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Aim: To evaluate the effect of repeated bonding on the shear bond strength of orthodontic
brackets using a cyanoacrylate adhesive. Material and Methods: Sixteen freshly extracted
human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The
teeth were cleaned, polished, and etched with a 35% phosphoric acid gel. The brackets were
bonded with an adhesive that contains ethyl-cyanoacrylate. The teeth were sequentially
bonded and debonded three times using the same orthodontic adhesive. All teeth were
debonded within 1⁄2 hour after bonding to simulate the clinical condition in which a newly
rebonded bracket is attached to the archwire. Results: The analysis of variance comparing
the shear bond strength at the three debonding attempts indicated the presence of a significant
difference between the three groups (F ratio = 8.277 and P = .001). Duncan posterior
tests indicated that the shear bond strength at the initial debonding sequence was significantly
stronger (mean = 5.7 ± 3.8 MPa) than the second (mean = 2.2 ± 2.6 MPa) and the third
debonding sequences (mean = 2.1 ± 1.5 MPa). There were no significant differences between
the last two debonding sequences. Conclusion: In general, the highest values for shear
bond strength were obtained after the initial bonding. Rebonded teeth have significantly
lower and inconsistent shear bond strengths. The changes in bond strengths may be related
to the changes in the morphologic characteristics of the etched enamel surface as a result of
the presence of adhesive remnants.
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