THE CHEMISTRY OF MATURE HUMAN ENAMEL Flashcards
What is enamel comprised mainly of?
Inorganic mineral: Millions of mineral crystals
How big is each individual mineral crystal the makes up enamel?
50nm in width
30nm in thickness
Length is unknown
How are the individual crystal organised in enamel?
They are organised into crystal bundles called enamel prisms
What is another name fo enamel prisms
Enamel rods
What structural features results in enamel having unique properties?
The interweaving of the enamel prisms relative to one another, with alternative prisms arranged in opposing directions
What are the mineral crystals hat make up enamel made-up of?
Calcium phosphate sal called hydroxyapatite
In what non biological system can calcium hydroxyapatite be found?
Granite
What shape does the T cell ornament of a hydroxyapatite crystal resemble?
A rhombohedron
What is the stoichiometry of pure hydroxyapatite?
Ca10(PO4)6(OH)2
Why is the hydroxyapatite inner bones and teeth called substituted or carbonated hydroxy apatite.?
As it is not pure
What is the simplified model of the structure of calcium hydroxyapatite called?
The stacking plate model
Briefly describe the stacking plate model of the structure of calcium hydroxyapatite
- hydroxyl groups are at the centre
- This is surrounded by a triangle of calcium ions ( calcium 2)
- Alternating with the calcium 2’s we have a triangle of phosphate groups
- Surrounding these triangles we have a hexagon of calcium ions (calcium 1’s)
What variations can apatite in enamel exhibit?
- Missing ions
2. Extraneous ion (impurities)
Which ions are often missing in apatite crystals found in enamel?
calcium and hydroxyl
What imputes can be found in apatite crystals in enamel?
- Carbonate
- Magnesium
- Sodium
- Fluoride
What can defects and substitutions in the apatite crystals in enamel lead to?
Can have a profound effect on the behaviour ofapatite especially with regards to its solubility at low pH
What is a key very important property of apatite in general?
That they can take up many different ions not their structure by substituting one of the endogenous ions heteroionic substitution. )1
What is heteroionic substitution?
substitution of one endogenous ion with a different one
Give examples of some substitutions that apatite crystals can do?
1, fluoride for hydroxyl ions
- Carbonate for hydroxyl or phosphate
- Magnesium
What is fluoride substituted with in apatite crystals?
Hydroxyl ions
Why does fluoride fit better in apatite crystals than hydroxyl ions?
Fluoride is highly symmetrical and highly electronegative
Is the fact that fluoride is high electronegative a good thing for the apatite crystal?
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
Why does the substitution of carbonate for hydroxyl or phosphate makes theatre less stable?
Due ti the poor shape of carbonate in the lattice
What accounts for much of the higher solubility product of enamel compared to stoichiometric HA.?
Carbonate substitutions along with ion vacancies
How and why does magnesium substitute n the apatite crystals ?
due to its charge density would have a destabilizing effect on the lattice.
What non apatite mineral phases may be preset in enamel?
Ca Mg(CO3)2.
Generally what happens to the density of crystals throughout the enamel?
Decreases from the tooth surface towards the dentine
Generally what happens to the porosity, water and organic content throughout the enamel?
Increases from the tooth surface towards the dentine
Where is the least amount of protein seen in the tooth?
The least protein we see is at the surface and increases towards the dentine and cervivlaly
Describe the distribution of carbonate in a human molars enamel?
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
Describe the distribution of magnesium in a human molars enamel?
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.
IS the distribution of magnesium and carbonate dependent on tooth morphology?
Nope
Where is the density of minerals highest in the tooth?
At the cusp
Where does caries usually start?
Dental caries start on the mesial or distal surfaces i.e. between teeth.
Describe the distribution of fluoride in a human molars enamel?
The outermost enamel contains the most fluoride.
What are Fluorotic teeth more resistant to?
They are more resistant to acid attacks
