Tooth root pain after a tooth is knocked out may be caused by periodontal membrane tear resulting in tooth concussion, root fracture, crown-root joint fracture and so on. 1. Concussion: If the periodontal membrane is torn after a tooth is knocked and causes concussion, the root of the tooth is more sensitive, and the root of the tooth will be painful. 2. Root fracture: If the root of the tooth is fractured after the tooth is knocked, it will lead to root pain. 3. Crown-root fracture: If the crown-root fracture occurs after the tooth is knocked, it will also cause root pain. After the tooth is knocked, do not eat too hard food to avoid aggravating the pain, go to the hospital in time, take a tooth root film to determine the part of the root that is broken, and listen to the professional doctor’s advice before choosing to extract the tooth and other treatment measures.