Gums that have undergone root canal treatment may have a bag because of imperfect root canal treatment, incomplete root canal treatment, and root fissure. 1. Incomplete root canal treatment: Usually, patients need to carry out anti-inflammatory treatment on the tooth during root canal treatment. If the inflammation at the root tip is not completely eliminated when the root canal treatment is carried out, the inflammation may spread to the root tip, and the inflammation will further develop, resulting in the formation of an abscess on the gums. 2. Incomplete root canal treatment: If the patient does not go to the follow-up appointment for a long time after the pulp drainage or root canal preparation, the inflammation may spread to the periapical tissues due to the root canal not being completely closed, resulting in the formation of abscesses in the gums. 3. Concealed fracture of the root: after root canal treatment, the tooth lacks nutrient supply, the tooth body becomes brittle, and eating harder food can cause trauma to the root of the tooth and cause concealed fracture, which stimulates the periapical tissues to form periapical periodontitis, resulting in the emergence of pus in the gums. Therefore, if the patient after root canal treatment gums up a bag, should go to the hospital in time to check, clarify the cause of the disease, for treatment.