The presence of a fistula in the gum indicates that the corresponding tooth is suffering from chronic periapical periodontitis, which is caused by pulpitis that is not treated in a timely manner. The inflammation in the pulp cavity spreads down the apical foramen into the bone tissue of the apical region, causing inflammatory exudate or even pus to appear in the bone tissue, and correspondingly a fistula for drainage of pus appears in the gum area of the root tip, causing redness, swelling, pressure and pain in the gum area, and inflammatory polyps and fistulas appear. In this case, root canal treatment is performed to remove the infected pulp from the pulp chamber, remove and disinfect the root canal, remove the source of infection, and then tightly fill the root canal. After this series of treatments, the inflammation in the root will be metabolized and absorbed by the body itself, and the inflammatory sinus tracts in the gums will gradually disappear.