Histology of PDL hard

Periodontal Ligament

• Connective tissue surrounding tooth root and connecting it to the alveolar bone
• Continuous with gingival connective tissue and communicates with bone marrow spaces
• Merges with dental pulp at the root apex
• Contains a rich blood supply and is very sensory

Functions of the Periodontal Ligament

• Sensory: Rich nerve fibers transmit touch, pressure, temperature and pain
• Physical: Attaches the tooth to the alveolar bone, maintains tooth position, transmits occlusal forces to bone, acts as a shock absorber
• Nutritive: Rich blood supply provides nutrition for cells, supports formation and resorption
• Formative & Resorptive: High cell turnover, facilitates bone and cementum formation and resorption

Periodontal Ligament Width

• Average width of the PDL is 0.2mm (range 0.15mm to 0.38mm)
• Width varies with loading conditions:
  • Heavy loaded: Wider at the crest and fundus of the alveolus
  • Normally loaded: Narrower at the crest and fundus of the alveolus
  • Functionless: Narrowest at the crest and fundus of the alveolus
• The PDL adapts to pressure and loading conditions, becoming wider and more noticeable on radiographs

Radiographic Appearance

• The PDL appears as the periodontal space on radiographs
• It is a radiolucent area between the lamina dura of the alveolar bone proper and radiopaque cementum
• The periodontal space is narrower in permanent teeth than deciduous teeth

Development

• The PDL develops from the dental follicle after root development begins.
• Fibroblasts in the follicle produce collagen.
• Initial fibers lack organization and become oblique to the tooth.
• The first fibers are apical to the cementoenamel junction (CEJ) and give rise to gingivodental fibers.
• As eruption progresses, more fibers develop and become attached to new cementum and bone.
• Cemental Sharpey's fibers appear first, followed by Sharpey's fibers in the bone.
• After eruption, alveolar fibers extend into the middle zone to join the lengthening cemental fibers, gaining thickness and strength during occlusal function.

Structural Elements

• Cells:
  • Formative: Osteoblasts, fibroblasts, cementoblasts
  • Resorptive: Osteoclasts, cementoclasts, fibroblasts
  • Progenitor: Undifferentiated mesenchymal cells, replacing dying cells
  • Defense: Mast cells, macrophages
• Epithelial Rests of Malassez: Epithelial cells found near the cemental side of the PDL, remnants of Hertwig's epithelial root sheath
• Extracellular Substance:
  • Fibers: Collagen fibers (mainly)
  • Ground Substance: Water, collagen fibers, tissue fluid pressure high (10mmHg above atmospheric pressure)

Blood Supply

• Main blood supply originates from:
  • Superior and inferior alveolar arteries
  • Penetrating vessels from the alveolar bone
  • Anastomosing vessels from the gingiva

Nerve Supply

• Two types of nerves:
  • Sensory: Touch, pressure, pain
  • Autonomic: Associated with PDL vessels
• Branches of the second and third division of the 5th cranial nerve (trigeminal nerve)

Principal Fiber Groups

• All fibers are made of collagen and are organized into groups according to orientation and function.
• Functions include distributing forces of mastication and speech.
• Principal fibers are embedded into cementum and bone, known as Sharpey's fibers.
• Main groups include:
  • Alveolar Crest Group: Prevents tooth extrusion, resists lateral, tilting, and intrusive forces
  • Horizontal Group: Resists horizontal and tipping forces
  • Oblique Group: Resists vertical masticatory forces, prevents tooth intrusion
  • Apical Group: Resists vertical, luxative, and twisting forces, protects nerves and vessels at the apex
  • Interradicular Group: Resists vertical and lateral movement, tipping, torquing, and luxation

Interdental Ligament (Transseptal Fibers)

• Important fibers that run through the gingival mucosa to connect neighboring teeth
• Insert interdentally into cervical cementum of neighboring teeth over the alveolar crest
• Resist rotational forces and keep teeth in alignment
• Maintain gingival integrity

Gingival Fiber Group

• Separate but adjacent fiber groups within the lamina propria of the marginal gingiva

Ground Substance Functions

• Exchange of metabolites
• Ion and water binding
• Fibre orientation
• Tooth support and binding mechanisms
• Removal of toxins and nutrient delivery

Age Changes

• Decrease in cells
• Increase in fibrous tissue
• Decrease in vascularity and mitotic activity
• Narrowing of PDL width
• Scalloping seen on calcified tissues (bone, cementum)

Clinical Considerations

• Understanding PDL function is crucial for dental practice.
• Considerations include:
  • Preventing damage to the PDL during procedures
  • Understanding how changes in PDL structure affect tooth movement and stability
  • Recognizing signs of PDL damage in periodontal disease

This quiz covers the essential aspects of the periodontal ligament, including its anatomy, functions, and characteristics. Explore how the periodontal ligament connects teeth to the alveolar bone and its role in sensory perception and nutrient supply. Learn about the average width of the PDL and how it varies under different loading conditions.