Comparison of arch width changes following orthodontic treatment with and without extraction using three-dimensional models.

OBJECTIVE: To compare the arch width changes in patients treated fixed orthodontic mechanics without extraction (Group 1), with upper and lower first premolar extractions (Group 2), and with upper first premolar extraction only (Group 3).

MATERIALS AND METHODS: The study was conducted with pre- and post-treatment digital models from 240 patients. Anterior, middle, and posterior distances were measured on pre- and post-treatment models. At T1 measurements, the distance among the canine cusp tips, the second premolar buccal cusp tips, and the first molar mesiobuccal cusp tips were measured. In addition, the distance (D) between the intercanine and intermolar lines and the distance (D') between the interpremolar and intermolar lines were defined on the anatomic y-axis, and this distance was maintained in calculating posttreatment measurements (T2). Mandibular and maxillary arch width changes were evaluated within and between groups.

RESULTS: Anterior, middle, and posterior arch widths increased significantly in Groups 1 and 3. Maxillary anterior and middle arch widths also increased in Group 2, but the increases were not statistically significant. Changes in maxillary anterior and middle arch widths were higher in Groups 1 and 3 when compared to Group 2. However, there was no statistically significant difference in mandibular arch changes between the groups.

CONCLUSION: Extraction treatment mechanics did not cause narrow dental arches, but nonextraction treatment increased arch width in all 3 measurements. Treatments with only upper arch extraction showed similar results with nonextraction treatment.