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Craniofacial and Tooth Biology > 15. Amelogenesis > Flashcards

15. Amelogenesis Flashcards

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1
Q

Amelogenesis is a 2 step process, which are …

A
  • when enamel first forms, it’s partially mineralised (around 30% by weight)
  • enamel is fully formed (mature) and mineral contents increase to around 96%
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2
Q

At late bell stage, shortly after dentine formation, what happens in amelogenesis?

A
  • inner enamel epithelium cells initiate morphologic changes in enamel organ
  • ameloblasts move away from dentine after formation of first enamel layer
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3
Q

Ameloblast change their … and … during life cycle

A
  • shape
  • function
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4
Q

3 main functional stages of amelogenesis

A
  • presecretory
  • secretory
  • maturation
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5
Q

6 stages of ameloblast life cycle in the 3 stages of amelogenesis

A

in presecretory
- morphogenetic stage
- histodifferentiation stage
in secretory
- initial secretory stage without Tomes process
- secretory stage (Tomes present)
in maturation
- ruffle-ended ameloblast
- smooth ended ameloblast
- protective stage

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6
Q

Explain ‘morphogenetic phase’

A
  • shape of crown is established during bell stage
  • IEE cells are short with centrally placed nuclei, basal lamina seen, dentine not yet mineralised
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7
Q

Explain histodifferentiation phase

A
  • IEE cells differentiate into ameloblasts
  • cells become taller (establishment of polarity)
  • development of ability to synthesize proteins
  • basal lamina fragmented
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8
Q

Explain ‘initial secretory stage’

A
  • ameloblasts elongate and secrete enamel matrix
  • form partially mineralised initial layer of enamel (rodless enamel layer)
  • ameloblasts move away from dentine after formation of first enamel layer
  • they do this to form secretory surface (later called proximal portion of Tome’s process) and to develop distal portion of it
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9
Q

Explain secretory stage

A
  • ameloblasts elongate with distal portion of Tome’s process to form enamel rod and proximal protion of Tome’s process to form interrod enamel
  • as enamel thickness increases and enamel rod grows width, distal portion elongates, becomes thinner and gets squeezed between rod and interrod enamel
  • it creates a narrow space between them which fills with organic material forming rod sheath
  • once outermost layer of enamel is being formed, ameloblast becomes shorter, loses distal portion of Tome’s and forms thin rodless enamel layer
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10
Q

2 proteins in enamel matrix

A
  • enamelins
  • amelogenins
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11
Q

Of the proteins in enamel matrix, …% are enamelins and …% are amelogenins

A

10
90

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12
Q

Role of enamelins

A
  • first matrix element secreted
  • due to hydrophilic and acidic nature, role in calcium and phosphate conc and crystal nucleation
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13
Q

Role of amelogenins

A
  • secondary to enamelin secretion
  • due to hydrophobic nature, 2 roles in mineralisation
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14
Q

Enamel biomineralisation in secretory phase

A
  • assembly of enamel matrix occurs extracellularly and resides in structure of protein
  • amelogenins and mineralized enamel ribbons secreted
  • amelogenins form nanospheres
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15
Q

Enamel biomineralisation in maturation phase

A
  • matrix disassembled during this phase
  • collapse of amelogenin nanospheres and thickening of crystal
  • ameloblasts pump calcium, phosphate and carbonate ions into matrix and remove water and degraded protein
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16
Q

In the bell stage, IEE layer has what shape cells?
IEE cells then …
Ameloblasts begin to … and actively deposit …

A
  • short columnar undifferentiated
  • differentiate into ameloblasts that induce differentiation of odontoblasts
  • secrete enamel matrix
  • enamel matrix
17
Q

Explain post decretory ameloblast proteins

A
  • proteins (enamelysin and kallikrein4) do post secretory processing and degradation of enamel proteins
  • non-amelogenins (like enamelin and ameloblastine) at periphery of enamel prisms form enamel sheath
  • basal lamina protein (amelotin) produced in maturation and present in junctional epithelium
18
Q

The maturation stage sees a growth in … and …

A
  • width
  • thickness
    of pre-existing cystals
19
Q

2 phases of maturation stage

A
  • transitional
  • maturation
20
Q

Explain transitional phase

A
  • after enamel thickness formed
  • decrease in height and volume of ameloblasts
  • 50% of ameloblasts die
21
Q

Explain maturation phase

A
  • removal of water and proteins in matrix
  • transport of ions
  • cyclic modulation of ameloblasts (alterations in permeability of enamel organ)
22
Q

How does cyclic modulation of ameloblasts occur in ruffle ended stage?

