3. Characterization of dentin caries.

Question 1

1. What are the 5 zones of dentine caries?

Answer 1

1. zone of destruction
2. zone of bacterial invasion
3. zone of demineralisation
4. Sclerotic Zone (known as Translucent Zone)
5. tertiary (reactive) dentine

Question 2

2. What are the characteristics of (1) Zone of Destruction?

Answer 2

‣ When enamel has been cavitated, bacteria
infect the dentine.

‣ The dentine becomes necrotic, and liquifies.
=> The liquified areas are called Liquefaction Foci

‣ Cracks appear in the dentine, usually at right angles to the direction of the dentinal tubules.
=> The cracks are called Transverse Clefts.

‣ With rapid caries, this zone is soft and yellow.

‣ With slowly progressing caries, it is harder and browner.

‣ Treatment: removed with an excavator.

Question 3

3. What are the characteristics of (2) Zone of Bacterial Invasion?

Answer 3

‣ The tubules are invaded by bacteria, which then multiply within the tutbule lumen.
‣ As well as decalcifying the dentine with acid, the bacteria dissolve the proteins (like collagen) within the tubules -> This is called proteolysis.
‣ Treatment: This region can be removed by a rose-head bur, gentle pressure running slowly.

Question 4

4. What are the characteristics of (3) Zone of Demineralisation?

Answer 4

‣ Acid produced by the bacteria travels down the dentinal tubules, causing demineralisation.
‣ The zone of demineralisation is the advancing front of the carious lesion, and may be very small (less than 1mm).
‣ Dentine is relatively easily dissolved/demineralised by acid, at pH 6.7.
‣ NO bacteria in this region.

Question 5

5. What are the characteristics of (4) Sclerotic Zone (known as Translucent Zone)?

Answer 5

‣ A defence reaction occurs within the tubules when acid initially starts to penetrate them.
‣ The (live) odontoblast processes start to lay down calcification within the tubules, and they become plugged with mineral deposits.
* This helps to slow down the acid advance, giving the pulp some protection from the acid.

Question 6

6. What are the characteristics of (5) Tertiary Dentine (also known as Reactive Dentine)?

Answer 6

‣ When the pulp is mildly inflamed by advancing acid, it produces tertiary dentine in an attempt to wall off the insult.
‣ The cavity is below the contact point, so accessible to a contra- angled probe.