Cementum PDF

Cementum Dr /Abdel-latif Galal Lecturer of oral Medicine& Periodontology  Cementu m 1  Introduction ❖Cementum is part of the periodontium ❖ Periodontium: Is the investing and supporting attachment system of the teeth. ❖It consists of: ❖Two soft tissue...

Cementum Dr /Abdel-latif Galal Lecturer of oral Medicine& Periodontology  Cementu m 1  Introduction ❖Cementum is part of the periodontium ❖ Periodontium: Is the investing and supporting attachment system of the teeth. ❖It consists of: ❖Two soft tissue Gingiva & Periodontal Ligament ❖Two hard tissues Cementum & Alveolar Bone. ❖ Cementum is a calcified; hard connective tissue, derived from ectomesenchyme of the dental follicle ; forming the outer covering of the anatomic root. ❖It begins at the cervical portion of the tooth at the cemento-enamel junction and continues to the apex. ❖A2 vascular and non- innervated.  Physical Characteristics ❖COLOUR : Yellow , lighter than dentin but darker than enamel. ❖HARDNESS : Lesser than dentin. ❖PERMEABILITY : Permeable to inorganic ions , bacteria; which diminishes with age ; cellular cementum is more permeable whan compared to acellular Cementum. ❖THICKNESS: It is thinnest at CEJ ( 20 – 50μm) but becomes gradually thicker apical ward ranging from (150 –200 μm) or more.  Chemical Composition 45-50 % Inorganic 50-55% Organic substances substances collagen fibers consists of calcium embedded in phosphate in the a ground protein form of hydroxy- apatite crystals substance Polysaccharides ❖ Cementum contains the greatest amount of fluoride in mineralized tissues  Histological structure of cementum ❑ Two forms of collagen are found in cementum : * collagen fibrils * collagen bundles ❖The collagen fibrils constitute the main bulk of the organic material of cementum. ❖The collagen bundles represent the embedded portion of the principle fibers of the periodontal ligament, that is Sharpey´s fibers. Histological structure of cementum : Two types of cells are functionally concerned with Cementum : * Cementoblasts. * Cementocytes. ❖Cementoblasts line the root surface and when active, they contain numerous mitochondria, well developed Golgi complex. However, in resting cementoblasts, these cytologic features become less pronounced. Then entrapped in cementum matrix and forming cementocyte. Cementocytes ❖ are seen located in lacunae in cementum matrix and typically have numerous processes ❖ These processes may branch and frequently anastomose with those of the adjacent cementocytes. ❖ This indicates that these cells are not functionally separated from each other ; Because cementum is avascular tissue, thus the processes of the cementocytes are oriented toward the periodontal ligament for nutrition. ❖ As a result of continuous phasic deposition of cementum, resting lines known Salter lines appear in cementum Incremental lines of Salter Dentin  Types of cementum I) Based on cellular content: 1 Cementum containing cells : a. Cellular cementum b. Intermediate cementum 2 Acellular Cementum II) Based on fibrillar content: ❖Intrinsic fibers cementum ❖Extrinsic fibers cementum ❖Mixed fibers cementum ❖Afibrillar cementum Based on cellular connotation : 1- Cementum containing cells Cellular cementum : is more frequently found on the apical half of the root.It contains cells called cementocytes in lacunae Intermediate Cementum : ❖Is a thin, amorphous layer of hard tissue approximately 10 micron ❖This type of cementum does not exhibit the characteristic features of either dentin or cementum, but it is intermediate between cementum and dentin. 2- Acellular cementum : ❖ It doesn’t contain cells. ❖ cementoblasts present on it’s outer surface and constitute an integral component of acellular cementum. ❖ Present on cervical 3rd or half of the root II) Based on fibrillar connotation : 1. Intrinsic fibers cementum : the fibers are derived from the synthetic and secretory activity of cementoblasts. 2. Extrinsic fibers cementum : in this form, the extrinsic fibers originate from the principal fibers of the periodontal ligament that is Sharpey´s fibers. 