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Treatment to improve malocclusion in patients with skeletal mandibular protrusion often involves the combined use of surgical treatment in orthodontic treatment to improve not only occlusion but also facial appearance. Mandibular setback surgery is known to cause displacement of the hyoid bone and affect the morphology of the respiratory tract. However, although there have been previous reports regarding displacement of the body of the hyoid bone, few reports have verified hyoid bone rotation taking complex muscle adhesion into consideration. Therefore, the aim of the present study was to comparatively investigate the position of the hyoid bone and morphological changes of pharyngeal airway taking preoperative and postoperative inclination into consideration in patients who underwent setback of the mandible with orthognathic surgery. The subjects comprised 14 patients who underwent sagittal split ramus osteotomy to treat skeletal mandibular protrusion, exhibited at least 8.0 mm (mean : 9.0mm) of mandibular retraction with model surgery directly before surgical treatment and consented to participate after being given an outline of this study. Data comprising lateral roentgenographic cephalograms taken directly before and one year after orthognathic surgery were used to measure reference points before and after surgery and measurement items determined with the following method. When analyzing hyoid bone displacement, the hyoid bone upper projection (H1), lower projection (H2) and lowest point of the third cervical vertebra (C3) were set as reference points. Measurement items were ∠ NSH1, ∠ NSH2, ∠ H1C3H2, C3-H1 and C3-H2. Hyoid bone rotation and displacement of the body of the hyoid bone were then evaluated. Morphology of the pharyngeal airway was analyzed by measuring respiratory tract diameter before and after surgery in the nasopharynx region, soft palate area, uvula area, angle of mandible area and epiglottis area. Results indicated that ∠ NSH1 and ∠ NSH2 increased significantly. However, no differences were observed in ∠ H1C3H2, C3-H1 or C3-H2, with the results clarifying that the hyoid bone had moved downward and backward without rotating. Evaluation of pharyngeal airway morphology found no differences in APW1-PPW1 and APW2-PPW2, which correspond to the upper section of the pharyngeal airway but APW3-PPW3 and APW4-PPW4, which correspond to the middle section, and APW5-PPW5, which corresponds to the lower section, were found to have 1)日本歯科大学附属病院矯正歯科(主任:小森 成教授) 2)日本歯科大学附属病院口腔外科(主任:荘司洋文准教授) 1)Division of Orthodontics, The Nippon Dental University Hospital at Tokyo (Chief : Prof. Akira KOMORI) 2)Division of Oral and Maxillofacial Surgery, The Nippon Dental University Hospital at Tokyo (Chief : Associate prof. Hirobumi SHOJI) 原 著 202 日顎変形誌 2015 年 鈴木みすず,他 narrowed significantly. Accordingly, it was found that setback of the mandible with orthognathic surgery does not affect the upper section of the pharyngeal airway but does cause narrowing in the middle and lower sections due to putting pressure on the respiratory tract.

Evaluation of Hyoid Bone Position and Pharyngeal Airway Morphology before and after Orthognathic Surgery for Mandibular Prognathism