The cause of periodontitis and mouth ulcers are distinguished from the following aspects: first, the cause, the cause of periodontitis is mainly the oral hygiene is not done properly caused by dental calculus, further stimulation to form gingivitis, gingivitis continues to develop to form periodontitis, of course, the cause of periodontitis also includes smoking, diabetes and so on. The cause of mouth ulcers is still not clear, for individuals, it may be a deficiency of trace elements, vitamin deficiencies, or changes in the body’s metabolic hormone levels, all of which may become the cause of mouth ulcers. Secondly, clinical characteristics, periodontitis is characterized by loosening of teeth, lack of power in biting, bleeding gums, destruction and resorption of alveolar bone, etc. The typical clinical feature of mouth ulcers is pain, which can occur in any part of the oral mucosa. Then, treatment for periodontitis is mainly cleaning, periodontal flap surgery, etc. The treatment of oral ulcers is merely symptomatic, promoting healing and relieving pain, and commonly involves topical medications applied topically. Finally, the prognosis, the prognosis of periodontal disease, the current means of treatment for periodontal disease can delay and reduce the onset of periodontal disease, etc. There is no better treatment to completely eradicate periodontal disease. Oral ulcers, too, do not have a complete cure, but the characteristics of oral ulcers tend to be self-limiting, with cycles healing on their own in about 10 days, while there is a possibility that they may flare up again after a while.