The swelling of the posterior sulcus can be caused by the following reasons: 1. Pericoronitis of the wisdom tooth: it occurs in patients aged 18-35 years old and is caused by the redness and swelling of the surrounding gums due to food embedding during the eruption of the wisdom tooth. First of all, the food residue around the wisdom tooth should be cleaned, and then given anti-inflammatory treatment, after the inflammation subsides, the doctor will decide whether to extract; 2, periodontitis: the prevalence of patients aged 35-60 years, is due to the formation of food embedding or calculus around the teeth resulting in gum redness and swelling. The calculus or food debris around the teeth should be removed, together with the use of anti-inflammatory drugs. If the patient has combined diabetes, extra attention should be paid to oral hygiene and strict monitoring of blood glucose levels to facilitate the recovery of periodontal disease.