PdL

• Periodontal ligament (PDL)

  Connective tissue structure that surrounds the root and connects it with the bone

  
• Periodontal ligament space

  • Has the shape of an hourglass and is narrowest at the mid root level
  • Width is approximately 0.25+ 50 percent
• Cells of PDL

  • Synthetic cells (Osteoblast, Fibroblast, Cementoblasts)
  • Resorpative cells (Osteoclasts, Cementoclasts, Fibroblasts)
  • Progenitor cells
  • Epithelial rest of malassez
  • Connective tissue cells (mast cells and macrophages)
• Osteoblasts

  Cover the periodontal surface of the alveolar bone and are responsible for the formation of alveolar bone
• Fibroblasts

  The most prominent connective tissue cells (65%), produce various types of fibers and connective tissue matrix
• Cementoblasts

  Line the cementum and are responsible for cementum deposition
• Osteoclasts

  Resorb the bone and tend to be large and multinucleated
• Fibroblasts (resorptive)

  Synthesize collagen and possess the capacity to resorb and degrade the old collagen fibers
• Cementoclasts

  Resorb cementum in certain circumstances
• Progenitor cells

  Differentiate into functional type of connective tissue cells
• Epithelial rest of Malassez

  Found close to cementum, can undergo rapid proliferation and produce cysts and tumors under certain pathologic conditions
• Mast cells

  Play a role in inflammatory reaction
• Macrophages

  Capable of phagocytosis
• Extracellular components of PDL

  • Fibers (Collagen, Oxytalan)
  • Ground substances (Proteoglycans, Glycoproteins)
• Periodontal fibers

  The most important elements of the periodontal ligament, collagenous in nature and arranged in bundles following a wavy course
• Sharpey's fibers

  The terminal portion of the principal fibers that insert into the cementum and bone

  
• Principal fiber groups of PDL

  • Alveolar crest fibers
  • Horizontal group
  • Oblique group
  • Apical group
  • Inter-radicular fibers
• Alveolar crest fibers

  • Extend obliquely from the cementum just beneath the junctional epithelium to the alveolar crest, retain tooth in socket and resist lateral movement

  
• Horizontal group

  • Extend from cementum to the alveolar bone at right angle to the long axis of the tooth

  
• Oblique group

  • The largest group, extend coronally in an oblique direction from the cementum to the bone, resist axial directed forces
• Apical group

  • Radiate from the cementum of root apex to the bone, prevent tooth tipping, resist luxation, and protect blood, lymph and nerve supply of the tooth

  
• Inter-radicular fibers

  • Extend from cementum of bifurcation areas, splaying from apical into furcal bone, resist luxation and also tipping and torquing

  
• Ground substance

  Made up of glycosaminoglycans (such as hyaluronic acid, proteoglycans) and glycoproteins (such as fibronectin and laminin), has high water content (70%)
• Development of principal fibers of PDL

  1. Small, fine brush like fibrils arise from root cementum

  2. Small fibers seen on bone surface in thin, small numbers

  3. Number and thickness of fibers originating from bone increase and elongate

  4. Fibers originating from cementum increase in length and thickness and fuse with fibers from bone

  5. Following tooth eruption, principal fibers become organized in bundles and run continuously from bone to cementum

  
• Structures present in the connective tissue of PDL

  • Blood vessels
  • Lymphatics
  • Nerve intervention
  • Cementicles
• Blood vessels in PDL

  Supplied by branches derived from dental, inter-radicular and interdental arteries
• Lymphatics in PDL

  Follow the path of blood vessels
• Nerve intervention in PDL

  Mainly supplied by dental branches of the alveolar nerve, has mechanoreceptors providing sense of touch, pressure, pain and proprioception during mastication
• Cementicles

  Calcified masses adherent to or detached from the root surface
• Functions of PDL

  • Physical
  • Formative and remodeling
  • Nutritional and sensory
• Physical functions of PDL

  • Provide soft tissue "casing" to protect vessels and nerves
  • Transmit occlusal forces to the bone
  • Attach teeth to the bone
  • Maintain gingival tissues in proper relationship to teeth
  • Resist the impact of occlusal forces (shock absorption)

  
• Formative and remodeling functions of PDL

  Cells control synthesis and resorption of cementum, ligament and alveolar bone, PDL undergoes constant remodeling
• Nutritive functions of PDL

  Provides nutrition to cementum, bone, and gingiva due to rich vascular supply
• Sensory functions of PDL

  Supplied with sensory nerve fibers which transmit sensation of touch, pressure and pain to higher centers
• The width of PDL space varies with age, location of tooth, degree of stress to which the tooth was subjected
• In compliance with the physiologic mesial migration of the teeth the PDL is thinner on the mesial root surface than on the distal surface

  
• A tooth in hyperfunction may have a wider PDL space and a tooth in hypofunction may have a narrow PDL space

  
• The width of PDL space is about 0.25mm in normal functions, widest at the cervical and apical portions of the root and narrowest at the middle
• The most interesting features of the PDL are its adaptability to rapidly changing applied force and its capacity to maintain its width at constant dimensions throughout its lifetime