ICP L7: Dentine caries Flashcards
Why does the enamel need dentine below it
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
Outline dentine composition and structure
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
What forms the dentine and aids in repair
Odontoblast cells on the lining of the pulp
Outline the formation of mantle dentine
- Odontoblasts differentiate from cells of the dental papilla
- GFs/Signal molecules from inner enamel epithelium induce odontoblast differentiation
- 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
- Odontoblasts move centrally forming process
- Odontoblast process secretes HAP crystals that mineralise collagen matrix
- Forms mantle dentine
Why do odontoblasts move centrally during dentine formation
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
Outline formation of primary dentine from mantle dentine
- Odontoblasts increase in size and eliminate extracellular resources for matrix
- Less collagen is secreted and there is greater organisation with a tight arrangement
- It is mineralised in an ordered fashion (heterogeneous nucleation)
- Primary mineralisation = expansion and fusion of calcospherules (discrete globules of HAP secreted and grow to form larger calcified masses)
- Secondary mineralisation = further expansion of globules into areas of complete fusion
- Production of primary dentine
What are dentine tubules
- 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
What is the role of peritubular and intratubular dentine
It is highly mineralised and helps to maintain and form the dentinal tubules
What is primary dentine
Laid down in dentinogenes = mantle and primary dentine
- normal dentine-pulp complex response
What is secondary dentine
Laid down slowly throughout life
- normal dentine-pulp complex response
What is tertiary dentine
Lain down in response to noxious stimuli when the odontoblasts are stimulated
- altered dentine-pulp complex response
Outline how early enamel caries happens in a non-cavitated lesion
- Plaque-acid demineralisation causes porosity within prism structure
- Subsurface demineralisation
- Surface zone is intact (due to fluoride)
- Inverted cone shape
- the lesion is sterile (no micro-organisms present)
- no dentine-pulp response
- reversible = white spot lesion
What happens in late enamel caries
- Progressing lesion approaches EDJ
- May still not have cavitated
- Defensive dentine-pulp reactions initiated
- May still not be symptoms
This is still reversible
Outline how dentine caries happens
- Lesion crosses EDJ and spreads into dentine
- Lateral spred
- hypomineralised mantle dentine
- increased side branching of tubules
- defects within tissues of EDJ - Penetration along dentine tubules towards pulp
What happens to dentine caries when the lesion is cavitated
- 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
What is caries infected dentine
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
What is caries affected dentine
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
What type of carious dentine must be removed form the tooth and which type can be left
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
What are the ways in which the dentine-pulp complex responds to injury
Tubular sclerosis (tertiary dentine)
- reactionary dentine
- reparative dentinve
- plural inflammation
When does tubular sclerosis occur and what changes happen to the dentine-pulp complex
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
When, where and why is reactionary dentine laid down
Tertiary dentine is laid down at the dentine-pulp interface
- increases distance between dentine-pulp and stimulus
- low grade stimulus causes slower deposition
How is reparative dentine laid down in response to a low grade stimulus
Slower deposition
- irregular tubules are formed
- the odontoblasts survive
- it is metabolically upregulated
How is reparative dentine laid down in response to a high grade stimulus
Faster deposition
- atubular dentine
- disorganised
- odontoblast vitality is compromised
- progenitor cells in sub-odontoblastic layers will differentiate and up regulate
When does plupal inflammation occur
Due to noxious stimulus; can be acute or chronic
- toxins are released from bacteria in the carious lesion
