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Development of the_periodontium


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Development of the_periodontium

  1. 1. Development of the Periodontium Development Of The Periodontium
  2. 2.  Periodontium is defined as those tissues supporting & investing the tooth. (Tencate 5th edi.) It consists of :-1. Cementum (derived from the latin word caementum, quarried stone i.e. chips of stone used in making mortar) Development Of The Periodontium
  3. 3. 2. Periodontal ligament (PDL)3. Bone lining the alveolus (socket)4. That part of the Gingiva facing the tooth Development Of The Periodontium
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  6. 6. GOMPHOSIS (Socketed Tooth) Relatively recent structure in evolutionary terms Almost exclusively mammalian Development Of The Periodontium
  7. 7. PERIODONTIUM Tissues of tooth support are odontogenic Derived from dental follicle Recent evidence indicating progenitor cells may be derived from cells of dental papilla that migrate into follicle at bell stage of development Development Of The Periodontium
  8. 8. DENTAL FOLLICLE Well defined layer of cells surrounding the tooth germ that is continuous with & derived from the dental papilla at the cervical loop. Dental follicle forms cementum, Periodontal ligament & bone Development Of The Periodontium
  9. 9. Functions of Dental Follicle To protect and stabilise the tooth during formation and later eruption. To provide nutrition and nerve supply to the developing tooth. To give rise to cells that form the cementum, the periodontal ligament & the inner wall of the bony crypt or alveolus. Development Of The Periodontium
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  11. 11. Crypt A crypt is a bony cavity enclosing a developing tooth and is formed by the dental follicle. Each crypt has an opening in its roof through which dental follicle fibres extend for communication within the oral mucosa. The fibrous extension of the dental follicle, which connects the permanent tooth germ to the oral mucosa is called gubernacular cord . Development Of The Periodontium
  12. 12. Dental Cementum The dynamic tissue covering the root Development Of The Periodontium
  13. 13. Hyaline Layer of Hopewell Smith / Intermediate Cementum It is a structure less highly mineralized layer some 10 um thick on the surface of the root dentin. Some investigators believe it may be a form of enamel. Development Of The Periodontium
  14. 14. Hyaline Layer (HL) Many fish have teeth covered with enameloid ( a tissue that resembles enamel but is partly formed by the dental papilla & internal dental epithelium) Enameloid & the hyaline layer are strikingly similar. It has been suggested that the function of HL is to cement cementum to dentin. Development Of The Periodontium
  15. 15. CEMENTOGENESIS Cementum is deposited on the surface of root dentin Hertwig’s epithelial root sheath initates the differentiation of root odontoblasts from the dental papilla, which then form dentin of the root. Development Of The Periodontium
  16. 16.  Before primary cementum can form, root sheath must fragment to allow follicular cells to reach the newly formed root surface. These follicular cells differentiate into cementoblasts. Development Of The Periodontium
  17. 17.  Generally assumed that epithelium/ epithelial product must be involved in initiating the differentiation of cementoblasts from the dental follicle. Eg:- When follicular tissue comes into contact with enamel, cementum is deposited on the enamel surface. Development Of The Periodontium
  18. 18.  Finally the epithelial derived product (enamel like proteins) incorporated into the hyaline layer may play a role in the differentiation of cementoblasts. Development Of The Periodontium
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  20. 20.  Cementoblasts insert cytoplasmic processes into unmineralised hyaline layer, begin to deposit collagen fibrils at right angles to the root surface. Cementoblasts then migrate away from the hyaline layer but continue to deposit collagen forming the fibrous matrix of acellular cementum. Development Of The Periodontium
  21. 21.  Cementoblasts also secrete noncollagenous proteins such as bone sialoprotein and osteocalcin. Development Of The Periodontium
  22. 22. ACELLULAR CEMENTUM This first formed cementum is acellular because the cells retreat into the ligament. It covers at least coronal two thirds of the root. This cementum thus consists of a mineralized layer with a fibrous fringe extruding from it. Development Of The Periodontium
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  24. 24.  Once the tooth is in occlusion, a more rapidly formed & less mineralized form is deposited around the apical third of root. The organic matrix consisting of noncollagenous proteins & collagen fibrils become mineralized as a result of cementoblasts budding off matrix vesicles. Development Of The Periodontium
  25. 25. Cellular Cementum At the same time, the cementoblasts get trapped in the matrix occupy lacunae & they become cementocytes. Thus this is called cellular cementum. This cementum is confined to the apical third of the root & the interradicular regions of premolars & molars. Development Of The Periodontium
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  27. 27. FATE OF HERTWIG’S ROOT SHEATH As the sheath fragments & follicular cells migrate through it, however most of the cells persist as strands or clusters called as epithelial cell rests of malassez These cells rests are remnants of the root sheath & are seemingly discrete clusters or islands of epithelial cells. Development Of The Periodontium
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  29. 29. Cell Rests of Malassez They exhibit dark staining nuclei & little cytoplasm & are inactive. At present there is no function for these cells, however it has been suggested that they have a protective function, preventing resorption of the root surface to a role in maintaining the width of periodontal ligament. Development Of The Periodontium
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  31. 31.  Alveolar Bone and the Alveolar Process ( The socket that is never stable) Development Of The Periodontium
