I. Mastodontic stage (4-5 years old) This stage is mainly applicable to the antipodontia of milk teeth (periosteum), and early orthodontic treatment is beneficial to the development of maxillary bone and the prevention of the antipodontia of permanent teeth. If the child has bad habits (such as tongue stretching, lip biting, etc.), it can also be corrected at this stage to prevent the occurrence of malocclusion. Second, replacement teeth stage (girls: 8-10 years old, boys: 9-12 years old) Applicable to functional malocclusion and bony malocclusion caused by bad habits, tongue interference and other factors in early patients. If you find that your child has bad habits (e.g. lip biting, tongue protrusion, jaw protrusion, etc.), abnormal facial shape and abnormal tooth alignment during the replacement stage, you should bring your child to the hospital in time to find an orthodontist for examination and consultation. Because this stage is the pre-puberty and peak of growth and development of children, if your child is functional or bony malocclusion, then the treatment at this stage can make full use of the growth potential of the jawbone, by promoting or inhibiting the growth of the jawbone to achieve the therapeutic purpose, and improve the child’s facial shape and function is more favorable. Early permanent teeth stage (girls: 11-14 years old, boys: 13-16 years old) Common malocclusion can be well treated at this stage. At this time, most of the permanent teeth in the oral cavity have erupted, the dental arch development has been basically completed, dental malocclusion has been basically stereotyped; and this age stage of the child’s maxillofacial development is still in the rapid growth period, orthodontic to a large extent need to take advantage of the potential of maxillofacial growth and development, so that the teeth to move and alveolar remodeling to the optimal level.