the chemistry of mature human enamel

Question 1

what is enamel comprised of

Answer 1

entirely inorganic mineral

Question 2

what is the enamel made from

Answer 2

entirely mineral crystals that are hexagonal

Question 3

what are the dimensions of the crystals

Answer 3

50nm in width and 30 nm in thickness

Question 4

what is the length of each crystal

Answer 4

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

Question 5

how are the crystals arranged in the structure

Answer 5

they are not arranged randomly

Question 6

what is the arrangement of the crystals

Answer 6

they are arranged in crystal bundles- called prisms or rods

Question 7

what are the mineral crystals made up of

Answer 7

inorganic salt

Question 8

what is the inorganic salt

Answer 8

hydroxyapatite( calcium phosphate salt)

Question 9

where does calcium hydroxyapatite naturally occur

Answer 9

granite

Question 10

what else is present in biological systems

Answer 10

many other crystals and apatite that varies in size

Question 11

what is the smallest unit of a crystal called

Answer 11

the unit cell

Question 12

what three axis are in the classical view of the crystal

Answer 12

the c axis
a xis
b axis

Question 13

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

Answer 13

one column of hydroxyl groups

Question 14

what does the unit cell resemble

Answer 14

stacking of plates

Question 15

what shape is the unit cell actually

Answer 15

rhomboidal in shape

Question 16

what is the formula for calcium phosphate

Answer 16

Ca10(PO4)6(OH)2

Question 17

what ions are shared between hexagonal unit cells

Answer 17

OH ions

Question 18

what surrounds the centre hydroxyl column

Answer 18

a triangle of Ca ions

Question 19

what is the triangle of calcium ions called

Answer 19

calcium 2

Question 20

what also surrounds the hydroxyl column

Answer 20

the triangle of phosphate ions

Question 21

what surrounds the calcium and phosphate triangles

Answer 21

a hexagonal structure of calcium ions called calcium 1

Question 22

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

Answer 22

calcium 1

Question 23

what degree does the hexagonal structures rotate by

Answer 23

60 degrees

Question 24

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

Answer 24

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

Question 25

what variations can be seen in apatite enamel

Answer 25

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

Question 26

what extraneous ions can be found in apatite crystals in enamel

Answer 26

sodium magnesium phosphate carbonate

Question 27

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

Answer 27

20-30%

Question 28

what issues can substituting and missing ions have

Answer 28

massive impact on its solubility at low pH and behaviour

Question 29

what ions do fluoride substitute

Answer 29

the hydroxy ions

Question 30

which ions can the apatite crystals take up

Answer 30

many which can result in heteroionic substitution

Question 31

what type of substitution do apatite crystals undergo

Answer 31

heteroionic

Question 32

what are the good properties of the fluoride ion

Answer 32

highly symmetrical so fits the hydroxyl ions place better | highly electronegative so pulls ions together stabilising the structure

Question 33

what are the advantages of fluoride substitution in apatite crystals

Answer 33

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

Question 34

what minerals destabilise the lattice structure

Answer 34

CO3 | Mg

Question 35

which minerals stabilise the lattice structure

Answer 35

F

Question 36

which ions can carbonate replace

Answer 36

phosphate | hydroxyl

Question 37

what are the disadvantages of carbonate substituting

Answer 37

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

Question 38

why does it make the lattice less stable is magnesium substitutes

Answer 38

due to its positive charges its charge density

Question 39

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

Answer 39

the density DECREASES

Question 40

what happens to the porosity as we advance to the dentine

Answer 40

INCREASES

Question 41

what happens to the water as we advance to the dentine

Answer 41

INCREASES

Question 42

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

Answer 42

INCREASES

Question 43

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

Answer 43

the incisal edge

Question 44

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

Answer 44

the occlusal surface and edge of the molar tooth

Question 45

what ion does magnesium substitute

Answer 45

calcium

Question 46

the distribution of calcium changes as

Answer 46

decreases from the surface to the dentine

Question 47

how does the distribution of the phosphorus change

Answer 47

it decreases as we reach closer to the dentine

Question 48

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

Answer 48

low mineral content meaning vulnerable to acid attack

Question 49

how does the protein distribution change

Answer 49

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

Question 50

what is carbonate distribution like

Answer 50

high conc near the dentine

Question 51

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

Answer 51

from 2%-4-6% | high conc can be found near the fissures in enamel molars

Question 52

what is magnesium distribution like

Answer 52

increases towards the dentine

Question 53

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

Answer 53

0.2%- 0.5%

Question 54

which direction do most carious lesions start

Answer 54

mesial to distal

Question 55

which layer of the enamel has the most fluoride

Answer 55

the outermost enamel

Question 56

what is the difference between apatite crystals in enamel and dentine

Answer 56

they are smaller

Question 57

what does dentine apatite have higher amounts of

Answer 57

carbonate and magnesium

Question 58

what forms the organic matrix in dentine

Answer 58

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

Question 59

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

Answer 59

90%

Question 60

how much % of the dentine is organic matrix

Answer 60

20%