Histology of enamel

Question 1

what is the strength of enamel like?

Answer 1

• brittle
• hard wearing

Question 2

what structure does enamel rely on for resilience?

Answer 2

dentine

Question 3

what is dentine made from?

Answer 3

• 4% water
• non-collagenous protein (organic material)

Question 4

what mineral is enamel made up of?

Answer 4

• HAP crystals
• same as dentine and bone but enamel HAP crystals are larger

Question 5

where is the enamel the thickest?

Answer 5

A incisal edge or in the cusp of a molar

Question 6

where is the enamel the thinnest?

Answer 6

at the knife edged margin of the cervical margin

Question 7

how are the HAP crystals arranged?

Answer 7

arranged in prisms or in rods

Question 8

how long are the crystals?

Answer 8

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

Question 9

what does the circadian rhythm in enamel production do?

Answer 9

produces regular, daily, cross-striations with roughly a 5µm periodicity.

Question 10

what is superimposed on the enamel (lies on top of the HAP crystals)?

Answer 10

Superimposed on this periodicity are other less frequent incremental lines called the (brown) striae of Retzius.

Question 11

how are the striae of retzius arranged?

Answer 11

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

Question 12

other structures can form due to

Answer 12

optical effects produced by the overall prisms

Question 13

what happens if all the top enamel is removed by acid

Answer 13

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

Question 14

what do tuft proteins represent

Answer 14

areas between prims and residual enamel proteins

Question 15

what shape is the ADJ

Answer 15

scalloped in appearance

Question 16

how do the prisms run in the enamel

Answer 16

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

Question 17

how do enamel tufts form

Answer 17

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

Question 18

where do spindles originate

Answer 18

at the ADJ AND PROJECT INTO the enamel

Question 19

what shape are spindles

Answer 19

distinct cigar shapes

Question 20

how can the visibility of tufts and spindles change

Answer 20

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

Question 21

what are the striae of retzius?

Answer 21

incremental growth lines that on the sides of the crown run obliquely across the prisms to approach the enamel surface.

Question 22

what depressions are the striae of retzius associated with

Answer 22

perikymata

Question 23

where are perikymata found more commonly

Answer 23

outer regions of the enamel and towards the cervical margin of the crown

Question 24

what do straie form the markings of

Answer 24

surface of the enamel at a particular time point in the crown’s development.

Question 25

what does the scalloping of the ADJ aid

Answer 25

aides retention of enamel on the dentine

Question 26

how does the ADJ resist shearing forces

Answer 26

resists shearing forces by providing a more irregular and greater SA at the point of contact.

Question 27

What shape is the enamel spindle

Answer 27

cigar shape

Question 28

what is the enamel spindle continuous with

Answer 28

dentinal tubules across the ADJ.

Question 29

how do enamel spindles form

Answer 29

by the growth of odontoblast processes across the forming ADJ into the developing enamel during crown development

Question 30

what angle do the enamel prims run on the outer surface of crown

Answer 30

On the side of crown, enamel prisms run in essentially straight lines to the surface at an angle approximating 90o to the ADJ

Question 31

what angle do the enamel prisms run at the cusp

Answer 31

disordered fashion - this is the so-called 'gnarled' enamel

Question 32

why is gnarled enamel good-

Answer 32

resist the greater loads and therefore shearing forces at the cusp.

Question 33

what are white spot lessons

Answer 33

opacities that occur by demineralization of enamel under the surface

Question 34

how do hunter schrenger bands run

Answer 34

optical phenomenon appear as alternating patterns of dark and light bands when cut enamel is viewed under reflected light

Question 35

what is a fissure lesion-

Answer 35

deep pits and grooves on the surfaces of the teeth often cause cavities

Question 36

why does a fissure lesion occur-

Answer 36

Not cleaning your teeth well, frequent snacking and sipping sugary drinks

Question 37

what does the smooth surface lesion contain-

Answer 37

demonstrates the classic zones - translucent zone, - dark zone - surface zone - lesion body.

Question 38

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

Answer 38

demineralisation of enamel

Question 39

why is there a translucent zone and how much mineral is lost?

Answer 39

because it takes up imbibing media into relatively uniformly sized pores produced by earliest stages of acid dissolution. It has lost approximately 1% of its mineral.

Question 40

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

Answer 40

20%

Question 41

what happens in the dark zone? and why is it dark?

Answer 41

Some remineralisation has occured within this zone so that the pores (produced by the initial demineralisation) demonstrate a range of sizes, some of which are relatively small and inhibit the ingress of the imbibing fluid. This causes scattering of the light and hence the dark colouration.

Question 42

what might the dark zone also have

Answer 42

high protein content.

Question 43

what % of mineral has been lost in the dark zone

Answer 43

5%

Question 44

what is a surface zone

Answer 44

is a characteristic of this lesion type ( in e lecture ) so that demineralisation is apparently sub-surface. The presence of this relatively intact zone appears to be independent of fluoride concentration.

Question 45

what can be found on a surface zone

Answer 45

Micro channels may be present passing through this zone when viewed at sufficiently high power.