Chemistry of enamel caries

Question 1

When will ionic materials precipitate?

Answer 1

when surrounding solution is above saturation point

Question 2

When will ionic materials dissolve?

Answer 2

surrounding solution is below saturation point

Question 3

What is the solubility product equation for calcium hydroxyapatite?

Answer 3

Ksp = [Ca]10 x [PO4]6 x [OH]2

Question 4

What will happen if supernatant is not supersaturated?

Answer 4

dissolution

leading to caries

Question 5

What effect does fluoride have on solubility product?

Answer 5

decreases solubility product

lowers saturation point

above which precipitation occurs

Question 6

What effect does carbonate and magnesium have on solubility product?

Answer 6

increase solubility product -> more soluble

Question 7

When do phosphate salts form?

Answer 7

when positively charged ions attached to the negatively charged oxygen atom on phosphate,

hence forming an ionic compound.

Question 8

What is the critical pH below which demineralisation occurs?

Answer 8

5.5

Question 9

What ion has lower concentration at lower pHs? Why?

Answer 9

PO4 3-

more hydrogen ions added

phosphate ions are less able to maintain bond to calcium

Question 10

Above pH 5.5, what is the dominant phosphate ion?

Answer 10

HPO4 2-

Question 11

Below pH 5.5, what is the dominant phosphate ion?

Answer 11

H2PO4 -

this ionic bond to lattice is weak so they move into solution and hydroxyapatite solution occurs

Question 12

What must be present for reprecipitation to occur?

Answer 12

high pH (above 5.5)

fluoride -> biofilm supersaturated with fluoroapatite

Question 13

What happens after exposure to sugars has ceased?

Answer 13

acids in biofilm are converted to salts by saliva

pH will increases

biofilm will be supersaturated with fluoroapatite and hydroxyapatite

Question 14

Describe fluoride

Answer 14

less susceptible to acid environment

less soluble

shifts towards equilibrium for precipitation even below critical pH of 5.5

Question 15

Why do white spot lesions occur?

Answer 15

dissolution of mineral by bacterial acid

producing tiny pores

these dry out

producing white spot due to light scatter

Question 16

What is the deepest part of the caries lesion?

Answer 16

translucent zone

Question 17

Describe the dark zone

Answer 17

positively birefringent zone

has increase in porosity

increase in small holes that are inaccessible to imbibing fluid

not certain if some reprecipitation has occurred

Question 18

What does the body of lesion show?

Answer 18

more porosity

very large pores

Question 19

In what cases is there higher fluoride?

Answer 19

greater in non-cavitated caries lesion than surrounding sound enamel

higher in sound enamel than sound subsurface enamel

higher in surface enamel overlying body of lesion than sound enamel

Question 20

What is the first material removed from enamel in dissolution?

Answer 20

carbonate

magnesium

Question 21

What supplementation has potential to facilitate fluoride?

Answer 21

bioavailable calcium and phosphate

Question 22

Describe casein phosphopeptide

Answer 22

stabilises high concentrations of calcium and phosphate -> binds these to form nano clusters

application of CPP-ACP pastes can bet attempted if fluoride applications alone are unsuccessful

Question 23

What are self-assembling peptides?

Answer 23

bioactive peptides synthesised from natural amino acids

Question 24

What do results from self-assembling peptides show?

Answer 24

• Increase net mineral gain via inhibition of demineralisation and promotion of remineralisation
• Nucleate hydroxyapatite de novo
• Mimic enamel matrix proteins which control initial mineral deposition (nucleation) and subsequent crystal growth
• Infiltrate early white spot lesions and generate subsurface bioactive scaffold capable of inducing mineral deposition
• These are candidate materials for filling without drilling