The evaluation of hyoid bone position and pharyngeal airway following mandibular setback surgery

Introduction: It has been advocated that treatment of dentofacial deformities with jaw osieotomies may influence upper airway morphology, and several studies has shown that mandibular setback surgery has the potential to diminish airway size and alter the hyoid bone position.Objective: The purpose of this study was to evaluate the effect of mandibular setback on the pharyngeal airway size, and hyoid bone position and to evaluate if a pre-surgical prediction on PAS can be made or not.Materials and methods: Twenty eight pre- and post-operative (۳-۴ months) lateral cephalograms of ۲۸ individuals (۱۶ females and ۱۲ males older than ۱۷) who had undergone vertical ramus ostetomy setback surgery to correct skeletal class III discrepancies. Cephalograms were traced and a paired-sample t-test was used to evaluate the difference between ۱۱ linear variables pre- and post-operative measurements. Coefficient correlation was calculated for the amounts of setback and the change in airway size.Results: The vertical and horizontal position of hyoid and hyoid-mandible distance do not change significantly. Hyoid-۲nd cervical vertebra and hyoid-pogonion distances reduced significantly. In the case of upper airway indicators, the width of pharynx was calculated at ۴ different levels. In all ۴ levels, statistical analysis revealed significant reduction but the correlation of reduction in the size of pharynx versus amount of setback is not significant (respectively from the most superior width to the most inferior one r=۰.۱۵, r=۰.۱۳, r=۰.۰۹, r=۰.۱۹).Conclusion: This study suggested that mandibular setback surgery can decrease the pharyngeal airway size.