Periodontal Ligament

Question 1

which 5 cells make up the PL

Answer 1

fibroblasts 
macrophages 
osteoblasts 
cementoblasts
osteoclasts
cell rests of malassez (cluster of epithelial cells)

Question 2

what components make up the extracellular matrix of the PL

Answer 2

type 1 collagen fibres (principle fibres)
ground substance (proteoglycans, glycoproteins)
oxytalan fibres (run obliquely from cementum)

Question 3

what are the 5 groups of principle fibres that collagen fibres arranged into

Answer 3

interradicular fibres 
apical fibres (root apex upwards)
horizontal fibres
oblique fibres
alveolar crest fibres

Question 4

describe how the principle fibres form

Answer 4

a triple helical tropo-collagen molecule is secreted, the teleo-peptides are cleaved, aggregate in staggered way, form 5-membered microfibrils, form collagen fibril with 64nm banding, form bundles of 1um

Question 5

what are oxytalan fibres

Answer 5

immature elastin, only seen when PL oxidised

Question 6

what do fibroblasts contain

Answer 6

gap junctions between cells

intracellular vacuoles- break down collagen

Question 7

how is collagen broken down in the PL

Answer 7

phagocytic process via fibroblasts, phagocytes, lyosomes

Question 8

blood supply to the PL

Answer 8

superior/ inferior alveolar arteries

Question 9

origin of capillaries to the PL

Answer 9

intra-boney spaces of alveolar bone

Question 10

origin of arterioles to the PL

Answer 10

the gingiva

Question 11

what are volkman’s channels

Answer 11

the channels the capillaries and arterioles run in within the plexus formed in the socket wall

Question 12

what is unique about the capillaries found in the PL

Answer 12

• high fenestrations
• high volume
• not arranged in orderly way

Question 13

4 functions of the PL

Answer 13

1. protect the dental tissues from damage
2. mechanoreceptors- neurological control of mastication
3. has cementoblasts/osteoblasts- maintain alveolar bone and cementum
4. gives tooth its functional position

Question 14

how does the PL resist the forces applied to tooth

Answer 14

load applied= initial rapid intrusion of tooth= elastic phase
load maintained= intrusion continues at a slower rate= creep phase…develops into viso-elastic phase
load removed= initial rapid recovery= elastic recovery phase..develops into a slower extrusion over time so tooth back into original position

Question 15

what are the phases of response to maintain tooth function when load is applied to tooth via PL

Answer 15

load applied= elastic phase
load maintained= creep phase
intrusion left to continue then= viso-elastic phase
load removed= initial rapid recovery phase
extrusion left to continue, then tooth back into original position

Question 16

the low stress/ strain failure point for the PL is similar to the tendon. how does this occur

Answer 16

1. load dissipated through oblique fissure system

2. load dissipated through fluid flow- forces fluid to move into crestal region= alveolar crests forced apart