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Enamel (Physical Properties (Hardest Biological Tissue (High abrasion …

- - - - 2.5mm over cusps of unworn perm teeth
      - 1.3mm over the cusps of delicious teeth
      - Thickness increases from 1st to 3rd molar
      - Up to 1.3mm on lateral surfaces
  - - - Impt because enamel cannnot be repaired or replaced
  - - - Together with flexibility of dentine, minimises the possibility of fractures
  - - - Richer in fluoride but less carbonate (main impurity) and magnesium
      - More highly mineralized and resistant to caries
- - - - Present in a form that contains impurities
        
        E.g. carbonate substituting for phosphate in the crystal lattice
      - Present in the form of crystallites
        
        75nm wide, 25nm thick, great length
        
        Typically extends across the full width of the tissue
        
        Mostly regularly hexagonal in cross-section
        
        Some are distorted by crowding during development
        
        Core of crystallite is more soluble than periphery
        
        Core of crystallite is richer in magnesium and carbonate
        
        Molecular Arrangement
        
        Each unit cell consist of OH group surrounded by 3 uniformly spaced Ca2+ ions , which are surrounded by 3 PO43- ions
        
        6 Ca2+ ions in a uniform hexagon enclose the PO43- ions
        
        Variations in Molecular Arrangement
        
        Carbonate may replace phosphate or hydroxyl group
        
        Main impurity in enamel
        
        Magnesium and carbonate increases solubility and increases towards dentine
        
        Magnesium may replace calcium
        
        Fluoride may substitute hydroxyl ions
        
        Greater stability and resistance to acidic dissolution
        
        Declines in amount from outer surface towards dentine
        
        Chloride, lead, zinc, sodium, strontium and aluminium
        
        Plane of ions may ‘slip’ from usual uniform arrangement
  - - - May be trapped within defects of crystalline structure
      - Remainder forms a hydration layer coating the crystals
      - May lie between crystals and surround organic material
  - - - Can be classified as
        
        Non-amelogenins
        
        Enamelin— superficial surface of enamel
        
        Ameloblastin— concentrated in prism sheath
        
        Tuftlin— concentrated in DE as tufts
        
        Amelogenins
        
        Removed during enamel development
      - Enamel proteins in adult enamel are remnants of a previously much larger component during development
    - - May represent the remnants of cell membranes remaining during development
      - Can be found in
        
        Cross strait ions
        
        Lines of Retzius
        
        Hunter-Schreger bands
        
        Prism sheath
        
        Prism core
- - - - No repair or replacement after that