More than half of all orthodontic patients require extractions. The purpose of extractions is to: (1) align crowded teeth using the extraction space. Patients with II-III degree of crowding are more likely to have their teeth extracted. (2) To use the space between extractions to align the anterior teeth, improve the arch protrusion, and improve the facial shape. For example, some people have protruding lips, but after extraction, the protrusion of lips will be reduced and the facial shape will become more beautiful. (3) Use the extraction gap to adjust the occlusal relationship of the posterior teeth, so that the cusps and sockets of the posterior teeth are staggered and the occlusal contact area is maximized to achieve the best chewing efficiency.