This randomized, controlled clinical trial, triple-blind, split-mouth type was conducted aiming to assess the absolute risk of sensitivity with and without sonic activation of a desensitizing gel previously to the in-office bleaching in adults.

This clinical trial evaluated the effect of sonic activation of a desensitizing gel on the occurrence of sensitivity associated with office bleaching. For this, 31 patients had their anterior superior teeth divided into right and left, according to the sonic activation (AS) or not (SS) of the desensitizer. Prior to bleaching, a desensitizing gel containing 5% potassium nitrate and 2% sodium fluoride (Desensibilize KF2%, FGM Dental Products,SC, Brazil) was applied. Sonic activation was performed with a sonic device (Smart, FGM Dental Products, SC, Brazil) at the 170 MHz frequency. A hydrogen peroxide gel (Whiteness HP Maxx, FGM Dental Products, SC, Brazil) was used in two whitening sessions. It was also performed, evaluation of the presence of cracks in enamel, through transillumination. The color change was verified using two color scales and a spectrophotometer. The dental sensitivity was recorded through a sensitivity diary answered by the patient, in the period up to 48 hours after each bleaching session. The absolute risk of tooth sensitivity was compared using the McNemar test (= 5%). The color change was analyzed from the variation of units of scale vita (SGU) and through the value of ΔE, which were compared through Student t test (α = 5%).

Inclusion Criteria:

• Patients had at least six upper anterior teeth free of caries and restorations on the vestibular surface, and at least one central or canine incisor showing A2 or darker coloration, evaluated in comparison with a visual scale of color orientated by the value of the teeth (Vita Classical, Vita-Zahnfabrik- Germany).

Exclusion Criteria:

• Users of fixed orthodontic appliances, pregnant or lactating, with the presence of severe intrinsic stains on the teeth (spots on the use of tetracycline, fluorosis and depolluted teeth), who were taking any medication with action Anti-inflammatory and antioxidant, using desensitizing dentifrice and participants with previous history of dental sensitivity or any associated pathology (bruxism, gingival recession, non-carious lesion with dentin exposure).

Neither the color evaluator nor the statistician were aware of the allocation of the hemiarcs, according to the sonic activation or not of them. In the execution of the intervention, the sonic activation was applied in sites such as marginal gingiva, premolars, palatal face of the teeth, in order to mask the treatment.