Tooth Development: Physiological Stages

Overview

• Tooth development is a complex process.
• Studied under morphological and physiological stages.
• Physiological stages focus on cellular mechanisms in tooth germ.
• Stages include:
  • Initiation
  • Proliferation
  • Histo-differentiation
  • Morpho-differentiation
  • Apposition
• Overlapping of stages occurs, unlike morphological stages.

Initiation Stage

• Shortest stage.
• Marks beginning of tooth development.
• Associated with dental lamina, a horseshoe-shaped extension of the oral ectoderm.
• Requires interaction between epithelium and ectomesenchyme.

Proliferation Stage

• Longest stage of tooth development.
• Involves increase in cell numbers.
• Begins right after initiation.
• Continues until differentiation of Ameloblasts and Odontoblasts.
• Occurs during Bud, Cap, Early Bell, and stops in Advanced Bell stage.

Histo-differentiation Stage

• Immature cells mature to carry out specific functions.
• Inner Enamel Epithelium differentiates to Ameloblasts for enamel deposition.
  • Cells transition from cuboidal to columnar.
  • Develop Tome's processes.
• Dental papilla cells differentiate into Odontoblasts.
• Other cells, such as Stellate Reticulum and Stratum Intermedium, also differentiate.
• Occurs during Cap, Early Bell, and Advanced Bell stages.

Morpho-differentiation Stage

• Enamel organ changes shape to form the tooth.
• Final tooth morphology is determined.
• Begins in Cap stage.
  • Inner Enamel Epithelium takes the shape of the crown.
• Shape varies according to the type of tooth.
• Hertwig's Epithelial Root Sheath determines root shape.

Apposition Stage

• Deposition of hard tissues of the tooth.
• Ameloblasts and Odontoblasts deposit enamel and dentin.
  • Characterized by regular, rhythmic deposition.
  • Leads to incremental lines in enamel and dentin.

Overlapping Processes

• Physiological processes overlap, except for initiation.
• In Cap and Early Bell stages, processes of proliferation, histo-differentiation, and morpho-differentiation occur simultaneously.
• Advanced Bell stage involves apposition at cusp tip, and other processes cervically and at the cervical loop.