An Investigation of Hyoid Bone Position and Airway Space in Class III Malocclusion after Orthognathic Surgery

Choi, Yong Ha; Kim, Bae Kyung; Choi, Byung Joon; Kim, Yeo Gab; Lee, Baek Soo; Kwon, Yong Dae; Ohe, Joo Young; Suh, Joon Ho

Abstract

PURPOSE
The purpose of this study was to investigate changes in the position of the hyoid bone and soft palate and the amount of airway space after bilateral sagittal split ramus osteotomy (B-SSRO).
METHODS
This study is a review of lateral cephalometric tracings of 30 patients who underwent B-SSRO with setbacks at Kyunghee Dental Hospital from 2005 to 2009. Lateral cephalograms were taken before (T0), within one month (T1), and more than six months after the surgery (T2).
RESULTS
The hyoid bone at T1 changed significantly towards the inferoposterior position. At T2, it had significantly moved superiorly, but not anteriorly. At T1, the nasopharyngeal space, extending from the posterior nasal spine to the posterior pharyngeal space, decreased significantly, but did not show a significant increase at T2. The nasopharyngeal space, extending from the middle of soft palate to the posterior pharyngeal space, decreased significantly at T1, but did not show a significant decrease at T2. The oropharyngeal airway space decreased significantly at T1 and did not return to its original position at T2. The hypopharyngeal space, extending from the anterior to the posterior pharyngeal space at the level of the most anterior point of the third cervical vertebrae, slightly decreased at T1, but the amount was insignificant; however, the amount of decrease at T2 was significant. The hypopharyngeal space extending from the anterior to the posterior pharyngeal space at the level of the lowest point of the third cervical vertebrae, decreased significantly at T1 but returned to its original position at T2.
CONCLUSION
B-SSRO changes the position of the hyoid bone and muscles inferoposteriorly. These change allows enough space for the tongue and prevent airway obstruction. Airway changes may be related to post-operative edema, posterior movement of the soft palate, anteroposterior movement of the hyoid bone, or compensation for decreased oral cavity volume. The position of the pogonion which measures anterior relapse after surgery did not show significant differences during the follow-up period.