papilla between the teeth.
The attached gingiva has a finely pitted or stippled surface due to the insertion of fiber bundles which help bind the lamina propria to the fibers of the periosteum and periodontal ligament.
Collagen fibers are the most essential component of the gingival fiber complex. Reticulin fibers are numerous in the tissue adjacent to the basement membrane and in the tissue surrounding large blood vessels. Oxytalin fibers are present in the connective tissue of the periodontium and appear to be concerned with vascular support. Elastic fibers are only found in gingiva and the periodontium in the connective tissue associated with blood vessels. In the lining mucosa, however, elastic fibers are numerous.
Hard palate: The mucosa of the hard palate is continuous with the gingiva on the palatal side of the maxillary teeth. A pattern of ridges with varying size and shape occurs toward the anterior half of the palate. These ridges are known as rugae and may be as characteristic in their pattern as finger prints. The most anterior feature is the incisive papilla which indicates the position of the incisive foramen. The palatal mucosa has no submucosa and is tightly bound to the palatal periosteum except for an area on either side of the midline, where the submucosa contains fat and more posteriorly, the palatine mucous glands. It also contains the palatine arteries, veins, and nerves.
Fig. 3.5 A diagrammatic representation of the epithelial attachment to the tooth. The junctional epithelium is a continuation of the sulcus epithelium but is physically attached to enamel by hemidesmosomes. Note the relationship between the cementoenamel junction (CEJ) and the crest of the alveolar bone. C, cementum; D, dentin; E, enamel.
Fig. 3.6 A diagrammatic representation of the gingival fiber attachment to the tooth and alveolar bone. The dentogingival fibers are anchored into the root by cementum. The alveolar crest fibers secure the gingiva to the alveolar bone. Circular gingival fibers provide a firm cuff around the tooth, holding the attached gingiva to the tooth. C, cementum; D, dentin; E, enamel.
3.3.2 Lining Mucosa
The lining mucosa covers the cheeks, vestibular sulcus, inner surface of the lips, floor of the mouth, and undersurface of the tongue. Most of the lining mucosa lies directly over muscle, and so there is little space for any submucosa. Where the submucosa is more substantial, there are minor salivary glands, vessels, and nerves. The lining mucosa of the floor of the mouth is particularly thin. It provides a useful route of entry for some drugs. Patients who suffer from angina (heart pain) may get relief by placing a tablet of nitroglycerine under the tongue. Recall that it is common practice to place a thermometer under the tongue as it is in close contact with blood vessels.
3.3.3 Gustatory Mucosa
The dorsal surface of the tongue is covered with a specialized mucosa which has both taste and masticatory function. Taste buds lie within the epithelium over the surface of the tongue, the soft palate, and epiglottis. The tongue is divided into two parts, an anterior two-thirds and a posterior third, by a V-shaped groove, the sulcus terminalis. The epithelium of the tongue is highly keratinized with pointed projections of keratin with a core of lamina propria. The keratin at the tip is extended into a short spiky process. These fine projections are known as filiform papillae. The tongue may appear fury if during illness this keratin is not worn away. The purpose of these papilla in man is uncertain. They probably serve a similar function as in other mammals where they protect the surface of the tongue from the abrasive action of rough foods. They also serve to provide a grip on slippery foods in order to form a bolus and to cleanse the oral surfaces of food debris. There are larger, less thread-like papillae of the tongue called fungiform papillae from their resemblance to a mushroom. They are scattered singly over the tongue but concentrated near the tip. The epithelium of fungiform papillae contains taste buds. The vallate papillae are prominent features, just anterior to the sulcus terminalis. There are only about 12 vallate papillae and they do not project above the surface. The furrow contains numerous taste buds and the openings of the serous glands of von Ebner. The foliate papillae are projections around the side of the tongue and have no special function.
Taste buds are oval structures within the epithelium of the tongue. They consist of elongated cells packed together whose ends open out into a pit below an opening in the epithelium. Not all the cells are active, but some may be either supportive to, or precursors of, active cells. The number of taste buds diminishes with age. The sensory supply to the anterior two-thirds is via the lingual branch of the mandibular nerve. The taste sensations are carried via the chorda tympani branch of the facial nerve. The posterior third receives its sensory supply from the glossopharyngeal nerve. The motor supply to all muscle of the tongue except the glossopharyngeus is the hypoglossal nerve.
The periodontium is a term used to describe the supporting and investing structures of the tooth. These comprise the alveolar bone, periodontal ligament, cementum, and the gingiva, an important component of which is the gingival attachment to the tooth by the junctional epithelium. We have reviewed the structure of the gingiva and gingival attachment, so what follows are the other components of the periodontium, the alveolar bone, cementum, and periodontal ligament.
Key Notes
A removable dental prosthesis may have to derive occlusal support from the residual alveolar ridge. The thickness, and resilience to displacement, of the mucosa overlying the residual ridge exhibits regional variation. This variation may limit the ability of the mucosa in certain regions to resist compression caused by masticatory forces. These limitations may determine the patient’s ability to tolerate the prosthesis.
3.4 Alveolar Bone
The roots of the teeth are held in a ridge of bone which is called the alveolus. Dense bone (cortical plate) covers the outer surface and lines the interior surface of each tooth socket. The dense appearance when seen on a radiograph, of the cortical plate around the tooth root, gave rise to the term lamina dura. Foramina (holes) in the outer cortical plate and the lamina dura allow for the passage of blood vessels and nerves. Within the dense bony plates covering the alveolar bone is a less dense network of bone trabeculae. These trabeculae are like inner girders, which are frequently remodeling in response to the changes in directions of the stresses and strains occurring in the bone during forces applied by the teeth during function. A thin septum of bone separates adjacent teeth and roots of multirooted teeth. The level of alveolar bone around each tooth is surprisingly constant in the unworn dentition at 1 to 2 mm below the level of the cement-enamel junction (CEJ). If this distance is greater than 1 to 2 mm, it is an indication that the bone has been resorbed or remodeled due to disease of the periodontium (chronic periodontitis). This distance does, however, increase quite normally in individuals who experience tooth wear, reflecting another compensatory mechanism, continued eruption (see ▶ Fig. 8.14). Radiographs of the teeth reveal the difference in density between the cortical plates and trabeculae and the level of bone around the roots of each tooth. If for any reason the teeth should not develop, the alveolar ridge of bone is absent. The alveolus gradually resorbs following the loss of teeth due to extraction. There is some evidence that alveolar bone can be distinguished from the rest of the bone of the mandible or maxilla, which is then described as basal bone. Elephants’ teeth erupt surrounded by a shell of alveolar bone, which is quite separate from the jaw bone until eruption occurs.
There is a clinically important regional variation in shape and thickness of the alveolar bone which is determined by the size and shape of the tooth roots and their position in the arch.
Maxillary alveolar bone: In the maxilla, alveolar bone is thinnest