Chemistry of Enamel Flashcards
What is the Structure of Calcium Hydroxyapatite?
3 axis - a,b,c - rhombohedron shape
- hexagonal planes of hydroxyl columns
- each twisted by 60º
What is the Formula of Hydroxyapatite?
Ca₁₀(PO₄)₆(OH)₂
What is the Effect of Fluoride Ions Substituting Hydroxyl Vacancies? (7)
- 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
What is the Effect of Carbonate Ions Substituting Hydroxyl Vacancies? (4)
- can replace hydroxyl or phosphate
- destabilises the structure
= less stable
= more acid soluble
What is the Effect of Magnesium Ions Substituting Hydroxyl Vacancies? (2)
can replace calcium
- destabilising effect on appetite and lattice
Why is Enamel at the ADJ less dense?
more carbonate and magnesium
less fluoride
How Does Density Vary from Surface of Enamel Towards Dentine?
Decreases
- highest at surface
What is Highest in Dentine?
porosity
water
organic content
Why does a Lesion Appear White? (4)
loss of minerals
acid produces pores
= dry out
= white spot due to light scatter
Define Saturation Point
the point at which no more of a substance can be absorbed or dissolved into a solution
What Happens to ionic Materials Above Saturation Point?
precipitation
anions and cations combine
= high forces of attraction
What Happens to ionic Materials Below Saturation Point?
Dissolve
- lower forces of attraction
What is the Effect of Adding Hydrogen Ions?
- ionises phosphate ions
= lowers pH
What happens at the Critical pH?
phosphate comes out of hydroxyapatite into the plaque fluid
- phosphate ions bind to calcium and weaken other ions
What are the Hydrogen Ion States above pH5.5 and below?
Above pH 5.5
[HPO₄]²⁻ = hydrogen phosphate state
Below pH 5.5
[H₂PO₄]⁻ = dihydrogen phosphate ion
Describe Minerals in the Stages of Lesion
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
What is the Purpose of Fluoride Based Technologies? (4)
- decreases solubility product
- fluorapatite is less soluble than hydroxyapatite
@ pH 4.5 - hydroxyapatite = unsaturated
- fluorapatite = supersaturated
What is the Purpose of Calcium Based Technologies?
- allows production of Ca-F minerals
- increase fluoride persistence at surface
Give an Example of a Calcium Protein and its uses.
Casein Phosphopeptide (CPP)
- increase remineralisation
- stabilise Ca-Phosphate ions
binds ions = nanocluster for a supersaturated environment
What is a CON of CPP?
the clinical date is limited
What are SAP’s, and what are 4 Therapeutic Purposes of Self-Assembling Peptides (SAP)?
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’