لكجر ١٦

• Periodontal Ligament


  The soft, specialized connective tissue situated between the cementum covering the root of the tooth and bone forming the socket wall

  
• Periodontal Ligament


  • Its width ranges from 0.15 to 0.38 mm
  • Its shape is like an hourglass apicocoronally
  • It is thinnest at the axis of rotation in the middle and widens coronally and apically

  
• Development of Periodontal Ligament


  1. As the crown approaches the oral mucosa during tooth eruption, the fibroblasts of dental follicle become active and start producing collagen fibrils

  2. These fibers initially lack orientation, but they soon acquire an orientation oblique to the tooth

  3. The first collagen bundles appear in the region immediately apical to the cementoenamel junction and give rise to the gingivodental fiber groups

  4. As tooth eruption progresses, additional oblique fibers appear and become attached to the newly formed cementum and bone

  
• Development of Periodontal Ligament

  1. Transseptal and alveolar crest fibers develop when the tooth merges into the oral cavity

  2. Alveolar bone deposition occurs simultaneously with periodontal ligament organization

  
• Development of Periodontal Ligament

  1. During eruption, cemental Sharpey's fibers appear first, followed by Sharpey's fibers emerging from bone

  2. Sharpey's fibers of bone are fewer in number and more widely spaced than those emerging from the cementum

  3. At a later stage, alveolar fibers extend into the middle zone to join the lengthening cemental fibers and attain their classic orientation, thickness and strength when occlusal function is established

  
• Constituents of Periodontal Ligament


  • Periodontal ligament fibers
  • Cellular elements
  • Ground substances (Glycosaminoglycans, Glycoproteins)

  
• Periodontal Ligament Fibers


  • Mainly collagen and oxytalan fibres
  • Elastic fibers are present only in the wall of blood vessels
  • Oxytalan are immature elastic fiber that support the blood vessels of periodontal ligament

  
• Collagen


  • Types I, III, V, VI, XII of collagen are present in periodontal ligament
  • Collagen is synthesized by fibroblasts, chondroblasts, osteoblasts, odontoblasts and other cells
  • It is secreted in an inactive form called as procollagen, converted into tropocollagen, and polymerized into collagen fibrils aggregated into collagen bundles by the formation of crosslinkages
  • There is rapid turnover rate of periodontal ligament collagen, with half life of only 10 - 15 days, which is about 5 times faster than gingival collagen
• Principal Fibers of Periodontal Ligament


  • Transseptal group
  • Alveolar crest group
  • Horizontal group
  • Oblique group

  
• Transseptal Group


  Functions: Reconstructed even after destruction of the alveolar bone has occurred in the periodontal disease, Responsible for returning teeth to their original state after orthodontic therapy

  Position: Extends interproximally over alveolar bone crest and embedded in the cementum of adjacent teeth

  
• Alveolar Crest Group


  Functions: Prevent extrusion, Prevent lateral tooth movements

  Position: Extends obliquely from the cementum just beneath the junctional epithelium to the alveolar crest

  
• Horizontal Group


  Position: Extends at right angles to the long axis of the tooth from cementum to alveolar bone

  
• Oblique Group


  Functions: Bear vertical masticatory stresses, Resist lateral tooth movements

  
• لا ضارمأ ًف ًخنسلا مظعلل رٌمدت ثودح دعب ىتح اهؤانب دٌعأ
• ًمٌومتلا جلاعلا


  دعب ةٌلصلأا اهتلاح ىلإ نانسلأا ةداعإ نع لوؤسم
• نانسلأا


  • طلام ًف جمدنٌو ًخنسلا مظعلا ةمل قوف برامتم لكشب دتمٌ
  • ةرواجملا
• Principal fibers of periodontal ligament


  • Alveolar crest group
  • Horizontal group
  • Oblique group
  • Apical group
  • Interradicular group

  
• Alveolar crest group


  • Prevent extrusion
  • Prevent lateral tooth movements

  
• Horizontal group


  Extends at right angles to the long axis of the tooth from cementum to alveolar bone

  
• Oblique group


  • Bear vertical masticatory stresses
  • Transform vertical stress into tension on the alveolar bone

  
• Apical group


  • Prevents tooth tipping
  • Resists luxation
  • Protects neurovascular supply to the tooth

  
• Interradicular group


  • Prevents luxation
  • Prevents tooth tipping and torquing
• Sharpey's fibers


  The ends of the periodontal fibers that are embedded in alveolar bone and cementum

  
• The Cells of PDL

  • Synthetic cells
  • Resorptive cells
  • Progenitor cells
  • Epithelial rests of Malassez
  • Defense cells
• Fibroblast


  The predominant cell in the periodontal ligament, derived in part from the ectomesenchyme of investing layer of dental papilla and from the dental follicle

  
• Fibroblasts on the bone side of the ligament show abundant alkaline phosphatase activity than those on the tooth side
• Fibroblasts near cementum are derived from ectomesenchymal cells of the investing layer of dental papilla, while fibroblasts near alveolar bone are derived from perivascular mesenchyme

  
• Function of fibroblasts


  Produce the structural connective tissue proteins, collagen and elastin, as well as proteoglycans, glycoproteins and glycosaminoglycans that comprise the periodontal ligament ground substance

  
• Fibroblasts


  Cells containing type I collagen molecules
• Fibroblasts


  • Produce structural connective tissue proteins (collagen, elastin, proteoglycans, glycoproteins, glycosaminoglycans) that comprise the periodontal ligament ground substance

  
• Fibroblasts from the periodontal ligament are derived from the dental follicle, while fibroblasts from the alveolar bone are derived from the surrounding connective tissue

  
• Fibroblasts are distributed evenly throughout the ligament, oriented parallel to the long axis of the collagen fibers

  
• Fibroblasts


  • Large cells with abundant cytoplasm and rough endoplasmic reticulum, associated with synthesis and secretion of type I collagen
• Osteoblasts


  Cells covering the periodontal surface of the alveolar bone, constituting a modified endosteum and not a periosteum

  
• Cementoblasts


  Cells lining the surface of cementum, not regularly arranged like osteoblasts, often indistinguishable from periodontal fibroblasts
• Osteoclasts


  Cells that resorb bone, can be large and multinucleated or small and mononucleated
• Fibroblasts in periodontal ligament


  • Show rapid degeneration of collagen through phagocytosis, basis for fast collagen turnover
• Cementoclasts


  Resemble osteoclasts, found occasionally in normal functioning periodontal ligament, important in resorption of cementum
• Progenitor cells


  Connective tissue cells with capacity for mitotic division, replace differentiated cells that die
• Epithelial rests of Malassez


  Epithelial cells found close to cementum, remnants of Hertwig's epithelial root sheath