6 - Fluoride

Question 1

what causes the dental caries (permanent teeth) in children to drop?

Answer 1

fluoride content in public water supply (0- 3 ppm)

Question 2

what are the potential benefits of systemic delivery?

Answer 2

apatite solubility

Question 3

what are the potential benefits of topical delivery?

Answer 3

• Inhibits demineralisation
• Promotes remineralistion
• Apatite solubility
• Plaque bacteria

Question 4

what is fluoride in apatite more resistant to?

Answer 4

acid

Question 5

what are the potential problems of fluoride?

Answer 5

Fluorosis and mottling

Question 6

what is the structure of hydroxyapatite?

Answer 6

lactice structure of OH, Ca2+ and PO43- arranged in sheets and stacked in layers

Question 7

what is the central ion in the structure?

Answer 7

OH-

Question 8

How is the asymmetrical H orientated?

Answer 8

in the same direction

Question 9

what can OH not have?

Answer 9

Cannot have H- ions towards each other -becomes unstable and OH is lost

Question 10

what occurs when OH ion is missing?

Answer 10

Voids

Question 11

what fills the voids and what does this produce?

Answer 11

F- ion

- Fluoroapatite

Question 12

what is this exchange of central ions called?

Answer 12

heteroionic exchange

Question 13

what is the structure when there are no OH ions at all?

Answer 13

fluorapatite

Question 14

what is the critical pH?

Answer 14

Below which apatite dissolves

Question 15

what is the criterial pH for hydroxyapatite?

Answer 15

pH 5.5

Question 16

what is the criterial pH for fluorapatite?

Answer 16

pH 4.5

Question 17

what does the difference in critical pH mean?

Answer 17

Fluorapatite requires larger pH falls to result in dissolution of mineral

Question 18

what is the main effect form fluoride?

Answer 18

topically derived (there is a small systemic benefit but topical is better)

Question 19

what is the result of fluorapatite shark teeth + plaque?

Answer 19

less mineral loss than human teeth and plaque

Question 20

what is the result of human teeth + plaque + F- rinse?

Answer 20

even less mineral loss than fluorapatite shark teeth and plaque

Question 21

what is the effect plaque on F-?

Answer 21

Plaque seems to accumulate fluoride :
– Plaque contains 4-10 ppm F-
– (of which ~ 1-2 ppm is ionic F-)
– saliva contains ~0.02 ppm

Question 22

what effect flies fluoride have on enamel?

Answer 22

– adsorbed onto apatite crystal surface
– protects apatite crystals from dissolution
– Inhibits demineralisation

Question 23

what is the outcome if oral or plaque pH is above critical pH?

Answer 23

– Fluids are supersaturated

– Dissolution does not occur

Question 24

what is the outcome if oral or plaque pH falls below critical pH?

Answer 24

– Fluids are under saturated
– Dissolution occurs
(ions removed from tooth and apatite dissolves)

Question 25

What happens if plaque pH falls below pH 5.5 ?

Answer 25

– Plaque becomes undersaturated with respect to hydroxyapatite – Dissolution of hydroxyapatite

Question 26

what happens if pH remains above pH 4.5?

Answer 26

– still supersaturated with respect to fluorapatite – in the presence of F-, Fluorapatite will form – Promotes remineralisation

Question 27

what is the surface zone in enamel caries?

Answer 27

- Relatively intact zone - ~30μm thick - Highly mineralised – high F- content

Question 28

what is the summary of fluoride?

Answer 28

Apatite: – Stable crystal structure – Lower critical pH therefore more resistant to dissolution – Adsorbed fluoride inhibits demineralisation – Promotes remineralisation

Question 29

what effect does F- have on oral bacteria?

Answer 29

- 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

Question 30

what is the overall effect of fluoride have on bacteria?

Answer 30

inhibits glycolysis pathway

Question 31

what is mild fluorosis?

Answer 31

fine white lines

Question 32

what is moderate fluorosis?

Answer 32

Opaque discoloured enamel

Question 33

what is severe fluorosis?

Answer 33

loss of enamel

Question 34

what causes fluorosis?

Answer 34

- High F- exposure during tooth development - Especially in high F- areas and supplemental ingested F-: > F- drops >Swallowed toothpaste

Question 35

Describe normal amelogenesis.

Answer 35

– Nearly all matrix proteins (amelogenins) are degraded and removed – This is a requirement for crystal growth

Question 36

what occurs in fluorosis?

Answer 36

– Reduced enamel matrix protein (amelogenin) degradation – Increased amelogenin retention – Incomplete crystal growth