Amelogenesis

Question 1

Give an overview of enamel:

Answer 1

• mineralised epithelial product
• 96% mineral - hydroxyapatite
• 1-2% matrix - enamel proteins, not collagen
• 2% water
• starts to form after dentine mineralises

Question 2

Give an overview of enamel formation from pre-ameloblasts to enamel crystals:

Answer 2

• pre-ameloblasts elongate into columnar cells from cervical loop
• as dentine begins to mineralise, basal lamina disintegrates and enamel is laid down in an upward and outward direction
• ameloblasts change shape - tomes process - gives rise to prismatic structure of enamel
• crystals appear in enamel straight away, no pre-enamel

Question 3

What governs enamel prism shape?

Are there any aprismatic areas?

Answer 3

Tomes process - governs enamel prism shape

Aprismatic areas formed without a tomes process:

• 1st formed: innermost 5 microns
• last formed: outermost 30 microns

Question 4

What is the final cue for amelogenesis?

What does the ameloblast secrete early?

How does maturation occur?

Answer 4

• dentine formation and breakdown of basal lamina

Ameloblast:

• secretes organic matrix, ~ immediate partial mineralisation

Maturation by:

• influx of mineral ions (calcium phosphate)
• breakdown and removal of most of the organic matrix

Question 5

What is the enamel matrix and what does it contain?

Answer 5

Enamel matrix - an epithelial product

• organic matrix: amorphous gel
• enamel proteins: amelogenins, enamelins, tuftelin
• enzymes

Question 6

What are some features of amelogenins?

What is the role of enamel proteins?

Answer 6

• rich in proline and glutamine
• similar in different species - clinically useful
• hydrophobic - aggregate
• spread throughout the developing enamel thickness
• thixotropic - flow under pressure

Enamel proteins:

• aid nucleation of hydroxyapatite: epitactic matrix
• orientate and stabilise crystal growth
• broken down and lost during maturation

Question 7

How are enamel crystals matured?

What is believed to be the matrix that flows out?

Remains?

Answer 7

• thin crystals grow in thickness
• requires mineral ions IN and enamel matrix OUT
• amelogenins: flow under pressure (thixotropic), enzymes break down amelogenins, bulk of breakdown products removed

Matrix that flows out - amelogenins

Matrix that remains - enamelin

Question 8

What is the enamel cuticle?

Answer 8

Enamel cuticle:

• formed when enamel maturation is ~complete
• final ameloblast secretion - the enamel cuticle
• 1 micron thick - like a basal lamina

Question 9

Answer 9

Question 10

When is the reduced enamel epithelium formed?

Derived from?

Function?

Answer 10

Reduced enamel epithelium:

• forms when enamel formation is complete
• derived from reduced ameloblasts, other remnants of the enamel organ OEE, etc
• attached to the cuticle

Function:

• protection of enamel surface from resorption, prevention of cementum formation
• provide an epithelial lined pathway for eruption
• forms initial junctional epithelium