Orthodontics can be divided into the following age groups: 1, milk teeth period: small children about 3-5 years old, 4 years old or so is the best, the child is a little older to cooperate with the treatment. Milk teeth are not yet replaced when the orthodontic appliances are also more able to play a better role; 2, replacement teeth: replacement teeth in the period of 10-12 years old is better, at this time the growth and development of small children faster, there are some bony deformities to be done earlier, but also can be pushed to the age of 8-9 years old earlier; 3, early permanent teeth: boys are generally 12-14 years old, the girls a little bit earlier in the age of 11-13 years old. Around the age of 12, all the permanent teeth grow out, and the body also develops faster, adding orthodontic treatment in this process can achieve twice the result with half the effort.