The role of the hyoid bone in mandibular advancement: insights from functional appliance therapy in patients with skeletal class II - a prospective cohort study.

STUDY

OBJECTIVES

Functional orthopedics induces mandibular advancement caused by neuromuscular adaptations. These adaptations can affect the position of the hyoid bone and may contribute to the amount of skeletal outcomes. The skeletal response is triggered by the quality and quantity of growth as well as muscular reactions. The aim of this clinical trial was to evaluate the hyoid bone position before and after functional orthodontic treatment.

METHODS

This prospective cohort study included 31 patients (mean age: 12.3 ± 0.9 years) with skeletal class II meeting the following inclusion criteria: ANB > 4°, > ½ Class II molar relationship, overjet > 6 mm, neutral/horizontal growth pattern, and CVMS II-III. All patients were treated with the Sander Bite Jumping Appliance (BJA) with wear time monitored through microsensors. Lateral cephalograms were taken at baseline (t0) and after 1 year (t1). Linear and angular hyoid measurements were analyzed. Statistical analysis was performed using IBM SPSS (v29.0.2.0), employing paired t-tests and an exploratory post hoc grouping based on total mandibular length changes (Δco-pg), with significance set at p < 0.05.

RESULTS

BJA therapy resulted in a significant more superior and anterior position of the hyoid in all patients. A greater increase in Δco-pg at t1 was associated with a more pronounced hyoid shift, while patients with a less Δco-pg showed a more inferior hyoid position at t0 and a greater tendency towards a vertical growth pattern.

CONCLUSION

A more inferior initial hyoid position was associated with limited mandibular advancement, suggesting a potential anatomical link to airway physiology, warranting further investigation into its implications for OSA risk.

CLINICAL TRIAL REGISTRATION: German Clinical Trials Register (DRKS); URL: http://www.germanctr.de; Identifier: DRKS00021090; registration date: 12.03.2020.