Changes In The Pharyngeal Airway Space And Hyoid Bone After Mandibular Setback Surgery For Skeletal Classâ…¢ Jaw Deformity

Objective:The purpose of this study was to examine the changes in stability of pharygneal airway space (PAS) and hyoid bone position after the mandibular setback surgery for skeletal Class III jaw deformity in comparison with a control group with two measuring methods, and find out whether there is different between the results get by the two measuring methods.Methods:The treated subjects included15Skeletal Angle Class III malocllusion patients from22-26years old (23.5±2.5on average) in Orthodontic Department, College of Shandong University. Each patient was taken standardized lateral cephalograms and computed tomography at the following stages:T1:before surgeryT2:within1week after surgeryT3:6months after surgeryThe control subjects include15volunteers from19-26years old(22.5±3.5on average)with normal occlusion, which were randomly selected from the Shangdong University. Each of them was taken standardized lateral cephalograms and computed tomography, too.A total of13landmarks were selected and evaluated between the different samples. All data were analyzed by SPSS V17.0software to show the comparisons between the skeletal Class Ⅲ jaw deformity and the normal occlusion and the comparisons in measurements at each treatment stages of the PAS and hyoid bone and the comparisons between the two measuring methods.Results:(1) The ClassⅢ subjects had a significantly wider PAS than did the control subjects.(2) Significant decreases in the lower PAS were observed after orthognathic surgery, and the hyoid bone showed considerable downward movement immediately after surgery.(3) The hyoid bone showed upward movement during the postsurgical stage, but is still lower than the control subjects.(4) There were differences between the two measuring methods during the three stages.Conclusion:(1) The Class Ⅲ patients showed significantly larger PAS than the control subjects and exhibited significant decreases immediately after the mandibular setback surgery of the PAS. The posttreatment morphology of the PAS in Class Ⅲ groups corresponded with that of the control group.(2) The vertical position of the hyoid bone of the Class Ⅲ patients moved remarkably downward immediately after the surgery and returned toward its presurgical position during the postsurgical period. (3)3-dimensional computed tomography scan had higher accuracy than lateral cephalograms in evaluating the change of PAS and hyoid bone after the mandibular setback surgery...