Development of the_periodontium
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Development of the_periodontium Presentation Transcript

  • 1. Development of the Periodontium Development Of The Periodontium
  • 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. 2. Periodontal ligament (PDL)3. Bone lining the alveolus (socket)4. That part of the Gingiva facing the tooth Development Of The Periodontium
  • 4. Development Of The Periodontium
  • 5. Development Of The Periodontium
  • 6. GOMPHOSIS (Socketed Tooth) Relatively recent structure in evolutionary terms Almost exclusively mammalian Development Of The Periodontium
  • 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. 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. 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
  • 10. Development Of The Periodontium
  • 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. Dental Cementum The dynamic tissue covering the root Development Of The Periodontium
  • 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. 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. 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.  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.  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.  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
  • 19. Development Of The Periodontium
  • 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.  Cementoblasts also secrete noncollagenous proteins such as bone sialoprotein and osteocalcin. Development Of The Periodontium
  • 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
  • 23. Development Of The Periodontium
  • 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. 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
  • 26. Development Of The Periodontium
  • 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
  • 28. Development Of The Periodontium
  • 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
  • 30. Development Of The Periodontium
  • 31.  Alveolar Bone and the Alveolar Process ( The socket that is never stable) Development Of The Periodontium
  • 32. Development Of The Periodontium
  • 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.  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.  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.  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.  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.  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
  • 39. Development Of The Periodontium
  • 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
  • 41. Development Of The Periodontium
  • 42. Development Of The Periodontium
  • 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.  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.  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.  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.  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. The Gingival Tissues The architecture of Periodontal Protection Development Of The Periodontium
  • 49. Development Of The Periodontium
  • 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.  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.  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.  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.  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.  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.  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.  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. THANK YOU Development Of The Periodontium