The Effect of Rapid Maxillary Expansion on the Upper Airway’s Aerodynamic Characteristics

Background: The effect of rapid maxillary expansion (RME) on the upper airway (UA) has been studied earlier but without a consistent conclusion. This study aims to evaluate the outcome of RME on the upper airway function in terms of airflow resistance by applying a computational fluid dynamics (CFD) simulation. Methods: : This retrospective cohort study consists of seventeen cases with two consecutive CBCT scans obtained before (T0) and after (T1) RME. Patients were divided into two groups with respect to patency of the nasopharyngeal airway as expressed in the adenoidal nasopharyngeal ratio (AN): group 1 was comprised of patients with an AN ratio < 0.6 and group 2 encompassing those with an AN ratio ≥ 0.6. CFD simulation at inspiration and expiration were performed based on the three - dimensional (3D) models of the UA segmented from the CBCT images. The aerodynamic characteristics in terms of pressure drop, midsagittal maximum velocity, and maximum wall shear stress were compared by independent samples t-test between the two groups at T0 and T1. Results: : At T0, the pressure drop at expiration was significantly higher in group 2 compared to group 1, whereas the difference between the two groups was not significant at T1. The midsagittal maximum velocity of the two groups decreased to some extent at expiration, but without significant difference. The midsagittal maximum velocity of group 2 was at inspiration significantly higher than that of group 1 at T0 and T1. Conclusion: RME had a positive effect on UA airflow resistance in patients with an AN ratio ≥ 0.6. The findings provide positive evidence of RME in airway function and should thus be recommended to patients with both a narrow maxilla and enlarged adenoid.