Chemistry Of Mature Enamel Flashcards
Is mature enamal cellular or acellular?
Acellular
What’s the rough composition of mature enamel?
95% inorganic hydroxyapatite
5% organic & fluid
Hydroxyapatite crystal have many repeating units, what’s this called
Unit cell
How many axis does a unit cell have & what’re they called?
3 (a,b,c)
What’s special about the axis c of a unit cell?
Column of -OH groups (central column)
- shares its ions with hexagonal plates
What’s the current accepted model structure of hydroxyapatite crystals?
Stacking plate model
How come F makes hydroxyapatite stronger?
- how does it do this
- fits better then -OH
- F has higher electro-negativity
- ‘pulls’ ions in closer = less likely to dissolve in acid - fluoridated hydroxyapatite is more stable
What happens when Mg(CO3)2 replaces the -OH column on the c-axis?
- worse fit
- less stable
- more acid soluble
What happens when Mg(CO3)2 (carbonate) replaces the -OH column on the c-axis?
- worse fit
What does Mg replace in the hydroxyapatite structure & what are its effects?
Replaces Ca
- similar to Mg(CO3)2
- poorer fit = less stable = more likely to dissolve in acid
What’s the reasoning for variation in local acid solubility?
Different substitutions in different hydroxyapatite crystles.
What’s the gradient of distribution of density of crystals from tooth surface -> dentine?
Density decreases from tooth surface -> dentine.
What’s the gradient of distribution of porosity, water & organic material from tooth surface -> dentine?
Increases from tooth surface -> dentine
Where is the low density of Ca & P in enamel
- what does this mean
Low density of Ca + P near occlusal fissures
- low mineral content = more porosity = poorer prism packing
Where are there more protein & water in the enamel
Inner regions (closer to dentine)
