Hyoid Bone Position as an Etiological Factor in Mandibular Divergence and Morphology

Objectives: The objective is to determine whether there are differences in the position of the hyoid bone at rest in natural head position in subjects with mandibular hyperdivergence and to evaluate whether there are differences in hyoid position and antegonial notch depth in mandibular hyperdivergent males and females. Methods and Materials: This is a retrospective cohort study involving a review of lateral cephalometric radiographs of 45 adult men and women with mandibular hyperdivergency. Hyperdivergency was determined by cephalometric ranges of: SN-GoGn as least +2 SD from normal, Y-axis, PP-GoGN, and gonial angle greater than +1SD from normal. A group of 45 normodivergent adults served as a control, with cephalometric ranges of: SN-GoGn within ±1 SD of normal, with only one measurement of the other three between +1 and +1.5 standard deviations. A custom digital cephalometric analysis, the Hyoid Analysis, was designed, to measure the vertical and horizontal position and inclination of the hyoid and the antegonial notch depth. Results: In hyperdivergent subjects, the posterior aspect of the hyoid is located lower and more posterior, compared to the control group, while there is no difference in position of the anterior surface of the hyoid and the antegonial notch is 0.6 mm deeper. In males, the posterior aspect of hyoid is lower by 8.5 mm, while the anterior surface is located 9.0 mm lower. In males, the hyoid is inclined more steeply than in females by 4.4 degrees and the antegonial notch is deeper than in females by 0.6 mm. Conclusions: There are differences in hyoid bone position and mandibular morphology in hyperdivergent subjects compared to normodivergent subjects and in males compared to females.