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