Fluoride and Caries Flashcards
What is hydroxyapatite made from?
Ca10(PO4)6(OH)2
Precipitated from calcium and phosphate ions.
When can fluoride get incorporated into a tooth?
Pre-eruptive:
- During mineralisation: incorporated into the bulk of the tooth
- Topically from tissue fluid on maturing enamel surface (the surface effect)
Post-eruptive:
- From saliva and fluoride containing products
Give some details on pre-eruptive enamel
Enamel apatite
Contains some ionic impurities including carbonate and fluoride
Explain the 3 types of oral retention of fluoride
- Firmly Bound - flurohydroxyapatite
- Loosely bound - calcium fluoride, fluoride absorbed to apatite
- Within plaque - reversibly bound to free calcium, 95% bound
What happens to critical pH is a patient has a higher salivary calcium conc?
It goes down. Higher acid conc can be withstood before dissolution.
What two things can change critical pH?
Critical pH is specific to a particular salivary calcium ion concentration. If this changes, the critical pH will also change. The structure of the hydoxyapitate can also change the critical pH.
Give details on the demineralisation - remineralisation cycle
Susceptible tooth surface where is biofilm is cariogenic and then processes the fermentable carbohydrates over time leads to a drop in pH and this will drop below 5.5 and therefore you will get mineral dissociation (demineralisation).
Other ions in the saliva and in the biofilm (hydroxyl ions, bicarbonate ions, phosphate ions) will return the pH back up towards neutral and then will then allow the mineral ions to re-associate and remineralise.
Why is the acid cycle essential for post-eruptive enamel maturation?
Loss of carbonate and incorporation of fluoride can then occur.
Does flurohydroxyapatite have a higher or low solubility than hydroxyapatite?
lower
What does fluoride rich apatite do to critical pH?
Fluoride rich apatite is less soluble, someone with the same salivary calcium conc, the critical ph shifts so it is lower so the mineral can tolerate more acid before it starts to dissolve.
Explain loosely bound flurodie
This is calcium fluoride.
It acts as a reservoir.
It is only formed with high-concentration fluoride solutions and it results from globules of CaF2.
These globules have a protein and phosphate rick surface which reduces rate of dissolution.
The mechanism of remineralisation of this loosely bound fluoride has 2 aspects.
1 - it can concentrate the calcium and phosphate ions and therefore promotes re-precipitation and therefore will fill any porosities in the enamel
2 - this narrows pores in the enamel so stop ion loss and protect from acid
What is amount of mineral loss due to?
What is most critical at low pH?
- pH and fluoride conc
- fluoride conc
Explain the effect that fluoride has on bacteria
Fluoride inhibits the carbohydrate mechanism of certain bacteria.
It must enter the bacteria and affect enzymes and transport systems involved in the carbohydrate mechanism.
The fluoride diffuses into bacteria as HF through a glucose-proton co transporter. Low external pH promotes HF formation and high pH of the bacteria causes the dissociation of HF to H+ and F-. There are mechanisms to eject H+ from the bacterial cell.
F- inside will affect enolase and the PEP phosphate transferase pathway so reduces the amount of glucose within the bacterial cell which reduces the amount of lactic acid produced by the cell.
Explain the fluoride effects on enolase and PEP phosphotransferase system
Enolase inhibition:
- may be a direct action of F-
- may be due to acidification of the cell
PEP:
- needs PEP for glycolysis to work
- PEP levels reduced by enolase inhibition
- results in less sugar uptake
- less lactic acid production
What does acidification of a bacterial cell do?
- Inhibition of ATP-ase dependant H+ pump by fluoride
- High H+ intracellular conc= inhibits enolase and other glycolytic enzymes, reduced pG gradient between outside of the cell and inside (reduced H+ - sugar transport which occurs normally at pH 5.5)
