When children are suitable for orthodontics, with the following specific circumstances: First, when the milk teeth occur anti (teeth together), it is best to wear movable orthodontic appliances at the age of 2-3 years old, to promote the upper front teeth lip to move, expand the width of the dental arch, inhibit the lower jaw forward. Second, if the child has bad habits such as tongue spitting and finger sucking, functional orthodontic appliances can be worn at the age of 3-4 to break bad habits so as not to affect the development of the upper and lower jaws. Third, the permanent teeth cleft occurs when tooth crowding, double (teeth together) protrusion, etc., can be fixed or invisible orthodontic treatment after the replacement of permanent teeth. Generally choose girls aged 11-13 years old, or boys around 12-14 years old, this period is the best orthodontic period, the child into the burst of growth and development, to achieve rapid movement of teeth and alveolar bone growth changes, to achieve good orthodontic effect.