histology of enamel e lecture

Question 1

what is the strength of enamel like

Answer 1

very brittle and hard wearing

Question 2

what does enamel rely on for its strength

Answer 2

the underlying dentine

Question 3

what is enamel made from

Answer 3

almost pure mineral- and organic material which is non collagenous protein
only 4% is water

Question 4

what mineral is in enamel

Answer 4

hydroxyapatite- but much larger in enamel than dentine

Question 5

where is the enamel thickest

Answer 5

A incisal edge or in the cusp of a molar

Question 6

where is the enamel thin

Answer 6

at the knife edged margin of the cervical margin

Question 7

how are the hydroxyapatite crystals arranged

Answer 7

they are arranged in prisms or in rods

Question 8

how long is the crystals

Answer 8

runs from the enamel to the dentine and is approx 5 micro milimetres in diameter

Question 9

what lies on top of the hydroxyapatite crystals

Answer 9

brown lines called the striae of Retzius

Question 10

how are the striae of retzius arranged

Answer 10

they are arranged more irregular at the cusp but more regular towards the cervical margin

Question 11

other structures can form due to

Answer 11

optical effects produced by the overall prisms

Question 12

what happens if all the top enamel is removed by acid

Answer 12

ribbons of protein can often be seen to run down the exposed dentine surface – this is tuft protein

Question 13

what do tuft proteins represent

Answer 13

areas between prims and residual enamel proteins

Question 14

what shape is the ADJ

Answer 14

scalloped in appearance

Question 15

how do the prisms run in the enamel

Answer 15

in a sinusoidal path to the surface with all the prisms running parallel to each other

Question 16

how do enamel tufts form

Answer 16

high protein content retained at the prism boundaries and, because of the superimposition, give the appearance of a tuft of grass

Question 17

where do spindles originate

Answer 17

at the ADJ AND PROJECT INTO the enamel

Question 18

what shape are spindles

Answer 18

distinct cigar shapes

Question 19

how can the visibility of tufts and spindles change

Answer 19

due to the changing of the focus and therefore it becomes visible and then no longer visible

Question 20

what are the striae of retzius

Answer 20

they are incremental growth lines that run obliquely to the enamel prisms

Question 21

what depressions are the striae of retzius associated with

Answer 21

they are associated with depressions called perikymata

Question 22

where are perikymata found more commonly

Answer 22

towards the outer regions of the enamel and the cervical margin which can be regularly spaced

Question 23

what do straie form the markings of

Answer 23

they form the markings of the enamel at a particular time in the crowns development

Question 24

what does the scalloping of the ADJ aid

Answer 24

aid-resists shearing forces

and aids the retention of the enamel on the underlying dentine

Question 25

how does the ADJ resist shearing forces

Answer 25

by providing a more irregular and greater surface area

Question 26

what is the enamel spindle continuous with

Answer 26

with the dentinal tubules

Question 27

how do enamel spindles form

Answer 27

They are thought to arise because of growth of odontoblast processes across the forming ADJ into the developing enamel during crown development

Question 28

what angle do the enamel prims run on the outer surface

Answer 28

the enamel prims run at 90 degrees to the ADJ

Question 29

what angle do the enamel prisms run at the cusp

Answer 29

the prisms run at a much more disorganised fashion and therefore are known as gnarled enamel

Question 30

why is gnarled enamel good-

Answer 30

can resist harder shearing forces at the cusp

Question 31

how do hunter schrenger bands run

Answer 31

run at slightly different paths which can form the visible enamel tufts

Question 32

what is a fissure lesion-

Answer 32

it is a lesion where it is much smaller than the underlying enamel and dentine lesion

Question 33

why does a fissure lesion occur-

Answer 33

- largely due to the divergent pathway of the prisms away from the fissure

Question 34

what does the smooth surface lesion contain-

Answer 34

the translucent zone the lesion body the dark zone surface zone

Question 35

why might the striae of retzius and the cross striations lines become more prominent-

Answer 35

due to the partial demineralisation of the enamel which makes them appear more distinct than in normal enamel

Question 36

the translucent zone-why

Answer 36

t appears translucent because it takes up media into its relatively uniform sized pores

Question 37

how are the uniform sized pores in the translucent zone produced-

Answer 37

by early acid demineralisation

Question 38

how much mineral is lost in the translucent zone-

Answer 38

around 1%

Question 39

how much mineral is lost in the body of the lesion-

Answer 39

greater than 20%

Question 40

what happens in the dark zone

Answer 40

some remineralisation has occurred and therefore the pores are different sizes. some are small and inhibit the ingressing of the imbibing fluid. this causes light to scatter therefore dark colouring

Question 41

what might the dark zone also have

Answer 41

high protein content

Question 42

what % of mineral has been lost in the dark zone

Answer 42

5%

Question 43

the surface zone

Answer 43

looks relatively intact so that the demineralisation can look like its sub surface

Question 44

the presence of the surface zone is-

Answer 44

independant of fluoride conc

Question 45

what may also be present in the surface zone

Answer 45

micro channels may be present in the surface zone