1. Occlusal period of deciduous teeth: When malocclusion or malocclusion (partial occlusion) of deciduous teeth occurs, it should be corrected as soon as possible. The best age of treatment is 4 ~ 6 years old, and the course of treatment is about 6 months.
2. Mixed (replacement) occlusal period: It begins at the age of 6- 12, when new permanent teeth begin to erupt, teeth grow rapidly, and occlusion is unstable, which is the frequent period of tooth deformity.
3. Occlusal period of permanent teeth: all deciduous teeth have been replaced, and the second and third big teeth erupt into another rapid growth period, generally around 12 ~ 18 years old. At this time, the diagnosis of tooth deformity is clear, and the correction speed is fast and the correction effect is stable in the rapid growth period.