Method: Eighty-four enamel/dentin discs from the buccal surface of bovine incisors were used. The baseline color was measured with a spectrophotometer using the CIE L* a* b*. Two sessions of in-office bleaching treatment with 35% Hydrogen Peroxide - HP (7 days between sessions) were performed under different protocols. Group 1 (n=28): 3 applications of HP (10 min each); Group 2 (n=28): 1 application of 30 min and Group 3 (n=28): 1 application of 40 min, with no gel reapplication. HP titration and pH evaluation at baseline, after 10, 30 and 40 min were also performed. The final color was measured 24h after the 2nd bleaching session. Data were submitted to ANOVA and Tukey’s test for statistical analysis.
Result: Forty minutes HP application (group 3) resulted in greater b* change (Δb=-5.19), and also greater total color change (ΔE=5.77), with statistical differences for group 2. There was no significant difference between groups 1 and 2. The HP titration showed no drop of concentration after 10, 30 or 40 min. The initial pH was 5.54 and 5.41 after 40 min.
Conclusion: The increase of time application of bleaching gel over enamel increased the efficacy of the therapy and the changes of gel during the bleaching session did not affect HP efficacy.