The distribution of mitoses and cells in the tissues bounded by the socket wall of the rabbit mandibular incisor

Abstract

The distribution of cell division has been the subject of a study of the continuous production of dental pulp and of the special cell layers directly concerned with the formation of the hard dental tissues, which underlies the extrusion of the rodent incisor. From two young and two adult rabbits, five axial microscopic sections of each mandibular incisor were selected and stained with haematoxylin. Before death, the left incisor of each animal had been made to erupt rapidly by being cut out of occlusion with its opponents. In each section the outlines of the tooth and socket and the positions of mitoses were measured. Cell populations were estimated in the special cell layers, basal 3 mm of the pulp, and intermediate layer of the lingual periodontal tissues. Young animals differed mainly from older in showing more mitoses on or near the socket walls. Rapidly erupting incisors showed 1-4 times more mitoses than their norm ally erupting fellows, having erupted 1-9 times faster during the period of measurement. The proportion of prophase and metaphase to later stages of mitosis was greatest in the enamel organ, least in the periodontal tissues. Mitoses were found in the internal enamel epithelium , stratum intermedium and stellate reticulum of the enamel organ, none further coronally than 700 µ from the base. The greatest concentrations of pulpal mitoses were found opposite the regions of proliferation of the internal epithelia of the enamel and cement organs. Of all pulpal mitoses, 65 % were found in the basal millimetre—coronal to this the axial distribution showed a sharp decline, but individuals were found up to 10 mm from the base; 16 % were in the walls of blood vessels. In the basal millimetre of the pulp few cell divisions occurred in the centre, many at the periphery: such disparity did not appear coronal to this. The pulps of rapidly erupting incisors were depleted of cells at the base : the basal centre—poor in mitoses— apparently contributes cells to pulpal growth, its cell density being maintained, presumably, by migration from the periphery. An explanation of the distribution of mitoses has been sought, by comparison with connective tissue orientation, in the tensions produced by eruptive movement. Mitoses were found the length of the intermediate layer of the periodontal tissues, with a distribution across the lingual periodontal membrane showing a sharp peak at about 20 µ from the cement surface. This distribution may be related to the processes whereby the incisor is permitted to erupt and yet is anchored to its socket.