Oral bio cementum

• Cementum


  Thin layer of calcified tissue covering the dentine of the root

  
• Cementum


  • Thickest at the root apex and Interradicular areas
  • Thickness is cervically 10-15um and apically is 50-200um
  • Light yellow in color
  • Softer and more permeable than dentin
  • 50-55% of weight organic material and water
  • 45-50% inorganic material

  
• Organic components of cementum

  • Collagen fibrils
  • Protein polysaccharides (proteoglycans)
• Inorganic components of cementum

  • Hydroxylapatite (calcium & phosphate)
  • Various trace elements, (Fluor, copper, zinc etc.)
  • Highest fluoride concentration of all tooth tissue

  
• Type 1 collagen


  • Predominant and constitute up to 90% of organic component of cellular cementum
• Other collagens found in cementum

  • Type III
  • Type XII
  • Type V
  • Type VI
  • Type XIV
• Non-collagenous proteins in cementum

  • Alkaline phosphatase
  • Bone sialoprotein
  • Proteoglycan
  • Proteolypids
  • Osteocalcin
  • Osteonectin
• Enamel proteins have also been suggested to be present in cementum

  
• Functions of cementum


  • Act as a medium for attachment of collagen fiber of PDL (Sharpey's fibers)
  • Continuous formation of cementum keeps the attachment apparatus intact
  • Cementum as it is harder then bone and has no blood supply, it doesn't show resorption under masticatory or orthodontic forces
  • Cementum is deposited apically to compensate for attrition, to replenish the lost tooth height due to occlusal wear or passive eruption of tooth
  • It is the major reparative tissue in case of fracture or resorption of rot surfaces
• Classification of cementum


  • Based on nature & origin of organic matrix: Extrinsic Fibre Cementum, Intrinsic Fibre Cementum, Mixed Fibre Cementum
  • Based on presence or absence of cells: Cellular Cementum, Acellular Cementum
  • Based on nature and origin of organic matrix and presence of cells: Acellular Extrinsic fibre Cementum (AEFC), Cellular Intrinsic Fibre Cementum (CIFC), Mixed Fibre Cementum (MFC), Acellular Afibrillar cementum (AAC)
• Acellular cementum


  • Primary cementum
  • Collagen is derived from Sharpey's fibers from PDL
  • Formed slowly as the tooth is erupting
  • Root surface is smooth
  • Incremental lines closer to each other
  • No distinct layer of cementoid (precementum)
  • Extrinsic fibres are round bundles 5-7um in diameter
  • Acellular cementum appears relatively structureless
  • Acellular cementum provides ANCHORAGE (provide attachment to tooth)

  
• Cellular intrinsic fibre cementum (CIFC)

  • Less mineralized variety of cementum
  • The fibres are produced by the cementoblasts (intrinsic fibers)
  • Intrinsic fibres are 1-2um in diameter & are parallel to root surface
  • Cellular cementum contains cells (cementocytes)
  • Cellular cementum develops at fast rate, so cementum forming cell (cementoblasts) become embedded in matrix with reduced secretory activity are called cementocytes
  • Precementum layer (cementoid) is present in cellular cementum
  • Widely spaced incremental lines in Cellular cementum
  • Formed after tooth is in occlusion
  • It is more frequent on the apical half of the root. Also present in inter radicular areas
  • It is always formed on the surface of acellular cementum
  • It is less in anterior teeth, but thicker in multi-rooted teeth
  • It has a role in ADAPTATION & REPAIR
• Acellular afibrillar cementum


  • Contains NO collagen fibers as well as NO cells
  • A type of cementum formed on the cervical part of the enamel for a short distance
  • It is formed due to the degeneration of the reduced dental epithelium covering the cervical area of the enamel before eruption
  • No known function

