Wisdom teeth, gingival hyperplasia, periodontitis, chronic periapical inflammation and other causes may be a lump on top of the big teeth inside the mouth. 1. Wisdom teeth: Wisdom teeth are the third molar in the mouth, the process of growing out may be swollen gums, a lump on the top of the big teeth inside the mouth, is a normal physiological phenomenon. 2. Gingival hyperplasia: If there is misalignment and crowding of teeth, food inclusions and other undesirable factors, may lead to plaque accumulation, triggering gingivitis, under the stimulation of inflammation, granulation may occur, resulting in a lump on the top of the big teeth in the mouth. 3. Periodontitis: Periodontitis is a chronic inflammation that occurs in the periodontal tissues, which may be related to tartar, plaque, food impaction, etc., and may appear as a lump on the top of the big teeth inside the mouth, accompanied by redness and swelling of the gums, tooth loosening and other symptoms. 4. Chronic periapical inflammation: occurs around the root of the tooth, is due to infection and physical stimulation, etc., can be manifested as a fistula in the mouth above the big teeth, accompanied by oral odor and other symptoms. When there is a pimple on the inside of the mouth above the big teeth, the patient should immediately go to the hospital, relevant examination, clear cause and active treatment.