Evaluation of Airway Resistance and Wall Shear Stress Affected By Mandibular Setback Surgery Using Computational Fluid Dynamics

Yajima, Yasuharu

Evaluation of Airway Resistance and Wall Shear Stress Affected By Mandibular Setback Surgery Using Computational Fluid Dynamics

Yasuharu Yajima DDS, Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine, Yokohama, Japan

Toshinori Iwai DDS, Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine, Yokohama, Japan

Hiroaki Kitajima DDS, Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine, Yokohama, Japan

Yoshihito Ohara DDS, Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine, Yokohama, Japan

Koji Honda DDS,PhD, Orthodontic Science, Division of Oral Health, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan

Naoki Shibutani D.D.S., Ph.D., Department of Oral and Maxillofacial Surgery, Yokohama City University Medical Center, Yokohama, Japan

Koichi Fujita DDS, PhD, Orthodontic Science, Division of Oral Health, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan

Yosuke Yamashita D.D.S., Department of Oral and Maxillofacial Surgery, Yokohama City University Medical Center, Yokohama, Japan

Shogo Murata DDS, PhD, Department of Oral and Maxillofacial Surgery, Yokohama City University Medical Center, Yokohama, Japan

Susumu Omura DDS, PhD, Department of Oral and Maxillofacial Surgery, Yokohama City University Medical Center, Yokohama, Japan

Marie Oshima PhD, Institute of Industrial Science, the University of Tokyo, Tokyo, Japan

Iwai Tohnai D.D.S., Ph.D., Department of Oral and Maxillofacial Surgery, Yokohama City University Graduate School of Medicine, Yokohama, Japan

Purpose

Airflow through airway receives resistance which is almost occurred by wall shear. It is important to investigate a distribution of wall shear stress (WSS) to understand airway resistance. Sleep study using computational fluid dynamics (CFD) revealed that WSS and airway resistance reduce significantly after treatments for sleep-disordered breathing.¹ In orthognathic surgery, volume of oropharyngeal and hypopharyngeal airway decreased significantly after mandibular setback surgery for mandibular protrusion.²However, there is few study of airway resistance change caused by mandibular setback surgery for mandibular protrusion. The purpose of this study is to investigate airway resistance and distribution of WSS affected by mandibular setback surgery.

Materials and methods

The subjects were 10 patients with mandibular protrusion who underwent bilateral sagittal split osteotomy (BSSO) for mandibular setback. Each three-dimensional airway model between nostrils and infraglottic cavity without paranasal sinuses was constructed using simulation software and CT data which were scanned just before surgery and 1 year after the surgery. CFD modeling with standard steady-state numerical formulation were used to characterize pharyngeal airflow behavior when patients inspired air at rest. Air flow rate was defined as 200ml/s. In this study, low Reynolds type k-ε model was used as turbulence model. Nasopharyngeal, oropharyngeal and hypopharyngeal airway resistances and WSSs were calculated. Distribution of WSS was showed as color map on the airway wall and was evaluated at 3 points (narrowest site behind soft palate, epiglottis and interarytenoid notch) where WSS was highest. Paired t-test was used to test the difference between pre-surgery and post-surgery values of airway resistance and WSS.

Results

Airway resistance in nasopharynx and oropharynx increased significantly after surgery (p<0.05). Airway resistance in hypopharynx did not increase significantly after surgery (p=0.22). Local peaks of WSS were found in narrowest site behind soft palate, epiglottis and interarytenoid notch. WSS in each local peak increased significantly after surgery (p<0.05).

Conclusions

Mandibular setback surgery (BSSO) for patient with mandibular protrusion causes increase of airway resistance in nasopharynx and oropharanyx. WSS was larger in narrowest site behind soft palate, epiglottis and interarytenoid notch and increased after mandibular setback surgery for patient with mandibular protrusion.

References

1. Powell NB, Mihaescu M, Mylavarapu G, Weaver EM, Guilleminault C, Gutmark E. Patterns in pharyngeal airflow associated with sleep-disordered breathing. Sleep Med 12:966–974, 2011.

2. Park S, Kim Y, Son W, Hwang D, Cho B-H. Cone-beam computed tomography evaluation of short- and long-term airway change and stability after orthognathic surgery in patients with Class III skeletal deformities: bimaxillary surgery and mandibular setback surgery. Int J Oral Maxillofac Surg 48:87–93, 2012.