Immunocytochemical detection of apoptosis in human odontoblasts

Pulpal chamber size decreases on ageing due to primary and secondary dentin deposition. This work was designed to find out the consequences of this pulp chamber reduction on odontoblast number and distribution. Twenty‐one healthy human premolars were equally divided into three groups from 11‐, 12.5‐ and 14‐yr‐old adolescents, respectively). The external and the internal perimeters of dentin were recorded on vestibulo‐lingual sections, from buccal to lingual cemento‐enamel junction using an image analysis system. Nuclei of the odontoblasts were recorded on 12 automatically selected fields. On nine erupted premolars (3 teeth from each 11‐, 12.5‐ and 14‐yr‐old patients), apoptosis was detected by confocal microscopy using a modification of the original TUNEL method. Apoptotic cells were labeled in central pulp fibroblasts, perivascular endothelial cells, and in odontoblasts. When the pulp volume decreases due to primary dentin production, the decrease of the surface available for odontoblasts is compensated for by a multilayer distribution of cells. Secondary dentin deposition, associated with odontoblasts reorganization in a single layer, results in a hyperbolic decrease of the odontoblasts number. This decrease seems to result from a programmed cell death, which eliminates half of the odontoblasts over a 4‐yr period.