Effects of miniscrew-assisted orthodontic treatment with premolar extractions on upper airway dimensions in adult patients with Class II high-angle malocclusion

Introduction: The primary aim of this study was to investigate the change in upper airway dimensions and in mandibular position after miniscrew-assisted treatment with premolar extractions in adult patients with Class II high-angle malocclusion. The secondary aim was to determine the correlation between changes in upper airway dimensions and changes in mandibular position in these patients. Methods: Eighteen adult patients with Class II high-angle malocclusion (mean ± standard deviation age = 21.2 ± 2.9 years) were selected retrospectively. All patients underwent 4 premolar extractions, and 2 miniscrews were implanted in the maxilla to intrude molar height. Cone beam computed tomography images were taken pretreatment and posttreatment for every patient. The primary outcome variable for the upper airway was the minimal cross-sectional area of the upper airway (CSAmin), and the primary outcome variables for the mandible were mandibular rotation (Mp-SN angle), mandibular horizontal position (SNB angle), and mandibular vertical position (ANS-Me distance). Results: The CSAmin significantly increased by 47.2 mm2 (t = −2.26, P = 0.04) after orthodontic treatment. The mandible significantly rotated counterclockwise by 0.9° (t = 2.20, P = 0.04) after treatment, which consisted of forward movement of 1.2° (t = −4.30, P = 0.00) and upward movement of 1.3 mm (Z = −1.98, P = 0.05). Furthermore, the change of the CSAmin showed a significant correlation with the change of the ANS-Me (P = 0.01). Conclusions: By using miniscrews to intrude maxillary molars, orthodontic premolar extraction treatment results in mandibular counterclockwise rotation, and upper airway dimensions increase in Class II high-angle young adult patients. The increase of the upper airway dimensions significantly correlates to the upward movement of the mandible.