5 - Tooth germ - Morphological stages in development of enamel organ Flashcards

1
Q

Morphological stages of tooth development

A
  1. Bud stage
  2. Cap stage
  3. Bell stage
  4. Crown formation
  5. Root formation
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2
Q

Initiation stages

A

Enamel organ is of epithelilal origin

After 6 weeks of embryo development:

  • Proliferation of cells (thick bands) appear ⇢ Upper + Lower jaw develop from here
  • These 1° epithelilal bands bifurcate into ⇢ Lingual process/Dental lamina + Buccal process/Vestibular lamina
  • Dental lamina ⇢ where teeth will form from ⇢ certain points of the lamina develop placodes
  • Permanent tooth germ ⇢ develop from lingual extensions of dental lamina = successional lamina
  • Vestibular lamina ⇢ gives rise to oral vestibule between cheeks + teeth
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3
Q

BUD stage

A
  • Placodes proliferate + take shape of bud
  • 1st incursion of epithelium into the ectomesenchyme of jaws
  • Tooth bud = enamel organ ⇢ gives rise to enamel of teeth

Stage is characterised by:

  • Epithelilal cells proliferation via mitosis
  • Increase in number of cells + their size
  • Condensation of ectomesenchymal cells around tooth bud
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4
Q

CAP stage

A

At this stage a concavity is formed at the top of the tooth bud under the control of mesenchymal factors

Histodifferentiation occurs here:

  • Outer enamel epithelium ⇢ single row of cuboidal cells
  • Inner enamel epitheliumCuboidal cells adjacent to dental papilla
  • Inside enamel organStellate reticulum ⇢synthesise + secrete glycosaminoglycans ⇢ Pull water into enamel organ

3 new strcutures are formed:

  • Enamel knotsClusters of non-dividing epithelial cells ⇢ Represents organisational centre of morphogenesis + is the epithelilal signalling centre ⇢ essential regulator of tooth shape
  • Enamel Cord ⇢ extended from group of cells between inner + outer epithelia ⇢ directs + binds enamel knot
  • Enamel NicheSpace between epithelium of dental lamina + outer enamel epithelium
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5
Q

BELL stage

A

Early bell stage events:

  1. Morphodifferentiation ⇢ Tooth crown assumes its final shape
  2. Histodifferentiation ⇢ Cells that make ameloblasts + odontoblasts acquire their distinctive phenotype
  3. Fragmentation of dental lamina ⇢ dental lamina + lateral lamina break up into clusters of epithelial cells ⇢ separating developing tooth from oral epithelium

Late bell stage:

  • Marked by formation + mineralisation of enamel + dentin
  • Stellate reticulate collapses
  • Ameloblasts + outer enamel epithelium fuse ⇢ forms reduced enamel epithelium
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