Association Between Upper Airway Morphology and Pulmonary Function in Vietnamese Orthodontic Patients: A Cone-Beam Computed Tomography and Computational Fluid Dynamics Study

Background: Current evidence on the relationship between upper airway morphology and respiratory function remains inconsistent and inconclusive. Although anatomical narrowing is often linked to respiratory impairment, its effect on measurable pulmonary function in asymptomatic individuals has not been consistently demonstrated. Methods: This cross-sectional study included 50 healthy young adults who underwent cone-beam computed tomography (CBCT) and spirometry. Airway volume, minimum cross-sectional area (MCA), and computational fluid dynamics (CFD)-derived airflow parameters were analyzed. Associations between structural and functional variables were assessed using Spearman’s correlation. Results: Significant correlations were found among structural airway parameters, particularly between MCA and total airway volume (ρ = 0.8025, p < 0.001). However, no significant associations were observed between airway morphology and spirometric indices (FVC, FEV1, MEF). Similarly, CFD-derived airflow velocity and pressure showed no correlation with pulmonary function. Conclusions: Within this cohort, no statistically detectable association was observed between upper airway morphology and pulmonary function, suggesting that structural assessment alone may not capture functional respiratory capacity in young, healthy adults. Given the cross-sectional design and sample size, this finding should be interpreted as an absence of a detectable association in this specific cohort rather than evidence against a relationship in the general population.