Figure 1520

Schematic diagram of gingiva. This schematic diagram of gingiva corresponds to the rectangular area of the orientation diagram. The gingival epithelium is attached to the enamel of the tooth. Here, the junction between epithelium and connective tissue is smooth. Elsewhere, the gingival epithelium is deeply indented by connective tissue papillae, and the junction between the two is irregular. The black lines represent collagen fibers from the cementum of the tooth and from the crest of the alveolar bone that extend toward the gingival epithelium. Note the shallow papillae in the lining mucosa (alveolar mucosa) that contrast sharply with those of the gingiva.

The periodontal ligament secures the attachment of the tooth to the surrounding bone

The periodontal ligament is the fibrous connective tissue joining the tooth to its surrounding bone. This ligament is also called the periodontal membrane, but neither term describes its structure and function adequately. The periodontal ligament provides for

• Tooth attachment (fixation)

• Tooth support

• Bone remodeling (during movement of a tooth)

• Proprioception

• Tooth eruption

A histologic section of the periodontal ligament shows that it contains areas of both dense and loose connective tissue. The dense connective tissue contains collagen fibers and fibroblasts that are elongated parallel to the long axis of the collagen fibers. The fibroblasts are believed to move back and forth, leaving behind a trail of collagen fibers. Periodontal fibroblasts also contain internalized collagen fibrils that are digested by the hydrolytic enzymes of the cytoplasmic lysosomes. These observations indicate that the fibroblasts not only produce collagen fibrils but also resorb collagen fibrils, thereby adjusting continuously to the demands of tooth stress and movement.

The loose connective tissue in the periodontal ligament contains blood vessels and nerve endings. In addition to fibroblasts and thin collagenous fibers, the periodontal ligament also contains thin, longitudinally disposed oxytalan fibers. They are attached to bone or cementum at each end. Some appear to be associated with the adventitia of blood vessels.

The gingiva is the part of the mucous membrane commonly called the gums

The gingiva is a specialized part of the oral mucosa located around the neck of the tooth. It is firmly attached to the teeth and to underlying alveolar bony tissue. An idealized diagram of the gingiva is presented in Figure 15.20. The gingiva is composed of two parts:

• Gingival mucosa, which is synonymous with the masticatory mucosa described above (page 436)

• junctional epithelium or attachment epithelium, which adheres firmly to the tooth. A basal lamina-like material is secreted by the junctional epithelium and adheres firmly to the tooth surface. The cells then attach to this material via hemidesmosomes. The basal lamina and the hemidesmosomes are together referred to as the epithelial attachment. In young individuals, this attachment is to the enamel; in older individuals, where passive tooth eruption and gingival recession expose the roots, the attachment is to the cementum.

Dental caries is an infectious microbial disease of teeth that results in the destruction of affected calcified tissues; i.e., enamel, dentin, and cementum. Carious lesions generally occur under masses of bacterial colonies referred to as "dental plaque." The onset of dental caries is primarily associated with bacterial colonies of Streptococcus mutans, while lactobacilli are associated with active progression of the disease. These bacterial colonies metabolize carbohydrates, producing an acidic environment that deminerallzes the underlying tooth structure. Frequent sucrose ingestion is strongly associated with the development of these acidogenic bacterial colonies.

Trace amounts of fluoride, from sources such as water supplies (0.5 to 1.0 ppm is optimal), toothpaste, and even diet, can improve resistance to the effects of cariogenic bacteria. Fluoride improves the acid resistance of the tooth structure, acts as an antimicrobial agent, and promotes remineralization of small carious lesions. Resistance to acid breakdown of enamel is facilitated by the substitution of fluoride ion for the hydroxyl Ion in the hydroxyapatite crystal. This decreases enamel crystal solubility in acid.

Treatment of cavitated lesions, or "tooth cavities" (Fig. 15.21), includes excavation of the infected tooth tissue and replacement with dental materials such as amalgam, composite, and glass ionomer cements. Microbial invasion of tooth structure can reach the "pulp" of the tooth and elicit an inflammatory response. In this case, endodontic treatment, or a "root canal," is generally recommended, with subsequent placement of a crown to add strength to the compromised coronal tooth structure.

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