Periodontal Ligament

Question 1

What is the periodontal ligament?

Answer 1

Specialised dense fibrous tissue which attaches tooth to alveolar bone

Question 2

Describe the PDL width.

Answer 2

Remarkably constant ~0.2mm

Narrower in middle region (wider at coronal and apical regions)

Question 3

What is the major cell type in the PDL?

Answer 3

Fibroblasts

Question 4

Give examples of things found in the PDL. (6)

Answer 4

Fibroblasts

Osteoblasts/cementoblasts

Epithelial cell rests of Malassez

Blood vessels

Nerves

Macrophages, mast cells, etc.

Question 5

What are epithelial cell rests of Malassez?

Answer 5

Persisting epithelial remnants of Hertwig’s epithelial root sheath (closer to tooth side)

Question 6

What may cause the cell rests of Malassez to become cystic lesions?

Answer 6

Deep inflammation

Question 7

What makes up the connective tissue matrix of the PDL?

Answer 7

Collagen I, III, V

Proteoglycans/ground substance

Oxytalan fibres

Question 8

Describe the PDL ground substance.

Answer 8

Amorphous, dense, hydrophilic gel throughout connective tissue

Question 9

What are oxytalan fibres?

Answer 9

Elastic fibres specific to PDL which run parallel to the tooth root

Question 10

What are the types of principal fibres found in the PDL?

Answer 10

Oblique

Apical

Horizontal

Crestal

Question 11

Where are the horizontal collagen fibres located in the PDL?

Answer 11

Close to alveolar crest

Question 12

Where are the crestal collagen fibres located in the PDL?

Answer 12

In gingiva and attached to bone

Question 13

What are Sharpey’s fibres?

Answer 13

Regions of principal collagen fibres embedded into tooth/bone

Partially mineralised

Question 14

How does the root and PDL develop (briefly)? (3)

Answer 14

HERS maps out root form; induces dentinogenesis

HERS breaks down and induces cementum formation

PDL derived from dental follicle mesenchymal cells

Question 15

What produces the final orientation of the PDL fibres after development?

Answer 15

Occlusal forces

Question 16

What type of joint is the PDL?

Answer 16

Gomphosis

Question 17

What are the functions of the PDL? (4)

Answer 17

Tooth eruption

Tooth retention

Absorption of occlusal forces

Neuromuscular

Question 18

How does the PDL allow absorption of forces?

Answer 18

Hydroelasticity of PDL matrix (proteoglycans) allows recoil

Forces are transmitted to the jaw bone by fibres and dissipate (bone is slightly elastic)

Question 19

What are the neuromuscular functions of the PDL?

Answer 19

Pain fibres and mechanoreceptors for proprioception allow masticatory control and salivation

Able to determine size and hardness of objects as PDL moves with tooth

Question 20

How does the PDL contribute in maintaining occlusion?

Answer 20

Remodelling ensures occlusion after wear

Question 21

What can change the degree of mobility of teeth? (3)

Answer 21

Occlusal load

Damage to PDL

Thickness of overlying bone

Question 22

How does the occlusal load affect the PDL daily?

Answer 22

Regulates maintenance of PDL width

Preserves structure of PDL

Question 23

What is periodontal disease?

Answer 23

Chronic inflammatory condition resulting in destruction of tooth attachment, loose teeth and ultimately tooth loss

Question 24

How do orthodontics affect the PDL?

Answer 24

Compression of PDL = bone resorption

Pulling of PDL = bone deposition

PDL keeps up with bone remodelling