A loss of mucous substance of the mouth showing local excavation of the surface, resulting from the sloughing of inflammatory necrotic tissue. It is the result of a variety of causes, e.g., denture irritation, aphthous stomatitis (stomatitis, aphthous); noma; necrotizing gingivitis (gingivitis, necrotizing ulcerative); toothbrushing; and various irritants. (From Jablonski, dictionary of dentistry, 1992, p842)