When the back of the last large tooth swells up and is very painful, you first need to determine whether the last large tooth is a second molar or a wisdom tooth. If it is the second molar that is swollen and painful, it may be due to gingivitis, periodontitis, or pulpitis. If the patient is not a lesion of the second molar, it may also be related to wisdom tooth pericoronitis or periodontal local tissue tumor. Common causes and treatments 1, gingivitis: the last big tooth behind the swelling very painful, and accompanied by bleeding symptoms when brushing or chewing patients, generally considered related to gingivitis, acute episodes of patients can use saline or hydrogen peroxide rinse the mouth to relieve symptoms, after the condition is stable, patients can go to the hospital for scaling treatment to remove the causes that induce the onset of gingivitis; 2, periodontitis: the last big tooth behind the swelling very painful, and accompanied by bleeding symptoms when brushing or chewing. The patient who has formed an abscess can go to the hospital for incision and drainage treatment, and at the same time can cooperate with metronidazole, tinidazole and other drugs to promote the elimination of inflammation and prevent the recurrence of the disease; 3, pulpitis: the patient feels that the second molar swells up very painful, and has involved the ipsilateral head and face with pain, usually due to The patient may consider removing the gum tissue to relieve the symptoms; 4, wisdom tooth pericoronitis: wisdom tooth is also called the third molar, wisdom tooth dysplasia or local bacterial infection, resulting in the onset of wisdom tooth pericoronitis, generally will also appear behind the last big tooth swelling very painful symptoms, the patient can first use ice water rinse mouth, ice towel local cold compress to relieve pain, to be stable after the consideration to the 5, tumor: when there is a protrusion in the posterior area of the molar and accompanied by pain, it may also be related to tumor, at this time the patient should immediately go to the hospital for a clear diagnosis, and then for related treatment. Patients should maintain good oral hygiene and use mouthwash or light salt water after eating to avoid the accumulation of food residues and prevent the re-occurrence of the disease.