目的　通过Kloehn口外弓推磨牙向后与Edgwise矫治器联合应用 ,比较其颌面部硬组织的变化 ,以了解使用口外弓的最佳治疗时期。方法　 7～ 8岁组与 10～ 11岁组各 16例安氏Ⅱ1错牙合患儿 ,对治疗前后X线头影测量及模型测量分析比较。结果　发现替牙期组 (7～ 8岁 )上磨牙远移的距离大于恒牙期组 (10～ 11岁 ) ,上颌骨向前生长所受的抑制较恒牙期明显。结论　在替牙期选用口外弓的治疗效果较恒牙期为好。 Objective To study the changes of hard tissue in maxillofacial region by using Kloehn's extraoral arch molars and Edgwise appliance. Methods Sixteen children with Angle Ⅱ malocclusion in the age group of 7 to 8 years old and the age group of 10 to 11 years old were measured and compared before and after X-ray. The results showed that the distal molars in the dentate-replacement group (7-8 years old) were more distant than those in the permanent dentition group (10-11 years). The maxillary forward growth inhibition was more obvious than that in the permanent dentition. Conclusion It is better to choose the treatment of oral bow during the dentition than the permanent dentition.