Dentinogenesis Lecture Notes

Overview

• Dentinogenesis: Process of dentin formation.
• Dentin: Calcified tissue forming the bulk of the tooth.
• Odontoblasts: Cells responsible for dentin formation, located in pulp.
  • Odontoblastic processes extend through dentin.

Chronology of Tooth Formation

• Primary Dentin Formation:

  • Begins just before enamel formation.
  • Continues after tooth eruption until root completion.

• Secondary Dentin Formation:

  • Starts after primary dentin formation.
  • Continues throughout tooth's lifespan until death.

Types of Dentin

• Coronal Dentin: Dentin in the crown of the tooth.
• Root Dentin: Dentin in the root of the tooth.

Differentiation of Odontoblasts

• Coronal Dentin:

  • Formed from inner enamel epithelium cells.
  • Ameloblasts develop, releasing signals to dental papilla cells to differentiate into odontoblasts.
  • Odontoblasts: Tall columnar cells (7 microns in diameter, 40 microns in length) with nuclei towards the dental papilla.

• Root Dentin:

  • Differentiation occurs after Hertwig's Epithelial Root Sheath formation.
  • The sheath releases signals for odontoblast differentiation in the dental papilla.

Formation of Odontoblastic Processes

• Unique feature of dentinogenesis.
• As odontoblasts deposit dentin, they move backwards, leaving extensions known as odontoblastic processes, reaching the dentino-enamel junction.

Dentinogenesis Steps

1. Formation of Organic Matrix:

   • Composed of proteins (90% collagen): predominantly Type I collagen.
   • Non-collagenous proteins: including dentin phosphoprotein (DPP), dentin sialoprotein (DSP), dentin glycoprotein (DGP), and dentin matrix protein (DMP-1).
   • Collagen forms a scaffold for mineral deposition; non-collagenous proteins regulate mineralization.

2. Mineralization:

   • Begins with the deposition of hydroxyapatite crystals (3nm wide, 100nm long).
   • Occurs via matrix vesicles released by odontoblasts (25nm to 250nm in size).
   • Mineralization Patterns:
     • Globular (Calcospheric) Pattern:
       • Predominantly in coronal dentin.
       • Faster rate of mineralization.
       • Crystals grow centrifugally and fuse into a mineralized mass; hypocalcified areas termed interglobular dentin.
     • Linear Pattern:
       • More common in root dentin and near the pulp.
       • Crystals fuse at a smaller size, creating a straight mineralization front.

Dentin Types and Formation Rates

• Primary, secondary, and tertiary dentin formation follows similar processes, differing in rates:
  • Secondary Dentin: Formation is slower compared to primary dentin.
  • Tertiary Dentin: Formation is inconsistently rapid, leading to structural irregularities.