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An overveiw on the histology of cementum

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  1. 1. PeriodontiumPeriodontium consists of Cementum Periodontal ligament Bone lining the alveolusTogether they form a joint called Gomphosis
  2. 2. Cementum Hard, avascular connective tissue that covers the roots of teeth Classified into ◦ Acellular cementum ◦ Cellular cementum Development divided into ◦ Prefunctional stage ◦ Functional stage ◦ At cervical margin it is 50µm thick, progresses apicallly to 200µm.
  3. 3. Composition of CementumSimilar to bone 45-50% inorganic (hyroxyapatite) 50% organic (Collagens & non- collagenous proteins)
  4. 4. Organic components  90% is type 1 collagen  Other collagens include Type III, V, VI, XII & XIV  Type XII is found in ligamentous tissues and PDL  Non-collagenous proteins: ◦ Alkaline phosphatase ◦ Bone sialoprotein & Dentin sialoprotein ◦ Dentin matrix protein 1 ◦ Fibronectin ◦ Osteocalcin, Osteonectin & Osteopontin ◦ Proteoglycans & Proteolipids ◦ Tenascin ◦ Growth factors including Insulin like growth factor, platelet derived growth factor
  5. 5. Cementum formation Cementum formation initiates at the advancing root edge HERS sends inductive signals to ecto- mesenchymal pulp cells > odontoblasts > predentin > interruption of HERS > contact of predentin with dental follicle > differentiate into cementoblasts Another theory says HERS differentiate into cementoblasts
  6. 6. Fate of HERS Some cells undergo apoptosis Some fragments form discrete masses surrounded by basal lamina, these are called Epithelial rests of Malassez Have a role in maintenance & regeneration of PDL Some odontogenic tumours are believed to arise from these rests If they remain attached to the forming root surface, they form enamell-pearls
  7. 7. Factors regulatingcementogenesis Growth factors Adhesion molecules Epithelial/Enamel proteins Collagens Gla Proteins Transcription factors Signalling Molecules
  8. 8. Growth factors Transforming growth factor ß superfamily ◦ Promotes cell differentiation & cementogenesis during development & regeneration Platelet & Insulin derived growth factor ◦ Promote cementum formation by altering cell cycle activities Fibroblast growth factor ◦ Promote formation & regeneration of PDL tissue by inducing cell proliferation & vasculogenesis
  9. 9. Adhesion molecules Bone Sialoprotein/Osteopontin ◦ Promote adhesion of cells to newly forming root ◦ BSP promotes mineralization & osteopontin regulates the extent of crystal growth
  10. 10. OthersEpithelial/Enamel Proteins:Periodontal repair & regenerationCollagensType I & III have a role in development & regeneration of PDLType XII maintains the PDL spaceGla Proteins (∂-carboxyglutamic acid)Prevent ectopic calcifications & preserve PDL widthOsteocalcin regulates crystal growth & extent of mineralization
  11. 11. OthersTranscription factorsi. Runt-related transcription factor 2(Runx-2)ii. OsterixBelieved to induce cementoblast differentiationSignaling moleculesOsteoprotegrin & RANKL are produced by osteoblasts & PDL fibroblasts, they mediate bone & root resorption by osteoclasts
  12. 12. Cementum Types Acellular ◦ Acellular extrinsic fiber cementum ◦ Acellular afibrillar cementum Cellular Intrinsic Fiber Cementum
  13. 13. Acellular Extrinsic FiberCementum(Primary Cementum)Formation: Principle tissue of attachment, covers 2/3rd of tissue or more Cementoblasts align along the newly formed unmineralized predentin (mantle dentin) These cementoblasts extend their cell processes into this predentin & deposit collagen fibrils within it Mineralization of mantle dentins starts from inside out & spreads across the cementum
  14. 14. Formation Initial layer of short fiber fringe > cells on root surface move away to deposit another 15-20µm of cementum (lengthens & thickens the initial FF plus non-collagenous proteins) > PDL fibroblasts deposit collagen fibrils that become stitched to the FF > cementoblasts secrete only non- collagenous proteins
