Clinical randomized single-blind trial, used to measure the level of tooth sensitivity (TS) after in-office dental bleaching sessions, on volunteers using a modified visual analog scale (VAS). The investigators selected for this study, 40 participants with color 2M2 or darker (Using OM1 - 5M3 Vita bleaching shade guide). The investigators performed two bleaching sessions with a 40% hydrogen peroxide gel with a 1-week interval. Participants were enrolled in two groups. In one group, the bleaching product was used according to manufacturer's instructions (40-minutes application in each section). In the other group, the bleaching product was used in two 20-minutes applications in each section.The investigators recorded the TS up to 48h with a VAS scale and the color at baseline and 30 days after bleaching with a value-oriented shade guide and a spectrophotometer. The risk and intensity of TS and the color change were compared between the two groups.