Comparative evaluation of the effects of bimaxillary and mandibular setback surgery on pharyngeal airway space and hyoid bone position in skeletal class III patients

BACKGROUND: To compare the effects of bimaxillary surgery ( Maxillary advancement and mandibular setback) and mandibular setback surgery (Bilateral Sagittal Split Osteotomy) on the pharyngeal airway space (PAS) and the hyoid bone position in a skeletal class III patients. MATERIAL AND METHODS: Thirty four subjects (21 males, 13 females, mean age 26.5 ± 8 years) with skeletal class III pattern (ANB angle of -2° to -6°) were divided into two groups of equal sizes. Group A consisted of 17 individuals who underwent Bilateral Sagittal Split Osteotomy (BSSO)and Group B consisted of 17 individuals who underwent bimaxillary surgery. In both the group, lateral cephalograms were taken, traced and analyzed for the specified parameters at 3 intervals, pre treatment (C1), post surgical (C2), and post orthodontic treatment (C3). Changes in PAS was evaluated at 3 levels i.e, nasopharynx (Upper PAS), oropharynx (Middle PAS) and hypopharynx (Lower PAS). Changes in hyoid bone position were evaluated in anteroposterior and vertical direction at all the 3 intervals. RESULTS: There was a significant constriction of airway at oropharyngeal and hypo-pharyngeal level at C2 and C3 in both the groups. However, the reduction at the oropharyngeal airway was greater in group A. In group B, there was significant increase in the airway at the level of nasopharynx, Hyoid bone was positioned more posteriorly post-surgery in group A which did not return to its original position post treatment. In group B hyoid bone was positioned postero-inferiorly post surgically which came back to its original position by the end of orthodontic treatment. CONCLUSIONS: Patients undergoing bimaxillary surgery showed a significant increase in the airway at the level of nasopharynx. Hyoid bone returned to its original position by the end of orthodontic treatment in the bimaxillary surgery group. This study suggested that while treating a skeletal class III malocclusion it is advised to perform maxillary advancements along with mandibular setback surgery. Key words:Bimaxillary surgery, Hyoid bone, Bilateral Sagittal Split Osteotomy, Pharyngeal airway space.