It is possible to extract 4 teeth at a time. There is no strict requirement for the number of teeth to be extracted at a time in dental clinical work, especially for patients with severe periodontal disease, where most of the teeth in the whole mouth are II-III degree loose. In this case, sometimes more than 10 teeth can be extracted together, which is also encountered clinically, but generally most of the orthodontic extractions are for 4 teeth. The orthodontic extraction is usually done for the first premolar, and there are 4 first premolars on the left and right. The general plan is to remove the 2 teeth on the left side of the upper and lower jaw, and then remove the first premolar on the right side after 1-2 weeks, mainly for the convenience of chewing.