A mouth ulcer (aphtha) is an ulcer that occurs on the mucous membrane of the oral cavity. Mouth ulcers are very common, occurring in association with many diseases and by many different mechanisms, but usually there is no serious underlying cause. Rarely, a mouth ulcer that does not heal may be a sign of oral cancer. These ulcers may form individually or multiple ulcers may appear at once (i.e., a "crop" of ulcers). Once formed, an ulcer may be maintained by inflammation and/or secondary infection. The two most common causes of oral ulceration are local trauma (e.g. rubbing from a sharp edge on a broken filling or braces, biting ones lip, etc.) and aphthous stomatitis ("canker sores"), a condition characterized by recurrent formation of oral ulcers for largely unknown reasons. Mouth ulcers often cause pain and discomfort and may alter the persons choice of food while healing occurs (e.g. avoiding acidic, sugary, salty or spicy foods and beverages). Definition
An ulcer (; from Latin ulcus, "ulcer, sore") is a break in the skin or mucous membrane with loss of surface tissue and the disintegration and necrosis of epithelial tissue. A mucosal ulcer is an ulcer which specifically occurs on a mucous membrane. An ulcer is a tissue defect which has penetrated the epithelial-connective tissue border, with its base at a deep level in the submucosa, or even within muscle or periosteum.
Other examples of systemic disease capable of causing mouth ulcers include lupus erythematosus, Sweet syndrome, reactive arthritis, Behçet syndrome, granulomatosis with polyangiitis, periarteritis nodosa, giant cell arteritis, diabetes, glucagonoma, sarcoidosis and periodic fever, aphthous stomatitis, pharyngitis and adenitis.The conditions eosinophilic ulcer and necrotizing sialometaplasia may present as oral ulceration. Macroglossia, an abnormally large tongue, can be associated with ulceration if the tongue protrudes constantly from the mouth. Caliber persistent artery describes a common vascular anomaly where a main arterial branch extends into superficial submucosal tissues without a reduction of diameter. This commonly occurs in elderly people on the lip and may be associated with ulceration. Treatment
Treatment is cause-related, but also symptomatic if the underlying cause is unknown or not correctable. It is also important to note that most ulcers will heal completely without any intervention. Treatment can range from:

Smoothing or removing a local cause of trauma
Addressing dry mouth
Substituting a problem medication or SLS-free toothpaste
Maintaining good oral hygiene and use of an antiseptic mouthwash or spray (e.g. chlorhexidine), which can prevent secondary infection and therefore hasten healing
A topical analgesic (e.g.