  15. 15. AEFC Cells remain on the surface therefore called acellular cementum Light microscope shows two sets of striations ◦ Incremental deposition running parallel to root surface ◦ Inserted PDL collagen fiber bundles as short striations perpendicular to root surface No cementoid is present Innermost layer is less mineralized & outer layer shows alternative bands of more & less mineralization
  16. 16. Cellular Intrinsic FiberCementum(Secondary root is formed, a rapidly After half the cementum) forming less mineralized variety of cementum is laid called CIFC Fount in the apical third Confined to the apical & inter-radicular regions of the tooth (usually absent in incisors & canines) Because of rapid cementum deposition, an un-mineralized layer of cementum is present called cementoid & cells become entrapped in the extra-cellular matrix to form cementocytes
  17. 17. Cementocytes Similar to osteocytes as they reside in lacunae but their processes within the canaliculi do not form syncytium to the root surface Nourishment occurs by diffusion so the cementocytes in deeper layers may not be vital
  18. 18. CIFC After a rapid initial haphazard deposition, it slows down & becomes more directional In this phase cells do not become entrapped so may lead to acellular cementum Collagen laid by cementocytes is parallel to the root surface After the PDL fibers are incorporated into the cementum, they become partially mineralized > Cellular mixed fiber
  19. 19. How to differentiate fromAEFC On light microscope ◦ Cementocytes within lacunae ◦ Laminated structure ◦ Cementoid on its surface
  20. 20. Cementocytes
  21. 21. How to differentiate EF & IF Intrinsic fibers are fine, paralled to root surface & uniformly mineralized Extrinsic fibers are larger, haphazard, mineralized variably & run perpendicular to the root surface
  22. 22. Acellular Afibrillar Cementum Lacks collagen No cementocytes No role in tooth attachment Appears uniform under light microscope Deposited over dentin & enamel near CEJ
  23. 23. Cemento-enamel junction Three types of joints are seen ◦ Cementum overlaps enamel (majority) ◦ Butt joint ◦ Gap between cementum & enamel leaving the dentin exposed
  24. 24. Alveolar Process Bone of the jaws containing sockets for the teeth Consists of ◦ Cortical plates (buccal & lingual) ◦ Spongiosa ◦ Alveolar bone (lining the socket) Cortical plate & alveolar bone meet at alveolar crest which is 1.5-2mm below CEJ
  25. 25. Alveolar bone Inner & outer components Contains many foramina b/c of which is also called cribriform plate. Because of increased radio-opacity also called lamina dura Inner alveolar bone incorporates PDL bundle fibers, therefore, also called bundle bone Bundle bone may be apposed on a lamellar bone or not
  26. 26. Cortical plates Surface layer of lamellar bone with haversian systems Central part of spongy bone Cortical plates are thinner in maxilla, thickest on buccal aspect of mandibular molars Spongy bone has yellow marrow rich in adipose cells, rarely has hematopoietic marrow Trabecular bone is absent in anterior teeth where cortical & alveolar bones fuse
  27. 27. Cementum Canaliculus GT Lacuna of cementocyte DentinAcellular cementumCellular cementumHyaline layer(of Hopewell Smith)Granular layer of tomes Dentin with tubules
  28. 28. AgingSmooth surface becomes irregular due to calcification of ligament fiber bundles where they are attached to cementumContinues deposition of cementum occurs with age in the apical area. [Good: maintains tooth length; bad: obstructs the foramen3. Resorption of root dentin occurs with aging which is covered by cemental repair
  29. 29. Cemental repair Protective function of cementoblasts after resorption of root dentin or cementum Resorption of dentin and cementum due to trauma (traumatic occlusion, tooth movement, hypereruption) Loss of cementum accompanied by loss of attachment Following reparative cementum deposition attachment is restored
  30. 30. Clinical CorrelationCellular cementum is similar to bone but has no nerves.Therefore it is non-sensitive to pain. Scaling producesno pain, but if cementum is removed, dentin is exposedcauses sensitivityCementum is resistant to resorption especially in youngerPatients. Thus, orthodontic tooth movement causes alveolarone resorption and not tooth root loss
  31. 31. The End