The best age for orthodontic treatment includes the following stages: 1, around 4.5 years old, at this stage, if there is a milk tooth retrusion, intervention can be made by simple orthodontic treatment or functional orthodontic treatment; 2, 8-10 years old, at this stage, the root development of permanent teeth is basically completed, and local intervention can be made for simple dental factors caused by encrustation; mild bony factors caused by encrustation can be intervened by functional orthodontic appliances; 3, after tooth replacement, that is, the early stage of permanent teeth; 4, severe bony encrustation requires combined orthodontic-surgical treatment after 18 years old.