The participants will be informed about the nature and objectives of the study; however, they will not be informed what desensitizing material they would receive. The study will be a double blinded (Patient and evaluator) randomized clinical trial with a sample size of 51, 17 participants for each group (n=17). Bleaching process: A lip and cheek retractor will be placed. The gingival tissues from the right first molar to the left first molar will be isolated using a light-cured resin dam to prevent the whitening gel from coming into contact with the gingival tissue. Participants' lips will be painted with Vaseline, and protective eyewear will be used. To aid in the isolation process, a plastic suction tip with high suction power will be used. Opalescence Boost in Office Whitening Gel, 40% Hydrogen Peroxide bleaching material (Ultradent Products, South Jordan, UT, USA) will be applied directly on the labial tooth surface from the right first premolar to the left first premolar. A total of three (20-minute) applications will be completed in each bleaching session. Participants will undergo 2 bleaching sessions with one-week interval. Participants will be scheduled for lower arch whitening after 14 days.

Application of the desensitizer: The participants will be assigned randomly to three study groups. The first group will receive a bio active desensitizer, the second group will receive a fluoride gel and the third group will receive a placebo gel without a desensitizer (Table 2). A small amount of the gel assigned for each participant will be applied directly on the labial surface of each tooth and left undisturbed for three minutes; care will be taken to cover the entire labial surface, and the gel will be carried interproximally as much as possible.

Shade evaluation: Teeth shade will be evaluated subjectively and objectively. Subjectively it will be evaluated using VITA classical shade guide which has 16 tabs ranging from B1 (lightest value) to C4 (darkest value) by matching the color with the middle third of the maxillary anterior teeth. One evaluator will record the shade of the participants' teeth at baseline (before whitening), directly after bleaching, and at days 3, 7, and 14 days follow up periods. Photographs will be taken using a digital camera immediately after the whitening and at each shade evaluation to document results. Also teeth shade will be evaluated objectively using VITA easy shade spectrophotometer (VITA Easyshade V; VITA Zahnfabrik, Bad Säckingen, Germany). The tooth must be well hydrated before analyzing the tooth color. The shade of the teeth in VITA classical A1-D4 and VITA 3D-MASTER shades will be instantly measured and displayed on the screen. One evaluator will record the shade of the teeth and the shade will be recorded at baseline, immediately after bleaching and at 3, 7 and 14 days follow up periods. Sensitivity Evaluation: Post-bleaching sensitivity will be evaluated by relying on patient's feeling of pain.

Sensitivity evaluation: All participants will be given a sensitivity sheet to record the post-whitening sensitivity of the whitened teeth on daily basis up to 14 days according to the visual analog scale of pain (VAS). The participants will be asked to record the stimulus that caused sensitivity, including hot, cold, or other. The duration of pain, whether seconds, minutes, or hours, will be recorded for the 14-day follow-up period.