The deviation of the midline of the upper anterior teeth has a great influence on aesthetics. Generally, the deviation of 0-2mm is considered acceptable, and it needs to be corrected by orthodontics if it exceeds 2mm. The midline deviation of lower anterior teeth has little effect on aesthetics. If the teeth are arranged neatly and the occlusal relationship is good, only the midline of the lower anterior teeth is offset, orthodontic treatment may not be performed.