In the period of teething (3 to 5 years old) and the period of replacement teeth (6 to 11 years old), general malocclusion such as individual teeth misalignment does not require immediate orthodontic treatment, should continue to observe and correct oral malocclusion habits, because in this period, the teeth and jaws are in the adjustment period, with the correction of bad habits, malocclusion can often be partially self-corrected, but for serious obstruction of growth and development of malocclusion, it is necessary to carry out a phase of orthodontic treatment, such as milk teeth retrusion, which will hinder the development of the upper jaw and affect the appearance of the face, should be treated early. If the child can cooperate, it can be corrected at the age of 3 to 5 years. Another example is severe jaw recession, early orthodontic treatment can be carried out during the teething period (7 to 10 years old) to stop its development to the serious, but also to reduce the difficulty of continuing to correct later. Most malocclusions are not corrected until the permanent period when teeth are replaced, about 12 to 14 years old. At this time, the permanent tooth roots are gradually developed and the occlusal relationship between the upper and lower teeth is adjusted, so that a clear diagnosis of the type of malocclusion can be made and the corresponding orthodontic treatment can be adopted. After the completion of orthodontic treatment, it is easy to maintain a stable effect and there will be no further major changes. Theoretically, the best age for orthodontic treatment of malocclusion in children is during the growth spurt of children. Boys are between 12 and 14 years old and girls are between 11 and 13 years old. However, there are individual differences in the growth and development of each child, and no generalizations can be made. The correct way to estimate the growth spurt is through certain tests. Such as taking wrist X-rays, continuous height measurements, knowing the first menstrual period of women, and paying attention to children’s shoes, socks, clothing and hats. Orthodontic treatment during this period is short and effective. If you miss the early stage of permanent teeth, such as to 15 to 17 years old, still in the adolescent period, growth and development is still relatively active, although the difficulty increases slightly, but the orthodontic effect is also better. If after the age of 18, into adulthood, growth and development is basically completed, orthodontic speed effect is not as good as childhood and adolescence, but the development of modern orthodontic technology so that adult orthodontics is not an obstacle. For severe bony malocclusion, the orthodontic treatment cannot be completed simply by orthodontic methods, but must wait until the adult period after 18 years old with surgery to treat.