This randomized single-blind, split-mouth clinical trial evaluated patient satisfaction with at-home dental bleaching using orthodontic retainers with different margin designs, as well as bleaching efficacy, tooth sensitivity (TS), and gingival irritation (GI).

The objective of the study will be to clinically evaluate patient satisfaction, as well as the effectiveness of colour change, tooth sensitivity and gingival irritation with home whitening using 10% carbamide peroxide performed with orthodontic retainers with different cut-outs. Forty patients will be selected to receive home teeth whitening with a straight or scalloped retainer on each half-arch (n=40). The whitening procedure will be performed with 10% carbamide peroxide (Pola Night 10%) for 2 hours over 14 days. Patient satisfaction will be assessed weekly for two weeks through a series of questions using the Visual Analogue Scale (VAS 0-10). Colour will be assessed initially, weekly for two weeks and 1 month after completion of whitening, using the subjective VITA Classical scale, VITA Bleachedguide 3D-MASTER and the objective VITA Easyshade spectrophotometer. The intensity and risk of tooth sensitivity and gingival irritation will be recorded on the Visual Analogue Scale (VAS 0-10). Patient satisfaction will be assessed using the paired Student's t-test. The colour change between the groups will be compared using the paired Student's t-test. The absolute risk of tooth sensitivity and gingival irritation in both groups will be compared using the McNemar test. The intensity of tooth sensitivity and gingival irritation will be analysed using the Student's t-test for paired samples. The significance level will be 5% in all statistical tests.

Inclusion Criteria:

• Completed of orthodontic treatment with Invisalign aligners (Align Technology Inc., CA, USA); willingness to undergo tooth bleaching as a complementary procedure; and current use of clear retainers. Additional criteria included age of ≥18 years of age, good general and oral health, and provision of informed consent. Eligible participants also needed anterior teeth free from carious and periodontal disease, with canines of shade A2 or darker on the VITA Classical scale (VITA Zahnfabrik, Bad Säckingen, Germany) and a Whiteness Index for Dentistry (WID) value ≤15.

Exclusion Criteria:

• History of previous bleaching; self-reported tooth sensitivity; continuous use of analgesics or anti-inflammatory drugs; pregnancy or breastfeeding; and deleterious habits such as bruxism or smoking. Participants with anterior teeth presenting fixed orthodontic appliances, attachments, restorations, endodontic treatment, color changes due to tetracyclines or fluorosis, or visible enamel cracks were also excluded.