Lecture 2: Enamel (Dr. Hibaldo)

Overview

• Focus on enamel: the hardest tissue in the body, covering teeth.
• Topics: Physical properties, chemical composition, histology.

Physical Properties of Enamel

• Hardness
  • Hardest tissue in the body.
  • Withstands shearing and impact forces.
  • High resistance to abrasion.
• Thickness
  • Varies: up to 2.5 mm at cusp area, thinner at cervical margins.
  • Primary teeth: uniform thickness (~1.3 mm).
• Repair
  • Cannot be repaired or replaced; ameloblasts undergo apoptosis after secretion.
• Strength
  • Low tensile strength, high modulus of elasticity (brittle).
  • Requires support from dentine.
• Surface Characteristics
  • Surface enamel: harder, denser, less porous than subsurface.
  • Hardness decreases from cusp tips to cervical margins.
  • Color changes: White in youth to yellow with age (due to increased translucency).

Chemical Composition

• Inorganic Material (96%)
  • Mostly calcium hydroxyapatite.
  • Crystal size: 17 nm width, 25 nm thickness.
  • Core rich in magnesium and carbonate.
• Organic Material (2%)
  • Includes amino acids, peptides, large protein complexes (amelogenins, non-amelogenins).
  • Amelogenins: hydrophobic, low molecular weight, aggregate into clumps.
  • Non-amelogenins: e.g., enamelin, ameloblastin, involved in mineralization.
• Water (2%)
  • Distributed in pores, between crystals, and in defects.
  • Facilitates ion travel (e.g., fluoride).

Histology of Enamel

• Basic Structure
  • Enamel rods (prisms): Long, thin rods composed of hydroxyapatite crystals.
  • Separated by inter-rod substance (crystals deviate 40-60 degrees).
• Rods/Prisms Patterns
  • Keyhole pattern most common.
  • Hunter-Schreger bands: optical phenomena due to different prism orientations.
  • Gnarled enamel: Twisted prisms in cusp areas for increased strength.
• Surface Enamel
  • Aprismatic: Crystals aligned at right angles to surface.
  • Incremental lines: Cross striations (daily growth), enamel striae (weekly/10-day growth).
  • Neonatal line: Differentiates pre and post-birth enamel.
• Enamel-Dentine Junction (DEJ)
  • Scalloped in high-stress areas, smooth in others.
  • Enamel spindles: Odontoblastic processes extending into enamel.
  • Enamel tufts: Hypomineralized areas rich in organic matrix.
  • Enamel lamellae: Structural faults through entire thickness, hypo-mineralized.
• Cemento-Enamel Junction (CEJ)
  • Three patterns: Cementum overlaps enamel (60%), meet end-to-end (30%), gap exposing dentine (10%).

Enamel Aging

• Wears slowly with age, darkens due to reduced translucency and stains.
• Surface composition changes due to interactions with oral fluids.
• Enhanced mineralization over time can reduce caries susceptibility.
• Enamel pearls: Small enamel droplets on root surface.

Upcoming

• Laboratory section: Review histological slides of enamel.

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End of Lecture