Enamel and critical pH

Question 1

List 3 conditions requiring restorations

Answer 1

Fracture
Caries
Erosion/abrasion

Question 2

What is the main component of enamel?

Answer 2

Biological apatite = mainly calcium hydroxyapatite

Question 3

How does solubility of HA increase?

Answer 3

Low pH

Question 4

Critical pH of enamel?

Answer 4

5.5

Question 5

Significance of critical pH?

Answer 5

Enamel dissolves more quickly below critical pH

Question 6

How does the time taken for pH to drop after sucrose exposure compare to the time taken to rise again?

Answer 6

Drop much quicker than rise

Question 7

Normal oral pH?

Answer 7

6.5

Question 8

What sits between enamel and plaque?

Answer 8

Enamel pellicle

Question 9

What is solubility product?

Answer 9

The product of the concentration of ions dissolved in solution

Question 10

CaF2 = Ca2+ + 2F-

Concentration of Ca2+ = 2.1x10-4
What is concentration of F-?
Hence what is solubility product?

Answer 10

2 x 2.1x10-4

(2.1 x 10-4) x (4.2 x 10-4)2

Question 11

What is the difference between Ksp (solubility product) and ionic product (IP)?

Answer 11

IP is in solution

Question 12

For solutions not in equilibrium
describe the solution if IP>Ksp
and
IP

Answer 12

solution is saturated (precipitation)

Solution is unsaturated (dissolution)

Question 13

At critical pH how do IP and Ksp compare?

Answer 13

Equal

Question 14

The Ksp of a sparingly soluble metal halide (‘MeHa’) is 4 x 10-8 (moles/L)2. How many moles of each element will dissolve in a litre of water?

Answer 14

2 x 10-8

Question 15

In acidic conditions, hydroxyapatite dissolves because ions are removed from solution. Which ions are likely to be removed?

Answer 15

OH- and PO43-