THE CHEMISTRY OF MATURE HUMAN ENAMEL

Question 1

What is enamel comprised mainly of?

Answer 1

Inorganic mineral: Millions of mineral crystals

Question 2

How big is each individual mineral crystal the makes up enamel?

Answer 2

50nm in width
30nm in thickness
Length is unknown

Question 3

How are the individual crystal organised in enamel?

Answer 3

They are organised into crystal bundles called enamel prisms

Question 4

What is another name fo enamel prisms

Answer 4

Enamel rods

Question 5

What structural features results in enamel having unique properties?

Answer 5

The interweaving of the enamel prisms relative to one another, with alternative prisms arranged in opposing directions

Question 6

What are the mineral crystals hat make up enamel made-up of?

Answer 6

Calcium phosphate sal called hydroxyapatite

Question 7

In what non biological system can calcium hydroxyapatite be found?

Answer 7

Granite

Question 8

What shape does the T cell ornament of a hydroxyapatite crystal resemble?

Answer 8

A rhombohedron

Question 9

What is the stoichiometry of pure hydroxyapatite?

Answer 9

Ca10(PO4)6(OH)2

Question 10

Why is the hydroxyapatite inner bones and teeth called substituted or carbonated hydroxy apatite.?

Answer 10

As it is not pure

Question 11

What is the simplified model of the structure of calcium hydroxyapatite called?

Answer 11

The stacking plate model

Question 12

Briefly describe the stacking plate model of the structure of calcium hydroxyapatite

Answer 12

1. hydroxyl groups are at the centre
2. This is surrounded by a triangle of calcium ions ( calcium 2)
3. Alternating with the calcium 2’s we have a triangle of phosphate groups
4. Surrounding these triangles we have a hexagon of calcium ions (calcium 1’s)

Question 13

What variations can apatite in enamel exhibit?

Answer 13

1. Missing ions

2. Extraneous ion (impurities)

Question 14

Which ions are often missing in apatite crystals found in enamel?

Answer 14

calcium and hydroxyl

Question 15

What imputes can be found in apatite crystals in enamel?

Answer 15

1. Carbonate
2. Magnesium
3. Sodium
4. Fluoride

Question 16

What can defects and substitutions in the apatite crystals in enamel lead to?

Answer 16

Can have a profound effect on the behaviour ofapatite especially with regards to its solubility at low pH

Question 17

What is a key very important property of apatite in general?

Answer 17

That they can take up many different ions not their structure by substituting one of the endogenous ions heteroionic substitution. )1

Question 18

What is heteroionic substitution?

Answer 18

substitution of one endogenous ion with a different one

Question 19

Give examples of some substitutions that apatite crystals can do?

Answer 19

1, fluoride for hydroxyl ions

2. Carbonate for hydroxyl or phosphate
3. Magnesium

Question 20

What is fluoride substituted with in apatite crystals?

Answer 20

Hydroxyl ions

Question 21

Why does fluoride fit better in apatite crystals than hydroxyl ions?

Answer 21

Fluoride is highly symmetrical and highly electronegative

Question 22

Is the fact that fluoride is high electronegative a good thing for the apatite crystal?

Answer 22

Yes as it “pulls” the other ions together and stabilises the structure.
This makes fluoridated crystals more difficult to dissolve in acid and makes it easier for re-deposition at lower solution concentrations

Question 23

Why does the substitution of carbonate for hydroxyl or phosphate makes theatre less stable?

Answer 23

Due ti the poor shape of carbonate in the lattice

Question 24

What accounts for much of the higher solubility product of enamel compared to stoichiometric HA.?
​

Answer 24

Carbonate substitutions along with ion vacancies

Question 25

How and why does magnesium substitute n the apatite crystals ?

Answer 25

due to its charge density would have a destabilizing effect on the lattice.

Question 26

What non apatite mineral phases may be preset in enamel?

Answer 26

Ca Mg(CO3)2.

Question 27

Generally what happens to the density of crystals throughout the enamel?

Answer 27

Decreases from the tooth surface towards the dentine

Question 28

Generally what happens to the porosity, water and organic content throughout the enamel?

Answer 28

Increases from the tooth surface towards the dentine

Question 29

Where is the least amount of protein seen in the tooth?

Answer 29

The least protein we see is at the surface and increases towards the dentine and cervivlaly ​

Question 30

Describe the distribution of carbonate in a human molars enamel?

Answer 30

Concentrations rise from the enamel surface from about 2% towards the dentine where concentration of 4-6% are found
Pockets of high conc may be found around fissure enamel

Question 31

Describe the distribution of magnesium in a human molars enamel?

Answer 31

Concentrations increase towards the dentine surface. About 0.2% at the enamel surface to .5% close to dentine.
isolated pockets of high concentration close to dentine.​

Question 32

IS the distribution of magnesium and carbonate dependent on tooth morphology?

Answer 32

Nope

Question 33

Where is the density of minerals highest in the tooth?

Answer 33

At the cusp

Question 34

Where does caries usually start?

Answer 34

Dental caries start on the mesial or distal surfaces i.e. between teeth.

Question 35

Describe the distribution of fluoride in a human molars enamel?

Answer 35

The outermost enamel contains the most fluoride.

Question 36

What are Fluorotic teeth more resistant to?

Answer 36

They are more resistant to acid attacks