Figure 157

Diagram of a section of an incisor tooth and surrounding bony and mucosal structures. The three mineralized components of the tooth are dentin, enamel, and cementum. The central soft core of the tooth is the pulp. The periodontal ligament (membrane) contains bundles of collagenous fibers that bind the tooth to the surrounding alveolar bone. The clinical crown of the tooth is the portion that projects into the oral cavity. The anatomical crown is the entire portion of the tooth covered by enamel. (Modified from Copenhaver WM, ed. Bailey's Textbook of Histology. Baltimore: Williams & Wilkins, 1964.)

Although the enamel of an erupted tooth lacks cells and cell processes, it is not a static tissue. It is influenced by substances in saliva, the secretion of the salivary glands, which are essential to its maintenance. The substances in saliva that affect teeth include

• Digestive enzymes

• Antibacterial enzymes

• Antibodies

• Inorganic (mineral) components

Mature enamel contains very little organic material. Despite its hardness, enamel can be decalcified by acid-producing bacteria acting on food products trapped on the enamel surface. This is the basis of the initiation of dental caries. Fluoride added to the hydroxyapatite complex makes the enamel more resistant to acid demineralization. The widespread use of fluoride in drinking water, toothpaste, pediatric vitamin supplements, and mouthwashes significantly reduces the incidence of dental caries.

Enamel is produced by ameloblasts of the enamel organ, and dentin by odontoblasts of the adjacent mesenchyme

The enamel organ is an epithelial formation that is derived from ectodermal epithelial cells of the oral cavity. The onset of tooth development is marked by proliferation of oral epithelium to form a horseshoe-shaped cellular band of tissue, the dental lamina, in the adjacent mes-

dentin showing dentinal tubules interglobular spaces odontoblasts gingival sulcus enamel lines of Retzius

noncellular cementum alveolar bone with marrow pulp canal cellular cementum apical foramen

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