Enamel

Question 1

Why is young enamel more white than mature enamel

Answer 1

Transparency increases with mineralisation

Question 2

Enamel thicker at incisal edge and thinner at cervical

Question 3

3 properties of surface enamel vs subsurface enamel

Answer 3

Surface enamel is harder denser and less porous

Question 4

Dimensions of a enamel rod (prism)

Answer 4

5um x 2.5mm (2.5mm is the thickness of enamel)

Question 5

How many crystallites are there in each rod

Answer 5

10^6

Question 6

What is the orientation of HA crystallites in the interrod and rod regions

Answer 6

Interrod - 65-70 degree angle

Rod - crystallites parallel to the rod

Question 7

Why is etch more effective in interrod compared to rod region

Answer 7

Etch works better on the sides of the rod compared to the tips. Sides of rod (ie interrod regions) have larger surface area to volume ratio

Question 8

Cross striations vs striae of retzius

Answer 8

Cross striations - daily 4um
Striae of retzius (brown transverse striae) - weekly intervals

Question 9

Head - rod
Tail - interrod

Question 10

Why are interrod regions more susceptible to losing mineral content under caries attack?

Answer 10

1. LESS DENSE, INCREASED POROSITY. IR regions are less densely packed, increased porosity providing more surface area for acid attack. Increased porosity at interrod regions allows acids to penetrate deeper than enamel rods
2. ORGANIC CONTENT HIGHER. Interrod regions had more organic material (proteins) which can be broken down by acid producing bacteria
3. MICROSCOPIC IMPERFECTIONS Interrod regions have more micro cracks that acts as entry points for acid attack

Question 11

What characteristic of the enamel sheath regulates the nano mechanical properties of enamel?

Answer 11

The sheath contains minor protein content. This minor protein content gives enamel a small level of flexibility to absorb biting forces

Question 12

How does tooth whitening affect enamel

Answer 12

Tooth whitening removes the protein content in the enamel, making it less flexible, less able to absorb biting forces and therefore more fragile.

Question 13

What angle are crystallites deposited to ameloblast membranes (tomes’ processes)

Answer 13

90 degrees

Question 14

How are crystallites developed from ameloblasts?

Answer 14

Ameloblasts secrete proteins
Proteins concentrate calcium and phosphate in an organised way (nucestion of calcium and phosphate)
Calcium and phosphate ions continue to accumulate and arrange themselves into a crystal lattice structure
Proteins removed

Question 15

Shape of HA crystallites

Answer 15

Hexagon

Question 16

What do magnesium carbonate and fluoride substitute

Answer 16

Magnesium subs calcium
Carbonate subs phosphate
Fluoride subs hydroxyl

Question 17

Chemical equation of hydroxyapatite

Answer 17

Ca10(PO4)6(OH)2

Question 18

Is the substitution of phosphate with carbonate good?

Answer 18

No. Carbonated apatite is less stable and resistance to acid attack.

Question 19

Where are Hunter schreger bands found and what causes them?

Answer 19

Found - inner enamel, doesn’t extend to enamel surface

Cause- periodic change of orientation of rods

Question 20

Enamel rods run a sinusoidal course

Question 21

Where is gnarled enamel found

Answer 21

Cusp tips
Makes enamel strong and more resistant to fractures

Question 22

How is perikymata and brown striae of retzius linked

Answer 22

Perikymata are found where the striae of retzius meets the enamel surface

Question 23

What’s neonatal line

Answer 23

Stress over ameloblasts during birth

Question 24

Enamel tufts, enamel lamellae , enamel spindles

Answer 24

Tufts - hypomineralised areas due to residual tuftelins (proteins)
Spindles - odontoblasts processes extending into enamel
Lamellae - incomplete maturation of groups of prisms or cracks after eruption