Periodontal Ligament

Periodontal ligament

• Cell-rich, fiber-rich dense CT between root surface of tooth and alveolar bone proper

• Binds cementum to alveolar bone

• Continuous with the CT of gingiva at crest of the alveolar bone

Contains fiber bundles

Supportive function of PDL

Pain and pressure

Sensory function of PDL

Maintains width of 2 hard tissues

Homeostatic function of PDL

• Fibroblasts

• Cementoprogenitor cells

• Osteoprogenitor cells

• Epithelial cells

• Undifferentiated mesenchymal cells

• Macrophages

• Leukocytes

Cells of the PDL

Fibroblasts

• Prinicipal cells of the PDL

• Densely packed, spindle or flat disk-shaped

• Long ovoid nuclei

• Numerous cytoplasmic processes of various length

• The cytoplasm contains abundance of organelles associated with protein synthesis & secretion

  • satisfy functional demands required to change in shape & migrate

Cementoprogenitor and Osteoprogenitor cells

• Found exclusively in those sections of the PDL adjacent to cementum and bone

• Closely resemble inactive fibroblasts

  • Cementoblasts

  • Cementoclasts

  • Osteoblasts

  • Osteoclasts

Undifferentiated mesenchymal cells

• Progenitor cells

• Located within 5 μm of blood vessels

• Source of new cells for the PDL

• Apoptosis — physiologic cell death

Macrophages

• Defense cells

• Phagocytic activity

  • bacteria, dead cells, foreign bodies

Leukocytes

Special lymphocytes and plasma cells may appear in the PDL when stressed by disease

• Alveolar crest group

• Horizontal fiber group

• Oblique fiber group

• Apical fiber group

• Interradicular fiber group

Principal collagen fibers of the PDL

• Oxytalan fiber

• Elaunin fiber

Immature elastin fibers of the PDL

Collagen fiber

• Predominantly present in the fiber system

• Basic component: collagen fibrils

  • Mix of type I & type III individual fibrils having an average diameter of 55 mm

• Several fibrils become arranged parallel with one another to form a fibril bundle

• Fibers within fiber bundle are not parallel with each other but are interwoven

parallel

Several collagen fibers become arranged _____ to form a fibril bundle

interwoven

Arrangement of fibers within fiber bundle

Dento-alveolar group

• Fiber apparatus that made up the principal fiber bundles

• Arranged in orderly fashion running from cementum to alveolar bone

Alveolar crest group

• Attached to the cementum just below the CEJ

• Running downward & outward to insert into the rim of the alveolus

• Function:

  • resist vertical and intrusive force

  • anchor the tooth to the alveolus

• Resist vertical and intrusive force

• Anchor the tooth to the alveolus

Function of alveolar crest group

Horizontal fiber group

• Found immediately apical to alveolar crest at right angles to the long axis of the tooth

• Run horizontally from cementum to bone

• Function:

  • resist horizontal and lateral pressure applied to the tooth crown

Resist horizontal and lateral pressure applied to the tooth crown

Function of horizontal fiber group

Oblique fiber group

• Most numerous and largest fiber group

• Run from cementum in an oblique direction to insert into bone coronally

• Function:

  • Sustain occlusal forces

  • Resist intrusive masticatory forces (similar to ACG)

• Sustain occlusal forces

• Resist intrusive masticatory forces

Function of oblique fiber group

Apical fiber group

• Radiating from cementum around the apex of the root of the bone

• Found at the base of the socket

• Function:

  • Prevents vestibulo-oral tipping

Prevents vestibulo-oral tipping

Function of apical fiber group

Alveolar bone proper

Tooth socket is aka _____

Interradicular fiber group

• Found only between roots of multirooted tooth

• Run from cementum into bone forming the crest of the interradicular septum

• Function:

  • Resists tipping and torque (rotation)

Resist tipping and torque

Function of interradicular fiber group

Circular fiber group

• Part of gingival fibers

• Encircle the tooth with free gingiva

• Keeps free gingiva against tooth and keeps it from receding

Sharpey’s fiber

Embedded portion of PDL fibers in the cementum or bone

Periodontal ligament

Permit the individual tooth a certain degree of mobility

Periodontal space

PDL is located in the _____

middle root

PDL is narrower at the _____

0.10-0.38 mm

PDL width

Loss of function

Results to smaller PDL & its fiber bundles become thinner and atrophic

Attrition

As a person ages, the contact point becomes larger because of _____

Radiolucent

Appearance of PDL in x-ray

thickened

By function, PDL should be _____

Transseptal

Gingival fiber group

• Cervical tooth to tooth mesial/distal to it

• Resists tooth separation (mesial-distal)

Attached gingival

Gingival fiber group

• Cervical tooth to attached gingiva

• Resist gingival displacement

Free gingival

Gingival fiber group

• Cervical tooth to free gingival

• Resist gingival displacement

Circumferential

Gingival fiber group

• Continuous around neck of tooth

• Resist gingival displacement

Interstitial space

• Found in between groups of fibers

• Contain network of blood vessels, nerves, & lymphatics & loose CT cells

  • Interstitial indefinite tissue

• Maintain the vitality of PDL

• Also contains network of finer fibers interlaced and support the dense collagen bundles

Oxytalan fibers

• Bundles of microfibrils

• Resemble elastic fibrils

• Intertwined lengthwise to form fiber

• Acid resistant

• Insert into the cementum especially at the cervical region

Elaunin fibers

• Embedded within a small quantity of elastin forming a network

• Together with oxytalan fibers - form a meshwork extending from cementum to bone & sheathing the collagen fiber bundles

Reticular fibers

Aid in the support of blood and lymphatic vessels & nerves

• 70% water

• Glycosaminoglycans

• Glycoproteins

• Glycolipids

PDL ground substance

Glycosaminoglycans

• Ligament dermatan sulfate (principal)

• Plays an important role in ligament function

Superior and inferior alveolar arteries and veins

→ Dental artery

→ Interalveolar and interradicular arteries

→ Periosteal arteries

Vascular supply of PDL

• Somatosensory

  • Superior & inferior dental plexus

  • Free nerve endings

  • Ruffini corpuscles

  • Coiled endings

  • Encapsulated spindle type ending

• Autonomic system

Nerve supply of PDL

Alveolar bone proper

Where sharpey’s fibers are embedded in

Dental follicle

All periodontal tissue are derived from _____

Alveolar clade

Fibroblasts and osteoblasts

Cemental clade

Fibroblasts and cementoblasts

Closing the apical foramen to prevent infection of surrounding tissues (PDL)

What is apexification?

Calcium hydroxide

• can help with apexification

• can stop caries progression bc it can encourage dentin formation

recede because tertiary dentin develops

What will happen to pulp horns if calcium hydroxide is placed in a cavity without pulp exposure?

Canals of Zuckerkandl and Hirschfeld

• Nutrient canals/perforating canals

• Channels in the interdental and interradicular septa that house interdental and interradicular arteries, veins, lymph vessels, and nerves

Canals of Zuckerkandl and Hirschfeld

What makes the vascular supply of PDL rich?

• Mesial migration/physiologic mesial drifting

• Periodontal space becomes narrower

• Functional stresses → thicker periodontal fiber bundles & less interstitial tissue (loss of function)

• PDL in permanent mandibular canine become thinner with age

Physiologic changes (PDL)

• Cysts/tumors

• Infections

• Excessive orthodontic movements

Examples of pathologic conditions/changes