Changes in upper airway airflow after rapid maxillary expansion considering normal craniofacial development as a factor: a retrospective study using computer fluid dynamics

Abstract Background/Objectives Evidence suggests nasal airflow resistance reduces after rapid maxillary expansion (RME). However, the medium-term effects of RME on upper airway (UA) airflow characteristics when normal craniofacial development is considered are still unclear. This retrospective cohort study used computer fluid dynamics (CFD) to evaluate the medium-term changes in the UA airflow (pressure and velocity) after RME in two distinct age-based cohorts. Materials/Methods The study included 48 subjects who underwent RME divided into two cohorts: a 6−9-year-old group (EEG group: early expansion group − 25 subjects) and an 11−14-year-old group (LEG group: late expansion group − 23 subjects). The nasal cavity and pharyngeal anatomy were segmented from Cone-beam computed tomography reconstructions taken before RME (T0) and 12 after RME (T1). The two UA airflow variables (pressure and velocity) were simulated using CFD. The maxillary expansion (PW) amount, two cross-sectional area measurements (CS1 = anterior cross-section and CS2 = posterior cross-section), and four UAs’ subregions (NC = nasal cavity, PAtotal = pharyngeal airway, NP = nasopharynx, VP = velopharynx, and OP = Oropharynx) were also considered. All data were statistically analyzed. Results At the baseline, the airflow pressure, velocity, and noted obstructions were significantly higher in the EEG compared to LEG. At T1, there was a significant improvement in the median airway parameters in both groups, which was remarkably greater in the EEG. A significant negative correlation was found between pressure/velocity and both CS2 and NP. According to the CFD plots, the airflow pressure and velocity changes could be attributed to the reduction of the adenotonsillar tissues’ sizes, which were remarkably more marked in the EEG. Limitations The results of this study cannot be generalized since they referred to a retrospective orthodontic sample without obstructive adenotonsillar hypertrophy. Conclusions/Implications Twelve months after RME, normal craniofacial developmental changes and spontaneous adenotonsillar tissues volume regression could represent the most significant factors influencing UA airflow changes.