I. The molars phase (4-5 years old) This phase is mainly applicable to molars retrusion (geodontia), early correction is beneficial to the development of the maxilla and prevention of permanent teeth retrusion. If the child has bad habits (such as tongue extension, lip biting, etc.), they can also be corrected at this stage to prevent the occurrence of malocclusion. Secondly, the replacement stage is suitable for patients with functional and bony malocclusion in the early stage due to bad habits, tongue interference and other factors. If you find that your child has bad habits (such as lip biting, tongue extension, jaw extension, etc.), abnormal facial shape and abnormal tooth alignment, you should take your child to the orthodontist for examination and consultation in time to determine whether it is a dental, functional or bony malocclusion, and use it to determine the treatment time and treatment plan. Third, the permanent dentition stage Generally, common malocclusion can be well treated in this stage. In addition, individual serious malocclusion, such as “severe antimandibular” with family history, should be treated by orthognathic surgery after the age of 18 to achieve the desired effect.