2O2 trans-amelodentinal diffusion (p > 0.05), decreasing bleaching cytotoxicity in comparison to PC (p < 0.05). Conclusion: Irrespective of the nature of the pigment used for staining enamel and dentin, the gel with 35% H2O2 effectively bleached the tooth structure. The presence of pigments in both dental tissues, regardless their nature, reduced the trans-amelodentinal diffusion of H₂O₂ and consequently the cytotoxicity of the bleaching gel.