At a workshop coordinated by the WHO Collaborating Centre for Oral Cancer and Precancer in the United Kingdom issues related to potentially malignant disorders of the oral cavity were discussed by an expert group. The consensus views of the Working Group are presented in a series of papers. In this report, we review the oral epithelial dysplasia classification systems. The three classification schemes [oral epithelial dysplasia scoring system, squamous intraepithelial neoplasia and Ljubljana classification] were presented and the Working Group recommended epithelial dysplasia grading for routine use. Although most oral pathologists possibly recognize and accept the criteria for grading epithelial dysplasia, firstly based on architectural features and then of cytology, there is great variability in their interpretation of the presence, degree and significance of the individual criteria. Several studies have shown great interexaminer and intraexaminer variability in the assessment of the presence or absence and the grade of oral epithelial dysplasia. The Working Group considered the two class classification (no⁄questionable⁄ mild -low risk; moderate or severe -implying high risk) and was of the view that reducing the number of choices from 3 to 2 may increase the likelihood of agreement between pathologists. The utility of this need to be tested in future studies. The variables that are likely to affect oral epithelial dysplasia scoring were discussed and are outlined here; these need to be researched in longitudinal studies to explore the biological significance of a low-risk or high-risk dysplasia.

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