There are large individual differences in dental development due to genetic or environmental influences. The ideal time for orthodontic treatment is around 11 or 12 years old (all the milk teeth before the first permanent molar are replaced), but some people have early tooth replacement and may lose all their milk teeth at the age of 10, while some people lag behind in the rapid growth of adolescence and may have milk teeth remaining at the age of 14 or 15, so there will be a difference of three or four years between the two types of patients to start treatment. From the point of view of the characteristics of dental, jaw and facial development, the anterior teeth of children with “backbite” malocclusion during the period of milk teeth, commonly known as “envelope”, can be effectively controlled within three to five months if detected early, using simple orthodontic appliances during the period of milk teeth; after the period of teeth replacement, the growth of the facial The lower third of the face grows slightly later than the middle and upper parts of the face after the period of dentition, so for children with underdeveloped lower jaw, functional orthopedic treatment (usually implemented around 8-10 years old) can improve and interrupt the development of facial skeletal deformities. For this type of jaw developmental deformity if treatment is delayed until after the age of 12, the effect of facial orthopedics will be greatly reduced. In cases of severe jaw deformities due to heredity, such as a “giant jaw” or a small jaw with a bird’s beak, orthodontic treatment alone cannot solve the underlying problem, and these patients need orthognathic surgery at the age of 18. Orthognathic surgery can completely change the patient’s skeletal deformity and restore a more perfect appearance, but in order to ensure that the patient can still have an ideal bite relationship after surgery, a matching pre- and post-operative orthodontic treatment must be performed before and after the surgery. Pre-operative orthodontics aligns the teeth, coordinates the shape and width of the upper and lower dental arches, and facilitates the adjustment of the upper and lower jaws during surgery; post-operative orthodontics then performs fine adjustment of the occlusal relationship, so that the morphology and function of the dental and jaw system can be improved simultaneously.