Salient Features of the Oral Mucosa

Oral mucosa is composed of a stratified epithelial layer and underlying connective tissue. The structure of the oral mucosa and the connection of the epithelial layer to the underlying connective tissue are highly variable, depending on the intraoral region. The structural features of the different types of intraoral mucosa develop during the fetal period. Human gingival epithelium consists of up to 20 cell layers, measuring 200 to 300 mm in thickness. The epithelial layer is stratified into four layers: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. The cells of the stratum basale are characterized by high mitotic activity, and they maintain epithelial regeneration. The keratinocytes of the stratum spinosum undergo differentiation. The stratum granulosum contains only a few cells expressing hyaline granules. The keratinized stratum corneum is the outermost layer and is of variable thickness, depending on intraoral location. Nuclei of these keratinocytes show signs of pyknosis. Three types of keratinization are found in human oral epithelia: nonkeratinized buccal mucosa, parakeratinized gingiva, and orthokeratinized hard palate mucosa.