3. Mixed fibers cementum : it contains both intrinsic and extrinsic fibers 4. Afibrillar cementum : ❖ As enamel is completely formed and become fully calcified, it is seen covered by the reduced enamel epithelium which is important in protecting enamel. ❖ However, the reduced enamel epithelium may retract from the cervical region of enamel. ❖ This allows for the adjacent mesenchymal cells to invade and intervene between enamel and its covering epithelium. ❖ The mesenchymal cells differentiate into cementoblasts and deposit a particular type of cementum, that is, afibrillar Cementum , on enamel surface. DIFFERENT Between ACELLULAR & CELLULAR CEMENTUM ACELLULAR CEMENTUM CELLULAR CEMENTUM ❖ First formed ❖ Secondary formed ❖ Present on cervical 3rd or ❖ Mainly on apical 3rd of root half of the root ❖ It contains cells called ❖ It doesn’t contain cells cementocytes in lacunae ❖ It is formed before the ❖ Formed after the tooth reaches tooth reaches the occlusal the occlusal plane plane ❖ Less calcified ❖ More calcified ❖ Sharpey’s fibers occupy smaller ❖ Sharpey’s fibers are the portion & are not the main main component component. 14  Cementoenamel Junction (CEJ) ❖In approximately 60% of teeth; cementum overlapping the cervical end of enamel for a very narrow area at the CEJ. This occurs as a result of degeneration or retraction of the reduced enamel epithelium at the cervical region of enamel. ❖ This allows for the adjacent mesenchymal cells to invade and intervene between enamel and its covering epithelium , The mesenchymal cells differentiate into cementoblasts and deposit a particular type of cementum, that is, afibrillar cementum, on enamel surface. ❖30% of all teeth, cementum meets the cervical end of enamel in a knife edge- to-edge pattern. ❖In approximately 10% of teeth, cementum does not meet enamel where a zone of root dentin appears devoid of cementum. This can result in dental hypersensitivity as the gingiva recedes exposing the 16 underlying root dentin. Relation of Cementum to Enamel at the Cementoenamel Junction (CEJ) In 60% of the teeth cementum Overlaps enamel In 30% of the teeth cementum just Meets enamel I1n 7 10% of the teeth there is a small Gap between cementum and enamel  Cementodentinal junction ❖ The dentin surface upon which cementum is deposited is relatively smooth in permanent teeth. ❖ The cementodentinal junction in deciduous teeth, however, is Permanent teeth sometimes scalloped. Deciduous teeth  Cementogenesis ❑It takes place in two phases: Matrix formation Mineralization ❑ There are 3 cell types responsible for the cementogenesis: Cementoblasts Cementocytes Fibroblasts ❑ All of these cells are derived from the ectomesenchymal cells. Cementogenesis ❑ Growth of cementum is a rhythmic process and as a new cementoid is formed, the old one is calcified. A thin layer of cementoid can be observed on cemental surface which is covered by cementoblasts. ❑ The mineralization begins after forming the first layer of matrix. ❑ The mineral crystals is deposited within and between the collagen fibers, the long axis of the crystals are arranged parallel to the long axis of the collagen fibers.  Cementogenesis: cementoid is uncalicified matrix secreted by cementoblasts. cementoid Cementodentinal junction Cementoblasts Cementogenesis ❖ After reaching the full thickness the cementoblasts enter aquiescent stage. ❖ During matrix formation fibroblasts form collagen fibers (sharpey`s fibers), which become embedded in the matrix to provide attachment of the root to the surrounding bone.  Clinical considrations 1) Hypercementosis: It is an abnormal thickening of cementum, appear in one tooth or all teeth, may be in local areas of one root or generalized to whole root. ❖ If the overgrowth occurs in functional teeth and improves the functional qualities of the cementum, it is termed cementum hypertrophy ( increase in the size of cells) permit better P.D.L. attachment. ❖ If the overgrowth occurs in nonfunctional teeth, it is termed cementum hyperplasia ( increase in the number of cells) were sharpey’s fibers are absent. 2) Cementum is more resistance to resorption from bone, therefore orthodontics therapy made possible. 3)Fusion of Cementum to alveolar bone with obliteration of P.D.L. is termed ankylosis, which may following resorption, chronic inflammation & tooth replantation. 4)Decrease permeability: by aging the permeability of cementum decreses gradually. 5) Cementicles: Calcified oval or round nodules found in the PDL,Single or multiple near the cemental surface. ❖Cementicles may be: ❖Free in the periodontal ligament. ❖Attached to the cementum and form excementosis. ❖Embedded in the cementum during its growth by age. Functions of cementum : ❖Cementum furnishes a medium for the incorporation of the principal periodontal fibers, thereby securing the binding of the tooth root to the alveolar bone proper. ❖Cementum serves as a reparative tissue in case of root fracture or resorption. ❖Functional adaptation of tooth by Cementum deposition at their apices can compensate for tooth loss occlusally by attrition. ❖Protects dentin by blocking the dentinal tubules. 31