[Comparing study on the hyoid bone position after treatment of class Ⅲ malocclusion using improved appliance FR Ⅲ].

OBJECTIVE: This study aims to compare the changes of hyoid bone position before and after treatment of Angle class Ⅲ malocclusion using improved appliance FR Ⅲ. METHODS: Forty patients with Angle class Ⅲ malocclusion were chosen and divided into two groups, namely, experimental and control. Each group had 20 patients. The young patients in the experi-mental group were treated using improved appliance FR Ⅲ, whereas those in the control group were treated using classic appliance FR Ⅲ. The hyoid bone position of the two groups were comparatively analyzed using an X-ray film before and after treatment. RESULTS: Compared with the condition before treatment, the condition after treatment showed that the hyoid bone position of young patients with Angle class Ⅲ malocclusion treated using improved appliance FR Ⅲ, H-FH, H-S, H-Ptm, and Ar-H-Me exhibited an increased angle (P<0.01), whereas the hyoid bone position of those treated using H-MP and H-Gn showed a decreased angle (P<0.01). The hyoid bone position of young patients with Angle class Ⅲ malocclusion treated using classic appliance FR Ⅲ, H-FH, H-S, and H-Ptm had an increased angle (P<0.05). Moreover, the hyoid bone position of those treated using Ar-H-Me had an increased angle (P<0.01), and the hyoid bone position of those treated using H-MP and H-RGn had a decreased angle (P<0.05). CONCLUSIONS: Compared with the hyoid bone position before treatment, the hyoid bone position after treatment of the young patients with Angle class Ⅲ malocclusion treated using improved appliance FR Ⅲ may move backward and downward, and the mandibular and hyoid bone position may move through clockwise rotation. The mandibular and hyoid bone position of young patients with Angle class Ⅲ malocclusion treated using classic appliance FR Ⅲ obtained a large angle by moving clockwise. The man-dibular bone moves backward and downward, thereby improving the hyoid bone in backward and upward directions. This condition makes a significant difference in treating the hyoid bone position of young patients with functional Angle class Ⅲ malocclusion. .