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. Describe the histology and functions of PDL.
Answer:

Functions of PDL:

1. Supportive:

• When a tooth is moved in its socket due to the force of mastication or orthodontic force, part of the periodontal space is narrowed while the other is widened.
• The periodontal ligament in the narrow periodontal space is compressed.
• The collagen fibers in this area act as a cushion for the displaced tooth.

2. Sensory:

• When teeth move in their sockets, they distort receptors in the PDL and trigger a response.
• PDL carries tactile sensation from teeth and hence helps in the localization of pain.
• PDL contributes to the sensation of touch and pressure.

3. Nutritive:

• The blood vessel within the PDL provides nutrition to the centrocytes of the PDL and osteocytes of the alveolar bone.
• The blood vessel also helps in the removal of the catabolites from the cells.

4. Homeostatic:

• The cells of the PDL have the capability to synthesize and resorb the extracellular substance of the connective tissue of the ligament.
• If the balance between synthesis and resorption is disturbed, the quality of the tissue is changed.
• This gradually leads to loss of attachment which results in tooth loss.
• In all areas of PDL, there is continual cell death which is replaced by new cells produced by the division of progenitor cells.

5. Eruptive:

• PDL components enable teeth to adjust their position.
• PDL provides space and acts as a medium for cellular remodeling and hence continued eruption occurs.

6. Physical:

• PDL protects vessels and nerves from mechanical forces.
• It offers resistance to impact from occlusal forces.
• Acts as a shock absorber to transmit occlusal forces to the bone.

7. Pormative/Resorptive:

• Cementoblast and osteoblast form cementum and bone respectively.
• Cementoclast and osteoclast resorb cementum and bone respectively.

Question 3. Cell rests of Malassez.
Answer:

• They were first described by Malassez in 1884.
• They are remnants of HERS.

Cell rests of Malassez Site:

• Found close to the cementum.
• Abundant in the furcation areas.

Cell rests of Malassez Features:

1. Cell-cuboidal, closely packed.

2. Cytoplasm.

• Scanty.
• Contains tonofibrils inserted into desmosomes and hemidesmosomes.

3. Nucleus

• Prominent and deeply stained.

4. Cell organelles.

• Mitochondria are distributed throughout the cytoplasm.
• Poorly developed rough endoplasmic reticulum and approx
• Less – in older individuals.
• More- in children.

2. In position.

Apical region – during the second decade of life

Cervically – later life.

Cell rests of Malassez Fate:

pathological conditions, they undergo rapid proliferation and produce a variety of cysts and tumors or may also undergo calcification to become clementines.

Question 4. Functions of PDL
Answer:

1. Supportive

• When a tooth is moved in its socket due to the force of mastication or orthodontic force, part of the periodontal space is narrowed while the other is widened
• The periodontal ligament in the narrow periodontal space is compressed
• The collagen fibers in this area act as a cushion for the displaced tooth

2. Sensory

• When teeth move in their sockets, they distort receptors in the PDL and trigger a response
• PDL carries tactile sensation from teeth and hence helps in the localization of pain
• PDL contributes to the sensation of touch and pressure

3. Nutritive

• The blood vessel within the PDL provides nutrition to the cementocytes of the PDL and osteocytes of the alveolar bone
• The blood vessel also help in the removal of the catabolites from the cells

4. Homeostatic

• The cells of the PDL have the capability to synthesize and resorb the extracellular substance of the connective tissue of the ligament
• If the balance between synthesis and resorption is disturbed, the quality of the tissue is changed
• This gradually leads to loss of attachment which results in tooth loss
• In all areas of PDL, there is continual cell death which is replaced by new cells produced by the division of progenitor cells

5. Eruptive

• PDL components enable teeth to adjust their position
• PDL provides space and acts as a medium for cellular remodeling and hence continued eruptions occur

6. Physical

• PDL protects vessels and nerves from mechanical forces
• It offers resistance to impact from occlusal forces
• Acts as a shock absorber to transmit occlusal forces to the bone

7. Formative/Resorptive

• Cementoblast and osteoblast forms cementum and bone respectively
• Cementoclast and osteoclast resorbs cementum and bone respectively

Question 5. Resorptive cells
Answer:

• Osteoclast
• Multinucleated giant cells
• Lies adjacent to the bone
• Undergoes resorption of bone
• Formed by monocytes
• Fibroblast
• Contains fragments of collagen
• These undergoes digestion
• Results in resorption of bone
• Cementoclast
• Located in Howship’s Lacunae
• Causes resorption of cementum

Question 6. Periodontium.
Answer:

• It is defined as those tissues supporting and investing in the tooth.
• It attaches the teeth to the bones of the jaws and supports the teeth.

It consists of:

• Cementum.
• Periodontal ligament.
• Bone lining the socket.
• Part of the gingiva facing the tooth.
• It is attached to the dentin of the root by cementum and to the bone of the jaws by alveolar bone,
• The periodontium loss can be repaired by the cells regulating the formation, maintenance, and regeneration of the periodontium.

