Effect of In-Office Whitening Gels Acidity on Tooth Sensitivity, Color Change, and Gingival Irritation in Patients with Fixed Orthodontic Appliances: A Randomized Clinical Trial.

PURPOSE: To compare tooth sensitivity (TS), gingival irritation (GI), and bleaching effectiveness between two commercial 35% hydrogen peroxide in-office bleaching formulation characterized by acidic and neutral-to-alkaline pH profiles in patients wearing fixed orthodontic appliances during the final stabilization phase of orthodontic treatment. METHODS: In this single-blind randomized clinical trial, 120 participants undergoing fixed orthodontic treatment were randomly allocated to receive either a 35% hydrogen peroxide bleaching gel with acidic pH (Whiteness HP Maxx) or a 35% hydrogen peroxide bleaching gel with neutral-to-alkaline pH (Whiteness HP AutoMixx Plus). Two bleaching sessions were performed at a 7-day interval. The primary outcome was the absolute risk and intensity of TS, assessed using a visual analogue scale (VAS). Secondary outcomes included GI (VAS) and bleaching efficacy, evaluated by spectrophotometric measurements (ΔE00, ΔEab, and ΔWID) and shade guide units (ΔSGU). Data were analyzed using chi-square and independent-samples t-tests (α = 0.05). RESULTS: Participants treated with the neutral-to-alkanine formulation showed a significantly lower absolute risk of TS than those treated with the acidic formulation (55% vs. 75%; RR = 0.73; 95% CI: 0.56-0.96; p = 0.02). TS intensity was also significantly lower in the neutral-to-alkaline group at multiple evaluation time points during both bleaching sessions (p < 0.05). No significant differences were observed between groups regarding the absolute risk or intensity of GI (p > 0.05). Both bleaching protocols produced clinically relevant and statistically comparable color changes according to objective (ΔE00, ΔEab, and ΔWID) and subjective (ΔSGU) assessments (p > 0.05). CONCLUSIONS: The neutral-to-alkaline commercial in-office bleaching system resulted in lower risk and intensity of tooth sensitivity than the acidic system, while no differences in bleaching effectiveness or gingival irritation were detected between the systems. CLINICAL SIGNIFICANCE: Among the two commercial bleaching systems evaluated, the neutral-to-alkaline formulation was associated with lower tooth sensitivity while providing clinically relevant whitening. Because the systems differed in characteristics beyond pH, this benefit cannot be attributed exclusively to pH.