Flashcards in 6 - Fluoride Deck (36)
what causes the dental caries (permanent teeth) in children to drop?
fluoride content in public water supply (0- 3 ppm)
what are the potential benefits of systemic delivery?
what are the potential benefits of topical delivery?
• Inhibits demineralisation
• Promotes remineralistion
• Apatite solubility
• Plaque bacteria
what is fluoride in apatite more resistant to?
what are the potential problems of fluoride?
Fluorosis and mottling
what is the structure of hydroxyapatite?
lactice structure of OH, Ca2+ and PO43- arranged in sheets and stacked in layers
what is the central ion in the structure?
How is the asymmetrical H orientated?
in the same direction
what can OH not have?
Cannot have H- ions towards each other -becomes unstable and OH is lost
what occurs when OH ion is missing?
what fills the voids and what does this produce?
what is this exchange of central ions called?
what is the structure when there are no OH ions at all?
what is the critical pH?
Below which apatite dissolves
what is the criterial pH for hydroxyapatite?
what is the criterial pH for fluorapatite?
what does the difference in critical pH mean?
Fluorapatite requires larger pH falls to result in dissolution of mineral
what is the main effect form fluoride?
topically derived (there is a small systemic benefit but topical is better)
what is the result of fluorapatite shark teeth + plaque?
less mineral loss than human teeth and plaque
what is the result of human teeth + plaque + F- rinse?
even less mineral loss than fluorapatite shark teeth and plaque
what is the effect plaque on F-?
Plaque seems to accumulate fluoride :
– Plaque contains 4-10 ppm F-
– (of which ~ 1-2 ppm is ionic F-)
– saliva contains ~0.02 ppm
what effect flies fluoride have on enamel?
– adsorbed onto apatite crystal surface
– protects apatite crystals from dissolution
– Inhibits demineralisation
what is the outcome if oral or plaque pH is above critical pH?
– Fluids are supersaturated
– Dissolution does not occur
what is the outcome if oral or plaque pH falls below critical pH?
– Fluids are under saturated
– Dissolution occurs
(ions removed from tooth and apatite dissolves)
What happens if plaque pH falls below pH 5.5 ?
– Plaque becomes undersaturated with respect to
– Dissolution of hydroxyapatite
what happens if pH remains above pH 4.5?
– still supersaturated with respect to fluorapatite
– in the presence of F-, Fluorapatite will form
– Promotes remineralisation
what is the surface zone in enamel caries?
- Relatively intact zone
- ~30μm thick
- Highly mineralised – high F- content
what is the summary of fluoride?
– Stable crystal structure
– Lower critical pH therefore more resistant to dissolution
– Adsorbed fluoride inhibits demineralisation
– Promotes remineralisation
what effect does F- have on oral bacteria?
- F- passes through bacterial membranes
- F- appears to inhibit numerous enzymes involved in glycolysis pathway:
> e.g. Enolase
> Result: less lactic acid production
- Inhibits storage of intracellular poly-saccharides :
> Prevents acid production between meals
- Toxic to bacteria:
> Only in high [F-] – e.g. topical F- therapy