MFD23

Question 1

How do you calculate Ksp? (solubility product)

Answer 1

Use RICE like you would in chemistry to find conc of aq. ions in solution, then times them together. if conc of Ca is 0.25, and the molecule in Cahydroxyapeptate,
you would do 0.25 to the power 10 timesed by the rest of the conc. to their power (which is determined by the number of moles in the equation).

Question 2

what is the ionic product?

Answer 2

same as solubility product except in solution

Question 3

If ionic product is greater than solubility product , the solution is said to be ___a-___ and ____b__ will occur unless ___c)what?___

Answer 3

1) supersaturated
b) precipitation will occur
c) ions stabilised by proteins i.e. the ones found in saliva

Question 4

If ionic product is less than solubility product , the solution is said to be ___a-___ and ____b__ will occur

Answer 4

a) unsaturated

b) enamel dissolution (as equilibrium shifted to right. )

Question 5

Is there a difference between what happens to a tooth if acid is dripped on it compared to when water is dripped on it?
2) why?

Answer 5

no

2) water is removed after and equilibrium never reached

Question 6

In water, the ionic product of hydroxyapatite=?

2) What will happen?
3) When will this stop?
4) Why doesn’t this happen in saliva?

Answer 6

1) 0 Moles/L
(• Hydroxide is present, but there is no Ca or P)
2) hydroxyapatite will dissolve…
3) … until an equilibrium is reached:
4) saliva is supersaturated with Ca and PO4–ie. IP > Ksp

Question 7

Why isn’t critical pH constant?

Answer 7

The levels of Ca+ and PO43- vary in plaque fluid and saliva between people. The more present the lower the critical pH.

Question 8

Why are white spot lesions reversible and surface erosion not?

Answer 8

In a white spot lesion, decalcification has occured bellow the tooth surface. Therefore, no pellicales have formed and there is a suitable matric for Calcium and phosphate deposition, provided by the supersaturated saliva. Clinically, fluoride varnish and sugar-free gum also help.
Enamel suffering surface erosion cannot be deposited into as there is no matrix for the ions to be deposited on and pellicles provided by saliva and plaque fluid inhibit mineral deposition.

Question 9

Acid at tooth surface causes dissolution of enamel. Why? sciencey time
(explain at not very low pH)

Answer 9

1. Loss of OH-
   • Hydrogen ions remove hydroxyl ions in water:
   • H+ + OH-⇌H2O
   • In water, [H+][OH-] = 10^-14(Moles/L)^2
   • As [H+] increases, [OH-] must decrease. Pulling the equilibrium towards dissolution.
2. Loss of PO43-
   • Phosphate exists in 4 forms BUT only PO43-important for IP of Hydroxyapatite.
   • As pH decreases, equilibrium is pushed away from PO43- and instead forms HPO4 ^2-

Question 10

1) What form of phosphate do we want to see in saliva?

2) As going from least to most acidic what forms of phosphate do we see?

Answer 10

1) PO4 ^3-
2) a)PO4 ^3-
b) HPO4 ^2-
c) H2PO4 ^-4
d) H3PO4

Question 11

What 3 conditions require restoration?

Answer 11

1) fracture
2) caries
3) erosion/abrasion

Question 12

What is the cause of loss in fracture

Answer 12

1)Fracture: Loss due to sudden impact force

Question 13

What is the cause of loss in caries

Answer 13

Caries: Loss due to acids of bacterial origin

Question 14

What is the cause of loss in erosion/abrasion

Answer 14

Erosion/abrasion: Loss due to dietary acids and mechanical wear

Question 15

What is enamel often called by dentists?

2) What is its major component?

Answer 15

it is often called biological apatite.

2) The major componentis calcium hydroxyapatite.

Question 16

What is the formula of calcium hydroxyapatite?

Answer 16

Ca10(PO4)6(OH)2

Question 17

Ca10(PO4)6(OH)2

What impurities can replace calcium in hydroxyapatite?

Answer 17

1) strontium, barium, lead, sodium, Magnesium

Question 18

Ca10(PO4)6(OH)2

What impurities can replace phosphate in hydroxyapatite?

Answer 18

carbonate and

mono-hydrogen phosphate

Question 19

Ca10(PO4)6(OH)2

What impurities can replace hydroxy in hydroxyapatite?

Answer 19

flouride

Question 20

Properties of calcium hydroxyapatite:

1) to do with structure and strength
2) solubility in saliva?
3) pH’s effect on solubility

Answer 20

1) Structure of crystal formation effects strength (different between patients).
2) Sparingly soluble in saliva
3) Increased solubility at low pH (Stephan curve)

Question 21

What curve is used to describe pH at tooth surface following a sucrose rinse?

Answer 21

stephan curve

Question 22

Describe the stephan curve

Answer 22

• Plaque pH drops when challenged i.e. by food
• Oral pH drops with acidic food and drinks
• Rise is much slower than drop ( this also links into individual variation in critical pH as some people have more alkali production may explain results: stronger pH rise at the end of the Stephan Curve in our caries-free subjects and the role of base production)

Question 23

At what pH does enamel dissolve more quickly?

Answer 23

bellow the critical pH, (which is usually around 5.5)

Question 24

Why doesn’t water erode teeth in the mouth?

Answer 24

1) as teeth are actually exposed ot saliva, a supersaturated rela. to phosphate and calcium.
2) Pellicle on the surface of the tooth, enamel never directly in contact with saliva, proteins will bind to the calcium or phosphate and stop them from crystallising. This maintains the enamel in its usual form.
3) Dental plaque is also composed of 30% fluid which acts as a buffer between the enamel and saliva. The fluid retains ions which buffer.

Question 25

What variation in critical pH depend on?

Answer 25

the concentrations of calcium and phosphate in the solution.

Question 26

Why is there individual variation in critical pH?

Answer 26

1) • Different people have different [Ca] and [PO4] in saliva
2) • There are also differences in the composition of biological apatite, which affect dissolution
3) some people have more alkali production, and this is more important than acid production (some studies show).

Question 27

What medical conditions does this link to?

Answer 27

xerostomia and balaemia

Question 28

which describes, Ksp and IP value, at the critical pH:

1) Ksp more than IP
2) they are equal
3) Ksp less than IP

Answer 28

2) they are equal

Question 29

which describes, Ksp and IP value, when precipitation occurs:

1) Ksp more than IP
2) they are equal
3) Ksp less than IP

Answer 29

3) Ksp less than IP

Question 30

which describes, Ksp and IP value, when dissolution occurs:

1) Ksp more than IP
2) they are equal
3) Ksp less than IP

Answer 30

1) Ksp more than IP

Question 31

which describes, Ksp and IP value, above the critical pH:

1) Ksp more than IP
2) they are equal
3) Ksp less than IP

Answer 31

3) Ksp less than IP

precipitation occurs its supersaturated,

Question 32

Why when above the critical pH is there not loads of tartar/ calculus forming?

Answer 32

precipitation occurs its supersaturated, and its only cause we have proteins that hold calcium and phosphate in solution that it doesn’t cause tartar all the time.

Question 33

which describes, Ksp and IP value, bellow the critical pH:

1) Ksp more than IP
2) they are equal
3) Ksp less than IP

Answer 33

1) Ksp more than IP

dissolution occurs its unsaturated.