Hello, some patients' lips are tilted until they are slightly crowded due to bony protrusion. Tooth extraction is needed, so the core purpose of tooth extraction is to provide gaps for other teeth to arrange neatly and solve congestion. Patients with moderate and severe crowding often need a large gap to arrange their teeth neatly on the alveolar bone. In orthodontic tooth extraction, most teeth in premolar area are selected and pulled out symmetrically. First, premolars do not play an important role, and second, they are located in the middle of dental arch, which is convenient for the application between tooth extraction and before and after dental arch. Considering the stability of the quality and the balance of the patient's face, tooth extraction is an important means. The correct position and stable upper and lower occlusal relationship are easier to clean and the teeth are more easily affected. The overall correction effect is obvious. I hope it helps you.