Periodontal Ligament Question And Answers

Periodontal Ligament

Question 1. Describe in detail the structure of the periodontal ligament, (or) Discuss the cells and fibers of the periodontal ligament.
Answer:

Cells of periodontal ligament:

1. Synthetic cells:

1. Fibroblasts:
   • It is the predominant cell of PDL.
     1. Fibroblasts Origin:
        • Ectomesenchyme of investing layer of the dental papilla.
        • Dental follicle.
   • Fibroblasts Features:
     • These are large cells with extensive cytoplasm and abundant organelles, associated with protein synthesis and secretion.
     • The nucleus occupies a large volume of cells and contains one or more nucleoli.
     • They have cilia, a well-developed cytoskeleton with a prominent actin network.
     • They show frequent cell-to-cell contact between the adherents and the gap junction types.
   • Fibroblasts Function:
     1. Remodeling of collagen.
     2. Fibroblasts produce growth factors and cytokines.
     3. Stimulates the synthesis of collagen and inhibits the synthesis of collagenase.
     4. The cilia of fibroblast may be associated with control of the cell cycle or inhibition of centriolar activity.
2. Osteoblasts:
   • They are bone-forming cells lining the tooth socket.
   • They are cuboidal with prominent round nuclei.
   • They contain abundant rough endoplasmic reticulum, mitochondria, and vesicles.
   • These cells contact each other through desmosomes and tight junctions.
   • They contact with underlying osteocytes through the cytoplasmic process.
     1. Osteoblasts Function:
        • Constant apposition of bone-
3. Cementoblasts:
   1. They are almost cuboidal, with large vesicular nuclei, one or more nucleoli and abundant
   2. cytoplasm lining the surface of the cementum,
   3. They have an irregular outline,
      1. Cementoblasts Function:
         1. Aid in the reattachment of PDL fibers to root by forming fresh cementum whenever required,

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2. Resorplive cells:

1. Osteoclasts:
   • They may be large and multinucleated or small and mononuclear,
   • They are formed by the fusion of precursor cells.
   • Sometimes appear to occupy Howships lacunae.
   • The plasma membrane lying adjacent to the bone being resorbed has a folding called a ruffled border.
2. Osteoclasts Function:
   • They resorb bone.
3. Fibroblasts:
   • They contain organelles associated with the degradation of collagen.
   • They show the rapid generation of collagen by fibroblast phagocytosis.
4. Cementoclasts:
   • They resemble osteoclasts.
   • They are often located in Howship’s lacunae but during resorption, they are found on the surface of the cementum.

3. Progenitor cells:

• They have a perivascular location.
• They tend to have small, close-faced nuclei and very little cytoplasm.

Progenitor cells Functions:

• They divide to give rise to daughter cells which differentiate into functional cells.
• They replace differentiated cells at the end of their lifespan.

4. Epithelial rests of molasses:

• They are remnants of HERS
• They occur close to the cementum as clusters or strands of cells.
• They are abundant in the furcation areas.
• They are cuboidal, with a prominent nucleus and scanty cytoplasm.
• Tight junctions are seen between the cells.
• These cells may proliferate to form cysts and tumors or may also undergo calcification to become cementicles.

5. Defense cells:

1. Mast cells:
   • They are round or oval cells, with numerous cytoplasmic granules and small, round nuclei.
   • Mast cells Functions:
     • Plays a role in the inflammatory reaction through the release of histamine.
     • Causes the proliferation of endothelial cells and mesenchymal cells.
     • Regulate endothelial and fibroblast cell population.
2. Macrophages:
   • Macrophages Site: Predominantly located close to blood vessels.
   • Derived: from monocytes.
     • Macrophages Functions:
       • Phagocytosing dead cells.
       • Secreting growth factors.
       • Regulate the proliferation of adjacent fibroblasts.
       • Enhance the growth of fibroblasts and endothelial cells.
3. Eosinophils:
   • Consist of one or more crystalloid structures.
   • Capable of phagocytosis.

Extracellular substance:

1. Ground substance:

• It binds tissue and fluids which leads to diffusion of gases and metabolic substances.
• It consists of glycoproteins and proteoglycans.
• It helps in tire transportation of materials from and to the cells.

2. Interstitial tissue:

• It is composed of blood vessels, nerves, and lymphatics.
• Blood supply is through branches of superior and inferior alveolar arteries.
• Types of nerve endings in PDL are free nerve endings, Ruffini corpuscles, knob type, and spindle type.
• A network of lymphatics follows the blood vessels.

Fibers of PDL:

• Principal fibers:

 

1. Alveolar crest group:

• Attached to the cementum just below the CEJ.
• Inserted into the rim of the alveolus.

2. Horizontal group:

• Located just apical to the alveolar crest group.
• They ran at right angles to the long axis of the tooth from cementum to bone just below the alveolar crest.

3. Oblique group:

• Run from the cementum in an oblique direction and insert into the bone coronally.

4. Apical group:

• Radiate from the cementum around the apex of the root to the bone.

5. Interradicular group:

• Found between the roots of multirooted teeth running from the cementum into the bone.

Fiber bundles composing ligament:

1. Dentogingival group:

• Extends from cervical cementum to lamina propria of the free and attached gingiva.

2. Alveologingival group:

• Extends from the bone of the alveolar crest to lamina propria of the free and attached gingiva.

3. Circular group:

• It forms a band around the neck of the tooth.

4. Dentoperiosteal group:

• Runs apically from the cementum up to the alveolar process.

5. Transseptal fiber:

• Run interdentally from the cementum of one tooth to the cementum of the adjacent tooth.

Elastic Fibers:

Elastic Fibers Types:

Elastin fibers:

• Observed only in walls of afferent blood vessels.

Oxytalanfibers:

• They are numerous and dense in the cervical region of the ligament.
• They run parallel to the gingival group of collagen fibers.
• They regulate vascular flow in relation to tooth function.

Elauninfibers:

• They are found within fibers of the gingival ligament.

Reticular fibers:

• They are composed of type 3 collagen.

Secondary fibers:

• They are located between and among the principal fibers and are randomly oriented.

Indifferent fiber plexus:

• These are small fibers running in all directions forming a plexus called indifferent fiber plexus.

Question 2. Alveolar crest group of fibers.
Answer:

• They radiate from the crest of the alveolar process and attach themselves to the cervical part of the cementum.
• They are located beneath the junction epithelium.

Alveolar crest group of fibers Function:

• They resist tilting, intrusive, extra use, and rotational forces.