demineralisation and remineralisation Flashcards
3 things requried for caries and demineralisation?
bacteria
sugar
weak saliva defences
appearance of initial caries lesion
- white spot
- indication of change of porosity of enamel surface
initial caires lesion under polarised light micrograph
hydroxyapatite chemical formula
Ca10(PO4)6(OH)2
effect of acidic pH on hydroxyapatite
- HAP converted into more stable salt
- has lower [Ca]/[PO4] molar ratio
Ca10(PO4)6(OH)2 + 8H+ -> 6 CaHPO4 +2H2O + 4Ca2+
effect of pH <4 on dicalcium phosphate
dicalcium phosphate is most stable at this pH and it dissociated into its constituent ions
CaHPO4 + H+ -> Ca2+ + H2PO4-
formulas for hydroxyapatite solubility produce equilibrium constant Ksp
if ionic activity product is higher than solubility product equilibrium constant (Ksp)
- solution is super saturated
- salt precipitation will occur
- remineralisation
if ionic activity product is lower than solubility product equilibrium constant (Ksp)
- solution is not saturated
- dissolution of solid will occur
- demineralisation
what is happening at stages 1 2 3 & 4
- Lowering the pH from ~7 to 4.5 at the enamel surface by fatty acids from bacteria
- Dissolution of calcium and phosphate
- saliva flows over the affected area resulting in rise of pH
- If fluoride is present, together with saliva the softened surface is repaired, at least partially.
- If fluoride is not present then step 4 stops at the enamel line.
As plaque pH decreases,
effect on calcium phosphate solubility
calcium phosphate solubility increases
rising pH effect on dicalcium phosphate
converts dicalcium phosphate into salt with high [ca]/[PO4] molar ratio
eventually becomes hydroxyapatite
remineralisation
what is the pellicle layer
- layer on top of enamel
- predominantly saliva components
- provides protective layer
- hydrophobic potential
- semipermeable barrier
- restricted movement of mineral ions through enamel surface
- acellular organic layer
- facilitates precipitation of mineral at surface
how do calcium salts pass between saliva and enamel through the pellicle ?
- they exist as ions in saliva and enamel layer
- must become electroneutral form to pass through pellicle layer and dissociate into ions once passing through
what factors does progress of demineralisation depend on
- the rate of acid produced externally
- the production of net-neutral species which diffuse more readily across the pellicle layer than charged species
- the rate of inward diffusion of the unionised forms of acids through the pellicle layer and the water filled inter-crystalline organic phase of enamel.
- the rate of apatite dissolution
- the outward dissolution of calcium phosphate in the form of uncharged aqueous complexes
what changes occur within the zone of caries lesions
- Pore structure
- Relative ion concentration
- Possible crystal changes
what factors influence enamel dissolution
- Biogenic apatites display some variety in their ion stoichiometry depending on tissue, developmental stage, individual etc.
- Incorporation of impurities such as magnesium, sodium and carbonate tend to increase solubility
- Calcium can be replaced by magnesium, sodium, potassium, lead, strontium, or barium
- Carbonate can replace either hydroxyl or phosphate
- Replacement of the hydroxyl group with fluoride leads to the formation of fluorapatite and fluoridated apatites, which reduces solubility
factors influencing tooth surface loss
biological
chemical
health
behavioural
strategies for prevention of demineralisation
- good dental hygiene and frequent rinsing
- toothpastes with fluoride
- interferes with enolase in glycolysis and inhibitors adhesion to teeth
- inhibits glucosyltransferase used by bacteria to produce dextran
- antibacterial agents
- zinc
- interferes with enolase in glycolysis and inhibitors adhesion to teeth
- fissure sealants
- prevents diffusion of neutral salts in and out of enamel surface
draw summary flowchart of demineralisation and remineralisation
