Enamel

Question 1

What is enamel designed for?

Answer 1

To withstand biting and wearing forces

Question 2

What is caries?

Answer 2

Loss of mineral due to plaque acids

Question 3

Where is the enamel thickest?

Answer 3

Cusps (up to 2.5mm)

Question 4

Where is the enamel thinnest?

Answer 4

Fissures

Question 5

Where do teeth decay first and why?

Answer 5

Fissures

Very deep and tight so hard to brush and thin enamel

Question 6

Where are mamelons present?

Answer 6

Incisal edges

Question 7

What are the surface features of newly erupted teeth? (4)

Answer 7

Mamelons

Perikymata

Tomes’ process pits

Pearls

Question 8

What are perikymata?

Answer 8

Grooves on surface due to lines of Retzius

Question 9

How small are Tomes’ process pits?

Answer 9

<100um

Question 10

What are pearls?

Answer 10

Bumps of enamel found at the cervical part of tooth

Question 11

What makes up an enamel prism?

Answer 11

10,000 hydroxyapatite crystallites

Question 12

How long are the enamel prisms?

Answer 12

4-7um

Question 13

What shape are the enamel prisms?

Answer 13

Horse-shoe shape, open end pointing toward root

Question 14

What shape are the crystallites and why?

Answer 14

Hexagonal

Packing of ameloblasts

Question 15

Why are there gaps between prisms and what is the function of these?

Answer 15

Crystallites do not line up as well at boundaries (discontinuity)

Allows distribution of fluids

Question 16

Why are the prisms not uniform in diameter all the way along the length?

Answer 16

Cross-striations created daily

Helps lock adjacent prisms together

Question 17

Which parts of the cross-striations appears darker and lighter?

Answer 17

Darker - thinner

Lighter - thicker

Question 18

What are the three types of incremental lines?

Answer 18

Cross-striations

Brown striae of Retzius

Neonatal line (special stria of Retzius)

Question 19

When and why do the brown striae of Retzius form?

Answer 19

Every 7-9 days

Rate of secretion slows and ameloblasts slightly change direction

Question 20

Why are brown striae of Retzius called brown?

Answer 20

Appear brown in transmitted light

Question 21

Where are the brown striae of Retzius most prominent?

Answer 21

Cervical third of enamel

Question 22

What is the neonatal line?

Answer 22

Most prominent brown stria of Retzius formed at birth

Question 23

Where are perikymata most prominent?

Answer 23

Cervical third of enamel surface

Question 24

What tissues are the dentin and enamel derived from?

Answer 24

Dentin - mesenchyme

Enamel - epithelium

Question 25

What triggers ameloblast differentiation?

Answer 25

Predentin

Question 26

What type of cell secretes enamel matrix?

Answer 26

Long ameloblasts

Question 27

What are the two types of enamel matrix protein?

Answer 27

Amelogenins Non-amelogenins/enamelins

Question 28

What part of the ameloblasts secretes enamel matrix?

Answer 28

Tomes' process

Question 29

Briefly describe enamel mineralisation.

Answer 29

Occurs within matrix - matrix gets thinner and hydroxyapatite crystallites grow

Question 30

What happens to the ameloblasts after secretion?

Answer 30

Mature and shorten

Question 31

What do the shortened ameloblasts do?

Answer 31

Remove proteins (mainly amelogenins) so enamel is not too porous

Question 32

What are the functions of the reduced enamel epithelium? (2)

Answer 32

Protective layer during eruption Fuses with oral epithelium to create junctional epithelium (seal)

Question 33

At what point is the enamel fully mineralised?

Answer 33

After eruption in mouth

Question 34

What does the saliva contain which is important in enamel mineralisation? (4)

Answer 34

Calcium ions Magnesium ions Phosphate ions Carbonate ions

Question 35

How long does an ameloblast secrete for?

Answer 35

1 year

Question 36

How long does matrix secretion for a permanent molar take?

Answer 36

4-7 years

Question 37

When is acid etch used?

Answer 37

Before restorations and composites

Question 38

Why is acid etch used?

Answer 38

Opens up enamel structure and removes smear layer Allows resin to infiltrate and create a strong bond with tooth

Question 39

What is decussation?

Answer 39

Sheets of prisms changing angles relative to each other (crossing over)

Question 40

Describe the path which prisms/ameloblasts take from EDJ to surface.

Answer 40

Inner third = sinuous Outer two-thirds = straight

Question 41

Where are the Hunter-Schreger bands?

Answer 41

Inner third of enamel

Question 42

What is the function of the Hunter-Schreger bands?

Answer 42

Stress-reliever (compressible)

Question 43

What is a tuft?

Answer 43

Where ameloblasts cross over each other

Question 44

What are diazones?

Answer 44

Prisms cut transversely

Question 45

What are parazones?

Answer 45

Prisms cut longitudinally

Question 46

What are the Hunter-Schreger bands?

Answer 46

Paired light and dark bands Optical illusion caused by reflection (parazones) and transmission (diazones) of light

Question 47

What does the enamo-dentin junction look like?

Answer 47

Scalloped line Concave towards pulp

Question 48

What would happen to the enamel if the dentin was compromised and why?

Answer 48

Fracture due to loss of support Enamel is very brittle

Question 49

What are the enamel spindles/spaces?

Answer 49

Where odontoblast processes are trapped

Question 50

What are lamellae?

Answer 50

Cracks from EDJ to surface containing organic material