Forces exerted by conventional and self-ligating brackets during simulated first- and second-order corrections

Introduction: Our aim in this study was to comparatively assess the forces generated from conventional and self-ligating bracket systems during the late leveling and alignment stage, specifically for first- and second-order movement. Methods: Three types of brackets were selected: Orthos2 (Ormco, Glendora, Calif), Damon2 (Ormco), and In Ovation-R (GAC, Bohemia, NY). The brackets were bonded on resin replicas constructed from a model of an aligned mandibular arch, and a 0.014 × 0.025-in copper-nickel-titanium wire (Ormco) was placed. First- and second-order corrections—buccolingual and intrusion-extrusion movements—were simulated on the orthodontic measurement and simulation system. A 2-mm displacement was applied on the x-axis and a 1-mm displacement on the z-axis, both in 0.1-mm intervals; 5 repetitions were performed for each wire-bracket-interval combination, and new brackets and archwires were used for each trial. The forces generated by manipulation of the bracket in the 2 directions were recorded directly with the orthodontic measurement and simulation system software and were statistically analyzed with 2-way ANOVA, with bracket and displacement as the discriminating variables. Group differences were further analyzed with the Tukey post-hoc comparisons test with the family error rate set at the 0.05 level. Results: In the first-order correction, the direction showed a significant effect on force magnitude, with inward (lingual) movement having lower force levels for the In Ovation-R. No significant difference was found between the Damon2 and the conventional appliance for this movement. In the second-order model, no difference was noted between the 2 self-ligating brackets in magnitude of force, but the conventional bracket showed higher force levels, which accounted for 20%, or 1 N, of the increase in magnitude. The effect of the direction of displacement (intrusion vs extrusion) on force variation did not produce a significant effect. Conclusions: The forces generated by first- and second-order corrections in self-ligating appliances do not show a consistent pattern and depend on the wire, the direction of movement, and the design of the ligating component.