A hard lump in the mouth may be caused by gingivitis, apical inflammation and other diseases, patients should consult a doctor in a timely manner to clarify the cause of the disease and then carry out the appropriate treatment. 1. Gingivitis: non-specific inflammation of the gum tissue caused by plaque on the surface of the teeth, occurring in the free gums and gingival papillae, the patient will have localized hard lumps in the mouth, and some of the people will also be accompanied by localized itching and swelling of the gums, pain, halitosis, chlorhexidine gargle under the guidance of a doctor can be used for treatment. 2. Apical inflammation: Inflammatory diseases occurring in the tissues around the root tip of the tooth, patients may feel localized hard lumps at first, and then may be accompanied by pain, biting pain, bad breath and other symptoms, such people should be removed from the local irritants, under the guidance of the doctor for appropriate treatment.