Cementum: An Overview

Definition and Location

• Cementum is a mineralized connective tissue on the root of the tooth.
• Extends from the cemento-enamel junction (thinnest) to the apex (thickest).
• May extend onto the inner dentinal wall of the root canal and coronal to the cemento-enamel junction onto the enamel surface.
• Part of the tooth but functionally part of the periodontium due to its position.

Development

• Develops during the Advanced Bell stage in tooth development.
• Hertwig’s Epithelial Root Sheath plays a key role in development.
• Cementoblasts are the cells responsible for depositing cementum.

Periodontium

• Osteoblasts line the alveolar bone.
• Fibroblasts are present in the periodontal ligament.
• Cementocytes: Entrapped cementoblasts with cytoplasmic extensions towards the periodontal ligament.

Histology

• Contains two types of collagen fibers:
  • Extrinsic fibers: Perpendicular to the surface; made by fibroblasts, 5-7 microns wide.
  • Intrinsic fibers: Parallel to the surface; formed by cementoblasts, 1-2 microns wide.

Classification of Cementum

Based on Cementocytes

• Cellular Cementum: Contains cementocytes; rapid deposition, presence of cementoid layer, and wide incremental lines.
• Acellular Cementum: No cementocytes; slow deposition, absence of cementoid layer, and closely spaced incremental lines.

Based on Organic Matter

• Extrinsic Fiber Cementum: Only extrinsic fibers.
• Intrinsic Fiber Cementum: Only intrinsic fibers.
• Mixed Fiber Cementum: Both intrinsic and extrinsic fibers.
• Afibrillar Cementum: No collagen fibers.

Schroeder Classification

• Acellular Extrinsic Fiber Cementum:
  • Covers whole root or 60-90% in single-rooted teeth; cervical 2/3rd in multi-rooted teeth.
  • Thickness: 50-200 microns; no cementocytes.
• Cellular Intrinsic Fiber Cementum:
  • May be absent or present in apical portion of single-rooted teeth; present in apical third and furcation area in multi-rooted teeth.
  • Contains cementocytes; major role in adaptation and repair.
• Cellular Mixed Stratified Cementum:
  • Present near root apex in single-rooted teeth; apical third and furcation in multi-rooted teeth.
  • Contains both intrinsic and extrinsic fibers in stratified layers; extrinsic fibers in peripheral most layer aid in anchorage.
• Cellular Mixed Fiber Cementum: Presence of cementocytes, intrinsic, and extrinsic fibers; non-stratified.
• Acellular Afibrillar Cementum: Found as isolated patches on enamel; no anchorage or repair function.

Intermediate Cementum

• Controversial origin; narrow homogeneous structure, 5-8 microns thick.
• Considered part of dentin by some, part of cementum by others.
• Referred to as Hyaline Layer of Hopewell-Smith (Acellular Extrinsic Fiber Cementum) or Intermediate Cementum (Cellular Mixed Stratified Cementum).