Question 7. Cell rest of Malassez.
Answer:

• They are remnants of HERS.
• They are found close to the cementum and are found abundant in furcation areas.
• They consist of closely packed cuboidal cells with prominent nuclei and scanty cytoplasm.
• They persist as strands, islands, or tubelike structures close to the cementum.
• They may show variations in number and site with respect to age.

Question 8. Oxytalin fibers.
Answer:

• They are a type of immature elastic fibers.
• They consist of microfibrillar components only.
• Size: 0.5 – 2.5 pm in diameter (approx.)
• They are not susceptible to acid hydrolysis.
• Fibers run in the axial direction.
• One end is embedded in cementum/bone and the other is in the wall of blood vessels.
• They play a role in tooth support and regulate vascular flow.
• They are numerous and dense in the cervical region of the ligament.

Question 9. Fibroblasts.
Answer:

• It is the predominant cell of PDL.
• They originate from the ectomesenchyme of the investing layer of the dental papilla.
• They are spindle-shaped large cells with extensive cytoplasm and abundant organelles with large nuclei.
• They consist of cilia which are associated with the control of the cell cycle.
• They play an important role in the remodeling of collagen which includes collagen synthesis and . degradation of collagen.

Question 10. Periodontal ligament.
Answer:

• It is soft, specialized connective tissue situated between the cementum covering the root of the tire tooth and the bone forming the socket wall.
• Width: 0.15 – 0.38 mm.

Periodontal ligament Cells:

1. Synthetic cells

1. Osteoblasts
2. Fibroblast
3. Cementoblast.

2. Resorptive cells.

1. Osteoclast
2. Fibroblast
3. Cementoclast

3. Progenitor cell.

4. Epithelial rest of malassez.

5. Defense cells.

• Macrophages
• Eosinophils.

Periodontal ligament Functions:

• Supportive
• Sensory
• Nutritive
• Homeostatic
• Eruptive
• Physical

Question 11. Cells of periodontal ligament.
Answer:

Question 12. Sharpey’s fibers.
Answer:

• These are collagen fibers that are embedded into the cementum on one side and into the alveolar bone on another side.
• Fibers in primary acellular cementum are fully mineralized while those in cellular cementum and bone are partly mineralized.
• Their mineralized part appears as a projecting covered with mineral clusters.
• Few of them pass uninterrupted through the alveolar bone to continue as principal fibers of PDL.
• It passes through alveolar bone only when it consists entirely of compact bone.
• It consists of noncollagenous proteins like osteopontin and bone sialoprotein.

Question 13. 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.

Question 14. Synthetic cells of PDL.
Answer:

Question 15. Transseptal fibers.
Answer:

• These fibers run interdentally from the cementum apical to the junctional epithelium of one tooth over the alveolar crest to a similar region of the adjacent tooth.
• By these, all tire teeth are connected in an arch.
• They are responsible for post-retention relapse of orthodontic treatment.
• They are capable of turnover and remodeling under normal physiologic conditions and therapeutic tooth movement.
• They ensure clinical stability of tooth position.

Question 16. Bundle fibers of the periodontal membrane.
Answer:

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.

Question 17. Age changes in the periodontal ligament.
Answer:

• The cell number and activity decrease with age
• PDL fibers become attached to the scalloping ends of the alveolar bone.
• PDL activity decreases.
• Destructive changes occur due to the presence of gingival and periodontal diseases in old age.
• Some of the teeth become non-functional.
• PDL width decreases.

Question 18. Birbeck’s granules
Answer:

• They are named after its discoverer Michael Stanley Clive Birbeck
• It is a rod-shaped cytoplasmic organelle
• Found in Langerhans cells

Birbeck’s granules Functions:

• They migrate to the periphery of Langerhans cells and release its contents into the extracellular matrix
• Act as receptor-mediated endocytosis

Question 19. Principal fibers
Answer:

1. Trans-septal fibers
   • Connects cementum of one tooth with that of other
2. Alveolar crest
   • Extends from cementum to alveolar crest

Principal fibers Functions:

1. • Retains tooth in the socket
   • Retains lateral tooth movement
2. Horizontal Group
   • Extends from cementum to alveolar bone
3. Oblique group
   • Extends coronally from the cementum to the bone
   • Periodontal Ligament

Functions:

• Resist axially directed forces
• Apical group
• Extends from the cementum to the bone of the alveolar fundus

Functions:

• Prevents tipping movement
• Resists luxation
• Inter-radicular fibers
• It is present between the cementum of multi-rooted teeth

Functions:

• Resists luxation Resists tipping and torquing

Question 20. The protective function of PDL
Answer:

• The periodontal ligament protects vessels and nerves from mechanical forces
• It offers resistance to impact from occlusal forces
• Acts as a shock absorber to transmit occlusal forces to the bone.