[Oral leukoplakias. I. Classification, differential diagnosis, etiological conditions for neoplastic transformation,...

Leucoplakia is due to abnormal keratinization of squamous epithelial mucosa and constitutes a pattern of reaction of the oral mucosa which is typical for the tissue but unspecific for any stimulus. Because of its numerous causes leucoplakia cannot be defined as a pathologic entity. There is leucoplakia in the narrow sense and leucoplakia in the broad sense; the first should be regarded as a polyetiologic symptom but not as a disease in itself. Leucoplakias in the broad sense comprise those caused by well defined disorders. A classification of oral leucoplakias must include both categories, for differential diagnostic reasons. Therefore a classification of leucoplakias in the broad sense (hereditary 1., endogenous-irritative 1.) and leucoplakias in the narrow sense (exogenous-irritative 1., precancerous 1.) is proposed. The latter category is largely identical with the WHO definition of leucoplakia. The most important clinical and histological grounds on which this classification is based are explained. The precancerous lesions and the present knowledge of stomatology and oral pathology are particularly taken into consideration.