Amelogenesis

Question 1

How much of enamel is mineral by weight and volume?

Answer 1

98% by weight

86% by volume

Question 2

Is dentin or enamel laid down first?

Answer 2

Dentin

Question 3

What part of the enamel organ differentiates to form the ameloblasts?

Answer 3

Inner enamel epithelium

Question 4

Where is enamel matrix secreted from?

Answer 4

Tomes’ process of long ameloblasts

Question 5

What are the two types of enamel protein?

Answer 5

Amelogenins

Non-amelogenins/enamelins

Question 6

What happens to the long ameloblasts after secretion?

Answer 6

Mature and shorten

Become resorbing cells

Question 7

What happens to the matrix protein during mineralisation?

Answer 7

Replaced by water

Then replaced by mineral

Question 8

When is the enamel very sensitive to excess fluoride?

Answer 8

Mineralisation/resorption of protein

Question 9

What are the dimensions of the hydroxyapatite crystals?

Answer 9

40x60x100s of nm

Question 10

What two epithelia fuse to form the junctional epithelium?

Answer 10

Reduced enamel epithelium

Oral epithelium

Question 11

When does the enamel finish mineralisation?

Answer 11

After eruption in mouth

Question 12

Where is the nucleus in the long ameloblasts?

Answer 12

Away from EDJ/towards OEE

Question 13

What two organelles are especially abundant in long ameloblasts?

Answer 13

Mitochondria

RER

Question 14

Where are the mitochondria in the long ameloblasts?

Answer 14

Closest to stratum intermedium

Question 15

What happens to the stellate reticulum on commencement of amelogenesis and why?

Answer 15

Collapses

To bring ameloblasts closer to mesenchyme outside OEE to get nutrients

Question 16

What is the function of the end terminal bars?

Answer 16

Close intercellular attachments to stop secretions going between cells

Question 17

How long does an ameloblast secrete matrix for?

Answer 17

1 year

Question 18

What are the majority of the type of enamel proteins?

Answer 18

Amelogenins

Question 19

Describe an amelogenin. (3)

Answer 19

Structural role

Unstable, 25kD

Have a hydrophobic end

Question 20

What do amelogenins do?

Answer 20

Thixotropic gels which help as a scaffold for mineralisation

Form 20nm supramolecular structures (nanospheres) to help organise growth (stop lateral growth)

Question 21

What are nanospheres?

Answer 21

20nm supramolecular structures of amelogenins which help organise growth

Question 22

What residues do the amelogenins mainly comprise of?

Answer 22

Glutamic acid

Proline

Histidine

Question 23

Describe a non-amelogenin.

Answer 23

More stable, 55kD

Glue/space-filler

Question 24

Give examples of non-amelogenins.

Answer 24

Ameloblastin

Amelotonin

Sulphated proteins

Question 25

Which type of enamel protein is not resorbed?

Answer 25

Non-amelogenins/enamelins

Question 26

What are the functions of non-amelogenins?

Answer 26

Initial nucleators of crystal growth at EDJ Remain as a glue/space-filler for crystallites

Question 27

Why can enamelins bond to HA crystals?

Answer 27

Acidic nature

Question 28

What residues do enamelins mainly consist of?

Answer 28

Aspartic acid Glutamic acid Glycine Serine

Question 29

What is the formula for hydroxyapatite?

Answer 29

Ca10(PO4)6(OH)2

Question 30

In what orientation do hydroxyapatite crystals grow?

Answer 30

With their C-axis at 90° to the secreting surface of the Tomes' process

Question 31

What angle is the average forming front?

Answer 31

45°

Question 32

Why is there discontinuity between prisms/keyhole shape?

Answer 32

90% of secretion comes from nose of Tomes' process Some matrix leaks around edges

Question 33

How does the size of the crystals in enamel compare with those of bone and dentin?

Answer 33

Larger

Question 34

Which enamelin controls prismatic enamel?

Answer 34

Ameloblastin (5%)

Question 35

What might ameloblastin be/do? (4)

Answer 35

Role in communication between ameloblast and matrix Residue of Tomes' process May inhibit lateral growth of crystallites Maintain channels for escape of enamel proteins from deeper layers

Question 36

What happens when ameloblasts mature?

Answer 36

Mitochondria move to enamel pole Plasma membrane may become deeply infolded - ruffle-ended May develop a smooth end and interameloblast spaces between - smooth-ended

Question 37

Give two examples of proteins important in resorption of enamel proteins.

Answer 37

MMPs - metalloproteinase enamelysin/MMP-20 Enamel matrix serine proteinase 1/EMSP1 (AKA: kallikrien 4/KLK4)

Question 38

What two substances are particularly accessible to the enamel at the maturation stage?

Answer 38

Fluoride Tetracycline

Question 39

What would high levels of fluoride and tetracycline during the maturation stage do?

Answer 39

Poison maturation process Cause fluorotic porosities

Question 40

What type of junction connects the maturation ameloblasts and enamel?

Answer 40

Hemidesmosomes

Question 41

What forms the primary epithelial attachment?

Answer 41

Internal basal lamina between maturation ameloblasts and enamel

Question 42

Which type of bur gives smoother cavity margins?

Answer 42

Tungsten carbide

Question 43

How can you observe the action of a bur on enamel?

Answer 43

Confocal microscope (wet tooth)