The dentinal tubules are filled with fluid. The odontoblast processes extend to about two thirds of the way into the tubule.
These odontoblasts produce dentinal fluid and the processes detect fluid movement which is relayed all the way to the brain.
Tertiary dentin is of two types. Tertiary dentin is of two types. REPARATIVE AND REACTIONARY.
When the stimulus is mild, there is an increase of the existing odontoblast cell activity and this is known as reactionary dentine. Reactionary dentine is therefore similar in structure to secondary dentine.
If the stimulus is severe, this causes death of the odontoblasts and recruitment of progenitor cells in the pulp which differentiate into odontoblast-like cells.
Reparative dentine is laid down that this is more highly mineralised than the reactionary or secondary dentine.