In response to dental caries, there may be more dentin production towards the pulpal direction. This new dentin is referred to as tertiary dentin.[80] Tertiary dentin is produced to protect the pulp as long as possible from advanced bacteria. As tertiary dentin production increases, pulp volume decreases. This type of dentin has been divided according to the presence or absence of the original odontoblasts.[83] If the odontoblasts remain long enough to react with caries, then the resulting dentin is called retrograde dentin. If the odontoblasts are killed, the dentin that is produced is called “reparative” dentin.
In the case of reparative dentin, other cells are needed to take over the role of the destroyed odontoblasts. Growth factors, particularly TGF-β[83],[83] are thought to initiate dentin production by fibroblasts and mesenchymal cells in the pulp.[84] Repairing dentin is produced at a rate of 1.5 μm/day, but it can be increased to 3.5 μm/day. The resulting dentin contains irregularly shaped dentin tubules that may not line up with the tubules in the teeth. This reduces the ability of tooth decay to progress within the dentinal tubules.
