The objective of this study was to evaluate if two different isolation techniques used during in-office bleaching influence the risk of gingival irritation. The secondary objectives were to investigate whether the isolation technique affects bleaching efficacy, the occurrence of tooth sensitivity, and the intensity of tooth sensitivity (TS).

1. Visit 1: Study information and delivery of informed consent. Recording of patient's medical history, general examination, and prophylaxis. Alginate impressions will be taken of the upper and lower arches for all the patients who meet the inclusion criteria. The impressions will be poured into plaster, and a positioning guide-finder tray will be fabricated for each patient for color measurement.
2. Visit 2: Initial color measurement with a spectrophotometer and the positioning guide. Two clinicians performed the assigned isolation technique (relative or absolute). Then after a correct isolation the clinicians apply over the buccal surface from premolar to premolar of both arches the bleaching agent (Opalescence Boost 40%, Ultradent Products, South Jordan, USA).Two application of 20 minutes each. Objective examination of gingival tissues was performed visually, documented with photographs, and verified using a periodontal probe. The sensitivity was recorded and patient were given a sensitivity test to record at home. c) Visit 3: One week after the first bleaching session. Color measurement with a spectrophotometer and the positioning guide. In this visit the second bleaching session was done with the same steps as visit 2. d) Visit 4: 15 days after the second bleaching session. Final data collection (color + patients sensitivity test)

Inclusion Criteria:

• No oral os systemic pathology
• Periodontally Healthy
• No cavities
• Tooth shade of the canines A2 or darker

Exclusion Criteria:

• Adhesive restorations or protheses in the anterior region
• Enamel or dentin alterations
• Smoking habits
• Pregnant women
• Undergone prior bleaching treatment