The position of hyoid bone after treatment of class III malocclusion with FRIII appliance in children

Objective: To compare changes of hyoid bone position before and after treatment of Angel Class Ⅲ malocclusion with FRⅢ appliance in children.Methods: 20 patients with Angle Class Ⅲ malocclusion at the average age of 9.5 years were treated with FRⅢ appliance,the hyoid bone position was analyzed before and after treatment by X-ray film,20 children with normal occlusion were enrroled as the controls.Results: Before treatment,in the vertical the hyoid bone measurements of functional Class Ⅲ malocclusion compared with those of normal occlusion group the H-FH,H-S and H-Mp were significantly lower(P0.01);in the horizontal H-Ptm was lower(P0.05);in the horizontal direction there was no significant difference in H-RGn(P0.05);in angle measurements Ar-H-Me increased significantly(P0.01);After treatment of functional Class III malocclusion compared with normal occlusion group,H-Mp was significantly lower(P0.01),Ar-H-Me was increased(P0.05);and there was no significant difference in H-FH,H-S,H-Ptm and H-RGn(P0.05).After treatment H-FH and H-S were increased significantly(P0.01),H-Ptm was increased(P0.05),Ar-H-Me was lower(P0.05),and there was no significant change in H-Mp and H-RGn(P0.05).Conclusion: After FRⅢ treatment of children with Class Ⅲ malocclusion,the hyoid bone position may move rearward and downward,mandibular and hyoid position may clockwise rotat.