1-18. CARIES IN DENTIN
From the small area on the surface of the tooth, caries continues its progressive
destruction. As noted in the preceding paragraph, decay spreads easily within dentin
after penetrating the enamel. The disease spreads laterally along the dentinoenamel
junction and directly toward the pulp.
a. The Destructive Process. The destructive process of caries differs in dentin
and enamel. In caries of enamel, the organisms cannot enter the substance of the
enamel until the acid produced by the organisms has destroyed the enamel substance.
This process is called demineralization. The reverse is true of the dentin, which is made
of many hollow tubules. These tubules offer a natural pathway for penetration by
bacteria and because the dentin contains a large proportion of organic materials,
progression is faster in dentin than in enamel. When the dentin has been reached,
acid-forming and proteolytic organisms can enter the dentinal tubules and produce acid
or break down the organic matrix within the tissue itself. Since dentinal tubules tend to
branch and communicate with each other at the dentinoenamel junction, the organisms
penetrate the dentin laterally in all directions along this junction. Accompanying this
lateral penetration is a penetration along the main tubules in the direction of the pulp.
This lateral and direct involvement tends to form a cone-shaped area of decay. The
apex of the cone is pointed toward the pulp of the tooth and the base at the
b. Limits to Dentin Destruction. Although dentin destruction in caries is
normally faster than enamel destruction, the rapidity of dentin destruction both in depth
and breadth will be governed by its structure. Because of the extensive organic matrix
of the dentin, enough substance is left after the dissolution of the inorganic salts to
retain its physical form until further destruction has taken place by other processes.
c. The Infected Layer and the Affected Layer. Caries in the dentin is
described as having an infected layer and an affected layer. In the infected dentin,
many microorganisms are present and most of the dentinal tubules have been
destroyed through demineralization and decomposition (destructive process of
proteins). The infected layer is soft on the surface but gets tough, leathery, or rubbery
underneath. Below the infected layer is the affected layer of dentin. Few
microorganisms are found in this area and the dentinal tubules are intact. Normal
dentin is found under the affected layer. The difference in these layers plays an
important role in the treatment of caries in the dentin.
1-19. ARRESTED CARIES
Arrested caries is the stage where the progress of the decay process has
stopped. The softened dentin has been lost or worn away so that the discolored (either
yellow, brown, or black), sound, hard dentin remains. The remaining dentin has a