Effect of Enamel Bleaching on Orthodontic Bond Strength- In Vitro

Objectives: To study the in vitro bond strength of orthodontic adhesives subjected to bleaching, and to determine if an anti-oxidant such as sodium ascorbate will reverse the effects of bleaching. Methods: 105 freshly extracted human premolars were randomly divided into seven groups (N=15). Groups II, III, IV were exposed to10% carbamide peroxide gel (following at home treatment regimen), groups V, VI, VII were exposed to 38% hydrogen peroxide (following professional treatment regimen), and a control group (I) with no treatment. After the respective bleaching agents, the teeth were exposed to either 10% Sodium Ascorbate for 3 hrs (Groups III and VI), or distilled water for 3 weeks (Groups IV and VII). Teeth were then etched with TransbondTM Plus self-etching primer. Brackets were bonded with TransbondTM XT light cure adhesive paste and debonded within 24 hours of their respective treatments. Data were analyzed using ANOVA and t-test at significant value p=0.05. Results: ANOVA showed significant differences in bond strength among the seven test groups (p<.05). Significant differences in bond strengths were found in unbleached (control, 10.96 MPa) vs bleached teeth (10% carbamide peroxide, 7.61 MPa; 38%H2O2, 2.03 MPa). The addition of Sodium Ascorbate significantly reversed the deleterious effect of 38% H2O2 (6.79 MPa vs 2.03 MPa) and improved the 10% carbamide peroxide group (8.71 MPa vs 7.61 MPa). Bond strength measurements of groups soaked in distilled water for 3 weeks after bleaching (Group IV at 12.40 MPa and VII at 11.10 MPa) were not significantly different than control. Conclusions: Brackets bonded to recently bleached teeth have an increased chance of bond failure. Exposure to bleaching agent of higher concentration poses a higher risk for bond failure. Bleached teeth exposed to anti-oxidant (Sodium Ascorbate) prior to bonding, improve bond strength comparable to unbleached teeth and those bonded 3 weeks after bleaching.