The presence of subodontoblastic cell-free and cell-rich layers in the coronal pulp of mature human teeth has been described by several authors, but data are lacking on the cellular arrangement in pulps from other species. This investigation aimed at providing information on the comparative histology of the subodontoblastic zone in adult rat and deciduous monkey molar pulps. Rat pulps did not show a cell-free zone in the subodontoblastic region and few nerve fibres were found in this area. A cell-free zone containing many nerve fibres was seen in the coronal pulp of monkey teeth. The presence of such a layer in human and monkey tissues and its absence from the rat may indicate the degree of specialization of the pulpal sensory apparatus and may therefore be of evolutionary significance. A prominent subodontoblastic cell-rich zone was found in the coronal pulp of rat and monkey tissues. This cell layer extended along the roof and lateral aspects of the pulp chamber, but was not present in the base of the coronal pulp nor in the root canals. It would appear that this cell layer may be of special importance in the functional activity of the pulp. © 1969.
