There are many reasons for swollen gums on one side, such as periodontitis, periapical periodontitis, tumors and so on. 1. Periodontitis: For example, gingivitis, wisdom tooth pericoronitis, apical inflammation and other diseases, due to inflammation stimulation will cause gum swelling, pain, will lead to one side of the gums swollen symptoms. 2. Periapical periodontitis: teeth caries, bacterial erosion will lead to inflammation of the dental pulp, resulting in pulpitis, pulpitis further development will lead to periapical periodontitis, periapical periodontitis abscess from the gums breakthrough will also be manifested as one side of the gums swollen. 3. Tumors: For example, tumors in the mouth, gums, or around the alveolar bone or jawbone can also cause swelling of one side of the gums. One side of the swollen gums, there may be other reasons, you need to go to the regular hospital in a timely manner to check, clarify the cause of the disease, early detection and early treatment.