OE L33 Fluoride at the Enamel Surface

Question 1

Name methods of topical fluroide delivery.

Answer 1

• Dentrifices
• Mouthwashes
• Gels/foams/varnishes
• Implantable/restorative materials e.g. GICs, copolymer membranes

Question 2

Name methods of systemic fluoride delivery.

Answer 2

• Fluoridated water
• Fluoride supplement tablets
• Salt high in fluoride (used for cooking purposes)

Question 3

What is the optimum fluoride level in water for maximum caries protection and minimal dental fluorosis?

Answer 3

1ppm

1mg/litre

Question 4

Is fluoride incorporation into enamel more effective pre- or post- eruptively?

Answer 4

Topical application of fluoride to erupted teeth is more beneficial in caries prevention than incorporation during tooth development.
Fluoride incorporation into the enamel mineral during tooth development has relatively little effect on the carries process.

Question 5

How does dental fluorosis present?

Answer 5

As white spots on the teeth, this tissue is more prone to erosion and abrasion.

Question 6

What is the chemical equation for the conversion of hydroxyapatite to fluorapatite?

Answer 6

Ca10(PO4)6(OH)2 +2F- —> Ca10(PO4)6(F)2 + 2OH-

Question 7

What are the mechanisms of fluoride’s cariostatic effects?

Answer 7

• Fluoride alters structure of developing enamel to make it more resistant to acid attack (small degree)
• Fluoride reduces the ability of bacteria to produce acid
• Topical fluoride encourages remineralisation with the formation of fluorapatite

Question 8

Give a simple explanation of glycolysis.

Answer 8

The metabolic pathway which converts glucose to pyruvate, ATP and NADH (x2).

Question 9

What does pyruvate produce and how?

Answer 9

Pyruvare produces lactic acid through the action of lactate dehydrogenase.

Question 10

How does fluoride interfere with glycolysis?

Answer 10

Fluroide interferes with the metabolism of glucose by bacteria.
It slows glycolysis and the bacterial cell dies.
- It inhibits enolase, so there’s no phosphoenolpyruvate formation, therefore no regeneration of ATP and no lactic acid production
- It inhibits ATPase so protons aren’t pumped out of the cell, so no protons can be pumped back in with glucose (no glucose = cell death) aka inhibition of glucose uptake via proton motive force

Question 11

What is the net result of fluoride’s actions on glycolysis?

Answer 11

• No recycling of ADP

- Reduction of lactic acid

Question 12

How much fluoride is necessary to produce the anti-bacterial effects?

Answer 12

• 2 minute exposure, twice a day
• 120ppm (1-3mM)
• Must remember that bacteria exists as biofilms, fluoride may only affect the surface level bacteria and not penetrate deep down and affect the rest of the biofilm, therefore, dentifrice concentrations must be high, in Europe this is 1500ppm

Question 13

How can dentrifices be modified to allow fluoride to penetrate deeper into the plaque?

Answer 13

• Addition of calcium
• Causes formation of calcium fluoride
• CaF2 can accumulate and penetrate deeper than F alone

Question 14

Describe fluorapatite formation.

Answer 14

• Fluroide substitutes the hydroxyl ion in HAP
• F- has a higher charge density, creates a tighter crystal lattice structure, lower lattice energy- stabilises crystal structure
• Fluorapatite crystals form in preference over hydroxyapatite, and forms more rapidly

Question 15

Does fluorapatite have a lower or higher Ksp than HAP?

Answer 15

Fluorapatite has a lower solubility product, and is more resistant to acid dissolution.

Question 16

Is fluoride presence more beneficial in demineralisation (pH drop) or remineralisation (pH rise)?

Answer 16

Fluoride present during remineralisation causes fluoride containing calcium phosphate salts and fluorapatite to be produced. Which means during the next acid challenge there is more defence.

If fluoride is present during demineralisation calcium phosphate salts are produced.

Question 17

How does fluoride pass through the pellicle layer?

Answer 17

• Must be uncharged

- Fluoride enters as calcium fluoride and then dissociates back into Ca+ and F-

Question 18

What is the optimal calcium concentration in remineralising solutions (ie mouthwashes)?

Answer 18

• 1mM calcium is more effective than 3mM
• 3mM: supersaturated with HAP, FAP, phosphates, calcium preciptates in the surface zone and cannot penetrate to deeper areas
• 1mM: prolonged deposition of mineral phases on existing crystals within the lesion, allows a more gradual “plugging” of the porosities and access to deeper regions of the lesion

Question 19

How does enamel structure influence fluoride penetration?

Answer 19

• Enamel lamellae allow deep penetration
• Enamel tufts and spindles don’t aid delivery of F deep into tissues
• Striae of Retzius help to provide entry points for fluoride deeper into the enamel layer

Question 20

How is fluoride delivered in dentrifices?

Answer 20

• Most use sodium monofluorophosphate which is hydrolysed within plaque to sodium fluoride
• Some use stannous fluoride which also has anti-microbial properties

Question 21

Explain the 2 major methods of targeted fluoride delivery.

Answer 21

Varnishes/gels

• Amine fluorides: positive amine head, organic hydrophobic tail, amine group attaches to fluoride, tail directs attachemnt of amine to enamel surface and prevents acid entry
• Amorphous calcium phosphate casein phospho-peptides: delivers high levels of calcium phosphate to tooth, maintains supersaturated state of essential minerals at the same time hindering colonisation of surface by bacteria