Third-order torque and self-ligating orthodontic bracket-type effects on sliding friction

Abstract

Objective: To examine the influence of third-order torque on kinetic friction in sliding mechanics involving active and passive self-ligating brackets. Materials and Methods: Wire-slot frictional forces were quantified and compared across five sets of brackets and tubes within a simulated posterior dental segment with -15°, -10°, -5°,0°, +5°, + 10°, and +15° of torque placed in the second-premolar bracket; a working archwire was pulled through the slots. Results: Increasing the torque from 0° to ±15° produced significant increases in frictional resistance with all five sets of brackets and tubes. At 0° and ±5° of torque, generally less friction was created within the passive than within the active self-ligating bracket sets, and the conventional bracket sets with elastomeric ligation generated the most friction. At ± 10° of torque, apparently with wire-slot clearance eliminated, all bracket-and-tube sets displayed similar resistances, with one exception at +10°.At ±15° of torque, one passive set and one active set produced significantly larger frictional resistances than the other three sets. Conclusions: Third-order torque in posterior dental segments can generate frictional resistance during anterior retraction with the archwire sliding through self-ligating bracket slots. With small torque angles, friction is less with passive than with active self-ligating brackets, but bracket design is a factor. Frictional forces are substantial, regardless of ligation if the wire-slot torque exceeds the third-order clearance. © 2009 by The EH Angle Education and Research Foundation, Inc.