Correlating position of Hyoid Bone and Mandible to Third Cervical Vertebra in patients with Class I, Class II and Class III skeletal malocclusion: A Cephalometric study

The present study was carried out to establish a control norm in skeletal class I patients for hyoid bone position and to compare and correlate hyoid bone position with reference to third cervical vertebra and retrognathion of mandible in skeletal class I , class II and class III groups. Lateral cephalometric radiographs of 100 subjects were divided into three groups, i.e., group 1, skeletal class I malocclusion; group 2, skeletal class II malocclusion and group 3, skeletal class III malocclusion respectively. Hyoid bone position is determined by using Hyoid triangle given by Bibby and Preston. Hyoid bone position is also compared and correlated in skeletal class I, class II and class III malocclusions by using Hyoid ratio which is obtained from hyoid triangle. Lateral cephalograms were hand traced and linear and angular dimensions calculated. The mean and standard deviation is obtained for all the variables studied. The hyoid ratio obtained is compared with all the three groups studied. The hyoid ratio obtained is very similar in all the three skeletal malocclusion group studied with very minimal standard deviation denoting the anteroposterior change of hyoid bone position with relation to change in mandibular position. The finding of this study has got significance with reference to oropharyngeal airway patency in skeletal class II malocclusions. The following conclusions were drawn from this study, 1. Standard values are given for the dimensions of the hyoid triangle. 2. Hyoid bone is positioned more anteriorly in class III skeletal malocclusion subjects, and it is placed more posteriorly in class II skeletal malocclusion subjects when compared to skeletal class I group with reference to third cervical vertebra and Retrognathion of mandible. 3. Hyoid ratio is obtained for skeletal class I, II and III skeletal malocclusion groups. The hyoid ratio for skeletal class I group is 2.0 ± 0.18, The hyoid ratio for skeletal class II group is 1.9 ± 0.19, The hyoid ratio for skeletal class III group is 2.0 ± 0.20. Hyoid ratio derived is very similar with minimal standard deviation in all the three groups studied. The present study has helped us to correlate the hyoid bone position in skeletal class I, class II and class III malocclusion and to determined the sexual dimorphism of hyoid bone. Hyoid bone position is important in determining successful orthopedic chin cup treatment in skeletal class III malocclusions, for prediction of surgical relapse following advancement BSSO for skeletal class II retrognathic patients, in predicting soft tissue morphology changes following orthognathic surgery and for maintenance of oropharyngeal airway. The study also determines the influence of skeletal malocclusion on oropharyngeal airway