A hard white bump on the gums can be caused by alveolar bone growth, keratinization of the gum mucosa, periapical inflammation, gingivitis, and root residue. 1. Alveolar Bone Hyperplasia: Hyperplasia of the alveolar bone below the neck of the teeth can lead to hard white bumps on the gums. 2. Gingival mucosa keratinization: Due to repeated local friction or other reasons, stimulation may lead to keratinization and hardening of the gingival mucosa, which may also appear as hard white bumps on the gums. 3. Periapical periodontitis: Periapical periodontitis will form a localized abscess, which may be manifested as a hard white bump on the gums, followed by the formation of a pustule, accompanied by pain and other phenomena. 4. Dental root remnants: Adults with a recent history of tooth extraction can also experience the appearance of a hard white bump on the gums if there are dental roots left behind. There may be other causes of hard white bumps on the gums, so you need to go to the hospital in time for examination and treatment as prescribed by your doctor.