Lecture Notes: Periodontium and Cementogenesis

Overview of Periodontium

• Definition: The periodontium is the tissue that forms the supporting structure of a tooth.
• Components: Includes cementum, radicular dentin, and periodontal ligament.

Cementum

• Location: Lies between radicular dentin and periodontal ligament.
• Extent: Extends from the cemento-enamel junction to the apical foramen.

Cementogenesis

• Definition: Formation of cementum.
• Cells Involved: Cementoblasts.

Stages of Tooth Development

• Advanced Bell Stage:
  • Ameloblasts and odontoblasts begin depositing enamel and dentin.
  • Hertwigs Epithelial Root Sheath (HERS) forms from cervical loop epithelium.
  • Signals dental papilla cells to differentiate into odontoblasts.

Differentiation of Cementoblasts

• Sources of Cementoblasts:
  1. Dental Sac Cells:
     • Degeneration of HERS exposes ectomesenchymal cells to radicular dentin.
     • These cells differentiate into cementoblasts to deposit cementum.
  2. Hertwigs Epithelial Root Sheath:
     • Cells undergo epithelial-mesenchymal transformation into cementoblasts.

Characteristics of Cementoblasts

• Location: Present at the periphery of cementum towards the periodontal ligament.
• Types:
  • From dental sac: Similar to osteoblasts (plump, cuboidal or slightly flattened).
  • From HERS: Similar to fibroblasts (fusiform shaped).

Cementum Formation

• Cementoblast Function:
  • Cells from Dental Sac: Form cellular intrinsic fiber cementum.
  • Cells from HERS: Form acellular extrinsic fiber cementum.
• Components:
  • Organic: Mainly collagen fibers (Type 1).
  • Mineralized: Formed by hydroxyapatite crystals.

Cementoid Formation

• Process: Organic deposition followed by mineralization.
• Cementoid: Outermost thin layer of non-mineralized cementum.

Collagen Fibers in Cementum

• Sources:
  1. Intrinsic Fibers: Secreted by cementoblasts, parallel to cementum surface.
  2. Extrinsic Fibers: Formed by periodontal ligament fibroblasts, perpendicular to surface.
• Sharpey's Fibers: Aid in tooth anchorage.

Mineralization of Cementum

• Process: Involves hydroxyapatite crystals.

Incremental Lines of Salter

• Deposition: Cementum deposited rhythmically, forming incremental lines.
• Comparison: Cellular cementum forms faster than acellular, with more widely spaced lines.

Cementodentinal Junction Formation

• Process: Involves intermingling of collagen fibers from predentin and cementoid.
• Hyaline Layer of Hopewell-Smith: The initial predentin layer.

Cemento-enamel Junction Formation

• Development:
  • Involves ameloblast deposition of enamel at cervical loop.
  • HERS replaced by cementoblasts for cementum deposition.
  • Types of Junctions:
    • Edge to Edge/Sharp: Normal development.
    • Gap: Due to failure in cementoblast differentiation.
    • Overlap: Exposed enamel leads to additional cementum deposition.