Fluoride and dental caries Flashcards
What is the main mineral of enamel and dentine?
Hydroxyapatite
How is hydroxyapatite made?
It is precipitated from calcium ions and phosphate ions from supersaturated solutions (some energy required)
How may fluoride get incorporated into the teeth pre-eruption?
During mineralisation - incorporated into bulk of tooth
Topically from tissue fluid on maturing enamel surface - surface effect
How may fluoride be incorporated into the tooth post-eruption?
Surface effect only: topically from saliva or fluoride containing products
Why may pre-eruptive enamel not be described as ‘pure hydroxyapatite’?
As it contains other ions, such as fluoride or carbonate or magnesium.
Contains ionic impurities
What is created in fluoride is firmly bound?
Fluorohydroxyapatite
What is produced if fluoride is loosely bound?
Calcium fluoride
Fluoride absorbed to apatite
How much fluoride can be found within plaque and how is it bound?
5-10 ppm
Reversibly bound to free calcium (dispersed CaF2)
95% bound
What is the critical pH for enamel (and hydroxyapatite)?
5.5
What cycle is an essential element of post-eruptive enamel maturation?
Acid cycle
What chemical difference is relevant when comparing pure hydroxyapatite with fluorohydroxyapatite? Also how does this affect the critical pH?
Fluorohydroxyapatite has a Lower solubility than hydroxyapatite.
This lowers the critical pH - the tooth is more susceptible to acid attack
What is the effect of calcium fluoride (i.e. loosely bound fluoride)?
Acts as a reservoir of calcium and fluoride.
Why is dissolution rate reduced with CaF2 (calcium fluoride)?
Because they have protein- and phosphate rich surface
What is fluoride release dependent on?
pH
What are the 2 mechanisms of loosely-bound fluoride in remineralisation?
- Binds calcium and phosphate ions dissolving from acid attack and promotes reprecipitation
- Reprecipitation narrows pores in enamel - affects acid diffusion into enamel, affects loss of dissolved ions.
The amount of mineral loss is a consequence of what?
pH
Fluoride concentration
At low pH, what is an important determinant of rate of mineral dissolution?
Fluoride concentration
How is fluoride antibacterial?
It can inhibit carbohydrate metabolism of oral streptococci and lactobacilli
For the fluoride to exert it’s antibacterial effect what must happen?
It must enter the bacteria.
It must effect enzymes and transport systems involved in carbohydrate metabolism
Outline how fluoride enters bacteria
- Fluoride diffuses into cells as HF
- Low external pH promotes formation of more HF
- High intracellular pH of bacteria favours dissociation of HF to hydrogen and fluoride ions
- this means more HF can enter
What are the 4 effects fluoride has on bacteria?
- ENOLASE INHIBITION:
May be direct action of fluoride.
May be due to acidification of the cell. - PEP PHOSPHOTRANSFERASE SYSTEM:
Needs PEP from the glycolysis to work.
PEP levels reduced by enolase inhibition
Results in less sugar uptake - ACIDIFICATION OF BACTERIA DUE TO:
HF dissociation
Inhibition of ATPase-dependent H+ pump by fluoride - HIGH INTRACELLULAR H+ CONCENTRATION
Inhibits enolase and other glycolytic enzymes
Reduces pH gradient between outside of cell and intracellular (reduces H+ sugar transport that occurs normally at pH 5.5)
What does fluoride have no effect on?
Bacterial adherence
Initial plaque formation
What does fluoride reduce?
Acid production in plaque
effect depends upon nature of fluoride application
How does fluoride effect apatite crystal growth?
Appears to impair growth of apatite crystals.
Retention of modulating matrix proteins through enhanced binding of mineral to matrix protein and/or
enhanced binding of the proteases responsible for processing prior to matrix removal
