Objectives: This study evaluated bleaching efficacy, enamel microhardness, and roughness of highly concentrated hydrogen peroxide (HP) gels (35%–40%) using different application protocols. Gel decomposition and pH alteration were also analyzed.

Methods and Materials: Bovine enamel/dentin specimens were divided into groups according to the bleaching gel—Pola Office Plus (POP–SDI, 37.5% HP), Opalescence Boost (OPB–Ultradent, 40% HP), Whiteness HP (WHP–FGM, 35% HP)— and application protocol—single application (SA) and multiple application (MA) during the in-office session. Deionized water was used in control group (no bleaching). Thus, seven final groups were obtained (n=15/group). Color (CIE L*a*b*), surface microhardness (SMH), and roughness (Ra) were assessed before/after treatments. The pH of gels was measured, and HP concentration was determined with potassium permanganate titration method in different times. Data were submitted to analysis of variance and Tukey tests (5%).

Results: All gels presented similar and clinically acceptable bleaching efficacy (ΔE>2.7) for both SA and MA, as well as no significant differences for SMH and Ra comparing the two protocols in the same gel. Peroxide decomposition significantly increased with time, but final gel concentrations were still high after 45 minutes (32.29% POP; 38.45% OPB; and 32.74% WHP). The pH decreased over time (initial - after 45 min) for WHP (6.83±0.07 - 5.81±0.06), but minimal alterations were observed for POP (8.09±0.09 - 7.88±0.07) and OPB (7.82±0.11 - 7.87±0.07).

Conclusions: Peroxide decomposition was very low for all gels tested, and pH remained stable for POP and OPB gels. Bleaching protocol did not influence whitening efficacy and hazardous effects over enamel, thus potentially there was no clinical significance. Therefore, for the products tested, there is no evidence for recommending the gel change during the bleaching session.

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