Unlike enamel, dentin reacts to the development of tooth decay. After the formation of teeth, the amyloplasts, which produce enamel, are destroyed once enamel formation is complete and therefore the enamel cannot be regenerated later after its destruction. On the other hand, dentin is produced continuously throughout life by odontoblasts, which are located at the border between pulp and dentin. Because odontoblasts are involved, a stimulus, such as tooth decay, can trigger a biological response. These defense mechanisms include the formation of dentin and tertiary sclerosis. [78]
In dentin from the deep layer to the enamel, the distinct regions affected by caries are the advanced front, the zone of bacterial penetration, and the zone of destruction.[74] The developed frontal represents an area of mineralized dentin due to acid and has no bacteria present. Areas of bacterial penetration and destruction are sites of bacterial invasion and ultimately decomposition of dentin. The zone of destruction contains a higher number of mixed bacteria as proteolytic enzymes have destroyed the organic matrix. Dentin caries is attacked reversibly because the collagen matrix is not severely damaged, giving it the potential to repair. The most superficial outer zone is highly demineralised by the proteolysis of the collagen matrix and as a result the dentin is irreversibly demineralized.[citation needed]
