[Morphometric study of variations related to human aging in pulp unmyelinated and myelinated axons]

The evolution of myelinated and unmyelinated axon population in dental pulps during human aging was followed by electron microscopy and morphometry. A total of 2684 nerve fibers were measured in 16 subjects aged 10 to 72 years. The total distribution is bimodal with a recovering zone of 9.8% between unmyelinated and myelinated fibers. The mean diameter of A delta fibers was 1.96 mu and that of C fibers was 0.52 micron. The old pulps showed a loss of A delta fibers of small sizes (0.35-2 micron), the presence of numerous unmyelinated C fibers of very small diameters (0.1-0.25 micron) and a decrease of unmyelinated fibers of 0.5 to 1 micron comparative to young pulps. The logarithms of the diameters unmyelinated axons varied linearly with that of the subjects ages (CR = 0.63; p = 8, 8.10(-3]. The older the patients, the more the fiber C diameters were reduced. The decrease in numbers of A delta fibers could result from a local reduction of pulpal volume related to age or a response to a more general aging process of cerebral origin. The decrease in diameter of unmyelinated fibers in aging pulps would be a reduction of metabolic energy.