The surface structure of the completely and incompletely orthokeratinized oral epithelium in the rat: a light, scanning and transmission electron microscope study.

Mucosa from the hard and soft palates, molar gingiva, cheek and dorsal surface of the tongue of the rat was examined in the light microscope, following Mallory's triple connective tissue stain, and in the scanning and transmission electron microscopes. The epithelium covering the hard palate, gingiva, the smooth band of mucosa at the junction of the hard and soft palates, intermediate zones of the soft palate, fungiform papilla-like structures in the central zone of the soft palate, the fungiform papillae, and the more superficial part and posterior surfaces of the filiform papillae of the tongue all exhibited complete orthokeratinization. The oral surfaces of the epithelial cells in all these areas had a honeycomb pattern of interconnecting ridges surrounding depressions. Imprints of the overlying cells that had been desquamated were apparent, and the lateral boundaries between the cells were formed by two raised ridges separated by a gap. The epithelium covering the cheek, central zone of the soft palate apart from the fungiform papilla-like structures, lateral zones of the soft palate, gingival crevice, and the mucosa between the fungiform and filiform papillae of the tongue all exhibited incomplete orthokeratinization. The oral surfaces of the epithelial cells in all these areas were relatively smooth and did not exhibit a honeycomb pattern of interconnecting ridges. Imprints of the overlying cells that had been desquamated and the lateral boundaries between the cells were only very occasionally found. In the transmission electron microscope the outlines of the cells were compatible with the surface patterns seen in the scanning electron microscope. The possible relationships between the degree of orthokeratinization and ultrastructure of the various epithelia are discussed.