There are many factors that affect whether or not to extract a tooth, whether the mouth and lips are protruding forward, the degree of crowding of the teeth, the occlusal relationship of the molars, the depth of the bite of the anterior teeth, and the degree of lip inclination of the anterior teeth. The purpose of tooth extraction is mainly three-fold: first, to align misaligned teeth need clearance, and in case of severe crowding, the number of teeth needs to be reduced so that the teeth are aligned; second, to improve the patient’s facial shape, such as buck teeth patients, they need to be corrected by tooth extraction; third, to adjust the bite relationship, poor bite of teeth sometimes also need to be corrected by tooth extraction. The doctor needs to do a lot of, preparatory work before deciding whether to extract teeth for orthodontic treatment, which requires measuring x-rays to calculate the ratio of bone tissue, soft tissue, measuring models, etc. If it is necessary to extract a tooth the most common is the extraction of the first premolar behind the tiger tooth.