Cellular and molecular basis of barrier function in oral epithelium.

The use of the oral mucosa for drug delivery and the erroneous belief that it is a nonkeratinized tissue have given rise to the suggestion that the oral mucosa is a permeable tissue. Such an assumption is not supported by studies which indicate that permeability differs significantly in different oral regions, depending on the pattern of epithelial differentiation. Keratinized regions such as hard palate and gingiva have a permeability which is significantly less than nonkeratinized regions like buccal mucosa and floor of mouth. Nevertheless, all oral regions are more permeable than skin. Associated with these differences in permeability are differences in the type and amount of intercellular lipid; areas of keratinized tissue contain predominantly neutral lipids (ceramides) apparently derived from lamellate membrane-coating granules. In nonkeratinized areas, the lipids consist of as yet uncharacterized glycosyl ceramides that appear to be derived from membrane-coating granules that differ morphologically from those present in nonkeratinized tissue.