(2) Anatomy and Histology of the Periodotium - Enamel (B)

Question 1

What section has to be taken to view enamel?

Answer 1

ground section

completely lost in demineralised section

Question 2

Can immature enamel be studied by a demineralised section?

Answer 2

yes

Question 3

What are the basic structural units of enamel?

Answer 3

Prisms (rods) / enamel prisms

Question 4

What comprises each enamel prism?

Answer 4

several million hydroxyapatite crystals packed into a long thin rod 5-6um in diameter and up to 2.5mm in length.

Question 5

What separates each prism?

Answer 5

inter-rod substance

Question 6

How do you differentiate enamel prisms and inter-rod substances?

Answer 6

Crystals with different orientation (deviate by 40-60°)

Question 7

Name structures A and B

Answer 7

A = interrod
B = rod

Question 8

How do you identify a prism boundary?

Answer 8

a sudden change in crystallite orientation.

Question 9

How would you describe a prism in a cross-section?

Answer 9

keyhole pattern (pattern III)

Question 10

Where does the tail of a prism lie? (cross section)

Answer 10

The tail of one prism lies between the heads of the two adjacent prisms

Question 11

What is responsible for the optical appearance at a prism boundary?

Answer 11

An abrupt change of crystal orientation at the prism boundary

Question 12

Name feature D

Answer 12

head of prism shown by cross-section

Question 13

Do the crystal heads run parallel with one another?

Answer 13

Yes

along the long axis of the prism

Question 14

What cut are each of these images?

Answer 14

cross sections

Question 15

Does the keyhole pattern give strength to enamel?

Answer 15

YES

Question 16

How to we see the difference between the head and tale sections?

Answer 16

the different orientation of crystals

In the tail, the crystals diverge gradually to become angled at 65-70° to the long axis.

Question 17

How would you describe the prism head and tail crystal orientations?

Answer 17

The change from head to tail is gradual in each prism, however a tail of one prism shows a sudden divergence from the head of an adjacent prism.

the crystal orientation

Question 18

What cut of the enamel can you see the boundaries of prisms easily?

Answer 18

the longitudinal

the run parallel running back

Question 19

What happens every 10-13 layers of prism?

Answer 19

Every 10-13 layers of prisms follow the same direction, but blocks above and below follow paths in different directions.

= Hunter-Schreger bands.

Question 20

What is shown here

Answer 20

Hunter- Schreger bands.

Question 21

What is the banding pattern of enamel called?

Answer 21

Hunter- Schreger bands.

Question 22

What is the approx. width of Hunter- Schreger bands?

Answer 22

50um

Question 23

Are Hunter- Schreger bands visible?

Answer 23

visible due to light reflection in different directions.

Question 24

Why cant you usually see visible due to light reflection in different directions in enamel?

Answer 24

In the outer ¼ of enamel, all prisms run in the same direction and so there is no banding.

Question 25

How do prisms appear over the cusps of enamel?

Answer 25

appear twisted around each other in a complex arrangement known as gnarled enamel

Question 26

What is shown here?

Answer 26

Prisms over the cusps appear twisted around each other in a complex arrangement known as gnarled enamel

Question 27

How tick is the outer surface layer of enamel in primary teeth?

Answer 27

20-100um

Question 28

How thick is the outer surface layer of secondary enamel?

Answer 28

20-70um

Question 29

What is the outer layer of enamel called?

Answer 29

aprismatic.

Question 30

How are the crystallites arranged in aprismatic enamel?

Answer 30

The crystallites are aligned at right angles to the surface and parallel to each other.

Question 31

Is the apirsmatic layer of enamel more or less mineralised to inner layers?

Answer 31

highly mineralised

Question 32

Why is the outer layer of enamel more highly mineralised?

Answer 32

The surface layer is more highly mineralised than the rest of the enamel. This is attributed to the absence of prism boundaries where organic material is located.

Question 33

How would you describe the way enamel is formed?

Answer 33

Incrementally

Question 34

Describe how enamel is formed incrementally

Answer 34

Enamel is formed in increments: periods of activity alternating with periods of inactivity. This results in incremental lines: short period (cross striations) and long period (enamel striae).

Question 35

How do cross striations appear on enamel?

Answer 35

Cross striations appear as lines crossing the enamel prisms at right angles to their long axes. They reflect a diurnal rhythm (daily increments of growth).

Question 36

When do cross striations appear closer together?

Answer 36

Closer to each other near the enamel-dentine junction.

Question 37

What is shown in the histological diagram?

Answer 37

stria of retzius (enamel striae) Enamel striae run obliquely across the prisms. They represent incremental lines and are known as the striae of Retzius.

Question 38

Do striae of retzius reach the surface of the enamel?

Answer 38

no

Question 39

How to stria of retzius appear in cross section of a tooth?

Answer 39

run circumferentially like the rings of a tree.

Question 40

How many cross striation are there between enamel and adjacent stira?

Answer 40

7-10 This suggests weekly intervals.

Question 41

When do the stria of retzius (cross section) run closest together?

Answer 41

cervically

Question 42

How to enamel stria appear on the surface of teeth?

Answer 42

appear as fine grooves running circumferentially around the crown.

Question 43

What are the stria on the surface of teeth referred to as?

Answer 43

The lines are termed Perikymata grooves, with perikymata ridges in between.

Question 44

Name the feature

Answer 44

Perikymata grooves

Question 45

How does surface enamel compare to subsurface enamel?

Answer 45

Physically and chemically, surface enamel differs from subsurface enamel. Surface enamel is harder, less porous, less soluble and more radio-opaque. Richer in trace elements. Less carbonate. Aprismatic, therefore highly mineralised.

Question 46

What are the arrows pointing to?

Answer 46

The pits are within the perikymata. formed on protected areas of enamel

Question 47

What do the small pits on perikymata represent?

Answer 47

They mark the ends of ameloblasts (prism end markings. 1-1.5μm in depth.

Question 48

What is the neonatal line?

Answer 48

prominent enamel stria

Question 49

What are the arrows pointing to?

Answer 49

enamel caps

Question 50

What is an enamel cap?

Answer 50

Enamel caps are small elevations 10-15μm across.

Question 51

How does an enamel cap form?

Answer 51

they result from enamel deposition on top of debris late during tooth development.

Question 52

What are the arrow pointing to?

Answer 52

focal holes

Question 53

What are focal holes on the surface of enamel?

Answer 53

Focal holes are depressions on the surface. loss of mineralised material on top of organic material

Question 54

How do focal holes form?

Answer 54

Loss of enamel caps with the underlying material. this happens through abrasion or attrition.

Question 55

What is shown here? (surface enamel)

Answer 55

Enamel brochs are elevations on the enamel surface.

Question 56

Where is the enamel broch usually found?

Answer 56

the cemento-enamel junction

Question 57

What tooth do you usually see the enamel broch?

Answer 57

premolar 6s

Question 58

What does an enamel broch look like?

Answer 58

extra piece of enamel with radiating crystalites

Question 59

What type of microscopy is used here?

Answer 59

transmission