23: Oral Mucous Membrane

Oral Mucous Membrane

• To name the three categories of mucosa and discuss where they are found

• To name the three stages of keratinization of oral mucous membrane and discuss where these different types are found

• To discuss the factors that affect the mobility of various types of mucosa

• To understand what the submucosa is and where it is found

• To describe the typical clinical picture of normal gingiva

• To describe some of the changes that are seen in diseased gingiva

• To describe the four stages of passive eruption

DIVISIONS OF MUCOUS MEMBRANE

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:

1. Specialized mucosa—mucosa on the upper surface or dorsum of the tongue (discussed in detail in Chapter 24)

2. Masticatory mucosa—comprises the gingiva and hard palatal tissue; undergoes trauma or compression during mastication

3. Lining mucosa—all other areas of oral mucosa

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.

FIG. 23.1 A, Keratinized epithelium. Notice the thick layer at the top without any sign of nuclei. These are dead cells. B, Parakeratinized epithelium. Although nuclei are present even at the top, there are fewer than in nonkeratinized epithelium, and they appear flattened and shriveled. C, Nonkeratinized epithelium. Nuclei are obvious even at the top. (From Bhaskar SN: Orban’s oral histology and embryology, ed 8, St Louis, 1976, Mosby.)

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.

3. Nonkeratinized—Cells on the surface all tend to have nuclei that appear fairly healthy and normal. The stratum granulosum is missing in this type of 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.

FIG. 23.2 Epithelium–connective tissue junction in a two-dimensional representation. Notice the interdigitation of the ridges or pegs of each tissue layer. (From Bhaskar SN: Orban’s oral histology and embryology, ed 8, St Louis, 1976, Mosby.)

FIG. 23.3 In a three-dimensional representation, connective tissue pegs can be seen projecting up from ridges into the epithelium. (Modified from Elias H et al: Human microanatomy, ed 4, Philadelphia, 1978, FA Davis Co.) FA Davis Co.

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

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/>

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Tags: Anatomy of Orofacial Structures A Comprehensive approach 7e

Jan 4, 2015 | Posted by mrzezo in General Dentistry | Comments Off

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