Effect of premolar extraction on upper airway volume and hyoid position in hyperdivergent adults with different mandibular length.

INTRODUCTION: The objective of this study was to investigate the morphological changes of the upper airway and the position of the hyoid bone in hyperdivergent adults with different mandibular lengths after premolar extraction. MATERIALS: The data of 57 hyperdivergent adults, aged 20-35 years, who had 4 premolar extractions were included for the study. Mandibular length (CoGn) was used for grouping (A: long CoGn, B: short CoGn). Pretreatment and posttreatment lateral cephalograms and cone-beam computed tomography images were used to assess the position of mandible, hyoid bone, and upper airway using paired t test. An independent sample t test was used to detect changes of the airway and hyoid position between groups A and B. Pearson correlation analysis was applied to estimate the correlation between pharyngeal spaces and dentoskeletal morphology at P <0.05. RESULTS: In all subjects, we observed retraction of the upper incisors, mesial movement of the lower molars, and reduction of the mandibular planes. In group A, differences were found in anterior and posterior movements of the hyoid bone, increase of airway volume, minimum cross-sectional area (MCA) and anteroposterior linear distance (APL) (P <0.05). There were notable differences in the change of hyoid position, airway volume, MCA, and APL between group A and group B. Glossopharyngeal and hypopharyngeal volumes, MCA, and APL were correlated with articular angle, mandibular plane, and hyoid bone position (P <0.05). CONCLUSIONS: With a comprehensive diagnosis and treatment, premolar extraction in hyperdivergent adults with favorable CoGn can facilitate improvement of esthetics, hyoid bone position, and the increase in glossopharyngeal and hypopharyngeal volumes and MCA.