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Cementum
 

Cementum

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oral histology by dr hesham dameer

oral histology by dr hesham dameer

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    Cementum Cementum Presentation Transcript

    • By/ Dr. HeshamDameer
    • Cementum is part of the peridontium
    • THE PERIODONTIUMThe peridontium consists of those tissues which surrounds ,support the tooth and is composed of :GingivaPeriodontal ligamentCementumAlveolar bone By/ Dr. Hesham Dameer
    • GingivaThe gingiva is that part of the oralmucosa which surrounds the tooth andcover the alveolar bone .In light-skinned individuals the gingiva(G) can be readily distinguished from theadjacent dark red alveolar mucosa (AM)by its lighter pink color. Its apical border,that separates it from the adjacentalveolar mucosa, is the mucogingivaljunction (MGJ). A similar tissuerelationship can be seen on the lingualaspect of the mandible
    • AM, alveolar mucosa .G, gingiva .MGJ, mucogingival junction
    • AM,alveolar mucosa .F, floor of the mouth .G, gingiva .MGJ, mucogingival junction
    • Periodontal ligamentDense connective fibers that connect thecementum covering the root of the toothwith the alveolar bone of the socket wall .Principal fibers of the periodontalligament :The periodontal fibers of the periodontalligament are primarily composed ofbundles of type I collagen fibrils. Theyhave been classified into several groupson the basis of their anatomic location:
    • The following constitute the principal fibergroups of the periodontal ligament:1. Alveolar crest group2. Horizontal group3. Oblique group4. Periapical group5. Interradicular group By/ Dr. Hesham Dameer
    • CementumBy/ Dr. HeshamDameer
    • Cementum is a hard connectivetissue that covers the root of thetooth to furnish a medium intowhich the principle fibers of theperiodontal ligament areterminally inserted . By/ Dr. Hesham Dameer
    • CementumIt begins at the cervical portion of the tooth at the cemento- enamel junction and continues to the apex.Cementum furnishes a medium for the attachment of collagen fibers that bind the tooth to surrounding structures. By/ Dr. Hesham Dameer
    • Physical Characteristics 1-ColorLight yellowLighter in color than dentin 2- ThicknessAcellular cementum (20-50 m)Cellular cementum (150-200 m) 3- Permeability Permeable from dentin and PDL sides.Cellular C is more permeable than acellular C.
    • Chemical Composition45-50 % Inorganic 50-55% Organic substances substances collagen consists of fibers protein calciumphosphate in the embeddedform of hydroxy- in a ground apatite crystals substance . PolysaccharidesCementum contains the greatest amount offluoride in all mineralized tissues By/ Dr. Hesham Dameer
    • Cementogenesis• It takes place in two phases: • Matrix formation • MineralizationThere are 3 cell types responsible for the cementogenesis: • Cementoblasts • Cementocytes • Fibroblasts• All of these cells are derived from the ectomesenchymal cells. By/ Dr. Hesham Dameer
    • CementogenesisCementum formation in the developing tooth is preceded bythe deposition of dentin along the inner aspect of Hertwig‘ssheath . Once dentin formation is underway breaks occur inthe epithelial root sheath allowing the newly formed dentin tocome in direct contact with the connective tissue of thedental sac , the undifferentiated mesenchymal cells derivedfrom the dental sac differentiate into cementoblasts . Thesecells have the ultrastructural characteristics typical of cellsactively synthesis protein and polysaccharide .The main product of cementoblasts is collagen and groundsubstances , both constitute the organic component ofcementum .The inorganic material of cementum is calcium phosphateHydroxy apatite .
    • Cementogenesis After degeneration of the epithelial root sheath ectomesenchymal cells from the inner portion of the dental Odontoblast follicle differentiate and become cementoblasts cementoblasts. By/ Dr. Hesham Dameer
    • Growth of cementum is a rhythmic process and as a newcementoid is formed, the old one is calcified . A thin layer ofcementoid can be observed on cemental surface which iscovered by cementoblasts .The mineralization begins after forming the first layer ofmatrix.The mineral crystals is deposited within and between thecollagen fibers, the long axes of the crystals are arrangedparallel to the long axis of the collagen fibers . Sometimes crystals can be seen clustered into groups of nucleation centers as found in bone.
