The common causes of crooked incisors in eight-year-old children are genetic factors, obstacles to the replacement of permanent milk teeth, and bad habits. 1. Genetic factors: the child’s mother and father or immediate family members have crooked teeth, then the child’s incisors crooked chances are greater. 2. Constant milk teeth alternation obstacle: before the permanent teeth eruption is usually in the root of the milk teeth below, if the child’s milk teeth have not yet fallen off, but the permanent teeth have grown out, or milk teeth off half a year later, the permanent teeth are not yet grown out, the teeth next to the lost milk teeth tilted, occupying the position of the lost teeth, both of which will result in the replacement of the incisors long crooked situation. 3. Bad habits: children often suck their fingers, lick their teeth, bite their lips, open their mouths to breathe and other habits during tooth replacement, can cause the phenomenon of crooked replacement incisors. It is recommended that parents usually supervise children to change bad habits, the phenomenon of milk teeth stagnation or milk teeth fall off, permanent teeth are slow to grow out, to go to the hospital in time for dental consultation, so as not to change the teeth when the symptoms of permanent teeth grow crooked.