Bleaching effectiveness, hydrogen peroxide diffusion, and cytotoxicity of a chemically activated bleaching gel

The objective of this study was to evaluate the bleaching effectiveness, hydrogen peroxide diffusion (H₂O₂), and cytotoxicity of a bleaching gel with 35 % H₂O₂ either associated with ferrous sulfate (FeSO₄) or not.

Enamel/dentin discs adapted to artificial pulp chambers were placed in compartments containing a culture medium (Dulbecco's Modified Eagle's Medium (DMEM)) and distributed into the following groups: G1—no treatment (negative control), G2—10 % carbamide peroxide (one application for 4 h), G3—35 % H₂O₂ (three applications for 15 min), and G4—35 % H₂O₂ + 0.004 g FeSO₄ (three applications for 15 min). After treatments, the extracts (DMEM + bleaching components that diffused across enamel and dentin) were applied on human dental pulp cells (HDPCs) and odontoblast-like cells (MDPC-23). Cell viability (MTT assay, Kruskal–Wallis and Mann–Whitney, α = 5 %), quantification of H₂O₂ diffusion, and color change of the enamel/dentin discs (Commission Internationale de I'Eclairage L*a*b* system) were assessed (analysis of variance and Tukey's tests, α = 5 %).

For both cells, a significant reduction in cell viability was observed for G3 and G4 compared with G1 and G2. No statistical difference was observed between G3 and G4. The rate of H₂O₂ diffusion was significantly higher in G3 compared with that in G2 and G4. The ΔE value for G4 was statistically higher than that of the other groups.

Chemical activation of H₂O₂ by FeSO₄ improves the bleaching effectiveness. However, this metal ion has no significant protective effect against pulp cell cytotoxicity.

Although the chemical activation of H₂O₂ by adding FeSO₄ to the bleaching agent improved the bleaching effectiveness, this metal ion has no significant protective effect against pulp cell cytotoxicity.