Hyoid bone position in different facial skeletal patterns.

Background: Hyoid bone plays a significant role in physiological functions of craniofacial region and it's position adapts to changes of the head. The purpose of this study was to determine the position of the hyoid bone among subjects with class I, class II and class III skeletal patterns and evaluate the gender differences.

Material and Methods: One hundred and ten lateral cephalograms (59 females and 51 males) from different skeletal patterns (class I, II and III) were selected. The skeletal patterns were determined according to ANB angle. Using MicroDicom software, different linear and angular measurements (6 variables) was carried out to determine the position of hyoid bone. Intraclass correlation coefficient was used to verify reliability. Descriptive statistics of the variables were calculated and analyzed using two-way ANOVA and Bonferroni statistical methods.

Results: The mean distance from the hyoid bone (H) to mandibular plane (MP), to palatal plane (PP), as well as to a third cervical vertebra (C3) was more in males than females ( p =0.023, p <0.001, p <0.001 respectively). The mean H to PP distance was significantly more in skeletal class I compared to class III ( P =0.01). The mean H to C3 distance was significantly more in skeletal class I compared to class II ( P =0.008). The mean angle between H-MP and H-PP did not show any statistical difference among three skeletal classes ( p =0.102, P =0.213) and among male and female groups ( P =0.172, P =0.904).

Conclusions: The hyoid bone is positioned more superior and posterior in females than males and its location differs among different skeletal classes. It is placed more posterior in skeletal class II patterns and more inferior and anterior in skeletal class I patterns. Key words: Hyoid bone, Lateral cephalometry, Class III, Class II, skeletal pattern, Orthodontics.