Chemistry of Enamel

Question 1

What is the Structure of Calcium Hydroxyapatite?

Answer 1

3 axis - a,b,c - rhombohedron shape
- hexagonal planes of hydroxyl columns
- each twisted by 60º

Question 2

What is the Formula of Hydroxyapatite?

Answer 2

Ca₁₀(PO₄)₆(OH)₂

Question 3

What is the Effect of Fluoride Ions Substituting Hydroxyl Vacancies? (7)

Answer 3

• higher symmetry
• fits better
• caries preventative

= highly electronegative so pulls the ions together
- hydrogen bonds point towards fluoride ion = stability
= lowers lattice energy
= harder to dissolve in acid
- becomes easier for mineral to deposit

Question 4

What is the Effect of Carbonate Ions Substituting Hydroxyl Vacancies? (4)

Answer 4

• can replace hydroxyl or phosphate
• destabilises the structure
  = less stable
  = more acid soluble

Question 5

What is the Effect of Magnesium Ions Substituting Hydroxyl Vacancies? (2)

Answer 5

can replace calcium
- destabilising effect on appetite and lattice

Question 6

Why is Enamel at the ADJ less dense?

Answer 6

more carbonate and magnesium
less fluoride

Question 7

How Does Density Vary from Surface of Enamel Towards Dentine?

Answer 7

Decreases
- highest at surface

Question 8

What is Highest in Dentine?

Answer 8

porosity
water
organic content

Question 9

Why does a Lesion Appear White? (4)

Answer 9

loss of minerals
acid produces pores
= dry out
= white spot due to light scatter

Question 10

Define Saturation Point

Answer 10

the point at which no more of a substance can be absorbed or dissolved into a solution

Question 11

What Happens to ionic Materials Above Saturation Point?

Answer 11

precipitation

anions and cations combine
= high forces of attraction

Question 12

What Happens to ionic Materials Below Saturation Point?

Answer 12

Dissolve

• lower forces of attraction

Question 13

What is the Effect of Adding Hydrogen Ions?

Answer 13

• ionises phosphate ions
  = lowers pH

Question 14

What happens at the Critical pH?

Answer 14

phosphate comes out of hydroxyapatite into the plaque fluid
- phosphate ions bind to calcium and weaken other ions

Question 15

What are the Hydrogen Ion States above pH5.5 and below?

Answer 15

Above pH 5.5
[HPO₄]²⁻ = hydrogen phosphate state

Below pH 5.5
[H₂PO₄]⁻ = dihydrogen phosphate ion

Question 16

Describe Minerals in the Stages of Lesion

Answer 16

Surface Zone
- higher mineral, high fluoride content

Body of Lesion
- mineral loss
- loss of re-precipitated mineral

Dark Zone
- further loss of mineral
- some re-precipitation

Transluscent Zone
- some mineral loss

Question 17

What is the Purpose of Fluoride Based Technologies? (4)

Answer 17

• decreases solubility product
• fluorapatite is less soluble than hydroxyapatite
  @ pH 4.5
• hydroxyapatite = unsaturated
• fluorapatite = supersaturated

Question 18

What is the Purpose of Calcium Based Technologies?

Answer 18

• allows production of Ca-F minerals
• increase fluoride persistence at surface

Question 19

Give an Example of a Calcium Protein and its uses.

Answer 19

Casein Phosphopeptide (CPP)
- increase remineralisation
- stabilise Ca-Phosphate ions

binds ions = nanocluster for a supersaturated environment

Question 20

What is a CON of CPP?

Answer 20

the clinical date is limited

Question 21

What are SAP’s, and what are 4 Therapeutic Purposes of Self-Assembling Peptides (SAP)?

Answer 21

bioactive peptides from natural amino acids

• mimic enamel matrix protein
  = mineral deposition
  = mineralisation
• increase net mineral gain
  = inhibit demineralisation

-infiltrate white spot lesions
- generate bioactive scaffold

candidate material for ‘filling without drilling’