Introduction: The lower frictional resistance produced by passive self-ligating brackets can be helpful during orthodontic sliding mechanics. The aims of this study were to evaluate the frictional resistance of brackets with passive ligation and to compare these values with corresponding controls.
Methods: Two passive self-ligating brackets (Damon SL II, Sybron Dental Specialties/Ormco, Orange, Calif; SmartClip, 3M Unitek, Monrovia, Calif) and 1 novel bracket with passive elastic ligation (Synergy, Rocky Mountain Orthodontics, Denver, Colo) were used. The brackets were coupled with 3 nickel-titanium archwires (0.014-in round, 0.016 x 0.022-in, 0.019 x 0.025-in) in a simulated ideal arch introducing first-order rotations of 3 degrees and 6 degrees, second-order intrusions of 0.5 and 1.0 mm, and a third-order labial crown inclination of 3 degrees . The dimensions of the brackets were measured with scanning electron micrographs. The results of initial maximum drawing forces (IMDF) were analyzed by 2-way ANOVA and 1-way ANOVA tests.
Results: The SmartClip bracket had larger critical angles and distances for binding than the other 2 brackets. When coupled with 0.019 x 0.025-in archwires in an ideal arch alignment, SmartClip brackets had lower IMDF than the other brackets. For the first-order rotations, Synergy brackets had significantly lower IMDF than the other brackets. Damon SL II brackets with smaller critical angles had greater IMDF. For the third-order inclination, the Damon SL II brackets with less torsional play also had greater IMDF. No significant differences of IMDF were found for all the brackets tested in second-order intrusions. However, IMDF increased as the severity of the malocclusion increased.
Conclusions: No significant bracket differences were found when binding occurred in second-order distances. In an ideal arch alignment, brackets with greater slot lumen have lower frictional resistance. First-order rotational control was influenced by slot depth, bracket width, and labial cover of the brackets with the same archwire. When a sliding mechanism was used with a third-order inclination change, the brackets with smaller third-order critical contact angles had greater frictional resistance.