Abstract: Objective To analyze the clinical effect of modified muscle activator in improving up per airway in adolescents with skeletal Class II mandibular retrusion. 
Methods A total of 60 adolescents with skeletal class Ⅱ mandibular retrusion admitted to our hospital were selected as the research subjects, and randomly divided into research group(n=30) and control group(n=30) by random number table method. The control group was treated with TWIN-BLOCK(TB), and the research group was treated with modified muscle activator. The changes in upper airway in both groups were compared. 
Results After treatment, SHP, STE and SMIN in the research group were greater than those before treatment, while ST and SMIN in the control group were greater than those before treatment(P＜0.05). LHP, LSP, LTE, APHP, APSP and APTE in the research group were greater than those before treatment(P＜0.05), and LSP in the research group was greater than that in the control group(P＜0.05). AHI in the research group was lower than that before treatment, while lowest oxygen saturation（LSaO2） was higher than that before treatment; AHI was lower than that in the control group, while LSaO2 was higher than that in the control group(P＜0.05). 
Conclusion The volume of upper airway in adolescents with skeletal Class Ⅱ mandibular retrusion treated with modified muscle activator is significantly increased, the inner diameter and cross-sectional area are enlarged, and the ventilation condition of upper airway as well as indicatorsof OSAS is improved. CBCT was used for clinical analysis, so as to provide data support for making the optimal surgical plan, ameliorating the problems of patients′ upper airway, evaluating the morphology and mechanism of upper airway, and making personalized treatment plan.

Key words: maxillofacial abnormalities, modified muscle activator, adolescent skeletal class Ⅱ