The proliferation of pulp cells in rat incisors

Twenty immature August rats were injected with tritiated thymidine and killed at intervals between 1 and 48 hr. Autoradiographs of saggital sections of the maxillary and mandibular incisors were prepared. The distribution of mitoses and labelled nuclei at 1 hr enabled the extent of the proliferative area of the pulp to be defined. This was strictly basal in position and within it gradients of proliferative activity were observed. Labelling indices of the labial and lingual aspects of the basal pulp were not found to be significantly different; there were, however, significant differences between values determined for the corresponding areas in maxillary and mandibular incisors. The components of the cell generation cycle were established for the mandibular pulp (T_G2 minimum, 1.3 hr; T_G2 maximum, 1.7 hr; T_M, 1.5 hr; T_S, 8.2 hr; T_G1, 10.9 hr; T_C, 22.1 hr) and for the maxillary pulp (T_G2 minimum, 1.3 hr; T_G2 maximum, 1.9 hr; T_M, 1.7 hr; T_S, 8.0 hr; T_G1, 12.2 hr; T_C, 23.5 hr). Small regional differences between the labial aspect (T_S, 7.8 hr) and lingual aspect (T_S, 8.5 hr) of the maxillary pulp were noted; these were not found in the mandibular pulp. A correlation between high cell population density and high cell proliferative activity was found to exist in the basal pulp. The presence of a cell-dense band of fibroblasts of low proliferative activity between the extremities of the odontogenic epithelia was noted. Migration of pulp cells from the proliferative area in a coronal direction was observed. Brief observations were made on the proliferative activity, migration and maturation of the ameloblasts and odontoblasts.