The Effects of Class-III Malocclusion on Hyoid Displacement during Swallowing

Objectives: The displacement of the hyoid bone(HB)is a critical biomechanical component of normal swallowing function. There has been little attention given to the relationship between variations in abnormal craniofacial morphology and swallowing physiology. The purpose of this study was to evaluate the maximal vertical and anterior displacement of the HB during in ClassIII malocclusion at four stages of deglutition with real time balanced turbo field echo cine-Magnetic Resonance Imaging. Methods: After cephalometric analysis based on skeletal malformation, 19 patients (mean age 21.5) with skeletally ClassIII (mild) (82°≤SNB≤85°; -6mm≤NV-Pog≤0mm), 16 patients (mean age 19) with skeletally ClassIII (severe) (85°≤SNB; 0mm≤NV-Pog) and 20 patients (mean age 19.5) with skeletally ClassI relationship (SNB=80±2°; NV-Pog=-6±1mm) as control group were included in the study. All patients were examined in a supine position by 1,5 Tesla Super Conducting MR scanner. Real Time Balanced B.T.F.E. images (2.1/1.09vs,sr TE one e.) of the patient were taken with an angle of 50° with mid sagittal plane, 10mm thickness, 350x350mm. (FOV) dimensions and 96x96 matrix width during swallowing 10ml water, which was given with an injector 100-dynamic scans were captured in 11sec. and radiographic outputs of the images showing four consecutive deglutition stages were taken to perform measurements. To determine the relationship between the position of hyoid bone and Class-III malocclusion, a specialist measured the vertical and horizontal position of the HB for each stage in each group. Results: The vertical position of HB was significantly lower in severe ClassIII group than mild and control groups at all stages. The anterior displacement of the HB was also significantly correlated with ClassIII malocclusion; the greater the magnitude of ClassIII deformity, the smaller the hyoid anterior displacement. Conclusions: This study demonstrated that abnormal variations in ClassI skeletal morphology may influence hyoid movement and therefore affect swallowing physiology.