CBCT-based three-dimensional morphometric analysis of the upper airway and its influencing factors in skeletal Class II average-angle patients across different bone ages

Objective Previous studies have largely treated skeletal Class II patients as a homogeneous group for overall analysis, without fully accounting for subgroup differences in vertical facial patterns or variations in developmental timing. Consequently, a systematic understanding of the associations between upper airway morphology, hyoid position, and craniofacial morphology remains insufficient, which limits the formulation of precise clinical intervention strategies. This study aims to analyze the three-dimensional morphological changes of the upper airway and their associated influencing factors in skeletal Class II average-angle patients, stratified by cervical vertebral bone age staging, so as to provide evidence for the development of stage-specific orthodontic treatment strategies. Methods A total of 205 skeletal Class II average-angle patients were enrolled and divided into four groups (T1–T4) according to cervical vertebral bone age staging. Upper airway morphology, hyoid position, and craniofacialparameters were assessed using cone-beam CT (CBCT) three-dimensional reconstruction combined with Dolphin and WinCeph software. Inter-group comparisons were conducted using analysis of variance (ANOVA). Spearman correlation analysis and multiple linear regression analysis were used to identify independent predictors of upper airway morphology. Results In females, total upper airway volume and nasopharyngeal volume increased significantly at stages T2 and T4, whereas palatopharyngeal and laryngopharyngeal volumes showed significant increased only at stage T4 ( P < 0.05). In males, significant volumetric increments across all airway segments were observed predominantly at stages T3 and T4 ( P < 0.05). Multiple regression analysis revealed that in females, the positive predictors of total upper airway volume included bone age stages T2 and T4, Mx'-Mx, H-RGn, and H-CVP. In males, the positive predictors comprised bone age stage T3, H-RGn, and H-CVP. Conclusion Upper airway volume in skeletal Class II average-angle patients exhibits a sex-dimorphic developmental pattern across bone age stages. Females display a biphasic growth pattern with leap-like increases at T2 and T4, whereas males demonstrate a steady and pronounced growth spurt from T3 to T4. Hyoid position parameters (H-RGn and H-CVP) consistently emerge as key determinants of upper airway volume, while the contribution of jaw morphology—primarily maxillary width—varies by gender.