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

Question 1

Morphological stages of tooth development

Answer 1

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

Question 2

Initiation stages

Answer 2

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

Question 3

BUD stage

Answer 3

• 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

Question 4

CAP stage

Answer 4

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

Question 5

BELL stage

Answer 5

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