Evaluation of the influence of dental bleaching with 35% hydrogen peroxide in orthodontic bracket shear bond strength.

OBJECTIVE The purpose of this study was to evaluate, in vitro, the bond strength of brackets bonded to premolars previously subjected to bleaching with a 35% hydrogen peroxide. METHODS Twenty one healthy premolars were selected and randomly divided into three groups (n = 7). Group I (G1) included teeth that were not submitted to bleaching. The enamel surfaces of Groups II (G2) and III (G3) were submitted to a bleaching process with 35% hydrogen peroxide (Whiteness HP Maxx). On Group II (G2), after bleaching, the teeth were stored for 24 hours in distilled water at 98.6 °F, and then, premolar metallic brackets were bonded using Transbond XT (3M) resin. Group III (G3) was submitted to the same procedure seven days after bleaching. After bonding, all teeth were stored in distilled water at 98.6 °F for 24 hours. All groups were submitted to a traction test using an EMIC DL2000 universal testing machine at a speed of 0.5 mm/min. RESULTS AND CONCLUSION The bracket resistance to debonding was compared between the groups by the Kruskal-Wallis nonparametric test (p < 0.05) and it was verified that the bleaching agent significantly reduced bracket adhesion when bonded 24 hours after bleaching. However, seven days after bleaching, there was no significant difference on the resistance to debonding among groups G1 (19,52 kgf) and G3 (18,44 kgf), meaning that it is necessary to wait longer after bleaching to bond brackets.