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  33. 33. ALVEOLAR BONE FORMATION As the root & its covering of primary cementum form, new bone is deposited against the crypt wall. The deposition of this bone gradually reduces the space between the crypt wall & tooth to the dimensions of periodontal ligament. As mentioned new bone is formed by osteoblasts originating from the dental follicle. Development Of The Periodontium
  34. 34.  Development of the alveolar process begins in the 8th week in utero. At that time, within the maxilla & mandible the forming alveolar bone develops a horse shoe shaped groove that opens towards the oral cavity. Development Of The Periodontium
  35. 35.  The bony groove or canal is formed by growth of facial & lingual plates of the body of maxilla & mandible & contains the developing tooth germs together with the alveolar vessels and nerves. Initially the developing tooth germs lie in a groove. Development Of The Periodontium
  36. 36.  Gradually bony septa develop between teeth, so that each tooth is eventually contained in a separate crypt. The alveolar process develops during the eruption of the teeth. Development Of The Periodontium
  37. 37.  During uterine life, the dental alveolus like the rest of skeleton is formed by an embryonic type of bone composed of bony spicules. This embryonic bone - a variety of coarse fibered or woven bone, is gradually replaced by compact & spongy bone. Development Of The Periodontium
  38. 38.  Both compact & spongy bones initially are composed of layers (lamellae) arranged in an orderly manner. The alveolar bone proper is formed by the outermost cells of the dental follicle which differentiate into osteoblasts. Development Of The Periodontium
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  40. 40.  They lay down the bony matrix or osteoid in which some osteoblasts become embedded as osteocytes . The matrix then calcifies to form bone. Development Of The Periodontium
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  43. 43. Periodontal Ligament Formation The Periodontal ligament forms shortly after root formation begins. At the commencement of ligament formation the ligament space consists of unorganized connective tissue with short fibre bundles extending into it from both cemental & bony surfaces. Development Of The Periodontium
  44. 44.  Next ligament fibroblasts begin to form collagen which remodels to the collagen bundles & establish continuity across the ligament space. Thereby it secures the attachment of tooth (cementum) to bone. Development Of The Periodontium
  45. 45.  Before the tooth erupts the crest of alveolar bone is above the CEJ & the developing fibre bundles of the PDL are all directed obliquely. As the tooth moves coronally during eruption the alveolar crest comes to coincide with the CEJ & the oblique fibre bundles become horizontally aligned. Development Of The Periodontium
  46. 46.  When the tooth finally comes into function, alveolar crest is below the CEJ, thus the horizontal fibres termed as alveolar crest fibres become oblique once more. Only after the teeth come into function do the fibre bundles of PDL thicken appreciably. Development Of The Periodontium
  47. 47.  The ligament fibre bundles are established & reoriented by the remodelling capacity of ligament fibroblasts. The PDL achieves the highest rate of collagen remodelling & tissue turnover so far demonstrated. Development Of The Periodontium
  48. 48. The Gingival Tissues The architecture of Periodontal Protection Development Of The Periodontium
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  50. 50. Dento gingival Junction Formation That part of the Gingiva facing the tooth is a part of periodontium & it is an adaptation of the oral mucosa. At the time of eruption the crown of the tooth is covered by a double layer of epithelial cells. Development Of The Periodontium
  51. 51.  Those cells in contact with the enamel are ameloblasts, which develop hemidesmosomes secrete a basal lamina & become firmly attached to the enamel surface. The outer layer consists of more flattened cells the remnants of all the remaining layers of dental organ. Together these 2 layers are called as reduced dental epithelium. Development Of The Periodontium
  52. 52.  Between the reduced enamel epithelium &the overlying oral epithelium is connective tissue which breaks down when the tooth is erupting. In response to degenerative changes in the connective tissues, the cells of the outer layer of the reduced dental epithelium & basal cells of the oral epithelium proliferate & migrate into the CT, eventually fusing to form a mass of epithelial cells over the erupting tooth (epithelial cuff ). Development Of The Periodontium
  53. 53.  Thus the cells of the cuff are proliferative, migratory & separated by widened intercellular spaces. Through these spaces, antigens enter from the oral cavity leading to an acute inflammatory response within the connective tissue. The clinical manifestation of this inflammatory response is called Teething. Development Of The Periodontium
  54. 54.  Once the cusp tip of erupting tooth emerges into the oral cavity, oral epithelial cells begin to migrate partially over the reduced enamel epithelium in an apical direction. At this time, the attachment of gingival epithelium to tooth is maintained by ameloblasts & their hemidesmosomes & basal lamina adjacent to the enamel surface. This is called Primary Epithelial Attachment. Development Of The Periodontium
  55. 55.  A process of transformation takes place whereby the reduced enamel epithelium gradually becomes junctional epithelium. The reduced ameloblasts which have lost their ability to divide get transformed into squamous epithelial cells. Development Of The Periodontium
  56. 56.  As the overgrowing epithelial cells from the cuff stratify, they further separate the cells of the transformed dental epithelium from the nutritive supply, with the latter cells degenerating & creating a Gingival Sulcus . The final conversion of reduced dental epithelium to junctional epithelium may not occur until 3 to 4 years after the tooth has erupted. Development Of The Periodontium
  57. 57.  Immediately after all the reduced dental epithelium has been transformed, the development of dentogingival junction may be regarded as complete. With the formation of the dentogingival junction, the dental epithelium is finally lost. Development Of The Periodontium
  58. 58. THANK YOU Development Of The Periodontium