Group with no desensitizing treatment. Prior to bleaching therapy, a water-soluble placebo gel, with non-active agent will be applied to dental vestibular surfaces. After bleaching therapy, the LASER tip will be positioned in two points (apical and cervical), without light emission (placebo).

Group treated with placebo gel before bleaching and with LLLT after in-office bleaching.

Group treated with desensitizing gel before bleaching and after in-office bleaching, the LASER tip will be positioned in two points (apical and cervical), without light emission (placebo).

Group treated with desensitizing gel before bleaching and with LLLT after in-office bleaching.

The group will receive in-office bleaching treatment. Three 15-minute applications of the 35% hydrogen peroxide gel were performed, totaling 45 minutes in each of the 3 sessions, with a 7-day interval.

The stimulated pain intensity was self reported by the patients with a modified visual analog scale, from 0 to 3, where 0 means "no pain", 1 is "mild pain", 2 is "moderate pain" and 3 is "severe pain". For all groups, the patients evaluated the stimulated pain intensity two times per session: before and after the treatment in the same day. Thus, in total each patient reported the pain intensity 6 times, two times in the first day (1st session), two times in the eighth day (2nd session) and two times in the fifteenth day (3rd session).

Self reported non-stimulated pain intensity was assessed daily, during 21 days, through self-perception questionnaire, answered by the patients from the first tooth bleaching session until one week after the last session. The evaluation was performed by each patient, according to a modified visual analog scale, as follows: 0- no pain, 1 mild pain, 2 - moderate pain and 3 -severe pain