Periodontium Ii Periodontal Ligament

Front 1

What is the Periodontal Ligament?

Back 1

• Soft connective tissue (and associated cells/structures) situated between and connecting cementum to alveolar bone.

• It ranges in thickness (when in a state of health)
from about 0.1 – 0.4 mm.

Front 2

Formation of the PDL -
Where does the PDL develop?

Back 2

• From the outer mesenchymal cells of the dental follicle.

Front 3

Formation of the PDL -
When does differentiation into fibroblasts begin?

Back 3

• Soon after the beginning of root formation, although there is considerable variation from tooth to tooth.

Front 4

What are the 4 roles of the PDL?

Back 4

1. Homeostasis
2. Supportive
3. Sensory
4. Nutrition

Front 5

What is Homeostasis?
(In relation to the ongoing remodelling of the
periodontium)

Back 5

Homeostasis refers to the dual function of formation and resorption.

Note - The turnover of alveolar bone and collagen within the PDL is higher within the periodontium than anywhere else within the body.

Front 6

How is the PDL supportive?

Back 6

The PDL attaches the tooth to the jaw and has a cushioning effect via an hydraulic mechanism which
incorporates the blood vessels right through to the
hydrophilic nature and water absorptive properties of the ground substance.

Front 7

How is the PDL Sensory?

Back 7

The PDL has an extraordinary proprioceptive
capacity with up to 50% of the brain’s proprioceptive
capacity devoted to oral functions.

A healthy dentition can detect thicknesses of as little as 5 microns between the teeth.

Front 8

How does the PDL provide Nutrition?

Back 8

Blood vessels carry anabolites etc as required by the cells within the PDL

(includes the more superficial osteocytes and cementocytes given that cementum is avascular).

Front 9

What is the Periodontal Ligament made of?

Back 9

• Cells
• Fibres
• Ground Substance
• Blood vessels
• Nerve supply
• Lymphatics
• Cementicles

Front 10

The 6 cell types?

Back 10

• Synthetic Cells.
• Resorptive Cells.
• Progenitor Cells.
• Epithelial Rests of Malassez
• Immunological Cells.
• Endothelial and Neural Cells.

Front 11

What makes up Synthetic Cells?

Back 11

- Osteoblasts
- Fibroblasts
- Cementoblasts

Front 12

What makes up Resorptive Cells?

Back 12

- Osteoclasts
- Fibroclasts
- Cementoclasts

Front 13

What are Progenitor Cells?

Back 13

Undifferentiated mesenchymal cells with the ability to differentiate into their predetermined cell type.

Front 14

What is Epithelial Rests of Malassez?

Back 14

Remnants of Hertwig’s root sheath.

Front 15

What makes up Immunological Cells?

Back 15

• Macrophages – responsible for phagocytosis. Make up 4% of total cell population within the PDL.

• Mast cells – small numbers only in healthy periodontium. Release histamine in inflammatory responses.

Front 16

Where are Endothelial and Neural Cells found?

Back 16

Blood vessels and nervous system.

Front 17

Principal Fibres of the PDL

How do the fibres of the Alveolar Crest Group run?

Back 17

Fibres from the crest of the alveolar bone run coronally/obliquely into the cementum (just below CEJ).

Front 18

Principal Fibres of the PDL

How do the fibres of the Horizontal group run?

Back 18

The Horizontal fibres are the next group apical to the alveolar crest group.

They run from cementum to bone in a horizontal direction.

Front 19

Principal Fibres of the PDL

How do the fibres of the Oblique group run?

Back 19

Oblique Group run at an angle from the alveolar bone apically towards the tooth, anchoring into the cementum.

Note - the most prevalent of all of the fibres.

Front 20

Principal Fibres of the PDL

How do the fibres of the Apical group run?

Back 20

These fibres radiate from the apical cementum to the alveolar bone at the base of the socket.

Front 21

Principal Fibres of the PDL

How do the fibres of the Interradicular group run?

Back 21

Found in multi-rooted teeth.

These fan out from the alveolar crest of the interradicular bone and insert into the cementum of the furcations of teeth.

Front 22

Other Collagen Fibres of the PDL

How do the fibres of the Dentogingival group run?

Back 22

Run from the cervical cementum immediately below the CEJ and extend into the lamina propria of the free and attached gingivae.

Note - They are the most numerous of the fibres outside of the strict PDL.

Front 23

Other Collagen Fibres of the PDL

How do the fibres of the Alveologingival group run?

Back 23

Alveologingival Group run from the bone of the alveolar crest to the lamina propria of the free and attached gingiva.

Front 24

Other Collagen Fibres of the PDL

How do the fibres of the Circular group run?

Back 24

Circular Group form a circular ring around the tooth within the region of the free gingiva which interlocks with the other fibres, helping bind the free gingiva to the tooth.

Front 25

Other Collagen Fibres of the PDL

How do the fibres of the Dentoperiosteal group run?

Back 25

These fibres leave the cementum between the dentogingival fibres and the first true fibres of the PDL, the alveolar crest group.
They then run over the alveolar crest and insert into the periosteum covering the outer cortical plates.

Front 26

Other Collagen Fibres of the PDL

How do the Transseptal fibres run?

Back 26

Transseptal Fibres run from cementum of one tooth to cementum of another tooth, traversing the interseptal bone.

Front 27

Fibres of PDL during Eruption

Back 27

Front 28

Ground Substance is a major component of the PDL.

Components of Ground Substance -

Back 28

• Estimated to be 70% water which significantly
aids with the protective function of the PDL.
• Other components include proteoglycans and
glycoproteins (i.e. combinations of various
proteins and polysaccharide units).

Front 29

Blood Vessels of the Periodontal Ligament

The very rich blood supply is derived from:

Back 29

• The appropriate superior and inferior alveolar arteries along with other supplies from the lingual and palatine arteries.

Front 30

Blood Vessels of the Periodontal Ligament

The Alveolar arteries run through bone and into the PDL through what?

Back 30

• Special canals termed Volkmann’s canals.

Front 31

Blood Vessels of the Periodontal Ligament

Apical vessels -

Back 31

• Apical vessels also branch before entering the tooth
and supply some of the apical regions Of the PDL.

Front 32

Nerves of the Periodontal Ligament

The PDL is very richly innervated with nerves, they enter through two main sources, these are?

Back 32

• Those which branch from the nerves entering the root apex.

• Those which enter into the middle and cervical thirds through canals within the alveolar bone.

Front 33

Nerves of the Periodontal Ligament

The two types:

Back 33

• Sensory – associated with nociception and mechanoreception.
• Autonomic – regulate the blood vessels of the PDL.