    • Cementogenesis cementoidCementodentinal junction Cementoblasts
    • Cementoblast is a protein forming and secreting cell. Maturation occur layer Collagen fibers + by layer for the ground substance. collagen fibers D Cementum Large open face nucleus Cementoblasts Cementoblast RER Cementoid layer Golgi apparatus Mitochondria Secretory granules Alkaline phosphatase
    • Cementogenesis After reaching the full thickness the cementoblasts enter a quiescent 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. Those fibers are also called perforating fibers. . By/ Dr. Hesham Dameer
    • Remnants of the Hertwig`s root sheath, which disintegrate into the PDL are the Malassez cells.intermediatecementum By/ Dr. Hesham Dameer
    • Histological structure :cementum cover the root dentin fromcementoenamel junction to the root apex .It is thinnest at this junction ( 20 – 50 μm ) butbecomes gradually thicker apicalward rangingfrom 150 – 200 μm ) or more . By/ Dr. Hesham Dameer
    • Two forms of collagen are found incementum : * collagen fibrils * collagen bundlesThe collagen fibrils are arranged in a verycomplex fashion and constitute the mainbulk of the organic material of cementum.The collagen bundles represent theembedded portion of the principle fibers ofthe periodontal ligament, that is Sharpey sfibers .
    • Two types of cells are functionally concerned with cementum : * Cementoblasts * CementocytesCementoblasts line the root surface and when active, they contain numerous mitochondria, well developed Golgi complex, and open-faced nucleus. However, in resting cementoblasts, these cytologic features become less pronounced . By/ Dr. Hesham Dameer
    • While cementum is being deposited,cementoblasts retreat leaving behind theformed cementum matrix. Occasionally,however, cementoblasts becomeentrapped in the forming matrix and thenknown cementocytes .
    • Cementocytes are seen located in lacunae in cementum matrix and typically have numerous processes lying in canaliculi . 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 . By/ Dr. Hesham Dameer
    • Cementocytes
    • Cementocyte lacuna
    • Cementocyte canaliculi CementocyteCementocyte process
    • Incremental Lines• Incremental lines of Salter. Incremental lines of Salter
    • Incremental lines of Salter Dentin
    • Resting lines of Salter
    • Types of cementum :I) Based on cellular connotation : 1- Cementum containing cells : a. Cellular cementum b. Intermediate cementum 2- Acellular cementumII) Based on fibrillar connotation : 1. Intrinsic fibers cementum 2. Extrinsic fibers cementum 3. Mixed fibers cementum 4. Afibrillar cementum
    • I) Based on cellular connotation : 1- Cementum containing cells : a. Cellular cementum is more frequently found on the apical half of the root where cementum does contain cementocytes in its matrix . b. Intermediate cementumIntermediate cementum is a thin, amorphous layer of hard tissue approximately 10 micron thick.Is more frequently seen in the apical two thirds of the roots of posterior teeth but rarely in incisors or primary teeth .This type of cementum does not exhibit the characteristicfeatures of either dentin or cementum, while in regard to itslocation, it is found intermediate between cementum and dentin.
    • In respect to the involved cells observed inintermediate cementum, there is argument about therederivation :1- The cells of the epithelial root sheath of Hertwig areproposed to become entrapped while dentin orcementum is being rapidly deposited .2- Other concept claims that odontoblasts are trappedon the outer dentin surface at the commencement ofdentinogenesis which subsequently being enclosed bythe forming cementum .
    • Cementogenesisintermediate cementum Cementoblasts
    • Remnants of the Hertwig`s root sheath, which disintegrate into the PDL are the Malassez cells.intermediatecementum By/ Dr. Hesham Dameer
