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Pdl Flashcards

1
Q

What is the periodontal ligament (PDL)?

A

The Periodontal ligament is the soft, richly vascular & cellular CT which surrounds the roots of the teeth & joins the root Cementum with alveolar bone proper.

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2
Q

What is the PDL space?

A

PDL SPACE represents periodontal ligament area. The thickness of the ligament varies from 0.25-0.40 mm.

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3
Q

What is the thickness / width of the ligament?

A

The thickness of the ligament varies from 0.25 - 0.40 mm, being wider at the socket mouth and apex and narrowest at the mid-area.

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4
Q

What factors affect the width of the pdl space?

A

Width of PDL space varies with:
•Patients- more in young persons
•Tooth- less in hypo function

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5
Q

What are the principal fibers of the PDL?

A

•Alveolar crest fibers
•Horizontal fibers
•Oblique fibers (resist apical-directed forces)
•Apical fibers
•Interradicular fibers (in multi-rooted teeth)

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6
Q

What factors influence tooth mobility?

A

In health there is normal range of
mobility, influenced by
•the amount & duration of applied load,
•length & shape of roots,
•thickness of PDL fibers (erupting tooth more mobile)
•amount of ground substance
•Incisors are more mobile

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7
Q

How does PDL width vary with function?

A

PDL is thicker with subject to functional forces
& thinner when tooth is functionless.

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8
Q

What is the structure / composition of PDL?

A
  1. Cells (synthetic, resorptive, progenitor, epithelial rests of malassez, defense cells)
  2. Extracellular substances (fibers & ground substance)
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9
Q

What are the synthetic cells in PDL?

A

Osteoblasts
Fibroblasts
Cementoblasts

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11
Q

What are the resorptive cells in PDL?

A

Osteoclasts
Fibroblasts
Cementoclasts

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12
Q

What are the defense cells in PDL?

A

Mast cells
Macrophages
Eosinophils

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13
Q

What are the extracellular substances in PDL?

A
  1. Fibers (collagen, oxytalan fibers)
  2. Ground substance (proteoglycans & glycoproteins)
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14
Q

Which structures form the attachment apparatus?

A

Cementum, periodontal ligament and alveolar bone.

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15
Q

Which cell is predominant in the PDL and what is its function?

A

Fibroblasts – they synthesize collagen.

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16
Q

What are the functions of fibroblasts?

A
  1. Synthesize collagen
  2. Synthesize fibrils
  3. Organize fibrous network and generate force for tooth eruption.
  4. Produce extracellular matrix of PDL.
  5. Have capacity to give rise to Cementoblasts and osteoblasts.
  6. Maintain normal width of PDL.
  7. Synthesize and shape the proteins of ECM in which collagen fibrils form bundles and insert as sharpeys fibers.
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17
Q

What are Sharpey’s fibers?

A

Certain fibrils form bundles, get inserted into tooth and bone and are known as Sharpey’s fibers.

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18
Q

What is the role of osteoblasts in the PDL?

A

• These cells cover the periodontal surface of the alveolar bone.
• Line the tooth socket and are cuboidal in shape with a prominent round nucleus at the basal end of the cell.

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19
Q

What are cementoblasts?

A

These cells line the surface of cementum.
They are cuboidal with a large vesicular nucleus, with one or more nucleoli and abundant cytoplasm.

20
Q

What are osteoclasts, and what do they do?

A

These resorb bone and tend to be large and multinucleated but can
also be small and mononucleated.

21
Q

What are cementoclasts, and when do they appear?

A

Cementoclasts are not usually found in the ligament. These cells only occur in certain pathologic conditions, during resorption of deciduous teeth and when regressive forces are applied on a tooth such as orthodontic therapy.

22
Q

What are progenitor cells in the PDL?

A

• All connective tissues including PDL contain progenitors cells that have the capacity to undergo mitotic division.
• Are the undifferentiated mesenchymal cells.
• When stimulated appropriately, these cells undergo mitotic division and can differentiate into fibroblast, osteoblast or cementoblast.

23
Q

What are the epithelial cell rests of Malassez?

A

• Remnants of the epithelium of Hertwig’s epithelial root sheath.
• Their function is not yet clear but they could be involved in periodontal repair and regeneration.
• These cells may undergo calcification to become CEMENTICLES.

24
Q

What are the two main components of extracellular substances in the PDL?

