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CSA SR > Chemistry of enamel > Flashcards

Chemistry of enamel Flashcards

aim: to understand the chemical structure of dental enamel as the background to the aetiology of caries objectives: recognise the structure of calcium hydroxyapatite to understand the apatite structure in terms of foreign ion substitutions the recognise the variations in the chemical composition of the dental enamel in relation to development and eventually disease

1
Q

what is enamel comprised of

A

95-96% inorganic mineral (impure calcium hydroxyapatite
4-5% fluid and organic material (usually containing protein)

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2
Q

what is the enamel made from

A

entirely mineral crystals that are hexagonal

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3
Q

what are the dimensions of the crystals

A

50nm in width and 30 nm in thickness

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4
Q

what is the length of each crystal

A

the length is unknown but it is assumed it is almost 1mm

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5
Q

how are the crystals arranged in the structure

A

they are not arranged randomly

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6
Q

what is the arrangement of the crystals

A

they are arranged in crystal bundles- called prisms or rods

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7
Q

what are the mineral crystals made up of

A

inorganic salt

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8
Q

what is the inorganic salt

A

hydroxyapatite( calcium phosphate salt)

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9
Q

where does calcium hydroxyapatite naturally occur

A

granite

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10
Q

what else is present in biological systems

A

many other crystals and apatite that varies in size

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11
Q

what is the smallest unit of a crystal called

A

the unit cell

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12
Q

what three axis are in the classical view of the crystal

A

the c axis
a xis
b axis

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13
Q

what is the cell comprised of when we look at it from the edge

A

one column of hydroxyl groups

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14
Q

what does the unit cell resemble

A

stacking of plates

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15
Q

what shape is the unit cell actually

A

rhomboidal in shape

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16
Q

what is the formula for calcium phosphate

A

Ca10(PO4)6(OH)2

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17
Q

what ions are shared between hexagonal unit cells

A

OH ions

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18
Q

what surrounds the centre hydroxyl column

A

a triangle of Ca ions

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19
Q

what is the triangle of calcium ions called

A

calcium 2

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20
Q

what also surrounds the hydroxyl column

A

the triangle of phosphate ions

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21
Q

what surrounds the calcium and phosphate triangles

A

a hexagonal structure of calcium ions called calcium 1

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22
Q

what is the hexagonal structure that surrounds the triangle of phosphate and calcium 2 called

A

calcium 1

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23
Q

what degree does the hexagonal structures rotate by

A

60 degrees

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24
Q

if we count the ions in the simplified view why does it not add up to the stoichiometry

A

as it is only a planar view the real unit cell is rhomboidal

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25
Q

what variations can be seen in apatite enamel

A 
missing ions eg calcium and OH( OH reported to be missing in 20-30%  
extraneous ions( impurities ) which include Na,Mg,CO3, PO4
26
Q

what extraneous ions can be found in apatite crystals in enamel

A

sodium
magnesium
phosphate
carbonate

27
Q

what % of OH ions can be reported missing from apatite crystals

A

20-30%

28
Q

what issues can substituting and missing ions have

A

massive impact on its solubility at low pH and behaviour

29
Q

what ions do fluoride substitute

A

the hydroxy ions

30
Q

which ions can the apatite crystals take up

A

many which can result in heteroionic substitution

31
Q

what type of substitution do apatite crystals undergo

A

heteroionic

32
Q

what are the good properties of the fluoride ion

A

highly symmetrical so fits the hydroxyl ions place better

highly electronegative so pulls ions together stabilising the structure

33
Q

what are the advantages of fluoride substitution in apatite crystals

A

makes the crystals more difficult to dissolve
makes it easier for redeposition at lower conc levels

34
Q

what minerals destabilise the lattice structure

A

CO3

Mg

35
Q

which minerals stabilise the lattice structure

A

F

36
Q

which ions can carbonate replace

A

phosphate

hydroxyl

37
Q

what are the disadvantages of carbonate substituting

A

poor fit of the carbonate ion in the lattice
less stable
more acid soluble

38
Q

why does it make the lattice less stable is magnesium substitutes

A

due to its positive charges its charge density

39
Q

what happens to the density of the prisms as we advance towards the dentine

A

the density DECREASES

40
Q

what happens to the porosity as we advance to the dentine

A

INCREASES

41
Q

what happens to the water as we advance to the dentine

A

INCREASES

42
Q

what happens to the organic content as we advance to the dentine

A

INCREASES

43
Q

where is the densest part (in regards to prisms) of the incisor

A

the incisal edge

44
Q

where is the densest part (in regards to prisms) of the molar

A

the occlusal surface and edge of the molar tooth

45
Q

what ion does magnesium substitute

A

calcium

46
Q

the distribution of calcium changes how

A

decreases from the surface to the dentine

47
Q

how does the distribution of the phosphorus change

A

it decreases as we reach closer to the dentine

48
Q

what is interesting about the fissure area of premolars and molars in regards to Ca and phosphorus %

A

low mineral content meaning vulnerable to acid attack

49
Q

how does the protein distribution change

A

least protein at the surface and increases at the dentine and cervically

50
Q

what is carbonate distribution like

A

high conc near the dentine

51
Q

what is the % change increases of carbonate ions from surface towards the dentine

A

from 2%-4-6%

high conc can be found near the fissures in enamel molars

52
Q

what is magnesium distribution like

A

increases towards the dentine

53
Q

what is the % change increases of Mg ions from surface towards the dentine

A

0.2%- 0.5%

54
Q

which direction do most carious lesions start

A

mesial to distal

55
Q

which layer of the enamel has the most fluoride

A

the outermost enamel

56
Q

what is the difference between apatite crystals in enamel and dentine

A

they are smaller in dentine

57
Q

what does dentine apatite have higher amounts of

A

carbonate and magnesium

58
Q

what forms the organic matrix in dentine

A

the HA crystals are arranged along and between the collagen fibril meshwork

59
Q

what % of the organic matrix is formed by HA crystals and the collagen fibril meshwork

A

90%

60
Q

how much % of the dentine is organic matrix

A

20%

CSA SR (52 decks)

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