严重骨性第Ⅲ类(近中(牙合))错(牙合)的病例,在早期发育阶段进行矫治是必需的。矫治的目的有二,第一靠矫治力改进骨骼的不平衡, 第二靠正牙的方法改善牙的排列并建立牙尖间关系。颏兜是一种最普通的矫治器,常用于乳牙期和混合牙列期拉下颌向后。虽然颏兜自十九世纪以来就被使用,其对下颌骨生长的 Severe bony Class III (occlusion) cases of occlusion, orthodontic treatment in the early stages of development is necessary. The purpose of orthodontic treatment is twofold. The first is to improve orthodontic skeletal imbalance and the second is orthodontic method to improve the arrangement of teeth and establish the relationship between the cusps. Chin is the most common orthodontic appliance, commonly used in deciduous teeth and mixed dentition jaws backwards. Although chinos have been used since the nineteenth century, its growth on the mandible