The timing of orthodontic treatment is very important, too early orthodontic treatment will lead to too long a course of treatment or secondary treatment due to orthodontic failure, too late orthodontic treatment will miss the timing of treatment and lead to some malformations can not be corrected. Nowadays, it is generally believed that simple mild to moderate dental crowding and tooth protrusion, generally in the second molar alliance after a comprehensive analysis of the deformity before orthodontic treatment; the earlier the treatment is not the better for patients in the growth and development period or teeth replacement, should strictly grasp the indications, affecting the growth and development or function, bad habits and periodontal disorders that cause malocclusion should be treated early, for example, the ground, small jaw, mouth For example, if you have bad habits, such as bunions, small jaws, mouth breathing, tongue spitting habits, etc., you need to wear functional or movable braces to improve the facial shape, and then wear fixed braces to correct the teeth after the second molar has come out.