First, the stage of deciduous teeth: deciduous teeth appear irregular arrangement or inverted dentition, which should be corrected as soon as possible. The treatment age is about 3 ~ 6 years old. At this time, the child's permanent teeth have not erupted, and the root of deciduous teeth has not been absorbed and is relatively stable. It can be corrected by wearing an oral appliance.

Second, mixed dentition: at about 7 ~ 1 1 year old, new permanent teeth began to erupt, teeth grew rapidly, and occlusion was unstable, which was the frequent period of tooth deformity. While overcoming and changing bad habits, according to different situations, movable or fixed appliances can be used to correct dentition in different degrees, and even external forces can be used for plastic surgery.

Third, the permanent tooth stage: all the deciduous teeth have been replaced, and the second and third big teeth erupt into another rapid growth stage, generally around 12 ~ 18 years old. At this time, the diagnosis of tooth deformity is relatively clear, and in this rapid growth period, the speed is fast and the orthodontic effect is stable.