Tooth Development: Cap Stage

Introduction

• Following the Bud Stage in tooth development, the Cap Stage occurs.
• Marked by changes in the shape and differentiation of the Enamel Organ.

Morphological Changes

• Transition from Bud to Cap Shape:
  • Enamel Organ develops a concavity and adopts a cap shape.
  • Shape change due to unequal growth in different parts of the Enamel Organ.
  • Tooth germ resembles a cap over a ball of condensed ectomesenchyme.
• Basement Membrane:
  • Surrounds the Enamel Organ.

Differentiation

• Morpho-differentiation:
  • Change from bud to cap shape.
• Histo-differentiation:
  • Cells of the Enamel Organ start to specialize.
• Types of Cells:
  • Transition from 2 types in Bud Stage to 3 types in Cap Stage.
  • Outer Enamel Epithelium: Cuboidal cells lining the convex surface.
  • Inner Enamel Epithelium: Tall columnar cells lining the concave surface, which differentiate into Ameloblasts to form enamel.
  • Stellate Reticulum: Star-shaped cells in the center between the inner and outer enamel epithelium.
  • Changes from polygonal cells in Bud Stage to star-shaped due to glycosaminoglycan release.

Function of Stellate Reticulum

• Acts as a shock absorber.
• Protects Inner Enamel Epithelium from mechanical trauma.

Cervical Loop

• Junction of Inner and Outer Enamel Epithelium.
• High mitotic activity, leading to rapid cap size increase.

Dental Lamina

• Attaches Enamel Organ to oral ectoderm.
• Enamel Niche: Appears due to 3D plate seen in 2D section, sometimes appearing as two lamina with entrapped ectomesenchyme.

Transient Structures

• Enamel Knot:
  • Dense cell collection in Stellate Reticulum above the Inner Enamel Epithelium.
• Enamel Cord & Septum:
  • Represents vertical extension of densely packed cells towards Outer Enamel Epithelium.
  • Enamel Septum divides Stellate Reticulum into two compartments.
  • Enamel Navel: Concavity on the Outer Enamel Epithelium where Enamel Septum meets.
  • These structures act as reservoirs of dividing cells and signaling centers.
  • Enamel Knot: Integral in determining tooth shape.
  • Temporary and disappear before enamel formation.

Surrounding Connective Tissue

• Ectomesenchymal Condensation:
  • Dense cell collection below and around Enamel Organ.
  • Proliferation continues.
• Differentiation into Components:
  • Dental Papilla: Forms within the concavity and below Enamel Organ, later forming pulp and dentin.
  • Dental Sac/Follicle: Surrounds Dental Papilla and Enamel Organ, forming cementum, periodontal ligament, and alveolar bone later.