The lining of the oral cavity is referred to as oral mucosa or oral mucous membrane. It is a stratified squamous epithelial arrangement that runs from the margins of the lips posteriorly to the area of the tonsils. Although this same epithelium is found posterior to this point, there it is part of the oral pharynx and not the oral cavity. Behind the tonsils and in the posterior throat wall it would be referred to as pharyngeal mucosa. Oral mucous membrane is divided into three categories:
Mucous membrane is composed of stratified squamous epithelium and connective tissue. Stratified squamous epithelium can have various characteristics on its surface (Fig. 23-1) depending on whether it is keratinized, parakeratinized or nonkeratinized.
1. Keratinized—On its surface are layers of dead cells without nuclei. This layer is generally called the stratum corneum. The stratum granulosum layer beneath the corneum is relatively evident at this stage of keratinization. As keratinization increases, there tends to be an increase in the thickness of the stratum spinosum as well.
2. Parakeratinized—On its surface are some dead cells without nuclei and some apparently dying cells with slightly shriveled nuclei. The stratum granulosum is not quite as evident as in the keratinized mucosa.
The lining mucosa is nonkeratinized to parakeratinized under most circumstances. The basal layer of cells rests on the underlying connective tissue with a basement membrane between these two components. Although this underlying connective tissue contains some well-developed collagen fibers, it is still loose enough to allow the overlying epithelium to be fairly movable. Also allowing for this mobility is the way in which the epithelium and the connective tissue interdigitate with one another.
As seen in Fig. 23-2, there is a definite interdigitation between the epithelium and the connective tissue. In this illustration the ridges appear to interdigitate between the two; however, looking at a three-dimensional representation (Fig. 23-3), you can see that there are not only ridges of connective tissue but also pegs of connective tissue projecting up into the epithelium. The length of these ridges and connective tissue pegs determines how tightly the epithelium attaches to the underlying connective tissue and therefore how movable the epithelium is. The connective tissue is attached to underlying bone in some areas or to fatty or muscle tissue in other areas.
The lining mucosa tends to have poorly developed epithelial-connective tissue interdigitations and therefore is rather movable on the underlying tissue. This degree of mobility is influenced as well by the attachment of the connective tissue to the type of tissue lying beneath it. The lining mucosa includes the mucosa of the cheeks, lips, soft palate, floor of the mouth beneath the tongue, undersurface or ventral surface of the tongue, and the alveolar mucosa, which is the movable tissue immediately apical to the gingiva.
Masticatory mucosa is the mucosa of the gingiva and hard palate. During mastication, food is forced off the teeth and onto the gingiva around the necks of the teeth. The pressure of the food on this tissue causes it to become parakeratinized or keratinized. Food in the hard-palate area and the slight pressure o/>