Periodontal ligament

Question 1

What is the composition of the periodontal ligament?

Answer 1

Fibroblasts, matrix consisting of type 1 collagen glycosaminoglycans, proteoglycans, glycoproteins and water, cementoblasts, osteoblasts, osteoclasts

Question 2

What do fibroblasts do?

Answer 2

Responsible for the synthesis and degradation of collagen and secretion of all components of the periodontal ligament.

Question 3

As well as type 1 collagen what other type of collagen is abundant in the PDL?

Answer 3

Type 3

Question 4

What are the collagen units in the PDL?

Answer 4

Triple helical tropocollagen molecule, into 5 membered microfibrils, classical fibrils then bundles - principle fibre bundles, the ligament acts in compression

Question 5

What is the proposed function of oxytalan fibres?

Answer 5

Aid fibroblast migration

Question 6

What is 60% of the 50% matrix made up of?

Answer 6

Ground substance

Question 7

What do fibroblasts have large amounts of?

Answer 7

Endoplasmic reticulum, gap junctions, fibrillar collagen in vacuoles which are degraded by phagosomes

Question 8

What are the epithelial cell rests of Malassez?

Answer 8

Islands of epithelial cells that are remnants of the epithelial root sheath which disintegrates following root development

Question 9

What are the two non calcified tissues of the periodontium?

Answer 9

Lamina propria and periodontal ligament

Question 10

What are the two calcified tissues of the periodontium?

Answer 10

Cementum and alveolar bone

Question 11

What are functions of the periodontal ligament?

Answer 11

• Resisting displacing forces and protecting dental tissues from damage caused by excessive occlusal loads
• Functional position of teeth
• Cells form maintain and repair alveolar bone and cementum
• Mechanoreceptors are involved in neurological control of mastication

Question 12

What does the lamina propria do?

Answer 12

Has insertions into both tooth and bone of alveolar crest, act with tissue fluid to support the free gingiva and hold the attached gingiva against the tooth (gingival cuff) part of the gingival cuff but not PDL is the junctional epithelium

Question 13

What is the junctional epithelium?

Answer 13

Specialised nonkeratinized stratified squamous epithelium unusual in having a basal lamina on both surfaces, basal lamina cells attach via hemi-desmosomes

Question 14

What is the tooth support mechanism?

Answer 14

Biphasic, visco elastic response to axial loading, some dissipated through the oblique fibre system, ligament appears to resist intrusive loads by compression and fluid flow

Question 15

How does the PDL fibres attach to the cementum and alveolar bone?

Answer 15

They run into the organic matrix of precementum that is secreted by cementoblasts, mineralisation of these fibres will incorporate these as Sharpey fibres - unmineralised in the ligament but mineralised in cementum. PDL forms Sharpey’s fibres into the alveolar bone, larger but less numerous than those in cementum

Question 16

How does the PDL form?

Answer 16

Once the crown has formed IEE and OEE proliferate downwards as a double layered sheet of flattened epithelial cells - epithelial root sheath of Hertwig. The root sheath induces peripheral cells of the dental papilla to differentiate into odontoblasts and to produce predentine. - ROOT SHEATH ONLY IN CONTACT WITH PREDENTINE LAYER FOR A SHORT TIME BEFORE CONTINUITY IS LOST
Cells of the dental follicle differentiate into cementoblasts fibroblasts and osteoblasts
Once cementogenesis has begun cells of the dental follicle become obliquely oriented along the root surface and show an increased content of intracellular organelles becoming the fibroblasts of the PDL. These fibroblasts secrete collagen of the PDL into the extracellular compartment, this collagen will become embedded as Sharpey’s fibres into the developing acellular cementum at the tooth surface and developing bone at the alveolar surface.

Question 17

What is the PDL’s rich blood supply derived from?

Answer 17

Superior or inferior alveolar arteries, makes up to 50% of the periodontal space