OB D7 - Amelogenesis

Question 1

what is enamel?

Answer 1

mineralised epithelial product

Question 2

what is the composition of enamel?

Answer 2

-96% -hydroxyaptite
-1-2% organic matrix :
enamel proteins
-2% - water

Question 3

what is not found in enamel?

Answer 3

collagen

Question 4

when does enamel form?

Answer 4

after dentine mineralises

Question 5

what happens in amelogenesis?

Answer 5

• pre-ameloblast (polarised nucleus and lots of organelles of synthesis and secretion
• basal lamina disintegrates
• now ameloblasts
• enamel formation begins
• cells retreat outwards and towards incised aspect (upwards and out)
• ameloblasts changes shape and a point forms a point (tomes process)

Question 6

what is the point on an ameloblast called?

Answer 6

Tomes process

Question 7

what is the final cue for onset of amelogenesis?

Answer 7

• dentine formation

- breakdown of basal lamina

Question 8

what does an ameloblast secrete?

Answer 8

organic matrix

Question 9

what occurs immediately after organic matrix is secreted?

Answer 9

partial mineralisation

Question 10

how does maturation occur in amelogenesis?

Answer 10

• influx of mineral ions

- breakdwon and removal of most of the organic matrix

Question 11

what enamel proteins are in the amorphous gel of the organic matrix (enamel)?

Answer 11

• amelogenins (90%)
• enamelins - (~2%) strongly binds to mineral
• tuftelin - confined to ADJ

Question 12

In addition to enamel proteins, what else is found in amorphous gel?

Answer 12

enzymes

Question 13

Describe properties of amelogenins.

Answer 13

• Rich in proline and glutamine
• Similar in different species (clinically useful)
• Hydrophobic (aggregate)
• Spread throughout the developing enamel thickness
• Thixotropic.

Question 14

what is the role of enamel proteins?

Answer 14

• aid of nucleation of hydroxyapatite (epitactic matrix)
• orientate and stabilise crystal growth
• broken down and let during maturation

Question 15

what is not involved in enamel mineralisation?

Answer 15

• No “pre-enamel”

- No MVs

Question 16

Describe the changes in composition of enamel during mineralisation from initial to rapid to maturation.

Answer 16

Initial secretion :
-virtualy immediate mineralisation
-15% mineral, 65% water and 20% proteins
Rapid mineralisation to 30%:
-immature or young enamel
Maturation :
-further mineralisation to 96%

Question 17

What happens during maturation and what does it require?

Answer 17

-thin crystals grow in thickness
-requires:
mineral ions IN and enamel matrix OUT

Question 18

what happens to amelogenin (enamel protein) in maturation?

Answer 18

– flows under pressure (Thixotropic)
– enzymes break down amelogenins
– bulk of breakdown products removed

Question 19

what is the matrix that flows out?

Answer 19

amelogenins

Question 20

what is the matrix that remains?

Answer 20

enamelin

Question 21

what happens once most of enamel thickness is laid down?

Answer 21

Tomes process is lost

Question 22

what does the loss of tomes process result in?

Answer 22

last formed enamel is aprismatic

Question 23

what else is also aprismatic?

Answer 23

1st formed 5μm (no tomes process

Question 24

what is formed when maturation is complete?

Answer 24

enamel cuticle ( final ameloblast secretion)
-1μm thick - like a basal lamina

Question 25

what forms when enamel formation is complete?

Answer 25

reduced enamel epithelium

Question 26

what is reduced enamel epithelium derived from?

Answer 26

• reduced ameloblasts

- other remnants of the enamel organ OEE etc

Question 27

what is reduced enamel epithelium attached to?

Answer 27

cuticle

Question 28

what are the 3 functions of reduced enamel epithelium function?

Answer 28

1. Protection of enamel surface from: 
• resorption
• prevention of cementum formation
2. Provide an epithelial lined pathway for
eruption
3. Forms initial junctional epithelium

Question 29

what is the fate of the reduced enamel epithelium?

Answer 29

• fusion of basal lamina
• cell death
• forms junction epithelium