RESEARCH – July 2006

Hyoid bone position and inclination in relation to different malocclusions


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Background. Various studies have documented the variability of hyoid bone position in relation to changed mandibular position or head posture. The aim of this study was to investigate hyoid bone position and inclination on the cephalometric radiographs of four groups of patients exhibiting Class I, Class II, Class III and sceletal open-bite

Material and methods. The material consisted of cephalometric radiographs, which were carefully matched with regard to age and sex; the number of boys, 36 (44%), and girls, 47, (56%) was almost equal. We observed 83 patients, 10– 13 years of age, who had class I (control group) malocclusion, 24 cases, class II, 17 cases, class III, 23 cases, and open-bite, 19 cases. The radiographs were taken in centric occlusion mandibular position and 19 measurements were performed on tracings.
We analysed the data statistically and initially the t-test was used to find features that would distinguish the diagnoses (p ≤0.005), further the MANOVA method was used which proved that the average values of the features of the diagnoses were different (p ≤0.001) and finally, by using the Dunnet method, we analysed which differences were significant (p ≤0.01).

Results. The findings revealed a significant difference in the position and inclination of the hyoid bone between the four groups. The most important differences between hyoid bone position and malocclusion were found for skeletal open-bite patients compared to the control group (p<0.001). We found that in skeletal open-bite patients the position of the hyoid bone is much more downand backward (which is very natural for skeletal open-bite malocclusion – retrognathic position of the upper jaw and the lower jaw in relation to the base of the cranium) and the hyoid bone is strongly inclined down- and backward.

Conclusion. The findings of this investigation support the hypothesis that there is an evident relationship between the hyoid bone and malocclusion, which means that these structures are coordinated and influence each other. This might have an implication in the function of the suprahyoid and infrahyoid muscles and hence in the direction of mandibular growth.As the hyoid bone is a very important element in the function of both the supra- and infrahyoid muscles, its role in contributing to a specific orientation and function of these muscles might be instrumental in the establishment of specific structural elements of the jaws and in occlusion of the teeth. Further investigation might be useful in clarifying the role of the hyoid bone in the rate and direction of growth and in the influence of mandibular growth through the control of the supra- and infrahyoid muscles. The practical and clinical benefit of futher investigations would help prevent, diagnose and treat such a serious disease as the syndrome of obstructive sleep apnoea for which, unfortunately, appropriate treatment has not yet been found.