Influence of Tooth Whitening After Resin Infiltration on the Shear Bond Strength of Orthodontic Brackets.

PURPOSE: To determine the influence of different bleaching methods on the shear bond strength (SBS) of orthodontic brackets bonded to resin-infiltrated (Icon, DMG) extracted human enamel. METHODS AND MATERIALS: 64 extracted wisdom teeth were randomized into four groups (n = 16): 1. (-)control (no treatment), 2. (+)control (RI), 3. RI followed by 25% H2O2 (IOB) and 4. RI followed by 10% carbamide peroxide bleaching (HB). After a standardized demineralization protocol, RI and bleaching were performed according to the manufacturer's instructions prior to storage for 14 days. Brackets (Mini Diamond Twin, Ormco) were bonded buccally and lingually (Transbond XT, 3M). SBS values (MPa, traverse speed 0.5 mm/min, Zwick Roell) and the Adhesive Remnant Index (ARI) were determined on the buccal side. Following 5000 thermal cycles (5-55°C; RC 20 CS Lauda), SBS and ARI values for the lingual brackets were determined analogously. Data were analyzed with mixed ANOVA and Kruskal-Wallis and Wilcoxon tests at a 0.05 significance level. RESULTS: Differences in SBS were observed among groups (F(3, 64) = 8.01, P 0.001). HB exhibited the lowest SBS values (14.99 ± 6.42 MPa; 10.84 ± 3.61 MPa), differing significantly from the negative control (P = 0.041; P = 0.002 after thermocycling). No significant differences were noted between IOB and HB. Thermocycling reduced SBS values across all groups (F(3, 64) = 25.83, P 0.001). CONCLUSION: RI followed by bleaching negatively impacts bracket bonding strength, with a significant reduction observed after home bleaching, while in-office bleaching showed no such effect.