Stages of Tooth Development Quiz

Stages of Tooth Development (Odontogenesis)

• Classified by morphological changes in the enamel/dental organ (epithelium) and histo-physiological processes within each stage.
• Morphological stages include: dental lamina, bud, cap, bell, and appositional/late bell stages.

Dental Lamina Stage

• Initiates odontogenesis.
• Ectomesenchymal neural crest cells induce proliferation of basal cells in oral epithelium.
• This forms localized epithelial proliferations on the facial aspect of the dental lamina, known as bud enamel organs.
• Five bud organs develop in each quadrant of the jaw, resulting in ten per jaw.

Bud Stage

• Occurs at the 8th week of intra-uterine development (WIU).
• Histological changes include:
  • Peripheral cells: cuboidal or short columnar.
  • Central cells: polyhedral, secrete glycosaminoglycans.
  • Dental papilla: condensed ectomesenchyme under the bud, shows increased cells and fibrous tissue.
  • Dental follicle/sac: dense fibrous ectomesenchyme surrounding the dental organ and papilla, forming an outer zone of loose ectomesenchyme.
• Main physiological processes:
  • Induction: neural crest cells induce formation of bud organs.
  • Proliferation: increase in cell numbers.

Cap Stage

• Unequal growth of the bud organ creates a cap shape.
• The cap stage is characterized by:
  • Outer enamel epithelium (OEE): cuboidal cells.
  • Stellate reticulum (SR): star-shaped cells, secrete glycosaminoglycans.
  • Inner enamel epithelium (IEE): short columnar cells.
  • Cell free zone: temporary structure between the IEE and dental papilla.
  • Dental papilla: increases its mass.
  • Dental sac (follicle): surrounds the organ and papilla.
• The enamel organ, dental papilla, and dental sac together are called the tooth germ.
• Histophysiological processes:
  • Proliferation: growth of all components.
  • Differentiation:
    • Morpho-differentiation: change in shape from bud to cap.
    • Histo-differentiation: formation of different cell types.
    • Cyto-differentiation: gradual transformation of undifferentiated cells to specialized cells.

Early Bell Stage

• The cap shape transforms into a bell shape due to continued unequal growth.
• The main dental lamina elongates and branches into:
  • Lateral dental lamina: connects deciduous organ to the main lamina.
  • Successional dental lamina: connects permanent successor to the main lamina, positioned lingual to the deciduous organ.
• Histologically:
  • Dental laminae (main, lateral, successional).
  • Dental sac.
  • Outer enamel epithelium (OEE).
  • Stellate reticulum (SR).
  • Stratum intermedium (SI).
  • Preameloblasts.
  • Odontoblasts.
  • Dental papilla.
  • Cervical loop: part of the organ at the cervical rim.

Bell Stage Features

• Preameloblasts: under influence of the IEE, they differentiate into ameloblasts.
• Odontoblasts: under influence of preameloblasts, the peripheral cells of the dental papilla differentiate into tall columnar odontoblasts with nuclei shifted to the apical end.
• Dental papilla: dense ectomesenchyme that gives rise to odontoblasts and pulp tissue.
• Cervical loop: growth center for crown formation, contributes to epithelial component for root formation.

Histophysiological Processes in Bell Stage

• Proliferation: continuous cell growth in the cervical loop.
• Differentiation: specialization of cell types.
• Morphogenesis: formation of the bell shape.