Orthodontic treatment is mainly to adjust the coordination of facial bones, nerves and muscles in the oral and maxillofacial region through various orthodontic devices, that is, to adjust the abnormal relations between the upper and lower jaws, between the upper and lower teeth, between the teeth and the jaws, and between the nerves and muscles connecting them, and its ultimate goal is to realize the balance, stability and beauty of the oral and maxillofacial system. The correction of deformity mainly depends on wearing an appliance inside or outside the mouth and applying appropriate "biological force" to teeth, alveolar bone and jaw to make them produce physiological movements, thus correcting deformity.