A hard lump on the inside of the gums may be caused by gingival hyperplasia, gingival cyst, jawbone cyst, bone augmentation, and so on. 1. Gingival hyperplasia: an infectious disease of the gum tissue caused by plaque biofilm, which can lead to an increase in the volume of the gums due to an increase in the cellular composition of the gum tissue, which can be mistaken for a hard lump. 2. Gingival cysts: when they are not obvious in the early stages, they may not be felt in the mouth, and when the ball is larger, a hard lump can be felt. 3. Jaw bone cyst: Jaw bone cyst grows in the jaw bone and gradually grows out of the surface of the alveolar bone, which can be manifested as a hard lump on the inside of the gums. 4. Bone protrusion: the elevation of normal bony structures, often occurring on the lingual side of the mandibular premolar teeth. It is recommended that those who have a hard lump on the inner side of the gums go to the regular hospital in time to clarify the cause, and if treatment is needed, standardize the treatment under the guidance of the doctor to avoid delaying the condition.