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)
Where is there more Carbonate (CO3) in enamel
- when does usually occur
During tooth development near dentine surface
Fissures of molars
Mg in enamel:
- where is it mostly located
- what does density usually have to do with its distribution
- what does this mean for acid dissolution
- dentine surfaces
- lower mineral dentist = high Mg conc
- less resistant to acids
Enamel close to the ADJ:
- density
- CO3
- MG
- F
- this means….
- less dense
- more CO3
- more Mg
- less F
- less stable & less resistant to acids
In enamel fluorosis:
- ______ _______ bands
- Mg distribution
Hypo mineralised bands
Mg still along dentine surface
How does mild/moderate fluorosis affect the enamels resistance to caries?
More resistant to caries = higher F conc
What does severe fluorosis cause?
Pitted enamel
Loss of fragile areas
Enamel closer to the ADJ has more or less :
- density/stability??
- CO3
- Mg
- F
- less dense
- more CO3
- more MG
- less F
