Structure of periodontal ligament

Question 1

What is the periodontal ligament?

Answer 1

The specialised dense fibrous tissue which attaches the tooth to the alveolar bone

Question 2

What are the basic dimensions of the periodontal ligament?

Answer 2

• width approx 0.2nm
• slightly narrower in middle region
• may become wider with disease or tooth mobility

Question 3

Give the main components of the periodontal ligament

Answer 3

•  Cells :
Fibroblasts - produce and degrade tissue 
Blood vessels
    •Nerve fibres
    •  (Macrophages / mast cells / etc)
 Matrix:
Collagen
Types I, III, V Collagen (approx 65% : 30% : 5%) 
Proteoglycans
   • Elastin etc.

Question 4

Give the cell types of the periodontal ligament

Answer 4

Fibroblasts
Osteoblasts / Cementoblasts 
Epithelial Cell Rests of Mallasez 
Blood Vessels
Nerves

Question 5

What are the epithelial cells of Mallasez?

Answer 5

• persisting epithelial remnants of Hertwigs root sheath
• may regulate maintenance of PDL width
• can give rise to cystic lesions following dental infection

Question 6

What are the principle fibres of PDL?

Answer 6

• Oblique fibres
• Apical fibres
• Horizontal fibres
• Crestal fibres

Question 7

What are Sharpey’s fibres?

Answer 7

Extension of principal PDL fibres into matrix of cementum and alveolar bone thus contributing significantly to organic matrix of cementum.

Lots of cementum is made up of these fibres which are only partially mineralised so cementum is the least mineralised structure because of this.

Question 8

Give 3 details on proteoglycans

Answer 8

Ground Substance of PDL
Amorphous hydrophilic gel throughout the connective tissue
Provides the glue to hold the tissue together

Question 9

What are oxytalan fibres?

Answer 9

A bit of a mystery ?
Elastic fibres specific to PDL
Orientated perpendicular to tooth root
??Involved in maintaining structure following mechanical deformation??

Question 10

Where does the blood supply to the PDL come from?

Answer 10

• Apical vessel
• Through alveolar bone
• Gingival vessels

Question 11

Explain the development of the PDL

Answer 11

Hertwigs epithelial root sheath maps out root form.

HERS breaks down and cementum formation induced.

PDL is derived from dental follicle mesenchymal cells.

Final organisation / structure of PDL only seen after tooth eruption once tooth is in function.

Question 12

What movements does the TMJ allow for?

Answer 12

Forward and backward

Up and down

Question 13

What are the functions of the PDL?

Answer 13

• Retention of the tooth (hold tooth in place)
• Adsorption of Occlusal Forces
• Neuromuscular :
  - Pain fibres and mechanoreceptors for proprioception, masticatory control salivation.
• Tooth Eruption

Question 14

What are occlusal forces on a tooth absorbed by?

Answer 14

• Hydroelasticity of PDL matrix (proteoglycans/ground substance)
• Transmission of forces by PDL fibres to jaw bone
• Elasticity of bone

Question 15

What affects mobility of a tooth?

Answer 15

Occlusal load on teeth
Damage to PDL
Thickness of overlying bone

Question 16

What does occlusal loading do to the PDL?

Answer 16

• Regulates maintenance of PDL width
• Regulates / preserves structure of PDL
• Results in physiological mobility of teeth

Question 17

What are the 3 summary points?

Answer 17

1. PDL is a dense fibrous tissue attaching the tooth tp the bone, and absorbs normal occlusal forces
2. Principal fibres of PDL are obliquely orientated type I collagen fibres
3. PDL undergoes constant remodelling and adaptive changes in response to loading and movement