Cementum PDF

cementum Cementum ENAMEL 1  cementum Cementum Cementum is a thin layer of hard dental tissue covering the anatomic roots of teeth. It is the mineralized connective tissue resemb...

cementum Cementum ENAMEL 1  cementum Cementum Cementum is a thin layer of hard dental tissue covering the anatomic roots of teeth. It is the mineralized connective tissue resembling bone that covers the roots of teeth and serves to anchor gingival and periodontal fibers. Unlike bone, cementum is not vascular and exhibits little turn over. Classification of cementum According to Development Origin of Cellularity Collagen Fibers 0 Primary Cellular Extrinsic Or Or IntrinsiC secondary Mixed Acellular 1- According to the development: Primary cementum Secondary cementum it is that part of cementum that formed during It is that part of cementum that formed after the root formation and before completion. completion of the root. 2  cementum 2- According to its cellularity: A- Acellular cementum It is clear and structureless, covering the granular layer of Tome's It covers the cervical two thirds of the root. Sharpey's fibers of P.L inserted into this type of cementum for the attachment of the root to the surrounding structure. When cementum is thin, Sharpey's fibers cross the entire thickness of the cementum. With increasing the deposition of the cementum, a larger part of the fibers is incorporated into the cementum. It is formed of the calcified ground substance plus the embedded portion of Sharpey's fibers. SHARPEY’S FIBERS PL Cementum B- Cellular cementum It has the same structure of acellular cementum but contain embedded cells (cementocytes). Note that.... the increase in thickness of cementum does not enhance the strength of attachment of the individual fibers, because the deeper portion of the fibers is calcified and the attachment proper is confined to the superficial layer of cementum only. 3  cementum 3- According to the origin of the collagenous matrix: Extrinsic fiber cementum Intrinsic fiber cementum Mixed fiber cementum Its fibers called Sharpey's fibers Its fibers produced by the Its fibers produced from both and produced by the fibroblast of developed cementoblasts. types of cells, fibroblast and the periodontal ligament. cementoblast. physical properties the thickness of cementum at the cervical area is about 20-50 µ Thickness gradually increases in thickness till it reaches its maximum about 150 200 µ at the apex and at the bifurcation area of the root. Color pale yellow in color. It can be distinguished from enamel by its lack of luster and darker hue. Permeability it is permeable from both the dentin and the periodontal ligament side. Chemical properties Cementum contains the greatest amount of fluoride in all mineralized tissues. Inorganic substances (45-50%) Organic matrix (55-50%) Consists mainly of calcium phosphate in the form Consists primarily of collagen fibers as, 90% type I, of hydroxyapatite crystals. 5% type III and 5% type VII, V & XIV. 4  cementum Cementum structure 1- Cementocytes These cells are similar to the osteocytes, has a granular cytoplasm and faintly stained nucleus. The cytoplasm of these cells sends processes which can anastomose with neighboring cells. Mostly, the cell processes are directed towards the periodontal ligaments to provide nutrition. The cell body lies in a lacuna and the cell processes are present in canaliculi. Cementocytes present in the deepest layer of cementum show signs of degeneration, as the cytoplasm contains few organelles, the endoplasmic reticulum is dilated and mitochondria are decreased in number. Also there is clumping of the cytoplasm with vesiculation. 2- Incremental lines of Salter: Both cellular and acellular cementum is separated by incremental lines into layers which indicate periodic formation. Histo-chemical studies indicate that incremental lines are highly mineralized areas with less collagen and more ground substance than other portions of cementum. The incremental lines are roughly parallel to the long axis of the root. The cellular cementum is formed at a faster rate than the acellular cementum so the incremental lines are therefore located further apart than in acellular cementum. 5  cementum 3- Cemento-enamel junction CEJ: It is the relation between the enamel and cementum edges at the cervix of the tooth. This relation is found to be either one of three forms: Edge to edge Denuded area of dentin Cement overlap enamel Incidence 30% 10%. 60%. proper when the Hertwig's local disruption of the reduced development. epithelial root sheath dental epithelium at its end Cause delayed in its separation (cervix of the tooth) that from the dentin, a zone of permits follicular cells to come the root dentin became into contact with the enamel devoid of cementum. surface and differentiate into cementoblasts. the cementum a bare dentin area found to histologically, it may appear as edge of the tooth be so sensitive at the cervix an island of cementum on the Description meets the enamel of the tooth especially if cervical enamel surface. It is edge in a sharp there is a called afibrillar cementum line all around. because its matrix doesn't contain collagen fibrils. EX 6  cementum Function of cementum 1- Cementum furnishes a medium for the attachment of the collagen fibers of the periodontal ligaments to the alveolar bone. Also it maintains this attachment apparatus by continuous cementum lying down on the most superficial layers. 2- Compensation of the lost tooth structure with wearing or fracture by deposition of new cementum at the apical part of the root. 3- Repair any damaged area of the root resulted from resorption. Age changes 1- Smooth surface becomes irregular due to calcification of ligament fiber bundles where they are attached to cementum 2- Continuous deposition of cementum occurs with age in the apical area. This could be a two-edged weapon as it maintains tooth length, while obstructs the apical foramen. 3- Cementum resorption: it is active for a period of time and then stops for cementum deposition creating reversal lines. 4- Resorption of root dentin occurs with aging which is covered by cemental repair. 5- The permeability of cementum decreases gradually. The permeability from the periodontal side is lost except in the most recent formed layer of cementum, while permeability from dentin side remains only in the apical region. 6- Cementicles: calcified ovoid or rounded nodule found in the periodontal ligaments, single or multiple near the cemental surface. It could be free, attached or embedded in cementum. It appears by aging or at site of trauma. It has a nidus of epithelial cells and is composed of calcium phosphate and collagen to the same amount as cementum (45% to 50% inorganic and 50% to 55% organic). 7  cementum Hypercementosis It is an abnormal thickening of cementum. It may affect one tooth or may be generalized in all teeth. It is either limited to a small area of the root or through the whole root length. It has two types: It is physiologic thickening of the cementum, found in the good functioning teeth as Cementum a response to increase the function of the tooth to improve the functional quality hypertrophy through increase the root surface area, and thus permitting more periodontal fibers to be attached to the tooth. Cementum It is pathologic overgrowth of the cementum in a non-functioning or embedded tooth. hyperplasia It is characterized by the absence of Sharpey's fibers. CLINICAL CONSIDERATIONS Cellular cementum is similar to bone but has no nerves; therefore it is non sensitive to pain. So in scaling procedures, it gives no pain. However, if cementum is removed, dentin is exposed and causes sensitivity on scaling. Cementum is resistant to resorption especially in younger patients. Thus, orthodontic tooth movement causes alveolar bone resorption and not tooth root loss. Note that.... Another difference between bone and cementum is the high fluoride content of cementum. The elevated fluoride content of cementum may contribute to its greater resistance to resorption. 8