FIGURE 16.16 • Dental pulp and structure of dentin. This photomicrograph of a decalcified tooth shows the centrally located dental pulp, surrounded by dentin on both sides. The dental pulp is a soft tissue core of the tooth that resembles embryonic connective tissue, even in the adult. It contains blood vessels and nerves. Dentin contains the cytoplasmic processes of the odontoblasts within dentinal tubules. They extend into the dentinoenamel junction. The cell bodies of the odontoblasts are adjacent to the unmineralized dentin called the predentin. 120. Left inset. Longitudinal profiles of the dentinal tubules. 240. Right inset. Cross-sectional profiles of dentinal tubules. The dark outline of the dentinal tubules, as seen in both insets, represents the peritubular dentin, which is the more mineralized part of the dentin. 240.
Supporting Tissues of the Teeth
Supporting tissues of the teeth include the alveolar bone of the alveolar processes of the maxilla and mandible, periodontal ligaments, and gingiva.
The alveolar processes of the maxilla and mandible contain the sockets or alveoli for the roots of the teeth.
The alveolar bone proper, a thin layer of compact bone, forms the wall of the alveolus (see Fig. 16.7) and is the bone to which the periodontal ligament is attached. The rest of the alveolar process consists of supporting bone.
The surface of the alveolar bone proper usually shows regions of bone resorption and bone deposition, particularly when a tooth is being moved (Fig. 16.20). Periodontal disease usually leads to loss of alveolar bone, as does the absence of functional occlusion of a tooth with its normal opposing tooth.
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 the following:  Tooth attachment (fixation) Tooth support  Bone remodeling (during movement of a tooth)
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 fbers. 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
FIGURE 16.17 • Electron micrograph of odontoblasts. The plasma membrane of one odontoblast has been marked with arrows. The cell contains a large amount of rough endoplasmic reticulum and a large Golgi apparatus. The odontoblast processes are not included in this image; one process would extend from the apical pole of each cell (top). The black objects in the Golgi region are abacus bodies. The tissue has been treated with pyroantimonate, which forms a black precipitate with calcium. 12,000.