Effect of Bleaching on Shear Bond Strength of Orthodontic Brackets

Objective: to determine the effect of In-Office and At-Home bleaching on the shear bond strength of orthodontic brackets using a composite adhesive. Methods: Two protocols were used on sixty human molar teeth to simulate two methods of bleaching; 1) At-Home bleaching performed using Opalescence bleaching agent (Ultradent Inc., South Jordan, Utah 84095) which contains 10% carbamide peroxide. The bleaching agent was changed every day after each bleaching cycle was completed. 2) An In-Office bleaching system (Zoom! Discus Dental Inc., Culver City, CA 90232) which contains 25% hydrogen peroxide gel. The bleached teeth were stored in artificial saliva at 37°C. The teeth of each bleaching group were then randomly divided into equal subgroups; 15 teeth were stored for 7 days and the other for 14 days, before bonding the brackets. The subgroups were used to evaluate the effect of time following bleaching on the adhesion to enamel. Shear bond strength test was performed on all the teeth. The Krushal-Wallis test for nonparametric means was used to determine if significant differences existed between the various sub-groups and an unbleached control group. Results: Kruskal-Wallis test (X2=8.089) comparisons indicated that there were no significant differences between the 5 subgroups compared (p=.088). The mean shear bond strength for the control group (no bleaching) was ¯x =5.6 ± 1.8 MPa, means for the At-Home groups were 5.2 ± 3.6 MPa and 7.2± 3.2 MPa, for the 7 and 14 days waiting period before bonding. The means for the In-Office groups were 5.1± 5.3 MPa and 6.6± 2.6 MPa, for the 7 and 14 days subgroups respectively.

Conclusions: The statistical results indicated that In-Office and At-Home bleaching did not affect the shear bond strength of orthodontic brackets to enamel