Histology of Digestive System Tooth PDF (Spring 2024)

Histology of Digestive system Tooth Prof. Dr. Soad A. Treesh. Spring 2024 Teeth & Associated Structures In adult humans, there are normally 32 permanent teeth. These teeth are disposed in two bilaterally symmetric arches in the maxillary and mandibular bones, with eight teeth in each quadrant:...

Histology of Digestive system Tooth Prof. Dr. Soad A. Treesh. Spring 2024 Teeth & Associated Structures In adult humans, there are normally 32 permanent teeth. These teeth are disposed in two bilaterally symmetric arches in the maxillary and mandibular bones, with eight teeth in each quadrant: two incisors, one canine, two premolars, and three permanent molars. Twenty of the permanent teeth are preceded by deciduous (baby) teeth; the remainder (the permanent molars) have no deciduous precursors. Each tooth is composed of a portion that projects above the gingiva—the crown— and one or more roots below the gingiva that hold the teeth in bony sockets called alveoli, one for each tooth. The crown is covered by the extremely hard enamel and the roots by another mineralized tissue, the cementum. These two coverings meet at the cervix of the tooth. The bulk of a tooth is composed of another calcified material, dentin, that surrounds a soft connective tissue-filled space known as the pulp cavity. The pulp cavity has a coronary portion (the pulp chamber) and a root portion (the root canal), extending to the apex of the root, where an orifice (apical foramen) permits the entrance and exit of blood vessels, lymphatics, and nerves of the pulp cavity.  Dentin Dentin is a calcified tissue that is harder than bone because of its higher content of calcium salts (70% of dry weight). It is composed mainly of type I collagen fibrils, glycosaminoglycans, phosphoproteins, phospholipids, and calcium salts in the form of hydroxyapatite crystals. The organic matrix of dentin is secreted by odontoblasts, pulp cells that line the internal surface of the tooth.  Odontoblast A slender polarized cell that produces organic matrix only at the dentinal surface. These cells have the structure of polarized protein-secreting cells with secretion granules in the apical cytoplasm and a basal nucleus. Have slender, branched apical extensions that penetrate perpendicularly through the width of the dentin—the odontoblast processes (Tomes' fibers). These processes gradually become longer as the dentin becomes thicker, running in small canals called dentinal tubules that are extensively branched near the junction between dentin and enamel. The matrix produced by odontoblasts is initially unmineralized and is called predentin. Dentin is sensitive to several stimuli, such as heat, cold, trauma, and acidic pH, and all of these stimuli are perceived as pain. Although the pulp is highly innervated, dentin has a few unmyelinated nerve fibers penetrating its internal (pulpar) portion.  Enamel Enamel is the hardest component of the human body. It consists of about 96% mineral, up to 1% organic material, and 3% water as the remainder. As in other mineralized tissues, the inorganic component of enamel is mostly hydroxyapatite crystals. Other ions, such as strontium, magnesium, lead, and fluoride. Enamel is produced by cells of ectodermal origin (ameloblasts ), whereas most of the other structures of teeth derive from mesodermal or neural crest cells. The organic enamel matrix is composed not of collagen fibrils but of at least two heterogeneous classes of proteins called amelogenins and enamelins. The roles of these proteins in the organization of the mineral component of enamel. Enamel consists of elongated rods or columns—enamel rods (prisms)—that are bound together by interrod enamel. Enamel matrix is secreted by cells called ameloblasts. These tall columnar cells possess numerous mitochondria in the region below the nucleus. Rough endoplasmic reticulum and a well-developed Golgi complex are found above the nucleus. Each ameloblast has an apical extension, knownas a Tomes' process, containing numerous secretory granules that contain the proteins that make up the enamel matrix.  Pulp Tooth pulp consists of loose connective tissue. Its main components are odontoblasts, fibroblasts, thin collagen fibrils, and a ground substance that contains glycosaminoglycans. Pulp is a highly innervated and vascularized tissue. Blood vessels and myelinated nerve fibers enter the apical foramen and divide into numerous branches. Some nerve fibers lose their myelin sheaths and extend for a short distance into the dentinal tubules. Pulp fibers are sensitive to pain, the only sensory modality recognized in teeth.  Periodontium The periodontium comprises the structures responsible for maintaining the teeth in the maxillary and mandibular bones. It consists of the Cementum, Periodontal ligament, Alveolar bone, and Gingiva. Cementum Cementum covers the dentin of the root and is similar in composition to bone, although haversian systems and blood vessels are absent. It is thicker in the apical region of the root, where there are cementocytes, cells with the appearance of osteocytes. Like osteocytes, they are encased in lacunae; unlike those cells, however, cementocytes do not communicate through canaliculi, and their nourishment comes from the periodontal ligament. Like bone tissue, cementum is labile and reacts to the stresses to which it is subjected by resorbing old tissue or producing new tissue. Periodontal Ligament  The periodontal ligament is composed of a special type of connective tissue whose fibers penetrate the cementum of the tooth and bind it to the bony walls of its socket ,fixing the tooth firmly in its bony socket (alveolus), while permitting limited movement of the tooth.  Its fibers are organized to support the pressures exerted during mastication.  Collagen of the periodontal ligament has characteristics that resemble those of immature tissue.  It has a high turnover rate. Alveolar Bone  The alveolar bone is in immediate contact with the periodontal ligament. It is an immature type of bone (primary bone) in which the collagen fibers are not arranged in the typical lamellar pattern of adult bone.  Many of the collagen fibers of the periodontal ligament are arranged in bundles that penetrate this bone and the cementum, forming a connecting bridge between the two structures (Sharpey's fibers).  The bone closest to the roots of the teeth forms the socket. Vessels run through the alveolar bone and penetrate the periodontal ligament along the root, forming the perforating vessels. Some vessels and nerves run to the apical foramen of the root to enter the pulp. Gingiva  The gingiva is a mucous membrane firmly bound to the periosteum of the maxillary and mandibular bones. It is composed of stratified squamous epithelium and lamina propria containing numerous connective tissue papillae.  A very specialized part of this epithelium, the junctional epithelium, is bound to the tooth enamel by means of a cuticle that resembles a thick basal lamina and forms the epithelial attachment of Gottlieb. The epithelial cells are attached to this cuticle by hemidesmosomes.  Between the enamel and the epithelium is the gingival sulcus, a small deepening up to 3 mm surrounding the crown.