![]() ![]() In general, the rods are aligned perpendicularly to the DEJ and the tooth surface in the primary and permanent dentitions except in the cervical region of permanent teeth, where they are oriented outward in a slightly apical direction. The rods are densely packed and intertwined in a wavy course, and each extends from the DEJ to the external surface of the tooth. The rods vary in number from approximately 5 million for a mandibular incisor to about 12 million for a maxillary molar. This spacing apparently is partially organic material. ![]() The inter-rod substance, or sheath, may be the increased spacing between crystallites oriented differently to where the “tail” portion of one rod meets the “head” portion of another. Structurally, enamel is composed of millions of enamel rods or prisms, which are the largest structural components, rod sheaths, and a cementing inter-rod substance in some areas. The remaining constituents of tooth enamel include organic matrix proteins (1%–2%) and water (4%–12%) volume. Other minerals and trace elements are present in smaller amounts. Hydroxyapatite, in the form of a crystalline lattice, is the largest mineral constituent (90%–92% by volume). Enamel usually decreases in thickness toward the junction of these developmental features and can approach zero where the junction is fissured (noncoalesced).Ĭhemically, enamel is a highly mineralized crystalline structure. The cusps of posterior teeth begin as separate ossification centers, which form lobes that coalesce. The thickness also varies from one class of tooth to another, averaging 2 mm at the incisal ridges of incisors, 2.3 to 2.5 mm at the cusps of premolars, and 2.5 to 3 mm at the cusps of molars. It is thicker at the incisal and occlusal areas of a tooth and becomes progressively thinner until it terminates at the cementoenamel junction (CEJ). Enamel covers the anatomic crown of the tooth and varies in thickness in different areas (see Fig. ![]() These cells originate from the embryonic germ layer known as ectoderm. The relationships of form to function are especially noteworthy when considering the shape of the dental arch, proximal contacts, occlusal contacts, and mandibular movement.Įnamel formation, amelogenesis, is accomplished by cells called ameloblasts. The form of a tooth and its contour and contact relationships with adjacent and opposing teeth are major determinants of muscle function in mastication, esthetics, speech, and protection. Proper tooth form contributes to healthy supporting tissues. The protective function of the tooth form is revealed by its impact on masticatory muscle activity, the supporting tissues (osseous and mucosal), and the pulp. Knowledge of the structures of teeth (enamel, dentin, cementum, and pulp) and their relationships to each other and to the supporting structures is necessary, especially when treating dental caries. Chapter 1 Clinical Significance of Dental Anatomy, Histology, Physiology, and OcclusionĪ thorough understanding of the histology, physiology, and occlusal interactions of the dentition and supporting tissues is essential for the restorative dentist. ![]()
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