Self-ligating vs conventional brackets in the treatment of mandibular crowding: a prospective clinical trial of treatment duration and dental effects.

INTRODUCTION The aim of this study was to investigate the duration of mandibular-crowding alleviation with self-ligating brackets compared with conventional appliances and the accompanying dental effects. METHODS Fifty-four subjects were selected from a pool of patients satisfying the following inclusion criteria: nonextraction treatment in the mandibular or maxillary arches; eruption of all mandibular teeth; no spaces in the mandibular arch; irregularity index greater than 2 in the mandibular arch; and no therapeutic intervention planned with any extraoral or intraoral appliance. The patients were randomly assigned to 2 groups: 1 group received treatment with a self-ligating bracket (Damon 2, Ormco, Glendora, Calif) and the other with a conventional edgewise appliance (Microarch, GAC, Central Islip, NY), both with 0.022-in slots. The irregularity index of the mandibular arch was normalized between the groups, and the time to alignment was estimated in days. Treatment duration was assessed by data modeling with the Cox proportional hazard regression. Lateral cephalometric radiographs were used to assess the alteration of mandibular incisor position before and after alignment. Measurements of intercanine and intermolar widths were also made on dental casts to determine changes associated with correction. RESULTS AND CONCLUSIONS Overall, no difference in the time required to correct mandibular crowding with Damon 2 and conventional brackets was observed. For moderate crowding (irregularity index <5), however, the self-ligating group had 2.7 times faster correction. This difference was marginally insignificant for subjects with irregularity index scores greater than 5. Greater crowding prolonged treatment by an additional 20% for each irregularity index unit. Increases in intercanine and intermolar widths associated with crowding correction regardless of bracket group were noted. The self-ligating group showed a statistically greater intermolar width increase than the conventional group. Also, an alignment-induced increase in the proclination of the mandibular incisors was observed for both bracket groups, but no difference was found between Damon 2 and conventional brackets for this parameter.