    • 2- Acellular cementum :The matrix of this type of cementum does not involve cementocytes . However, cementoblasts present on its outer surface and constitute an integral component of acellular cementum .Acellular cementum may cover the root dentin from the cementoenamel junction to the root apex, but with frequent absence on the apical third 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 of paramount importance 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 . By/ Dr. Hesham Dameer
    • Cementoenamel Junction (CEJ)• 3 patterns may be present• 1) 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 premature 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 .• 2) 30% of all teeth, cementum meets the cervical end of enamel in a knife edge-to-edge pattern .• 3) 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 underlying root dentin
    • Relation of Cementum to Enamel at the Cementoenamel Junction (CEJ)In 60% of the teeth cementum Overlaps enamelIn 30% of the teeth cementum just Meets enamelIn 10% of the teeth there is a small Gap between cementum and enamel
    • Edge to edge 30%By/ Dr. HeshamDameer
    • Cementum do not meet enamel 10%By/ Dr. HeshamDameer
    • Cementum overlaps enamel 60%By/ Dr. HeshamDameer
    • Cementodentinal junctionThe dentin surface upon Permanent teeth which cementum is deposited is relatively smooth in permanent teeth.The cementodentinal junction in deciduous teeth, however, is sometimes scalloped. By/ Dr. Hesham Deciduous teeth Dameer
    • Functions of cementum :1. 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 .2. Cementum serves as a reparative tissue in case of root fracture or resorption .3. Functional adaptation : * When the superficial layer of cementum functionally ages, a subsequent layer is deposited thus restoring the integrity of the attachment apparatus . * Another feature of functional adaptation is the excessive formation of cementum on the apical root surface to compensate for the occlusal and incisal wear and restore the normal occlusion . By/ Dr. Hesham Dameer
    • Histological cross-section through a periodontal ligament . The periodontalligament fibers (F) originate from the cementum. and insert into bundle bone (BB),so named because it contains numerous Sharpeys fibers (SF). Neurovascularchannels (NV) that house blood vessels, lymphatics and nerves in a looseconnective tissue sheath course throughout the periodontal ligament. Theligament also contains cell rests of Malassez (M). By/ Dr. Hesham Dameer
    • Age changes of cementum 1) Hypercementosis: It is an abnormal thickening of cementum, may be diffuse or circumscribed. It may affect all teeth of the dentition, be confined to a single tooth, or even affect only Parts of one tooth. If the overgrowth occurs in functional teeth and improves the functional qualities of the cementum, it is termed cementum hypertrophy. If the overgrowth occurs in nonfunctional teeth, it is termed cementum hyperplasia .Hyperplastic cementum covering the enamel drops termedexcementosis
    • the enamel drops
    • Localized hypercementosis Generalized hypercementosis
    • Age changes of cementum In Localized hypertrophy prong like extension of cementum may be formed. This condition frequently is found in teeth that are exposed to great stress (ortho) (compensatory cementum). This extension of cementum provide a larger surface area for the attaching fibers; thus a firmer anchorage of the tooth to the surrounding alveolar bone is assured.
    • Root resorption andforming Reparatorycementum
    • Root resorption – lost D. has been replaced by cellularcementum, on the top of which acellular C. has formed
    • HypercementosisBy/ Dr. HeshamDameer
    • 2) Decrease permeability : by aging the permeability ofcementum decreses gradually , the permiability from theperiodontal ligament side is lost except in the most recentformed layers of cementum .3) Cementicles : they are ovoid or round calcified structurethat exhibits by dystrophic calcification of the degeneratedperiodontal tissue or the epithelial rests of Malssez . Theynidus favoring the deposition of concentric layers ofcalcosherites around the degenerated or hemorrhageticareas .Cementicles may be: 1. Free in the periodontal ligament. 2. Attached the cementum and form excementosis. 3. Embedded in the cementum during its growth by age.
    • Free Cementicles CementumBone Periodontal ligament
    • Periodontal ligamentFree Cementicles Attached Cementicles
    • THE My best wishes for youEND Dr. HESHAM Dameer