One-Year Color Stability of a Reduced 37.5% Hydrogen Peroxide In-Office Bleaching Protocol: A Randomized Clinical Trial

This randomized clinical trial evaluated the one-year color stability and patient satisfaction regarding dental esthetic improvement after 37.5% hydrogen peroxide (37.5HP) in-office bleaching with a reduced application protocol.

Forty participants with a shade mean C2 or darker were randomly allocated into two treatment groups (n = 20): two (37.5HP2) or three (37.5HP3) 8-min applications per clinical session. Three bleaching sessions were performed at one-week intervals. Tooth color was measured using a spectrophotometer at baseline, 1 week (1 W), 6 months (6 M), and 1 year (1 Y) post-bleaching. Esthetic self-perception was assessed using a 6-point visual analogue scale. Statistical analysis was performed using the Shapiro-Wilk, Student's t-test, Tukey, Mann-Whitney, and Friedman tests (p < 0.05).

No significant differences were observed between 37.5HP2 and 37.5HP3 for Δ $E_{\mathrm{ab}}^{*}$ , ΔE ₀₀, or ∆WI_D across the evaluation periods (p > 0.05). Although both treatment protocols remained effective at 1Y post-bleaching, a significant color rebound was observed from the 6 M assessment (p < 0.05). Patient satisfaction with dental esthetics was comparable between groups (p = 0.3).

Two and three 37.5% HP applications provided similar bleaching stability after one year. Patients remained highly satisfied with their smile, regardless of the number of gel applications.

Clinicians may consider using a neutral 37.5% HP in-office bleaching gel with two 8-min applications per session, as it provides the same one-year bleaching longevity as the manufacturer's recommended protocol of three applications.