5 - Tooth germ - Morphological stages in development of enamel organ Flashcards
1
Q
Morphological stages of tooth development
A
- Bud stage
- Cap stage
- Bell stage
- Crown formation
- Root formation
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
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
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 epithelium ⇢ Cuboidal cells adjacent to dental papilla
- Inside enamel organ ⇢ Stellate reticulum ⇢synthesise + secrete glycosaminoglycans ⇢ Pull water into enamel organ
3 new strcutures are formed:
- Enamel knots ⇢ Clusters 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 Niche ⇢ Space between epithelium of dental lamina + outer enamel epithelium
5
Q
BELL stage
A
Early bell stage events:
- Morphodifferentiation ⇢ Tooth crown assumes its final shape
- Histodifferentiation ⇢ Cells that make ameloblasts + odontoblasts acquire their distinctive phenotype
- 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