Aphthous ulcer (Canker sores)Aphathous ulcers are small ulcer craters in the lining of mouth that are frequently painful and sensitive. Exact etiology is not known; it may be autoimmune process, nutritional deficiency (vitamin B1„ folic acid, iron), viral or bacterial infection, food allergies or due to hormonal changes or stress. Aphathous ulcers typically starts in childhood or adolescence., Characterized by recurrent, small, round or oval ulcers with circumscribed margins, erythematous haloes, and yellow or gray floor. They resolved spontanously in third decade. The lesiosn may be single or multiple and usually involve movable mucosa, i.e., inner surface of lips, buccal mucosa, tongue, floor of mouth and soft palate, while sparing mucosa of hard palate and gingivae.​Treatment :  - If lesions do not resolve spontaneously, topical steroid and cauterization of base with 10% silver nitrate can be tried. In severe cases tetracycline mouth rinse can be given. For pain lignocaine viscous may be used.