Comparison of the Effects of Functional Treatment and Orthognathic Surgery on Hyoid Bone Position Following Mandibular Advancement

Objective: To compare the effects of functional orthopedic treatment and mandibular advancement induced by orthognathic surgery on hyoid bone position in individuals with skeletal Class II malocclusion, relative to an untreated control group. Methods: Fifty-six individuals were divided into functional (n=20), surgical (n=16), and control groups (n=20). Lateral cephalometric images obtained at pretreatment (T0) and posttreatment (T1) were analyzed using WebCeph software. The linear (aC2-H, aC3-H, aC4-H, S-H, N-H, ANS-PNS- H) and angular (SNA, SNB, ANB, Go-H-S, H-S-N, H-PNS-ANS) describing hyoid bone position were measured. Data normality was assessed with the Shapiro-Wilk test, followed by one-way ANOVA or Kruskal-Wallis test, as appropriate. Intragroup changes were evaluated using paired tests, and post-hoc analyses were performed using Tukey honestly significant difference or Dunn-Bonferroni methods. Measurement reliability was confirmed (intraclass correlation coefficients >0.90). Results: At T0, the orthognathic surgery group showed significantly higher aC2-H, aC3-H, aC4-H, S-H, N-H, and ANS-PNS-H measurements compared to the other groups (p<0.05), while angular variables did not differ significantly. At T1, intergroup differences in hyoid position were no longer significant (p>0.05). Intragroup analysis revealed significant increases in aC2-H, aC4-H, S-H, and N-H in the functional treatment group, whereas significant decreases in N-H, H-S-N, and H-PNS-ANS were observed in the orthognathic surgery group. Changes in the control group were minimal. Conclusion: Functional treatment resulted in anterior-inferior displacement of the hyoid bone, whereas orthognathic surgery predominantly induced superior displacement without significant anteroposterior change. Both treatment modalities improved mandibular skeletal relationships, while hyoid position remained largely stable in untreated individuals.