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Am J Orthod Dentofacial Orthop. 2011 Sep;140(3):e99-e105. doi: 10.1016/j.ajodo.2011.03.019.

Comparative assessment of conventional and self-ligating appliances on the effect of mandibular intermolar distance in adolescent nonextraction patients: a single-center randomized controlled trial.

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Department of Orthodontics and Dentofacial Orthopedics, Dental School Medical Faculty, University of Bern, Bern, Switzerland.



Our aim in this study was to compare intermolar widths after alignment of crowded mandibular dental arches in nonextraction adolescent patients between conventional and self-ligating brackets.


Fifty patients were included in this randomized controlled trial according to the following inclusion criteria: nonextraction treatment in both arches, eruption of all mandibular teeth, no spaces in the mandibular arch, mandibular irregularity index from canine to canine greater than 2 mm, and no therapeutic intervention planned involving intermaxillary or other intraoral or extraoral appliances including elastics before the end of the observation period. The patients were randomized into 2 groups: the first received a conventional appliance, and the other a passive self-ligating appliance, both with a 0.022-in slot. The amount of crowding of the mandibular dentition at baseline was assessed by using the irregularity index. Intermolar width was investigated with statistical methods of linear regression analysis. On an exploratory basis, the effect of appliance type on intercanine width was also assessed. Additionally, the effects of appliance type on time to alignment and crowding on time to alignment were assessed by using the Cox proportional hazards model.


No evidence of difference in intermolar width was found between the 2 bracket systems (β = 0.30; 95% CI, -0.3 to 0.9; P = 0.30). No evidence of difference in intercanine width was observed between the 2 bracket systems (β = 0.33; 95% CI, -0.8 to 0.1; P = 0.15). The time to reach alignment did not differ between appliance systems (hazard ratio, 0.68; 95% CI, 0.4 to 1.2; P = 0.21), whereas the amount of crowding was a significant predictor of the required time to reach alignment (hazard ratio, 0.88; 95% CI, 0.8 to 0.9; P = 0.02).


The use of conventional or self-ligating brackets does not seem to be an important predictor of mandibular intermolar width in nonextractions patients when the same wire sequence is used.

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