A hard lump in the lower jaw of the mouth may be an inflammation of the gums, mostly related to the usual bad hygiene habits, perhaps not brushing and rinsing on time or the usual incorrect posture of brushing, not being able to clean the teeth thoroughly. It may also be due to improper choice of toothbrush or too short brushing time, resulting in food residues in the mouth, food residues, soft scale in the mouth breeding bacteria, causing oral inflammation, soft scale will also calcify to form harder calculus, calculus will stimulate the gums cause gum redness and swelling. It is recommended to go to the hospital to remove dental calculus and plaque in the mouth, and usually to develop good hygiene habits to maintain oral hygiene. A hard bump on the lower jaw of the mouth may also be a mouth ulcer, which will heal on its own in a week or so.