The Oral Cavity

The oral cavity consists of the following structures:

Buccal mucosa

Hard and soft palates Teeth

Salivary glands

The oral cavity extends from the inner surface of the teeth to the oral pharynx. The hard and soft palates form the roof of the mouth. The soft palate terminates posteriorly at the uvula. The tongue lies at the floor of the mouth. At the most posterior aspect of the oral cavity lie the tonsils, between the anterior and posterior pillars. The oral cavity is illustrated in Figure 12-1.

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The buccal mucosa is a mucous membrane that is continuous with the gingivae and lines the insides of the cheeks. The linea alba, or bite line, is a pale or white line along the line of dental occlusion. It may be slightly raised and show impressions of the teeth.

Lips are red as a result of the increased number of vascular dermal papillae and the thinness of the epidermis in this area. An increase in desaturated hemoglobin, cyanosis, is manifested as blue lips. The common blue discoloration of the lips in a cold environment is related to the decreased blood supply and increased extraction of oxygen.

The tongue lies at the floor of the mouth and is attached to the hyoid bone. It is the main organ of taste, aids in speech, and serves an important function in mastication. The body of the tongue contains intrinsic and extrinsic muscles and contains the strongest muscle of the body. The tongue is supplied by the hypoglossal, or 12th cranial, nerve.

The dorsum of the tongue has a convex surface with a median sulcus. Figure 12-2 shows the tongue viewed from above. At the posterior portion of the sulcus is the foramen cecum, which marks the area of the origin of the thyroid gland. Behind the foramen cecum are mucin-secret-ing glands and an aggregate of lymphatic tissue called the lingual tonsils. The texture of the tongue is rough as a result of the presence of papillae, the largest of which are the circumvallate papillae (Fig. 12-3). There are approximately 10 of these round papillae, which are located just in front of the foramen cecum and divide the tongue into the anterior two thirds and the posterior one third. Filiform papillae are the most common papillae and are present over the surface of the anterior portion of the tongue. The fungiform papillae are located at the tip and sides of the tongue. These papillae can be recognized from their red color and broad surface.

The taste buds are located on the sides of the circumvallate and fungiform papillae. Taste is perceived from the anterior two thirds of the tongue by the chorda tympani nerve, a division of the facial nerve. The glossopharyngeal, or ninth cranial, nerve perceives taste sensation from the

Figure 12-4 Palatal rugae.

Figure 12-4 Palatal rugae.

posterior third of the tongue. There are four basic taste sensations: sweet, salty, sour, and bitter. Sweetness is detected at the tip of the tongue. Saltiness is sensed at the lateral margins of the tongue. Sourness and bitterness are perceived at the posterior aspect of the tongue and are carried by the glossopharyngeal nerve.

When the tongue is elevated, a mucosal attachment, the frenulum, may be seen underneath the tongue in the midline connecting the tongue to the floor of the mouth.

The hard palate is a concave bone structure. The anterior portion has raised folds, or rugae. Figure 12-4 shows the palatal rugae. The soft palate is a muscular, flexible area posterior to the hard palate. The posterior margin ends at the uvula. The uvula aids in closing off the nasopharynx during swallowing.

Teeth are composed of several tissues: enamel, dentin, pulp, and cementum. Enamel covers the tooth and is the most highly calcified tissue in the body. The bulk of the tooth is the dentin. Under the dentin is the pulp, which contains branches of the trigeminal, or fifth cranial, nerve and blood vessels. The cementum covers the root of the tooth and attaches it to the bone. Figure 12-5 shows a cross section through a molar tooth.

The primary dentition, or the deciduous teeth, consists of 20 teeth that erupt from the ages of 6 to 30 months. The primary dentition per quadrant of jaw consists of two incisors, one canine, and two premolars. These teeth are shed from the ages of 6 to 13 years. The secondary dentition, or the permanent teeth, consists of 32 teeth that erupt from the ages of 6 to 22 years. The secondary dentition per quadrant of jaw consists of two incisors, one canine, two premolars, and three molars. Figure 12-6 illustrates the primary and secondary dentition, and Table 24-5 summarizes the chronology of dentition.

Although not part of the oral cavity proper, the salivary glands are considered part of the mouth. There are three major salivary glands: the parotid, the submandibular, and the

Incisors

Incisors

Premolars

Incisors

Canine

Molars

PRIMARY DENTITION

SECONDARY DENTITION

Figure 12-6 Primary dentition (left) and secondary dentition (right).

sublingual glands. The parotid gland is the largest of the salivary glands. It lies anterior to the ear on the side of the face. The facial, or seventh cranial, nerve courses through the gland. The duct of the parotid gland, Stensen's duct, enters the oral cavity through a small papilla opposite the upper first or second molar tooth. The submandibular gland is the second largest salivary gland. It is located below and in front of the angle of the mandible. The duct of the submandibular gland, Wharton's duct, terminates in a papilla on either side of the frenulum at the base of the tongue. The sublingual gland is the smallest of the major salivary glands. It is located in the floor of the mouth, beneath the tongue. There are numerous ducts of the sublingual gland, some of which open into Wharton's duct. In addition to these major salivary glands, there are hundreds of very small salivary glands located throughout the oral cavity.

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