Changes of hyoid, tongue and pharyngeal airway after mandibular setback surgery by intraoral vertical ramus osteotomy

Abstract

Objective: To assess changes in hyoid, tongue, pharyngeal airway, and head posture in patients who had mandibular setback surgery by intraoral vertical ramus osteotomy (IVRO) and to investigate the influence of LeFort I osteotomy.

Materials and methods: Sixty patients with skeletal Class III malocclusion were evaluated. All patients had mandibular setback surgery via IVRO, and 45 patients had additional maxillary impaction surgery via LeFort I osteotomy. Lateral cephalograms were taken before, immediately after, approximately 1 month after, and at least 1 year after surgery. Parameters indicating the hyoid, tongue, pharyngeal airway, and head posture were evaluated.

Results: The hyoid significantly moved inferoposteriorly immediately after surgery and relapsed superoanteriorly during observation periods. The tongue significantly moved posteriorly during all periods. The final position of the hyoid and tongue was significantly posterior, and the final pharyngeal airway was significantly narrower compared with its presurgical position. Significant cervical hyperflection occurred during observation periods and was strongly correlated with anterior movement of the hyoid. The hyoid and tongue showed similar positions regardless of the presence of different genders or LeFort I osteotomy after the long-term observation period.

Conclusions: The hyoid and tongue moved posteriorly after mandibular setback surgery via IVRO, and there was a tendency to relapse back to its original position. However, the final pharyngeal airway width remained narrower after the long-term observation period. Based on our results, careful monitoring of the airway may be needed after mandibular setback surgery via IVRO.

Figure 1

Cephalometric linear and angular measurements. (1) < SNA. (2) < SNB. (3) < ANB. (4) PNS-Ptm: closest distance between posterior nasal spine and pterygomaxillary fissure. (5) HRP-B: perpendicular distance from horizontal reference plane to B point. (6) VRP-B: perpendicular distance from vertical reference plane to B point. (7) HRP-Hy (hyoidale): perpendicular distance from HRP to hyoidale. (The hyoidale is the most superoanterior point of the hyoid.) (8) VRP-Hy: perpendicular distance from VRP to hyoidale. (9) Hy-C point: (most posterior point of mandibular symphysis). (10) D1: line parallel to VRP from PNS to dorsum of tongue. (11) D2: closest distance from basion to dorsum of tongue. (12) < SN-OPT: odontoid process tangent (Cv2ip-Cv2tg). (13) < SN-CVT: cervical vertebral tangent (Cv4ip-Cv2tg). *Cv2ip indicates the most inferoposterior point of the body of second cervical vertebra; Cv2tg, tangent point at superoposterior extremity of the odontoid process of second cervical vertebra; Cv4ip: the most inferoposterior point on the body of fourth cervical vertebra.