Oral Pathology

1. Zones Of Enamel And Dentine
Presented By: Muhammad Ammar
2nd Year BDS

2. Histopathology Of Caries In Enamel
 Enamel is composed of tightly packed hydroxyapatite crystals.which are
organized in long columnar rods (enamel rods),but during caries progression
certain histological changes are seen in enamel.
 In pits and fissures,it spreads in triangular pattern with base towards DEJ and
apex towards surface.
 Microscopically 4 Zones are seen
A) Translucent Zone
B) Dark Zone
C) Body of lesion
D) Surface Zone

3. A) Translucent Zone:
>Unrecognizable clinically and
radiologically.
>Occurs due to formation of
submicroscopic pores at enamel rod
boundaries and striae of Retzius.
>This zone is Slightly more porous than
sound enamel having a pore volume of 1%
compared to 0.1% of sound enamel.

4. B) Dark Zone:
>Lies superficial to translucent zone.
>Called positive zone as it is always
present.
>pore volume is 2-4% increased porosity
in this zone is due to greater degree of
demineralization in this zone.

5. C) Body Of Lesion:
>Forms bulk of the lesion and lies
between relatively unaffected surface
zone and dark zone.
>Area of greatest demineralization,having
a pore volume of 5% near the periphery
to about 25% in the center of body of
lesion.

6. D) Surface Zone:
>Interestingly, this zone not only remains
intact during the early stages of attack by
caries, but also REMAINS MORE HIGHLY
MINERALIZED.
>1% mineral Loss, About 40um thick.
>Little Change in early lesion.
>The surface of normal enamel differs in
composition from the deeper layer, being
more highly mineralized so interpretation
of possible chemical changes in this zone
is difficult.

7. Histopathology of Caries In Dentine
 Dentine caries develops from enamel caries: when the lesion reaches the
amelodentinal junction, lateral extension results in the involvement of great
numbers of tubules.
 The early lesion is cone-shaped, or convex, with the base at the
amelodentinal junction.
 In dentine caries, demineralization by acid is always in advance of the
bacterial front, the subsequent bacterial invasion being followed by
breakdown of the collagenous matrix.

8. Zones of Dentine Caries
1. Zone of sclerosis
2. Zone of demineralization
3. Bacterial invasion
4. Destruction
5. Reactionary dentine

9. 1) Zone of sclerosis:
> The Sclerotic or translucent zone is
located beneath and at the sides of the
carious lesion.
> Dead tract may be seen running through
the zone of sclerosis because the death of
odontoblast at an earlier stage in the
process of caries.

10. 2) Zone Of Demineralization:
> In the demineralization zone the
intratubular matrix is mainly affected by
a wave of acid produced by bacteria in
the zone of bacterial zone.
> It may be stained yellowish-brown as a
result of the diffusion of other bacterial
products interacting with proteins in
dentine.

11. 3)Zone Of Bacterial Invasion:
> In this zone bacteria extend down and
multiply within the dentinal tubules.
> The Bacterial invasion probably occurs
in two waves:
i.1st wave consist of acidogenic organism,
mainly lactobacilli, produce acid which
diffuses ahead into the deminrelized
zone.
ii.2nd wave of mixed acidogenic and
proteolytic organism then attack the
diminrelized matrix.
> The walls of the tubules are softened
by the proteolytic activity resulting in
elliptical areas of proteolysis-liquefaction
foci.

12. 4) Zone Of Destruction:
 In this zone of destruction, the
liquefaction foci enlarge and increase
in number.
 This produces compression and
distortion of adjacent dentinal
tubules.
 In acute, rapidly progressing caries
the necrotic dentine is very soft and
yellowish-white ; in chronic caries it
has a brownish-black color and is of
leathery consistency

13. 5) Reactionary( Tertiary)Dentine:
 When The original odontoblast that
made secondary dentine are
responsible for focal tertiary dentine
formation.
 Rate of formation of dentine is
increased.
 Tubules remain continuous with the
secondary dentine.