The morphologies and aerodynamic characteristics of the upper airway in class II adolescents with different minimum cross-sectional area.

To investigate whether different upper airway minimum cross-sectional area (CSAmin) in Class II adolescents correspond to distinct upper-airway morphology and aerodynamic characteristics. One hundred and fifty-nine Class II adolescents were enrolled in this cross-sectional observational study and stratified into three groups according to the upper airway CSAmin, Group 1(40 ≤ CSAmin < 80 mm²), Group 2 (80 ≤ CSAmin ≤ 120 mm²), and Group 3(CSAmin > 120 mm²). Cone-beam computed tomography (CBCT) data were used to measure upper-airway morphological characteristics and to reconstruct three-dimensional models of the upper airway. Computational fluid dynamics (CFD) simulations were performed to calculate velocity, pressure, wall shear stress and resistance of upper airway during inspiration and expiration. The three groups exhibited significant differences in upper airway volume (P < 0.01). Upper airway airflow velocity, wall shear stress and resistance of Group 1 were significantly higher than those of the other two groups. Nasopharyngeal volume and aerodynamic variables differed only between Group 1 and Group 3; Group 1 and Group 2 were statistically indistinguishable. At the level of the palatopharynx and glossopharynx, significant differences in most measured variables were observed across all three groups. Smaller CSAmin was consistently associated with reduced total volume, greater negative intraluminal pressure, higher peak velocity, wall shear stress, and airway resistance. Class II adolescents with CSAmin < 80 mm² should be flagged for closer airway surveillance before initiating any treatment that could further narrow the airway.