Oral mucosal ulcerations are common. Most are self-resolving and transient (e.g., after a simple cheek bite). However, some may require the intervention of a medical or dental practitioner. For example, the serious and potentially life-threatening condition oral carcinoma often initially manifests as a solitary oral mucosal ulceration. The diagnosis of the more common oral ulcerations, in an otherwise healthy patient, is straightforward and determined from the medical history and clinical examination. However, patients with impaired immunological function (e.g., HIV, chemotherapy, malnutrition) may present with more severe, widespread, atypical presentations that require a comprehensive assessment.
Most of the mucosa lining the oral cavity (e.g., floor of the mouth, cheeks, ventral tongue) is thin and delicate, rendering it susceptible to trauma. By contrast, the mucosa of the hard palate and gingiva is keratinised and more resistant to injury. The biologically dynamic nature of the oral mucosa makes it vulnerable to the effects of systemic disease. 
An oral ulcer or ulceration is characterised by the complete loss of epithelium accompanied by variable loss of the underlying connective tissue, which results in a crateriform appearance. It may be augmented by oedema and/or proliferation of the surrounding tissue. 
Ulcers that do not heal within 2 weeks may be considered persistent or chronic. A classification system based on distinguishing whether the ulceration is simple, complex, or destroying has been suggested. 
Simple: a single ulcer without the involvement of the remaining mucosa.
Complex: a single or multiple ulcers with changes to the surrounding mucosa, skin, and/or systemic manifestations. The lesion may be white, red, or vesiculobullous.
Destroying: diffuse lesion with tissue destruction and severe systemic involvement.
Oral ulcerations are common, but most occurrences go unreported because they tend to resolve within a few days without the need for medical or dental intervention. Of those ulcerations that are reported, the most common is recurrent aphthous stomatitis, which affects 5% to 25% of the general population. 
Oral Medicine Subject Expert
Department of Comprehensive Dentistry
UTHSCSA School of Dentistry
MAH is an author and co-author of a number of references cited in this monograph. He lectures extensively on oral medicine-related topics. MAH has been reimbursed by Met Life for the development of web-based continuing education courses. He has been reimbursed for speaking at local, state, and national dental meetings.
Oral Medicine and Special Needs Dentistry Unit
Division of Maxillofacial Diagnostic, Medical and Surgical Sciences
UCL Eastman Dental Institute
Professor of Oral Medicine
University of London
SP declares that he has no competing interests.
Oral Medicine Attending & Associate Surgeon
Division of Oral Medicine and Dentistry
Brigham and Women's Hospital
Department of Oral Medicine, Infection and Immunity
Harvard School of Dental Medicine
NT declares that he has no competing interests.
Division of Oral Pathology
College of Dental Medicine
Medical University of South Carolina
AC declares that she has no competing interests.
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