Swollen and painful gums are mostly caused by gum disease or periodontitis, and systemic diseases such as leukemia and diabetes can also trigger swollen and painful gums. Gum disease and periodontitis are in turn caused by poor oral hygiene of the patient and plaque accumulation resulting in local gum inflammation and swelling and pain.
The specific cause suggests that the patient consult the stomatology department and do relevant examinations to confirm the cause.