19. Enamel and pH Flashcards
3 conditions that require restoration
- fracture
- caries
- erosion/abrasion
Define ‘fracture’
loss of tooth due to sudden impact of force
Define ‘caries’
loss of tooth due to acid of bacterial origin
Define ‘erosion/abrasion’
tooth loss due to dietary acids and mechanical wear
What is biological apatite?
- main component of enamel
- made of mainly calcium hydroxyapatite
Chemical formula of calcium hydroxyapatite
Ca10(PO4)6(OH)2
Calcium hydroxyapatite is sparingly soluble in … and solubitlity increases in …
- saliva
- low pH
What does the Stephan curve have on axises?
- pH on y-axis
- minutes after sucrose rinse on x
What does Stephan curve show?
- plaque pH drops when challenged (by food)
- oral pH drops with acidic food and drinks
- rise is much slower than drop
- enamel dissolves more quickly below critical pH (around 5.5)
Silver chloride is a … solubility salt
sparingly
What happens to equilibrium of silver and chloride ions in silver chloride at saturation?
- some silver ions and some chloride ones dissolve into solution
- product of conc of silver and chloride ions (moles/L) is called solubility product (Ksp)
Why is calcium flouride’s solubility product more complex than silver chloride?
- number of dissolved cations is different than anions (as 2 F ions to 1 Ca)
- have to measure free calcium
How to work out solubility product
- measure calcium at equilibrium (only need conc of 1 ion)
- multiply by 0.6 for phosphate (as calcium is for 10, only 6 phosphate) and by 0.2 for OH as only 2
- then times these numbers together to the power of however many molecules of each for example calcium is to power of 10
- put in moles/L (to power of 18 as 10+6+2 for number of molecules)
What’s the ionic product?
- same as solubility product but in solution
For solutions not in equilibrium, if IP is largee than Ksp, what does that mean?
- solution is supersaturated
– precipitation unless ions are stabilised
For solutions not in equilibrium, if IP is smaller than Ksp, what does that mean?
- solution is unsaturated
- dissolution
In water, IP of hydroxyapatite is …
- 0 moles/L
- hydroxide is present but no calcium or P
When tooth is placed in water, what happens?
- hydroxyapatite will dissolve
- until equilibrium is reached
- when IP equals Ksp
Saliva is normally … for calcium and phosphate
What does this mean?
supersaturated
IP is larger than Ksp
In dissociation of calcium hydroxyapatite, there is loss of … and …
- hydroxide ions
- phosphate ions
Explain loss of OH- in dissociation of calcium hydroxyapatite
- hydrogen ions remove hydroxyl ions in water
- H+ + OH- = H2O
- in water, conc of hydrogen and hydroxide ions are 10-14
- as hydrogen increases, hydroxide must decrease
Explain loss of PO4 3- in dissociation of calcium hydroxyapatite
- phosphate exists in 4 forms but only the 3- form is important for IP of HA
- as pH decreases, equilibrium is pushed away from phosphate 3-
Different people have different calcium and phosphate in saliva. What does this mean?
- lower conc lead to higher critical pH (up to 6.5)
- differences in biological apatite, which affect dissolution
- measurements of pH in saliva show alkali production is more important than acid (not all about critical pH)
