Penetration and cytotoxicity of a bleaching gel activated by LED/laser in restored teeth.

To evaluate the amount of hydrogen peroxide (HP) in the pulp chamber of teeth restored with composite resin and its cytotoxic effect on fibroblast cell line 3T3/NIH. 112 human premolars were randomized into groups according to the combination of factors: Restoration: no restoration (NR); shallow (S); deep (D) and Activation by Light: yes (A) or no (NA). With exception of the groups Control and NR, Class V cavities (3 mm x 2 mm x 1 mm [S] and 3 mm x 2 mm x 2 mm [D]) were prepared and restored with composite resin. An acetate buffer was placed in the pulp chamber. The bleaching procedure was performed with 35% HP and activated or not with a LED/laser light. The buffer was mixed with leucocrystal violet and peroxide enzyme for the spectrophotometric evaluation of the optical density of the solution. For viability cell assays, different concentrations of HP were applied to fibroblast cell line. After 24 hours, the MTT and neutral red assays were evaluated. The lethal concentration of 50% of cells (LC50) was determined. Data were submitted to ANOVA and Tukey's test (α = 0.05). All experimental groups showed HP in the pulp chamber, but a higher amount was found in the pulp chamber of teeth with deep restorations (P = 0.026), regardless of light activation. The concentrations of HP that were found in the pulp chamber did not affect cell viability.