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Oral Biology > Tooth Development II - Amelogenesis > Flashcards

Tooth Development II - Amelogenesis Flashcards

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1
Q

What’s a Ameloblast?

A
  • Epithelial derived cell only present in tooth development
  • Synthesize and secrete enamel matrix proteins. The enamel matrix proteins self-assemble to form a matrix, which mineralises (Enamel)
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2
Q

What’s the life cycle of the Ameloblast?

A
  1. Presecretory Stage
  2. Secretory Stage
  3. Transition Stage
  4. Maturation Stage
  5. Post-maturation stage
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3
Q

What occurs during the Pre-secretory stage?

A
  • Differentiation of the pre-ameloblast
  • Formation and subsequent resorption of a basal lamina

(All activities before any production of enamel matrix)

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4
Q

Pre-secretory Stage: What happens during Internal enamel epithelial cell differentiation into Pre-ameloblasts?

A
  • Occurs at the cusp tip
  • Differentiation progresses then cervically
  1. Epithelial cells become columnar and polarise; nuclei at the end of the cell in contact with the Stellate reticulum cells
  2. Endoplasmic reticulum, Golgi Apparatus and secretory vesicles enlarge and lie between the nucleus and adjacent dental papilla
  3. Pre-ameloblasts secrete enzymes via exocytosis that degrade the basal lamina and then resorb the degradation products by endocytosis
  4. Pre-ameloblasts are joined by desmosomes forming the proximal terminal web
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5
Q

Secretory Stage: What happens during this stage?

A
  1. Basic enamel matrix proteins are assembled in the ER and are processed by the Golgi App. = packed into dense secretory granules
  2. Formation of a thin layer of enamel matrix
  3. Secretory end becomes pyramidal in shape = TOMES PROCESS
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6
Q

Does the shape of Tomes’ processes determine the structure of enamel?

A

YES

  • Prongs (spikes) develop between adjacent processes - they deposit the peripheries of the prisms (pits) = INTER RODS
  • The processes fill the Prisms’ cores
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7
Q

What happens to Ameloblasts as they lay down matrix?

A
  • The Ameloblasts are pushed/move outwards away from the dentine surface
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8
Q

What’s the shape of the mineralising front?

A
  • Picket fence arrangement
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9
Q

What happens at the end of the Secretory Stage?

A
  • Ends once the full thickness of enamel matrix has been laid down
  • Tome’s process retracts and a thin layer of APRISMATIC ENAMEL is formed at the surface
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10
Q

What’s the difference between the early and mature enamel crystals?

A
  • Early crystals are thin and needle-like

- Mature crystals are larger

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11
Q

Why are the enamel matrix crystals aprismatic?

A
  • Enamel matrix is deposited while the cell end is flat, therefore, there is no change in crystal orientation in that layer
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12
Q

In what direction to the enamel crystals grow?

A

Direction of their concentration gradient

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13
Q

Transition Stage: What does this stage mark?

A
  • Transformation of the secretory ameloblasts into the maturation form
  • Maturation of enamel is its conversion into the mineralised form
  • Matrix deposition ceases and much of the organic matrix removed (mainly amelogenins)
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14
Q

What’s the composition of the initial enamel matrix and how does it change?

A
  • High in water and protein & low in mineral
  • Maturation is carried out by the same cells that secrete the primary matrix
  • Enamel secretion stop and a large proportion of AMELOGENIN is REMOVED
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15
Q

What happens to Ameloblast morphology and numbers during the Transition Stage?

A
  • Height is reduced
  • 50% reduction in Ameloblast numbers via apoptosis
  • Those that remain, Autophagocytosis reduce the conc. of protein synthesising organelles
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16
Q

Does invagination of the enamel organ with blood vessels occur during this stage?

A

YES

17
Q

What happens after Ameloblasts change morphology?

A
  • Form basal lamina (basement membrane) over the immature enamel and attach themselves to it by HEMIDESMOSOMES
18
Q

What’s the bulk of the developing enamel matrix and what happens to it during the Transition Stage?

A
  • 90-95% amelogenin protein
  • Amolegenins are hydrophobic and clump
  • Amoleginins are removed during the transition stage
19
Q

What comes after the Transition Stage?

A
  • Maturation Stage

- The process by which enamel changes into its final form

20
Q

What is the level of mineralisation at the start of the Maturation Stage?

A
  • 30%
21
Q

How does maturation occur in the enamel?

A
  • Water and Amelogenins are removed
  • Calcium and phosphate ions are added to increase the crystal size
  • Only 1-2% of the remaining enamel is organic
22
Q

What happens to Ameloblasts during the Maturation stage?

A

Ameloblasts undergo:

  • Tomes’ process loss
  • Organelle content reduction
  • Organelle congregation at the distal side of the cell
23
Q

What changes occur with Ameloblast plasma membrane?

A
  • Plasma membrane folds to form a striated border (ruffle ended)
  • Alternates with a smooth ended ameloblast (5-7 times)
  • This is a cycle between RESORPTIVE & SECRETORY phases
24
Q

What role do the RESORPTIVE & SECRETORY phases have on Maturation?

A
  • Degradation of the enamel matrix by serine proteases released from the enamel organ precede mineral gains
  • Matrix degradation and removal are essential to facilitate crystal growth
25
Q

The alternating Ameloblast morphology is linked to?

A
  1. Movement of calcium ions
    - Active during the ruffled stage and passive diffusion during the smooth stage
  2. Local pH change modulated by the carbonate level
    - Normal pH favours mineralisation (ruffled)
    - Acidic pH handicaps mineralisation (smooth)
26
Q

What happens after the maturation phase?

A
  • Ameloblasts flatten
  • Development of a primary cuticle - an amorphous layer of protein which separates the ameloblasts from the enamel
  • During eruption, the reduced Enamel Epithelium protects the tooth
  • Post eruption. the surface layer shows increasing mineralisation through interactions with saliva
27
Q

Mineralisation: What’s the main source of calcium for the enamel?

A
  • Enamel organ
  • Calcium travels mainly extracellularly
  • May be an active transport mechanism utilising carriers in the cell membranes of the Ameloblasts OR calcium may flow passively from high conc. in the blood plasma to low conc. in the enamel matrix
28
Q

What guides Crystal growth and Nucleation?

A
  • Tuftelin
29
Q

Where is it theorised that the initial nucleation occurs?

A
  • Dentine

- Then mineralisation crosses the enamel-dentine junction

Oral Biology (33 decks)

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