Diameter of odontoblastic tubules at the point of origin, at their pulpal end

Between the odontoblastic processes and the peritubular dentin is the periodontoblastic space which contains the dentinal fluid. The tubules are broader at their point of origin, i.e., at their pulpal end (3–4μm) and become gradually narrower at their point of termination (1μm), i.e., at dentinoenamel or cementoenamel junction. Also the tubules are closer together at the pulpal end (50–90,000 tubules/mm2) and further apart at their terminal end.