Aerodynamic characteristics in upper airways among orthodontic patients and its association with adenoid nasopharyngeal ratios in lateral cephalograms

Xin Feng,Stein Atle Lie,Yicheng Chen,Kristina Hellén-Halme,Xie-Qi Shi,Weihua Cai

doi:10.1186/s12880-021-00659-4

Abstract

BackgroundAdenoid hypertrophy among orthodontic patients may be detected in lateral cephalograms. The study investigates the aerodynamic characteristics within the upper airway (UA) by means of computational fluid dynamics (CFD) simulation. Furthermore, airflow features are compared between subgroups according to the adenoidal nasopharyngeal (AN) ratios.MethodsThis retrospective study included thirty-five patients aged 9–15 years having both lateral cephalogram and cone beam computed tomography (CBCT) imaging that covered the UA region. The cases were divided into two subgroups according to the AN ratios measured on the lateral cephalograms: Group 1 with an AN ratio < 0.6 and Group 2 with an AN ratio ≥ 0.6. Based on the CBCT images, segmented UA models were created and the aerodynamic characteristics at inspiration and expiration were simulated by the CFD method for the two groups. The studied aerodynamic parameters were pressure drop (ΔP), maximum midsagittal velocity (Vms), maximum wall shear stress (Pws), and minimum wall static pressure (Pw).ResultsThe maximum Vms exhibits nearly 30% increases in Group 2 at both inspiration (p = 0.013) and expiration (p = 0.045) compared to Group 1. For the other aerodynamic parameters such as ΔP, the maximum Pws, and minimum Pw, no significant difference is found between the two groups.ConclusionsThe maximum Vms seems to be the most sensitive aerodynamic parameter for the groups of cases. An AN ratio of more than 0.6 measured on a lateral cephalogram may associate with a noticeably increased maximum Vms, which could assist clinicians in estimating the airflow features in the UA.

Highlights

Adenoid hypertrophy among orthodontic patients may be detected in lateral cephalograms
Hans Wilhelm Meyer first described the clinical condition of nasal obstruction caused by adenoid hypertrophy (AH) in 1868 [1]
The inclusion criteria were individuals aged 9 to 15 years who had had both a lateral cephalogram and cone beam computed tomography (CBCT) scan examined within one week

Summary

Introduction

Adenoid hypertrophy among orthodontic patients may be detected in lateral cephalograms. The study investigates the aerodynamic characteristics within the upper airway (UA) by means of computational fluid dynamics (CFD) simulation. Hans Wilhelm Meyer first described the clinical condition of nasal obstruction caused by adenoid hypertrophy (AH) in 1868 [1]. Early identification of the airflow alteration caused by AH in orthodontic patients is essential to avoid further complications. The nasendoscopy is considered the standard for clinically assessing the adenoid size on cooperative children [8]. Cone beam computed tomography (CBCT), computed tomography (CT), and magnetic resonance imaging have been investigated to evaluate the size, shape, and location of the adenoid [9–12]. The lateral cephalogram has been widely applied in children and adolescents to depict and trace skeletal structures and occlusion during the orthodontic treatment process. Since the presence of AH affects occlusion and craniofacial morphology [7, 13], adenoid assessment is an integral part of cephalometric analysis for this group of children

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Results

Conclusion