A
  • leaky junctions between ameloblasts at proximal/basal end
  • tight junctions at the distal/enamel end
  • selective transfer of calcium ions across ameloblast layer
23
Q

How does cyclic modulation of ameloblasts occur in smooth ended stage?

A
  • leaky junctions distally
  • proteins and water exit
  • interstitial fluid leaks into maturing enamel between ameloblasts
  • trace elements incorporated in interstitial fluid and enter enamel fluid in enamel layer
24
Q

Explain movement of ions in maturation stage

A
  • selective transfer of ions across ameloblast layer between interstitial and enamel fluid
  • rate of calcium transfer is 4 times higher in maturation phase
  • active transport of calcium out and passive transport of trace elements in
25
Q

What 4 structures form in the maturation stage?

A
  • papillary layer
  • primary enamel cuticle
  • reduced enamel epithelium
  • Nasmyth’s membrane
26
Q

What is the Nasmyth’s membrane?

A
  • covers enamel of unerupted teeth
  • leaky
27
Q

Role of reduced enamel epithelium

A
  • protects unerupted crown surface from resorption by osteoclasts and from deposition of cementum
  • REE on Nasmyth’s membrane prevents bleeding
  • forms junctional epithelium
28
Q

Role of primary enamel cuticle

A
  • acquired pellicle on exposed crown
29
Q

Explain the gradient of mineralisation of enamel

A
  • gradient increase from EDJ to surface
  • and from occlusal to cervical region
30
Q

Which are more mineralised? Primary or secondary?
Why?

A
  • secondary
  • more time in maturation phase
31
Q

Throuhgout life, teeth have a dynamic what?

A
  • dynamic enamel demineralisation/remineralisation cycle
  • mature enamel is in chemical equilibrium with surrounding media
32
Q

Fluoridation benefits

A
  • water fluoridation (1ppm) means incorporating fluoride ion into HA crystal and becomes more resistant acid and reducing dental caries
33
Q

Fluoridation risks

A
  • long term excessive consumption of fluoride ions
  • disturbs ameloblasts causing mottled enamel fluorosis
34
Q

How does acid-etching work?

A
  • etching enamel surface with acid (called enamel conditioning) beneficial for adhesive dental restorative materials
  • appears matter and whiter
35
Q

Explain abnormal enamel

A
  • related to poor oral hygeine e.g white spot legions
  • related to enamel formation or defects in all teeth (amelogenesis imperfecta -fluorosis etc) or in some teeth due to non-systematic or systematic causes affecting teeth developing like enamel hypoplasia or hypomineralisation
36
Q

Enamel defects which affect all teeth are caused by what?
Give examples

A
  • environmental and systemic factors like febrile disease, treatment with tetracycline antibiotics, chronic ingestion of fluoride ions/fluorosis
  • genetic factors like genetic dysplasia (syndromic vs non-syndromic, pattern of inheritance - autosomal dominant, recessive or x-linked)
37
Q

Explain amelogenesis imperfecta

A
  • inherited defects
  • can be hypoplastic, hypocalcific or hypomaturation
  • associated with pulp calcification, delayed eruption and other issues
38
Q

Explain molar incisor hypomineralisation

A
  • affects teeth formed in 1st year of life (permanent first molars and incisors)
  • molars worse affected than incisors
  • associated with opacities and loss of enamel in severe cases - caries
  • more common in children who take amoxicillin in first year of life, often for otitis media
  • associated with hypomineralisation
39
Q

Explain ‘chronological/linear enamel hypoplasia’

A
  • disruption of enamel formation
  • causes deep grooves to form on tooth surface
  • caused mainly by poor nutrition, stressful event or high fever during tooth development

Craniofacial and Tooth Biology (25 decks)

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