Objective: To compare rebonding of orthodontic brackets based on the hypothesis that no difference would be found between the adhesive systems with respect to shear bond strength, mode of failure, and clinical failure rates.
Materials and Methods: The three adhesive systems included two self-etch primers (Transbond and M-Bond) and a conventional phosphoric acid etch (Rely-a-Bond). The sample size was 20 premolars for each adhesive system. The shear bond strength was tested 24 hours after bracket bonding with the bonding/debonding procedures repeated two times after the first debonding. Bond strength, adhesive remnant index (ARI), and failure sites were evaluated for each debonding. Statistical analysis consisted of a two-way analysis of variance (ANOVA) followed by Scheffè analysis. The clinical portion evaluated 15 patients over a 12-month period.
Results: The mean shear bond strengths after the first, second, and third debondings for Rely-a-Bond were 8.4 ± 1.8, 10.3 ± 2.4, and 14.1 ± 3.3 MPa, respectively; for Transbond 11.1 ± 4.6, 13.6 ± 4.5, and 12.9 ± 4.4 MPa, respectively; and for M-Bond 8.7 ± 2.7, 10.4 ± 2.4, and 12.4 ± 3.4 MPa, respectively. After the three debondings the mean shear bond strength increased significantly from the first to the third debonding for Rely-a-Bond and M-bond (P 
.001), but did not change for Transbond (P = .199).
Conclusions: The original hypothesis is not rejected. The two self-etching primers showing higher or comparable bond strength to the conventional phosphoric etch with less adhesive remnant on the enamel surface after the first debonding. With repeated bonding/debonding, the differences in the bond strength, ARI, and failure site were not significantly different. There was no difference in the clinical performance of the three adhesive systems (P = .667).
