OBJECTIVE: Compare the tooth sensitivity (TS) and bleaching efficacy (BE) of in-office dental bleaching performed with 35% hydrogen peroxide (HP) or 37% carbamide peroxide (CP). MATERIALS AND METHODS: Sixty-six participants were randomly divided into two groups according to the bleaching gel applied to the right hemiarch: 35% HP, or 37% CP. TS was recorded immediately after, up to 1, 24, and 48 h after bleaching, using the VAS and NRS scales. BE was assessed before bleaching and 1 month after using color guide units (ΔSGUs) and a spectrophotometer (ΔE RESULTS: TS risk and intensity were lower for the 37% CP (p = 0.003 and p <
0.005). Despite significant differences between the groups after 1 month (ΔSGU and ΔE CONCLUSION: In-office dental bleaching using 37% CP resulted in reduced risk and TS intensity, without prejudice to the BE. CLINICAL RELEVANCE: The use of 37% CP for in-office dental bleaching could decrease TS risk and intensity without affecting BE. TRIAL REGISTRATION: ClinicalTrials.gov identifier: RBR-683qhf.