Chemistry of enamel caries Flashcards
1. To understand the chemical changes occurring in dental enamel during caries, against the background of enamel chemistry. 2. To understand how the chemistry of enamel caries is related to therapeutic measures such as fluoride and calcium-based technologies.
When will ionic materials precipitate into solution
will only precipitate if the surrounding solution is above the saturation point.
when will ionic materials dissolve
if the surrounding solution is below the saturation point.
when is saturation achieved
when the solubility product reaches a certain value
what is the solubility product for a binary salt XY
Ksp = [X] x [Y]
what is the solubility product for hydroxyapatite
Ksp = [Ca]10 x [PO4]6 x [OH]2
what do carbonate and magnesium ions do to the solubility product
increase the solubility product
what does fluoride do to the solubility product
decreases the solubility product making it more difficult to dissolve fluoridated crystals making it easier
what is the KSP of crystals with fluoride
With Fluoride = [Ca]10 [PO4]6 [OH]n-1[F]n+1
how do phosphate salts form
when +vely charged ions attach to the negatively charged oxygen atoms of the phosphate ions
what type of salt is hydroxyapatite crystals
calcium phosphate salt = Ca10 (PO4)6(OH)2 the positive ion is Ca2+
when will a tooth dissolve
if the pH is reduced to less than the critical pH
how many forms does the inorganic phosphate salt present in saliva or fluid
The forms depend on what
H3PO4, H2PO4–, HPO42– and PO43–, and the proportions depend entirely on the pH
at what ph does (PO4)3- change to (HPO4)2-
a pH of 9
at what ph does (HPO4)2- become H2PO4-
ph of 5
where are h+ ions produced from
from cariogenic bacteria which ferment sugars and produce lactic acid
what is the critical pH
What happens at this point
5.5 and this is when the enamel starts to dissolve
what happens at the critical pH
At around pH 5.5 and below, the phosphate in solution is in the acid form and has two protons (dihydrogen phosphateion H2PO4-
what extraneous ions can be found within the crystal structure
carbonate
magnesium
sodium and fluoride
what happens to enamel if the ph is greater than 4.5-5.5 and F is present
the biofilm fluid is supersaturated with respect to fluorapatite (FA) and there is re-precipitation of minerals in the enamel as FA.
what does the solubility of HA depend on
the pH
also the ionic levels of the HA component( calcium and phosphate of the surrounding medium
what are acids in the biofilm converted to in the saliva
converted into salts by the bicarbonate buffer system
what happens as a result of acid being converted into salts
the pH increases to above 5.5
biofilm becomes super saturated in regard to hydroxyapatite or fluroapatite
calcium and phosphate lost by enamel can be more efficiently recovered if fluoride is still present in the biofilm.
what is a white spot lesion
This is due to dissolution by acid produced by bacteria. The acid produces tiny pores which dry out producing a white spot due to light scatter
describe the translucent stone
large and uniform pores
what is the dark zone
INCREASE OF POROSITY but also small pores inaccessible to the imbibing fluid
what is the body of the lesion
much more porosity with very large pores and as if some re-precipitation of dissolved mineral has occurred
what is removed from the first layer of enamel
magnesium and carbonate rich
how much calcium is lost from sound enamel
37%
how much P is lost from sound enamel
18.5%
how much CO3 is lost from sound enamel
2-4%
how much Mg is lost from sound enamel
0.2-0.4%
how much Ca is lost from translucent zone
around 30%
how much P is lost from translucent zone
around 13%
how much CO3 is lost from translucent zone
around 28%
how much MG is lost from translucent zone
around 2%
how much Ca is lost from the dark zone
around 35%
how much P is lost from the dark zone
16.6%
how much CO3 is lost from the dark zone
3%
how much Mg is lost from the dark zone
3%
how much Ca is lost from the body of the lesion
37%
how much P is lost from the body of the lesion
18.5%
how much CO3 is lost from the body of the lesion
1%
how much Mg is lost from the body of the lesion
0.16%
why might the amount of carbonate lost from sound enamel and lost from dark zone be similar
due to re precipitation
what is the conclusion of % chemistry loss
The conclusion is that there is selective removal of easily dissolved mineral at an early stage. This agrees with the effect of both magnesium and carbonate on hydroxyapatite.
where is fluoride conc highest in the zones of a carious lesion
at the carious surfaces and in the translucent zone
which minerals are lost first
magnesium and carbonate
what is biomimetic remineralisation
techniques which attempt to mimic nature with respect to remineralisation.
what is an example of biomimetic remineralisation
Casein Phospho-peptide: Amorphous Calcium Phosphate (CPP-ACP): Tooth mousse
self assembling peptides(SAPS)
describe CPP-ACP
Ca2+ and PO3−4 in solution by binding to form nanoclusters.
The desired effect is inhibiting demineralization and driving remineralisation down a concentration gradient.
DESCRIBE sap
bioactive peptides synthesised from natural amino acids which have shown some promising results
how do SAPs work
Mimic enamel matrix proteins which control initial mineral deposition ‘nucleation’ and subsequent crystal growth.
Increase net mineral gain via inhibition of demineralisation and promotion of remineralisation.
Are candidate materials for “Filling without Drilling”