  
• Mixed fibre cementum


  • Collagen fibres are derived from both extrinsic fibers (PDL) and intrinsic fibres (cementoblasts)
  • Intrinsic fibres are 1-2um in thickness & are parallel to surface and extrinsic fibres are round bundles 5-7um in diameter
  • If the rate of formation is slow it is termed as acellular mixed fibre cementum and is generally well mineralized AND if the rate of formation is fast cellular mixed fibre cementum and is less mineralized
  • Acellular cementum contains primarily extrinsic fibres arranged perpendicularly to root surface and cellular cementum has intrinsic fibers arranged parallel to root surface
  • ROLE IN ADAPTATION
• Structures of cementum


  • Incremental lines of Salter
  • Cementodentinal junction
  • Cementoenamel junction
  • Sharpey's fibers
  • Cementicles

  
• Incremental lines of Salter


  • Formed by fiber-free amorphous substance and represent intervals between successive deposition of cement
  • Highly mineralized areas with less collagen and more ground substance

  
• Cementodentinal junction


  • Relatively smooth in permanent teeth
  • Sometimes scalloped in deciduous teeth

  
• Cementoenamel junction


  • Cementum meets the cervical end of enamel in a relatively sharp line (30% of teeth)
  • Enamel and cementum do not meet, a zone of the root is devoid of cementum and is covered by reduced enamel epithelium (10% of teeth)
  • Cementum overlaps the cervical end of enamel for a short distance (60% of teeth)

  
• Cementicles


  Small-mineralized bodies, which may be found in the periodontal ligament

  
• Sharpey's fibers


  Fibers of the periodontal Ligament that pass into the cementum
• In acellular cementum Sharpey's fibers are usually calcified, in cellular cementum each fiber commonly shows an uncalcified core with a calcified Periphery

  
• Localized hypertrophy of cementum may form prong like extensions to provide a larger surface area for the attaching fibers, thus a firmer anchorage of the tooth to the surrounding alveolar bone is assured

  
• Localized hypercementosis may sometimes occur due to periapical inflammation
• Most teeth show minute areas of root resorption which may extend through the cementum and into the root dentin, generally repaired by rapid deposition of cellular cementum once the initiating factor is removed

  
• Differences between acellular and cellular cementum

  • Acellular cementum: Incremental lines closer, less regular & more in number, Sharpe's fibers more mineralized, First formed cementum forms before tooth reaches occlusal plane, More calcified, Border with dentin no clearly demarcated

  Cellular cementum: Wide separation of incremental line, irregular & less in number, Sharpe's fibers less mineralized, Formed after tooth reaches occlusal plane, Less calcified, Border with dentin clearly demarcated

  
• Factors involved in cementum formation and regeneration

  • Growth factors: Transforming growth factorsβ superfamily, Platelet-derived growth factor, Insulin-like growth factor, Fibroblast growth factors

  Adhesion molecules: Bone sialoprotein, Osteopontin

  Epithelial/enamel proteins

  Collagens: Type I, Type III, Type XII

  Gla proteins: Matrix Gla protein, Bone Gla protein (osteocalcin)

  Transcription factors: Runx II

  Signaling molecules: Osteoprotegerin, Receptor-activated NF-κB ligand, Receptor-activated NF-κB

  Cementum-specific proteins: Cementum protein-1
• Cementicles are small-mineralized bodies, which

  may be found in the periodontal ligament.

  They may be attached to the cementum or the

  alveolar bone, or occur free in the

  periodontal ligament. When present,

  cementicles are generally found about all or

  most of the teeth.

  Cementicles may be formed by mineralization of

  degenerating epithelial rests or thrombosed

  vessels.
• At the surface of the cement the principal fibers of the

  periodontal Ligament pass into its substance.

  • The fibers, which embedded in the cement, are known as

  sharpey's fibers.

  • In the acellular cementum sharpey's fibers are usually

  calcified.

  • In the cellular cementum each fiber commonly shows an

  uncalcified core with a calcified Periphery.

  • In dried ground sections they appear as dark lines as a result

  of their disintegration