ICP L7: Dentine caries

Question 1

Why does the enamel need dentine below it

Answer 1

Because the enamel is a highly mineralised tissue (96%) which makes it brittle and so increases chances of fracture without the appropriate support; dentine makes the enamel more resilient

Question 2

Outline dentine composition and structure

Answer 2

It makes up the bulk of the tooth

• 70% inorganic
• 20% collagen
• 10% water

It is harder than bone, made of multiple close packed tubules, has incremental growth and the degree of mineralisation is variable

It is non-vascular but encloses and communicated with the central pulp chamber which contains the vascular and nerve supply

Question 3

What forms the dentine and aids in repair

Answer 3

Odontoblast cells on the lining of the pulp

Question 4

Outline the formation of mantle dentine

Answer 4

1. Odontoblasts differentiate from cells of the dental papilla
2. GFs/Signal molecules from inner enamel epithelium induce odontoblast differentiation
3. Collagen matrix is secreted adjacent to IEE (cusp tip) = type I collagen which is laced by type VII to form the matrix of the mantle dentine
4. Odontoblasts move centrally forming process
5. Odontoblast process secretes HAP crystals that mineralise collagen matrix
6. Forms mantle dentine

Question 5

Why do odontoblasts move centrally during dentine formation

Answer 5

Because as the odontoblasts get bigger there is less intercellular space and so there is no more room for the odontoblasts and so they move to where the pulp will eventually be

Question 6

Outline formation of primary dentine from mantle dentine

Answer 6

1. Odontoblasts increase in size and eliminate extracellular resources for matrix
2. Less collagen is secreted and there is greater organisation with a tight arrangement
3. It is mineralised in an ordered fashion (heterogeneous nucleation)
4. Primary mineralisation = expansion and fusion of calcospherules (discrete globules of HAP secreted and grow to form larger calcified masses)
5. Secondary mineralisation = further expansion of globules into areas of complete fusion
6. Production of primary dentine

Question 7

What are dentine tubules

Answer 7

• minute wavy tubules within dentine
• contain cytoplasmic processes of odontoblasts
• extend from odontoblast layer at pulp to EDJ/CDJ
• s shaped
• widest near pulp ~ 2.5um
• narrowest at EDJ ~ 0.9um

Question 8

What is the role of peritubular and intratubular dentine

Answer 8

It is highly mineralised and helps to maintain and form the dentinal tubules

Question 9

What is primary dentine

Answer 9

Laid down in dentinogenes = mantle and primary dentine

- normal dentine-pulp complex response

Question 10

What is secondary dentine

Answer 10

Laid down slowly throughout life

- normal dentine-pulp complex response

Question 11

What is tertiary dentine

Answer 11

Lain down in response to noxious stimuli when the odontoblasts are stimulated
- altered dentine-pulp complex response

Question 12

Outline how early enamel caries happens in a non-cavitated lesion

Answer 12

1. Plaque-acid demineralisation causes porosity within prism structure
2. Subsurface demineralisation
3. Surface zone is intact (due to fluoride)
4. Inverted cone shape

• the lesion is sterile (no micro-organisms present)
• no dentine-pulp response
• reversible = white spot lesion

Question 13

What happens in late enamel caries

Answer 13

1. Progressing lesion approaches EDJ
2. May still not have cavitated
3. Defensive dentine-pulp reactions initiated
4. May still not be symptoms

This is still reversible

Question 14

Outline how dentine caries happens

Answer 14

1. Lesion crosses EDJ and spreads into dentine
2. Lateral spred
   - hypomineralised mantle dentine
   - increased side branching of tubules
   - defects within tissues of EDJ
3. Penetration along dentine tubules towards pulp

Question 15

What happens to dentine caries when the lesion is cavitated

Answer 15

• this allows micro-organisms to directly penetrate lesion
• could cause acute pulpits
• degenerative and reparative processes occur in different parts of the lesion simultaneously
• zones are detectable and continuous

Question 16

What is caries infected dentine

Answer 16

When the bacterial invasion has digested collagen and there is dissolution; this is when the demineralisation cannot be reversed due to loss of structure because the dentinal tubules are non existent

soft, dark brown, wet, mushy

Question 17

What is caries affected dentine

Answer 17

This is where the HAP has been demineralised but the collagen matrix is intact (damaged by proteolysis but not denatured) so remineralisation can occur as there is only a low bacterial lode and the dentinal tubules are intact

leathery, sticky, scratchy

Question 18

What type of carious dentine must be removed form the tooth and which type can be left

Answer 18

Caries infected dentine must be removed; caries affected dentine can remain because it can make the restoration stronger and increase its longevity as it will remineralise

Question 19

What are the ways in which the dentine-pulp complex responds to injury

Answer 19

Tubular sclerosis (tertiary dentine)

• reactionary dentine
• reparative dentinve
• plural inflammation

Question 20

When does tubular sclerosis occur and what changes happen to the dentine-pulp complex

Answer 20

It is a response to noxious stimuli to the odontoblasts

• peritubular dentine is laid down
• this occludes the tubules
• this protects dentine-pulp complex from further injury
• dead tracts are formed distal to the occlusion
• tubular sclerosis is translucent on ground section as hyper mineralised

Question 21

When, where and why is reactionary dentine laid down

Answer 21

Tertiary dentine is laid down at the dentine-pulp interface

• increases distance between dentine-pulp and stimulus
• low grade stimulus causes slower deposition

Question 22

How is reparative dentine laid down in response to a low grade stimulus

Answer 22

Slower deposition

• irregular tubules are formed
• the odontoblasts survive
• it is metabolically upregulated

Question 23

How is reparative dentine laid down in response to a high grade stimulus

Answer 23

Faster deposition

• atubular dentine
• disorganised
• odontoblast vitality is compromised
• progenitor cells in sub-odontoblastic layers will differentiate and up regulate

Question 24

When does plupal inflammation occur

Answer 24

Due to noxious stimulus; can be acute or chronic

- toxins are released from bacteria in the carious lesion

Question 25

What happens in chronic pulpits

Answer 25

Cellular changes = fibrosis
Vascular changes = plasma cells and lymphocytes
This is slow progressing

Question 26

What happens in acute pulpits

Answer 26

Vascular changes = PMNs and MO

This is fast progressing

Question 27

Describe the changes in an advances carious lesion

Answer 27

• dentine architecture destruction
• micro-organisms close to pulp
• sterile zone demineralisation
• irreversible pulpits/ pulpal necrosis
• endodontics required

Question 28

What is the overlapping continuum

Answer 28

When there are simultaneous areas of sclerotic, reactionary and reparative dentine (thus chronic and acute pulpitis)

Question 29

How are micro-organisms involved in the carious process

Answer 29

1. Acidogenic bacteria dissolve inorganic mineral
2. Proteolytic bacteria destroy organic collagen matrix
3. Form liquefaction foci that coalesce to form transverse clefts at right angles to tubules
   - streptococcus mutants, lactobacillus sp.