Unit 7 Study Notes on Periodontium and Cementum

Unit 7

The study of Periodontium, which comprises various structures such as Cementum, Gingival Tissues, Periodontal Ligament, and Alveolar Bone.

Cementum

  • Definition: Cementum is a type of hard connective tissue found on the surface of the tooth root, essential for connecting the tooth to the periodontal ligament and supporting the structure of the tooth in the alveolar bone.
Physical and Chemical Properties
  • Hard connective tissue: Cementum is categorized as a hard connective tissue, indicating its structural robustness.
  • Mineralization: It is slightly less mineralized than bone and dentin, which means it has a lower content of mineral substances.
  • Colour: The color of cementum is light yellow.
  • Distinction: It can be distinguished from enamel as it lacks specific features characteristic of enamel (noted that it has no vascularity, implying a lack of blood supply).
  • Avascular: Cementum does not contain blood vessels, emphasizing its dependency on surrounding tissues for nourishment.
  • Non-innervated: It lacks nerve endings, making it insensitive to pain.
Chemical Characteristics
  • Organic Matrix: Cementum consists of approximately 50-55% organic material.
  • Inorganic Material: Constitutes about 45-50%, primarily in the form of hydroxyapatite crystals (which provide strength and structure).
Development of Cementum
  • Intermediate Cementum: The first type of cementum formed, also known as the Hyaline layer, characterized by:
      - Formation by inner epithelial root sheath cells.
      - It mineralizes more than the adjacent dentin.
      - Composed of enamelin-like protein instead of collagen.
  • Cementogenesis Process:
      1. Cells of the Hertwig’s Epithelial Root Sheath (HERS) secrete a layer of intermediate cementum that is highly mineralized (10-20 µm thick) on root dentin, sealing dentinal tubules.
      2. After deposition of intermediate cementum, the root sheath fragments, allowing follicular cells to migrate.
      3. Ectomesenchymal cells from the dental follicle differentiate into cementoblasts; these cells commence the deposition of the organic matrix of cementum.
      4. The organic matrix of the first cementum is subsequently calcified by hydroxyapatite spread from the root dentin, and this process does not require matrix vesicles.
  • Organic Matrix of Cementum is termed Cementoid.
Classification of Cementum
  • Cementum can be classified based on three factors:
      - Time of Formation: Primary versus Secondary cementum.
      - Cellular Composition: Acellular versus Cellular cementum.
      - Collagen Fiber Origin:
        - Intrinsic: Fibers produced by cementoblasts.
        - Extrinsic: Fibers produced by periodontal ligament fibroblasts (Sharpey’s Fibers).
Acellular vs. Cellular Cementum
  • Acellular Cementum:
      - Type: Primary cementum.
      - Location: Extends from cervical margin to two-thirds of the root.
      - Characteristics: Contains no cementocytes, mainly extrinsic fibers, and is more calcified.
      - Function: Provides anchorage to the tooth.
  • Cellular Cementum:
      - Type: Secondary cementum.
      - Location: Typically found on the apical third of the root.
      - Characteristics: Presence of cementocytes within lacunae, lesser extrinsic fibers, mainly intrinsic fibers.
      - Function: Involved in adaptation and repair of periodontal structures.
Cementocytes
  • Cementoblasts transition into Cementocytes as they become embedded within the matrix, taking on a spider-like appearance.
  • Cementocytes reside in lacunae, exhibiting numerous processes known as canaliculi radiating from their bodies, facilitating communication and nutrient exchange.
Functions of Cementum
  1. Attachment: Serves as the medium connecting other periodontal structures (like periodontal ligament) to the tooth; perforating fibers become embedded in cementum, anchoring the tooth.
  2. Sealing: Closes off open dentinal tubules on the root dentin, offering protection to the tooth structure.
  3. Protective Role: Cementum is generally less prone to resorption compared to bone. The formation of secondary cementum continues throughout an individual's life and is enhanced by:
      - Traumatic Occlusion: Excessive stress on teeth can lead to cementum deposition.
      - Hypereruption: Over-eruption of teeth increases cementum deposition, potentially leading to conditions like Hypercementosis.
CEJ Variations (Cementoenamel Junction)
  • The relationship between enamel and cementum can be classified into three variations:
      1. Overlap (60%): In this variation, cementum overlaps with enamel.
      2. Meet (30%): Cementum and enamel meet at a defined junction.
      3. Gap (10%): There is a gap where cementum does not meet enamel.
Age Changes in Cementum
  1. The surface becomes increasingly irregular due to calcifications at ligament fiber bundle attachments.
  2. Continuous cementum deposition in the apical zone may lead to apical canal obstruction.
  3. Cementum may undergo resorption throughout life.
Cementicles
  • Definition: Mineralized bodies of cementum found within the periodontal ligament space, categorized as free, attached, or embedded and can occur singly or in groups.
  • Formation Theories:
      - Development from epithelial rests of Malassez.
      - Formation around undifferentiated mesenchymal cells in the PDL.
      - Development around cellular debris.
  • Cementicles are more common in older individuals but can also appear in areas experiencing trauma.

Bone Histology and Alveolar Bone Structure

  • Bone is a specialized form of connective tissue composed of various cells and intercellular materials.
Bone Cells
  • The major types of bone cells include:
      - Osteoblasts: Cells responsible for bone formation.
      - Osteocytes: Mature bone cells which manage bone maintenance.
      - Osteoclasts: Cells involved in bone resorption.
Intercellular Material
  • Composed of both organic and inorganic components:
      - Organic Material: Approximately 35% including cells, collagen fibers, and ground substance (proteins).
      - Inorganic Material: Approximately 65% consisting chiefly of calcium and phosphate found in form of hydroxyapatite crystals.
Classification of Bone Types
  • Bones can be classified into various shapes:
      - Long: Examples include femur and humerus.
      - Short: Examples are carpals and tarsals.
      - Flat: Includes skull bones and ribs.
      - Irregular: Such as vertebrae.
  • Bone tissue comes in two patterns:
      - Compact Bone: Also referred to as cortical bone, dense layer at the outer surface.
      - Spongy (Trabecular) Bone: Also known as cancellous bone, characterized by a porous, lattice-like structure.
Membranes Associated with Bone
  • Periosteum: A thin connective tissue membrane covering the outer surface of all bones, involved in growth, repair, and nutrition of the bone.
  • Endosteum: A delicate connective tissue lining the internal surfaces of bones, involved in the growth and repair processes within the cortical and cancellous bones.
Additional bone structures**

  - Bone Marrow: The central, vascular пространцы within the bone that produces blood cells and stores fatty acids.
  - Trabecular/Cancellous Bone: This is the spongy, inner part of the bone, which is less dense than compact bone and contains marrow spaces.

Conclusion

Understanding the structure and function of cementum and bone within the periodontium is crucial for comprehending oral health and disease, as these components play vital roles in dental stability and overall periodontal health.