Histology - Periodontium Structure

Question 1

What are the 4 connective tissues of type I collagen origin in the PDL?

Answer 1

Cementum
– Bone like material (acellular/cellular)
Lamina propria
– Underlying connective tissue
Alveolar bone
– (Lamina dura) many gaps to allow passage of nerves + arteries
Periodontal ligament
– Fills periodontal space between root and socket wall

Question 2

What are the benefits of the periodontium?

Answer 2

Mammals require excellent occlusion for mastication (meat + vegetables) teeth must be retained within socket for occlusion ( wear from opposing teeth)
Acts as a shock absorber protects the hard and brittle enamel surface of tooth
Allows for eruption to take place

Question 3

Describe the lamina propria

Answer 3

Dense and fibrous tissue inserts into booth tooth & and alveolar crest
Fibres run in many different directions fibres act in supporting free gingiva & holding gingiva to tooth surface

Question 4

Describe the junction epithelium

Answer 4

Junction epithelium also form part of the gingival cuff

• Mucogingival junction (MGJ) where keratinised mucosa around tooth meets soft mucosa that form support teeth
• Cementoenamel junction (CEJ) junction between enamel and cementum

Question 5

Describe the structure of cementum

Answer 5

Composition: Inorganic= 65% Organic- 23% Water=12%
Structurally similar to bone (calcified & Hydroxylapatite)
Acellular region covers the whole of the root formed first
Cellular region is formed last and covers root apex (contains Cementocytes)
Cementoblasts are found on surface of cementum and produce cementum matrix HAP

Question 6

Describe the cementoenamel junction

Answer 6

3 types of junction

Cementum overlaps with enamel (70%)
Butt join between cementum and enamel (20%)
Gap between cementum and enamel (10%)

Incremental growth lines are observed in enamel (lines of salter)

Question 7

Describe the periodontal ligament – dentine boundary

Answer 7

Cementum between this boundary
Lines of salter are observed within the cementum
Cementoblasts line the periodontal ligament, they form cementum (part of PDL not cementum)
Pale area can be observed; this is pre cementum (unmineralised)

Question 8

Describe the cementum and periodontal ligament boundary

Answer 8

Periodontal ligament project Sharpey’s fibres into the cementum (extrinsic fibres)
Sharpey’s fibre is unmineralised in PDL & mineralised in cementum
Cementum between the mineralised Sharpey’s fibres are termed intrinsic cementum formed by Cementoblasts
Sharpey’s fibres are formed from periodontal fibroblasts

Question 9

Describe the bone and periodontal ligament boundary

Answer 9

Periodontal ligament protrudes Sharpey’s fibres into bone known as bundle bone continuous with transalveolar fibres these insert into base of adjacent tooth
Osteocytes/osteoid/ osteoblasts are seen

Question 10

What cells are present in the periodontium?

Answer 10

Fibroblasts
Cementoblasts
Osteoblasts
Osteoclasts
Cell rests of mallasez
Macrophages

Question 11

What is the role of Fibroblasts?

Answer 11

Responsible for producing/degrading extracellular matrix (type 1 collagen)

Question 12

What is the role of Cementoblasts?

Answer 12

form cementum

Question 13

What is the role of Osteoblasts?

Answer 13

form bone

Question 14

What is the role of Osteoclasts?

Answer 14

remove bone

Question 15

What is the role of Cell rests of mallasez?

Answer 15

periodontal epithelial cells

Question 16

What is the role of macrophages?

Answer 16

act as white blood cells

Question 17

What are the periodontal fibres?

Answer 17

Crestal (Alveolar crest upwards inserts into cementum)
Horizontal (run horizontally from bone to tooth)
Apical (Radiate from root apex)
Oblique (Largest group of fibres)
Interradicular (Run from Interradicular bone (beneath tooth in multirooted tooth))

Question 18

Describe collagen structure

Answer 18

Tropopcollagen – helical structure 
Microfibrils 
Classic fibres – classical banding of 64nm, individual fibre length= 8-400nm, width= 40-50nm
Bundles length = 1 micron upwards 
Principle fibre bundles

Question 19

Describe oxytalan fibres

Answer 19

Run from cementum to terminate in periodontal capillaries
Little/no elastin found within the fibres
Stained purple when sectioned

Question 20

Explain the high cellularity of the peridontium

Answer 20

Many cells are seen within the ligament (mostly fibroblasts) so many nuclei observed.
Ligament is 50% matrix of this only 60% is ground substance & 40% is collagen.
Tendons reduce in cellularity as they mature

Question 21

What are fibroblasts?

Answer 21

Have large amounts of RER which is used in production/transportation of proteins for e.g. collagen production
Metabolically co-ordinated as contain gap junctions between them to help co ordinate collagen production turnover.
Contain vacuoles within cells that store collagen
Fibroblasts can degrade surrounding collagen by degrading extracellularly using collagenases (this occurs in connective tissue).
Within the periodontal ligament fibroblasts break down collagen phagocytically, lysosomes fuse with the phagosome forms phago lysosome leads to degradation.

Question 22

What are rests of mallasez?

Answer 22

Cells that are remainders of tooth developing process

No role so may play a role in peri apical cysts

Question 23

What are macrophages?

Answer 23

Contain lysosomes + membrane bound organelles

Found mostly in areas of blood vessels

Question 24

Describe the blood supply of the periodontium

Answer 24

Blood supply from superior and inferior alveolar arteries
Blood from apex of tooth or intrabony spaces (form arterioles in gingivae)
Capillaries and arterioles form a plexus around tooth
Capillaries have fenestrations
Fenestrations are small holes in side of capillary of 50 nm
Capillaries with fenestrations have more efficient filtering + diffusion and number of fenestrations is proportional to tooth eruption
Volksmans canals carry blood between intrabony spaces and ligament