chemistry of enamel caries

Question 1

the solubility product (ksp) for HAP is..

Answer 1

Ca]10[PO4]6[OH]2.

Ksp is the product of the concentrations (mol/L) of the component ions, raised to the appropriate power, in a saturated solution

Question 2

affect of mg, carbonate, and fl on the ksp of HAP.

Answer 2

mg and carbonate INCREASE the solubility product (harder to achieve)

fl. decreases the solubility product

Question 3

why does fl decrease the ksp/solubility product of HAP

Answer 3

FAP has a lower ksp than HAP therefore its harder to dissolve FAP in acid

Question 4

what is the affect of H+ ions on the ksp of HAP

Answer 4

INCREASE the solubility product

also H+ change the pH to below the critical pH = at which HAP will dissolve

Question 5

at ph 5.5 and below the phosphate ion dominating is..

Answer 5

H2PO4–.

Question 6

describe how the protonation of enamel by plaque acid causes the dissolution of HAP

Answer 6

1. as cariogenic bacteria break down fermentable sugars they make H+ ions
2. H+ ions bind to PO43- GRADUALLY reducing the ionic binding of these phosphate ions to the ca2+ ions in the HAP lattice
3. at pH 5.5 the H2PO4–. ions ionic bond to the lattice is sufficiently weak thus allowing these ions to move into solution causing the dissolution of HAP

Question 7

cariogenic bacteria produce acid which creates tiny pores in an early enamel lesion. why does this lesion appear white?

Answer 7

the pores of the lesion and the enamel have a similar refractive index, there is light scatter= appear white

Question 8

what are the 3 ‘zones’ of a carious lesion

Answer 8

1. transluscent zone
2. dark zone
3. body of lesion

Question 9

what is ions are massively lost from the translucent zone in the caries process

Answer 9

mg and carbonate

this is because there is selective removal of easily dissolved HAP at an early stage.

Question 10

fl accumulates during the carious process therefore more fl will be on the _____ of the carious lesion

Answer 10

enamel surface