There are many reasons why teeth are crooked, such as retained milk teeth, abnormal eruption of permanent teeth, bad habits, etc. Corrective methods include extraction of retained milk teeth, orthodontic correction, and improvement of bad habits. 1. Retained milk teeth: If the permanent teeth grow out before the milk teeth fall off, the permanent teeth will grow crooked easily due to the obstruction. Therefore, it is possible to correct the crooked permanent teeth by pulling out the unerupted milk teeth. 2. Abnormal eruption of permanent teeth: such as ectopic eruption of permanent teeth, abnormal order of eruption of permanent teeth, etc., which can be corrected by orthodontic methods. 3. Bad habits: such as the correction of finger-sucking habits, the correction methods include movable braces (such as maxillary movable braces with tongue spurs, vestibular shields), fixed braces, etc., through the auxiliary appliances to help young children to improve their bad habits. If the above situation occurs, it is recommended to go to the hospital stomatology department and take the correct correction method under the doctor’s guidance.