Changes in the upper airway, hyoid bone and craniofacial morphology between patients treated with headgear activator and Herbst appliance: A retrospective study on lateral cephalometry

Background: The present study compared the treatment changes in the upper airway, hyoid bone position and craniofacial morphology between two groups of children with skeletal class II malocclusion treated with the headgear activator (HGA) and Herbst appliance (Herbst).
Setting and sample population: Orthodontic population from the Faculty of Dentistry of the University of Hong Kong.
Methods: Thirty-four skeletal class II patients treated with the HGA (17 patients, mean age 10.6 ± 1.5 years) and the Herbst (17 patients, mean age 11.0 ± 1.4 years) were matched for sex, age, overjet, skeletal class and mandibular divergence. The patients received lateral cephalometric radiographs (LCRs) at the beginning of treatment (T1 ), after treatment (T2 ) and at follow-up (T3 ). In the HGA group, patients underwent LCRs 7 months before the beginning of treatment (T0 ), which were used as growth reference for intra-group comparison. Paired Student's t tests were used for intra- and inter-group comparisons (α = .05).
Results: Treatment changes (T2 -T1 ) did not differ significantly between the groups. However, at follow-up (T3 -T1 ) the Herbst group showed a smaller increase than the HGA group in the vertical position of the hyoid bone relative to the Frankfort plane (P = .013) and mandibular plane (P = .013).
Conclusions: There were no significant differences in the upper airway, hyoid bone position and craniofacial morphology between the groups at the end of treatment. However, the Herbst may provide better long-term control of the vertical position of the hyoid bone than the HGA in children with skeletal class II malocclusion.