Type and variability of the stratum corneum in normal and diseased human oral stratified epithelia.

Strata cornea of normal human gingival and palatal epithelia and of metaplastic lesions (leukoplakia simplex) in the mucosa of the cheek and floor of the mouth were examined by light- and electronmicroscopy. The overall thickness of the stratum corneum, individual corneocyte thickness, number of corneocyte layers, and the type of keratin pattern expressed by individual corneocytes were determined. The data demonstrated that (1) the oral gingival and hard palate epithelia produce similar strata cornea with corneocytes ranging from 0.9 to 1.3 micron in thickness and displaying a high degree of conformity with respect to the keratin pattern, (2) the normal keratin pattern expressed in oral corneocytes differs from that reported for epidermal corneocytes, (3) under conditions of metaplastic keratosis, the strata cornea of lesions developing in the mucosa of the cheek and floor of the mouth are of variable thickness with 15 to 30 layers of corneocytes displaying either the oral or, more often, the epidermal keratin pattern. It is suggested that (1) the expression of a particular keratin pattern is independent of the presence or absence of nuclei and (2) the mechanism generating and alteration in cell differentiation from normal, non-keratinizing cheek epithelium to an epidermal one possibly operates through an intermediary step usually encountered as an expression of the oral keratin pattern of normal gingiva and hard palate.