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Mandibular arch changes following nonextraction treatment.

OBJECTIVE
To evaluate mandibular tooth position changes following treatment with a lip bumper and fixed appliance. Specifically, we aimed to determine how space was obtained to align crowded lower incisors.


METHODS
Thirty-four consecutively treated children with a mean age of 10.6 years (SD: 1.14 years) were selected from a specialist orthodontic practice in Eire. All subjects were treated with a lip bumper followed by a fixed appliance. The positions and angulations of the lower first molars and most proclined lower incisor were measured on the pretreatment and post-treatment lateral cephalometric radiographs and study models with a reflex metrograph. The changes were also compared with published growth data.


RESULTS
After lip bumper and fixed appliance treatment the mandibular arch depth decreased (Mean difference: 1.2 mm; p < 0.01) and the mandibular intermolar width increased (Mean difference: 1.73mm; p < 0.01). The mandibular molars moved mesially (Mean difference: 2.14 mm; p < 0.01 and tipped distally (Mean difference: 4.36 degrees; p < 0.01). There were no significant differences between the pre- and post-treatment positions or angulations of the mandibular incisors. Compared to published growth data the arch depth decreased less, the intermolar width increased more and the mandibular molars were uprighted. There was no difference in the positions of the mandibular incisors in the treated group compared with published growth data.


CONCLUSIONS
The main effects of nonextraction treatment with a lip bumper followed by fixed appliance treatment were to maintain the leeway space, expand the mandibular arch and 'upright' the lower molars. The treatment had no effect on the position of the lower incisors.