Penetration and Citotoxicity of a Bleaching Gel Activated by LED/LASER in Restored Teeth

Objectives: This in vitro study aimed to evaluate the amount of hydrogen peroxide in the pulp chamber of teeth with composite resin and its cytotoxic effect on fibroblast cell line 3T3/NIH.
Methods: 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 × 2 mm × 1 mm [S] and 3 mm × 2 mm × 2 mm [D]) were prepared and restored with composite resin according to the manufacturer’s instructions. To assess the amount of hydrogen peroxide in the pulp chamber, all teeth were sectioned 3 mm from the cement-enamel junction. The pulp tissue was removed and 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. After treatment, the solution of acetate buffer in the pulp chamber of each tooth was removed and leucocristal violet and peroxide enzyme solutions were added. The optical density of the resulting blue solution was determined spectrophotometrically and converted into micrograms equivalent of hydrogen peroxide. For viability cell assays, different concentrations of HP were applied to fibroblast cell line. After 24 h, 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).
Results: 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.
Conclusions: The concentrations of HP that were found in the pulp chamber did not affect cell viability.