Fluoride and Caries

Question 1

What is the principal mineral of enamel & dentine?

Answer 1

Hydroxyapatite

Question 2

How does fluoride affect the production of these hydroxyapatite crystals?

Answer 2

Pre-eruptive: during mineralisation, it can get incorporated into the bulk of the tooth

Or as the tooth is erupting or just erupting: there may be tissue fluid on maturing enamel surface, giving a v small topical effect

Or post-eruptive: any effect is a surface effect only, topically originates from saliva or any fluoride containing products

Question 3

What are the constituents of pre-eruptive enamel?

Answer 3

It isn’t pure hydroxyapatite, it contains many ionic impurities e.g. fluoride, carbonate, magnesium ions etc.

Question 3

How does the fluoride bound to the pre-eruptive enamel?

Answer 3

look at the slide

Question 4

What is the critical pH specific to?

Answer 4

It’s specific to the hydroxyapatite crystal at a particular salivary calcium ion saturation & if that saturation changes, the critical pH can also change.

look at the slide

Question 5

What is the critical pH of enamel?

Answer 5

5.5 (the pH at which hydroxyapatite dissociate)

look at the slide

Question 6

What else can change the critical pH?

Answer 6

If the structure of the hydroxyapatite changes.

Question 6

Describe how demineralisation and remineralisation occur:

Answer 6

1. Fermentable carbohydrates
   2.pH falls
   3.demineralisation
   4.Saliva and OH- + PO4 3- ions return pH to neutral
2. Remineralisation occurs

look at the slide

Question 7

How does enamel change if it’s post-eruptive?

Answer 7

It can lose some carbonate ions & incorporation of fluoride from pre-eruptive enamel can occur to form fluorapatite, or fluorohydroxyapatite if it’s substituted.

Question 8

What is a key point about having fluoride that’s firmly bound within the crystalline structure of the hydroxyapatite?

Answer 8

It has a lower solubility than hydroxyapatite.

look at the slide

Question 9

What is the effect of fluoride on apatite solubility?

Answer 9

Fluoride rich apatite is less soluble than hydroxyapatite so the critical pH shifts to a lower pH meaning that mineral can withstand lower pH (higher acidity) compared to hydroxyapatite.

look at the slide

Question 10

Describe the properties of calcium fluoride.

Answer 10

It’s a loosely bound fluoride which can act as a reservoir of both calcium & fluoride (both critical ions in the process of remineralisation).

Only formed with high-concentration fluoride solutions & results in globules of CaF2 which have protein- and phosphate-rich surfaces which reduces the rate of dissolution.

Question 11

What are the mechanisms of loosely bound fluoride in remineralisation?

Answer 11

1. It can bind Ca2+ and PO4 3- ions dissolving from acid attack and promotes re-precipitation
2. This can fill in any porosities (narrows pores in enamel) occurring e.g in white spot lesions of early stage of caries process

Question 12

What is fluoride release dependent on?

Answer 12

pH

Question 13

What are the antibacterial effects of fluoride?

Answer 13

• Fluoride can inhibit carbohydrate metabolism of oral streptococci and lactobacilli
• To exert this effect, fluoride must enter the cytoplasm of bacteria cells & affect enzymes and transport systems involved in carbohydrate metabolism

Question 14

What is the amount of mineral loss a result of?

Answer 14

2 things:
1. pH
2. Fluoride concentration

At low pH, fluoride concentration is an important determinant of rate of mineral dissolution

Question 15

How does fluoride get into the bacterial cell in the first place?

Answer 15

1. Fluoride diffuses into cells as HF
2. Low external pH promotes formation of more HF
3. High intracellular pH of bacteria favours dissociation of HF to H+ and F-
4. And so more HF can enter

Question 16

What are the effects of fluoride on plaque?

Answer 16

-Fluoride has NO effect on bacterial adherence or initial plaque formation

-Fluoride reduces acid production in plaque but the effect depends upon nature of fluoride application e.g loosely bound or tightly bound

Despite antibacterial effects, it’s not clear to what extent this action contributes to caries prevention

Question 17

What are the effects of fluoride on bacteria?

Answer 17

1. Fluoride can directly inhibit Enolase

This prevents glycolysis, and lactic acid production, stopping bacteria from producing acid that causes demineralisation

2. Fluoride can affect the phosphotransferase system, causing less glucose (sugar) uptake, reducing lactic acid production that causes demineralisation.

3 Once HF enters the bacterial cell, it dissociates causing the pH of cytoplasm to drop and become more acidic.

4. Fluoride can also affect the ATPase-dependent H+ pump BUT it could possibly not as Aluminium ions (Al3+) are needed for this
5. High intracellular H+ concentrations inhibits enolase and other glycolytic enzymes, regulating lactic acid production and reduces it

Question 18

What happens if we have too much fluoride?

Answer 18

It appears to impair the growth of apatite crystals,

-Retention of modulating matrix proteins through enhanced binding of mineral to matrix proteins

-AND enhanced binding of the proteases responsible for processing prior to matrix removal.

Question 19

What is fluorosis?

Answer 19

Excessive fluoride, soft chalky enamel (READ PICKARDS AND ADD MORE INFO)