If a patient has a painful swelling behind the last tooth, it is recommended that the cause of the disease be clarified first and then targeted treatment be carried out separately to achieve better results. The common reasons that may cause the patient to have swelling and pain behind the last tooth are wisdom tooth pericoronitis, gingivitis, pulpitis, mouth ulcers, etc. 1, wisdom tooth pericoronitis: If the patient grows a wisdom tooth after the last tooth, wisdom tooth pericoronitis may occur. Patients are advised to undergo anti-inflammatory and anti-swelling treatment first, such as taking metronidazole and other drugs under the guidance of a doctor, and if there is purulent material the abscess can be cut open for treatment. After the inflammation is eliminated, it is recommended that the patient consider removing the wisdom tooth to avoid recurrent inflammatory reactions; 2. Gingivitis: If the patient has gingivitis at the last tooth because of improper oral hygiene care, the bacteria remaining at the tooth causes the patient to have gingivitis, and there may also be swelling and pain in the meat behind the last tooth, it is recommended that the patient undergoes scaling treatment to reduce the bacterial residue at the gum and improve the swelling and pain symptoms; 3. Pulpitis. If the patient has caries at the last tooth, it may invade the internal nerve of the tooth for a long time, thus causing the patient to have pulpitis, which may lead to the swelling and pain of the flesh behind the last tooth. Patients are suggested to undergo root canal treatment under doctor’s guidance, remove the pulp under local anesthesia, and then carry out root canal filling treatment after the inflammation recovers; 4, oral ulcer: If oral ulcer appears at the gum of the last tooth of the patient, it may lead to the flesh pain at the last tooth. Patients are advised to use watermelon cream spray, ice borax and other medications sprayed on the mouth ulcers as prescribed by the doctor to relieve the painful symptoms. Patients can also consider using ice packs and pressing local acupuncture points to relieve swelling and pain. If patients feel more intense pain, they can also use non-steroidal anti-inflammatory drugs, such as ibuprofen, to relieve pain under the guidance of a doctor. Patients are advised to maintain oral hygiene and adhere to timely brushing or rinsing in the morning and after meals to reduce bacteria or food residue residue and reduce the occurrence of oral diseases.