PL

• Periodontal ligament


  Connective tissue that attaches the teeth to the bones of the jaws and continually adapting apparatus for support of teeth during function
• Components of the periodontium


  • Cementum
  • Periodontal ligament
  • Alveolar bone
  • Gingiva facing the bone
• Periodontal ligament


  • Fibrous connective tissue that is noticeably cellular and contains numerous blood vessels
  • Occupies the periodontal space
• Terms synonymous with periodontal ligament


  • Periodontal membrane
  • Pericementum
  • Dental periosteum
  • Alveolo-dental ligament
  • Desmodont
  • Gomphosis
• Development of periodontal ligament


  1. Elongation of Hers

  2. Separation of Hers

  3. Migration of cells to the external surface of the newly formed root dentin

  4. Differentiation of migrant dental follicle cells into cementoblasts, fibroblasts, osteoblasts
• Cells in the periodontal ligament


  • Synthetic cells (osteoblast, fibroblast, cementoblast)
  • Resorptive cells (osteoclast, fibroblast, cementoclast)
  • Progenitor cells
  • Epithelial cells (epithelial rests of Malassez)
  • Cells derived from hematopoietic line (mast cells, macrophages)
• Resorptive cells


  • Osteoclasts (multinucleated cells that resorb bone, occupy Howship's lacuna)
  • Fibroblasts (have lysozymes)
  • Cementoclasts (may resemble osteoblasts, cause resorption of cementum under certain conditions)
• Synthetic cells


  • Secrete proteins, have active RER and Golgi apparatus, large number of mitochondria
  • Osteoblasts (found on the periodontal surface of alveolar bone)
  • Fibroblasts (lie in the body of CT in close proximity to the periodontal ligament, run parallel to the collagen fibers)
  • Cementoblasts (lie in the periphery of the cementum tissue)
• Progenitor cells


  • Cells in CT that have the capacity to undergo mitotic division in response to repair, death, trauma, or normal biological requirements
  • After division, these cells differentiate into resorptive or synthetic cells
  • Have small nucleus and very little cytoplasm
• Extracellular substances in the periodontal ligament


  • Fibers (collagen, oxytalan, elastic)
  • Ground substance (proteoglycans, glycoproteins)
• Collagen fibers


  • Type I and III
  • Fibrils gather to form fibers
  • When gathered into bundles with clear orientation, they become principal fibers (exit cementum or alveolar bone)
• Types of principal collagen fibers


  • Dento-alveolar
  • Gingival (alveolar crest group, horizontal group, oblique group, apical group, interradicular group)
• Epithelial rests of Malassez


  • Epithelial cells that are remnants of Hers
  • Appear as network, strands, islands or tube-like structures near the parallel surface of the root
  • Can undergo rapid proliferation and produce cysts and tumors of the jaw under certain pathologic conditions
• Cells derived from hematopoietic line


  • Mast cells (small round/oval cells with numerous cytoplasmic granules, play role in inflammatory reactions, regulate endothelial and fibroblast cell production)
  • Macrophages (located adjacent to blood vessels, appear similar to fibroblasts but have prominent phagocytosed material in cytoplasm, sparse organelles, function for phagocytosing dead cells)
• Gingival fibers


  • Dentogingival group (most numerous, cervical cementum to lamina propria of gingiva)
  • Alveologingival group (alveolar crest to lamina propria of gingiva)
  • Circular or circumferential (continuous around the neck of tooth)
  • Transseptal fibers (cervical cementum of one tooth to the cervical cementum of another tooth)
• Structures present in the connective tissue of the periodontal ligament


  • Blood vessels
  • Lymphatics
  • Nerves
  • Cementicles (calcified bodies in the periodontal ligament space)
• Functions of the periodontal ligament


  • Supportive (attach cementum to alveolar bone, provide cushion for displaced tooth, hydraulic cushion from blood vessels)
  • Sensory (proprioceptive mechanism)
  • Nutritive (blood vessels provide anabolites and other substances)
  • Homeostatic (cells have capacity to resorb and synthesize)
• Sharpey's fibers


  Part of the collagen fibers embedded into cementum on one side of periodontal space and into alveolar bone on the other
• Oxytalan fibers


  Immature elastic fibers that run in axial direction, one end embedded in cementum or bone and the other in the wall of blood vessel, support blood vessels
• Elastic fibers


  Restricted to the walls of blood vessels
• The thickness of the periodontal ligament varies in different individuals, different teeth, and different locations
• The periodontal ligament is thinnest at the middle region of the root, thin in functionless and embedded teeth, and wide in teeth under excessive occlusal stresses
• The periodontal ligament in the periapical area of the tooth is often the site of pathologic lesions such as periapical abscesses, dental granulomas, and apical cysts
• Orthodontic tooth movement depends on resorption and formation of both bone and periodontal ligament
• If orthodontic tooth movement is within physiologic limits, there is compression/shortening of the periodontal ligament on the pressure side and elongation/widening on the tension side
• In restorative dentistry, the supporting tissues of a tooth long out of function are poorly adapted to carry the load suddenly placed on the tooth by a restoration
• Safeguarding the integrity of the periodontal ligament is one of the most important challenges for a clinician
• Pathological conditions that can affect the periodontal ligament include gingivitis and periodontitis