Abstract
Introduction: A retrospective study evaluating posttreatment symmetry in dental arch form and midlines was carried out in Class II subdivision patients treated with unilateral and bilateral maxillary premolar extractions. Methods: Using Geomagic (version 14; Geomagic, Research Triangle Park, NC) and MATLAB (version 8.4; MathWorks, Natick, Mass) software, best-fit curves expressed as quartic polynomials were generated for 13 Class II subdivisions treated with unilateral extractions and 20 treated with bilateral maxillary premolar extractions. Transverse and sagittal measurements were recorded to assess symmetry. Dental models were superimposed on constructed reference planes to generate average posttreatment arches. Statistical comparisons were performed with the significance level set at P <= 0.05. Results: The unilateral extraction group showed significant differences in transverse arch forms between the right and left sides in the anterior, anterior-middle, and middle segments of the arch, and all regions other than the posterior segment in the sagittal dimension. Significant differences were found between groups in the anterior and anterior-middle segments of the arch transversely, the middle and middle-posterior segments sagittally, and the midline deviation relative to the midsagittal plane. Superimposed average arches showed similar results. Conclusions: Unilateral maxillary extraction treatment generally results in a narrower and more posteriorly displaced arch form on the extraction side, with a deviated maxillary midline toward the extraction side of the arch.