A

• Fibers: Collagen, elastic, reticular, secondary, oxytalan, indifferent fiber plexus.
• Ground Substance: Proteoglycans, glycoproteins.

25
Q

What are the main types of collagen in the PDL?

A

Main types of collagen in the PDL: Type I and type III

26
Explain type I collagen in the PDL?
More than 70% of PDL is type I. Type I is uniformaly distributed in the ligament.
27
Explain type III collagen in the PDL?
Type III collagen accounts for about 20% of collagen fibers, found in periphery of Sharpey's fiber attachments into alveolar bone.
28
Explain type IV and type VII collagen fibers?
Type IV and type VII are associated with epithelial cell rests and blood vessels.
29
Explain type XIII collagen fibers?
Type XIII collagen occurs within the PDL only when the ligament is fully functional.
30
Define Principle Fibers.
Collagen fibers in the PDL form bundles, approximately 5 µm in diameter. These bundles are termed as Principle Fibers, that attach the tooth to bone.
31
What are the collagen fibrils?
Within each collagen bundle, subunits are present called collagen fibrils.
32
What is the ground substance in the PDL?
Gel like matrix synthesized by fibroblast family & fills the space between fibers and cells.
33
What is the composition of ground substance in the PDL?
• Consists of a biochemically complex, highly hydrated, semisolid gel. • 70% water content. • Glycosaminoglycans - hyaluronic acid, Proteoglycans (versican, decorin) • Glycoproteins (fibronectin, laminin, vibronectin, tenascin).
34
What are the functions of PDL?
Physical Functions Formative & Remodeling Function Nutritional Function Homeostatic Function Sensory Function
35
What are the physical functions of PDL?
• Provide a soft tissue cushioning effect to protect the vessels and nerves from injury by mechanical forces. • Transmission of occlusal forces to the bone. • Attachment of the teeth to the bone. • Resistance to the impact of occlusal forces (Shock absorption).
36
What are the formative and remodeling functions of PDL?
• Cells of the PDL participate in the formation and resorption of cementum and bone. • Remodeling : The 3-D organization of the fiber meshwork is adapted to accommodate for positional changes of the tooth in its socket or changes in functional state. • The PDL is constantly undergoing remodeling. Old cells & fibers are broken down & replaced by new ones.
37
What is the nutritional function of PDL?
PDL supplies nutrients to the cementum, bone, and gingiva by way of blood vessels and provides lymphatic drainage.
38
What is the homeostatic function of PDL?
Adaptability to rapidly changing applied forces and its capacity to maintain its width at constant diameter throughout life.
39
What are the sensory functions of PDL?
• Supplied with sensory nerve fibers that transmit tactile, pressure & pain sensations by the trigeminal pathway. • provides a most efficient proprioceptive mechanism. •4 types of neural transmissions seen in PDL: Free nerve endings, Ruffini-like mechanoreceptors, Meissner’s corpuscles, Spindle-like pressure & vibration endings.
40
What are the 4 types of neural transmissions seen in PDL?
1. Free nerve endings – Detect pain (at regular intervals along the length of the root). 2. Ruffini-like mechanoreceptors (found in the apical area, sense pressure) 3. Meissner’s corpuscles – mechanoreceptors, located in the mid-PDL, sense fine touch. 4. Spindle-like endings – Detect vibration and positional changes (located at the apex).
41
What is the PDL relationship with implants?
PDL is absent around implants.
42
What happens in the absence of the PDL around dental implants?
1. No resilient connection between the tooth and jaw bone. 2. Any occlusal disharmony affects the bone-implant interface. 3. No intrusion or migration can compensate for premature contact. 4. Reduced tactile sensitivity and reflex function due to absence of PDL.
43
How does the PDL respond to forces?
• Axial forces are absorbed readily. • Lateral/rotational forces absorb less easily. • On loading, PDL fibers assume their full length and the tooth is compressed in the socket. • Tension side: Fibers extend. • Pressure side: Fibers compress. • Further compression leads to bone resorption and further tension causes bone deposition.
44
How does the PDL develop?
• PDL & cementum originate from the dental follicle (loose CT which surrounds the tooth bud). • Principal fibers develop with tooth eruption. • Principal PDL fibers organize when tooth comes in contact in occlusion.
45
Where Sharpey's fibers are thicker and where they are thinner ?
1. Alveolar bone (sharpeys fibers are thicker) 2. Cementum (Sharpey's fibers are thnner).

Periodontology (6 decks)

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