• The korean journal of orthodontics
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• v.30 no.2 s.79
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• pp.261-272
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• 2000

Severe skeletal anteroposterior and vertical discrepancy is difficult to obtain satisfactory result by only orthodontic treatment, and much anteroposterior movement and treatment stability require orthodontic treatment with orthognathic surgery. The treatment goal of mandibular prognathic patients is to promote the function of stomatognathic system including mastication and phonetics, to improve the esthetics of facial profile and to maintain stability. Positional changes of hyoid bone, pharynx and tongue were seen with mandibular movement after orthognathic surgery. This study was performed to observe the changes of perimandibular tissues of orthodontic patients with skeletal mandibular prognathism who treated with orthodontic treatment, and the changes of hyoid bone, pharyx and tongue by relapse or recurrance after before and after orthognathic surgery and retention. The 22 patients who had mandibular prognathism were selected. They treated with orthodontic treatment with sagittal split ramus osteotomy as orthognathic surgery. And lateral cephalometric radiographs were taken 3 times : pre-surgery (T1), immediate post-surgery (T2) and 2 years alter retention (T3). The results were as follows : 1. The hyoid bone returned back after clockwise rotation to maxilla and occlusal plane during retention (P<0.01). 2. The hyoid bone moved posterior-inferiorly by mandibular surgery and returned back anterior-superior after retention. (P<0.01) 3. The changes of pharyngeal depth showed a little decrease at upper area in post- surgery, but it was not a significant difference generally through before, after and retention. 4. In relating to tongue base, the angle of tongue base was decreased and the dorsal area of tongue base moved to inferior-posterior direction and to superior direction again after retention (P<0.01). 5. Related to the thickness of upper and lower lip, the thickness of upper lip decreased after surgery, and the soft tissues below lower lip increased after surgery and decreased after retention.