In the process of orthodontics, the teeth that need to be extracted depend on many factors, such as the arrangement of teeth, the function of teeth, the purpose of orthodontics and so on. Here are some cases that may require tooth extraction:

1. Bad tooth: If the tooth is seriously damaged or infected and cannot be preserved by treatment, it needs to be extracted.

2. Extra teeth: If there are too many teeth, which leads to crowding or abnormal eruption, it may be necessary to pull out some teeth to improve the correction effect.

3. Teeth that affect orthodontics: If the position, angle or size of some teeth affect the implementation and effect of orthodontics, they may need to be removed.

4. Impacted wisdom teeth: If wisdom teeth are impacted or affect the position and health of other teeth, they may need to be removed.

When making a corrective plan, the doctor will conduct a comprehensive examination and evaluation according to the specific situation of the patient to determine the number and types of tooth extraction. Tooth extraction generally creates enough space for teeth to be arranged neatly, improves chewing function and maintains oral health. After tooth extraction, the doctor will carry out corrective treatment and adjust the position and arrangement of teeth to achieve the best corrective effect.