In-vivo and in-vitro comparison of bond strengths of orthodontic brackets bonded to enamel and debonded at various times

Introduction: The purpose of this study was to measure and compare in-vivo and in-vitro bond strengths of orthodontic brackets bonded to human enamel and debonded at various times. An in-vivo debonding device was validated and used to measure bond strengths in the oral environment. Methods: For the in-vitro study, mini-twin metallic premolar brackets (Opti-mesh XRT, Oromco Corp, Glendora, Calif) precoated with Transbond XT composite resin (3M Unitek, Monrovia, Calif) were bonded to 60 extracted premolars. The teeth were divided into 4 groups of 15, and shear bond strength was tested on a universal testing machine at 4 time periods: 10 minutes, 24 hours, 1 week, and 4 weeks. For the in-vivo test, 60 premolars in 22 volunteers (dental students) from King Saud University were bonded with Mini-Twin metallic premolar brackets and divided into 4 groups; bond strengths were measured at 10 minutes, 24 hours, 1 week, and 4 weeks. Results: Statistical analysis with 1-way ANOVA at P <.05 showed no significant differences among the in-vitro or the in-vivo groups. Two-way ANOVA at P <.05 was used to compare the in-vitro results with the in-vivo results; the in-vivo group had significantly lower mean bond strength values. In addition, survival analysis, used to calculate the probability of bond failure at P <.05, confirmed the significant difference between in-vitro and in-vivo environments. Conclusions: Reported bond strength values are not time dependent.