Histopathology of Dentinal caries

  1. As the carious lesion invades dentin, dentinal tubules become involved.
  2. As dentin is part of the dentin pulp complex, it leads to reparative dentine formation.


  1. Zone 1: Zone of fatty degeneration of Tomes fibers.
    1. Starts at pulp
    2. No fat degeneration (misnomer name)
    3. Alteration by dentin by fat deposition leads to impermeability of tubules which leads to sclerosis 
    4. Sclerosis is reaction between vital pulp and vital dentin
    5. It is the calcification of tubules against further penetration of microorganisms.
  2. Zone 2: Zone of dentinal sclerosis characterized by deposition of calcium salts in dentinal tubules.
    1. Sclerotic zone is minimum in rapidly advancing caries and prominent in slow/chronic caries.
    2. This is a translucent zone due to the vital reaction of odontoblasts
    3. High mineral content
    4. Reflected Light: Appears Dark
    5. Transparent Light: Appears White
  3. Zone 3: Zone of Decalcification of dentin
    1. Tubules are made of pure microorganisms such as pioneer bacteria (Cocci and Bacilli etc)
    2. Intertubular matrix is mainly affected by waves of acid produced by bacteria in the zone of bacterial invasion
    3. Initial decalcification occurs in the wall of tubules. 
    4. Softened infected dentin cannot be differentiated with sterile soft dentine, clinically.
    5. Appears yellow-brown
  4. Zone 4: Zone of bacterial invasion of decalcified but intact dentin.
    1. Bacteria multiply within dentinal tubules.
    2. Acidogenic microorganisms: Seen in early caries
    3. Proteolytic organisms—predominate in deeper layers
    4. It supports the hypothesis that initiation and progression are two distinct processes and must be differentiated
  5. Zone 5: Zone of decomposed dentin.
    1. Bacteria invade both peritubular and intertubular dentin. Hence, Little architecture of dentin remains
    2. Liquefaction foci of miller enlarge and increase in number.
    3. Transverse Clefts: Perpendicular to tubules
    4. Acute Caries: necrotic dentin is very soft and yellowish-white
    5. Chronic Cases: Dentin is leathery and brownish-black

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