Moments Generated during Simulated Rotational Correction with Self-Ligating and Conventional Brackets

Objective: To assess comparatively the magnitude of moments generated during rotational correction from different bracket systems during the late leveling and alignment stage of orthodontic treatment. Materials and Methods: The three types of brackets assessed were Orthos2 (ORMCO, Glendora, CA), Damon2 (ORMCO), and In Ovation-R (GAC, Bohemia, NY). The brackets were bonded on replicas made of resin from models constructed from an aligned patient's mandibular arch, and a 0.014- x 0.025-inch CuNiTi (ORMCO) wire was inserted. Orthodontic rotational correction was simulated on the Orthodontic Measurement and Simulation System from -5 degrees to +5 degrees rotation in 0.25 degrees increments on the distal and mesial direction. The moments generated at each increment of rotation throughout the full rotation path were statistically analyzed using a two-way analysis of variance and Tukey test at the .05 level of significance. Results: Both bracket type and direction of rotation showed an effect on moment magnitude. The highest moment (27.2 Nmm) was observed for the Damon2 bracket assigned to its noncompliant slot wall door. Higher moments were found during distal premolar rotation. The In Ovation-R showed a magnitude of moment in the range of 9.0 Nmm in the same direction, whereas conventional brackets presented the lowest moments (5.0 Nmm). Conclusions: A wide variation in magnitude of moments exerted by self-ligating and conventional brackets is noted in the simulated rotational correction of teeth, which relates to the geometry of the dental arch, the tooth position, and the rigidity of the closing component of the bracket slot.