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OCB02 > Amelogenesis > Flashcards

Amelogenesis Flashcards

1
Q

How much of enamel is mineral by weight and volume?

A

98% by weight

86% by volume

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2
Q

Is dentin or enamel laid down first?

A

Dentin

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3
Q

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

A

Inner enamel epithelium

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4
Q

Where is enamel matrix secreted from?

A

Tomes’ process of long ameloblasts

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5
Q

What are the two types of enamel protein?

A

Amelogenins

Non-amelogenins/enamelins

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6
Q

What happens to the long ameloblasts after secretion?

A

Mature and shorten

Become resorbing cells

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7
Q

What happens to the matrix protein during mineralisation?

A

Replaced by water

Then replaced by mineral

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8
Q

When is the enamel very sensitive to excess fluoride?

A

Mineralisation/resorption of protein

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9
Q

What are the dimensions of the hydroxyapatite crystals?

A

40x60x100s of nm

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10
Q

What two epithelia fuse to form the junctional epithelium?

A

Reduced enamel epithelium

Oral epithelium

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11
Q

When does the enamel finish mineralisation?

A

After eruption in mouth

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12
Q

Where is the nucleus in the long ameloblasts?

A

Away from EDJ/towards OEE

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13
Q

What two organelles are especially abundant in long ameloblasts?

A

Mitochondria

RER

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14
Q

Where are the mitochondria in the long ameloblasts?

A

Closest to stratum intermedium

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15
Q

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

A

Collapses

To bring ameloblasts closer to mesenchyme outside OEE to get nutrients

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16
Q

What is the function of the end terminal bars?

A

Close intercellular attachments to stop secretions going between cells

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17
Q

How long does an ameloblast secrete matrix for?

A

1 year

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18
Q

What are the majority of the type of enamel proteins?

A

Amelogenins

19
Q

Describe an amelogenin. (3)

A

Structural role

Unstable, 25kD

Have a hydrophobic end

20
Q

What do amelogenins do?

A

Thixotropic gels which help as a scaffold for mineralisation

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

21
Q

What are nanospheres?

A

20nm supramolecular structures of amelogenins which help organise growth

22
Q

What residues do the amelogenins mainly comprise of?

A

Glutamic acid

Proline

Histidine

23
Q

Describe a non-amelogenin.

A

More stable, 55kD

Glue/space-filler

24
Q

Give examples of non-amelogenins.

A

Ameloblastin

Amelotonin

Sulphated proteins

25
Q

Which type of enamel protein is not resorbed?

A

Non-amelogenins/enamelins

26
Q

What are the functions of non-amelogenins?

A

Initial nucleators of crystal growth at EDJ

Remain as a glue/space-filler for crystallites

27
Q

Why can enamelins bond to HA crystals?

A

Acidic nature

28
Q

What residues do enamelins mainly consist of?

A

Aspartic acid

Glutamic acid

Glycine

Serine

29
Q

What is the formula for hydroxyapatite?

A

Ca10(PO4)6(OH)2

30
Q

In what orientation do hydroxyapatite crystals grow?

A

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

31
Q

What angle is the average forming front?

A

45°

32
Q

Why is there discontinuity between prisms/keyhole shape?

A

90% of secretion comes from nose of Tomes’ process

Some matrix leaks around edges

33
Q

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

A

Larger

34
Q

Which enamelin controls prismatic enamel?

A

Ameloblastin (5%)

35
Q

What might ameloblastin be/do? (4)

A

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

36
Q

What happens when ameloblasts mature?

A

Mitochondria move to enamel pole

Plasma membrane may become deeply infolded - ruffle-ended

May develop a smooth end and interameloblast spaces between - smooth-ended

37
Q

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

A

MMPs - metalloproteinase enamelysin/MMP-20

Enamel matrix serine proteinase 1/EMSP1 (AKA: kallikrien 4/KLK4)

38
Q

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

A

Fluoride

Tetracycline

39
Q

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

A

Poison maturation process

Cause fluorotic porosities

40
Q

What type of junction connects the maturation ameloblasts and enamel?

A

Hemidesmosomes

41
Q

What forms the primary epithelial attachment?

A

Internal basal lamina between maturation ameloblasts and enamel

42
Q

Which type of bur gives smoother cavity margins?

A

Tungsten carbide

43
Q

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

A

Confocal microscope (wet tooth)

OCB02 (19 decks)

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