The causes of difficulty in opening mouth after tooth extraction are as follows: 1. If the patient’s teeth are difficult to be extracted, such as wisdom teeth and buried multifocal teeth, it can cause serious swelling in the extraction area, which can lead to functional limitation of the nearby muscles or masticatory muscles, thus leading to difficulty in opening mouth. Patients can apply ice after surgery, and the symptoms will gradually subside and return to normal after 2-3 days; 2. When the lower alveolar nerve block anesthesia, the anesthetic drug penetrates into the masticatory muscle and causes the masticatory muscle to stay in the contraction period, and causes the patient’s masticatory muscle to be unable to recover the chewing ability in the short term, and the recovery period is usually 1-2 weeks; 3. It is necessary to review the patient as soon as possible and treat accordingly.