Number and size spectra of non-myelinated axons of human premolars

Abstract

The aim of this study was to determine the number and size of apical non-myelinated (C) axons of healthy human premolars. The material was derived from a large collection of specimens prepared for a previous quantitative investigation on the myelinated (A) axons of human premolars. A total of 16 teeth (six maxillary first and five each of mandibular first and second premolars), removed from adolescents for orthodontic reasons, were used. Root discs of about 0.6 mm thickness were prepared at about 2 mm cervical to the root apex and processed for light and electron microscopy. The number of non-myelinated axons was determined by taking a total census of such fibres that could be identified and reconstructed by standardized composite electron micrographs from each root disc. The measurement of axons was done on a statistically representative sample of axons (n = 1810) using an electronic image processing unit. The 16 teeth had an average of 2000 +/- 1023 non-myelinated axons at the juxta-apical level (range 534-3912). The average diameter of the non-myelinated axons was found to be 0.5 +/- 0.4 microns (range 0.05-2.4 microns).

Pulp microenvironment and mechanisms of pain arising from the dental pulp: From an endodontic perspective

“…The sensory neurons of the dental pulp have their cell bodies in the trigeminal ganglion. The long axons of the sensory neurons travel through the apical foramen in the neurovascular bundle and ascend to the radicular pulp . Each tooth is innervated by a multitude of trigeminal axons, which may have branched before entering the apical foramen and may innervate more than one tooth .…”

Quantitative Ultrastructural Analysis of the Neurofilament 200–Positive Axons in the Rat Dental Pulp

“…For example, the conduction velocity of axons that innervate the dental pulp is higher in the extrapulpal than in the intrapulpal segment (5,6), and the proportion of myelinated to unmyelinated axons is higher in the inferior alveolar nerve than in the intrapulpal nerve (7,8). In addition, a large number of electron microscopic (EM) studies have reported that only 22%-45% of the intradental axons are myelinated in the radicular pulp of rats, cats, dogs, marmosets, and humans (9)(10)(11)(12)(13), whereas our previous study found that most axons innervating the rat dental pulp are myelinated at their site of origin in the trigeminal ganglion (TG) (14). Taken together, these results suggest that at least a large fraction of parent axons innervating the dental pulp lose their myelin between leaving the TG and entering the dental pulp.…”

3D-Imaging of Whole Neuronal and Vascular Networks of the Human Dental Pulp via CLARITY and Light Sheet Microscopy

“…Studies by Nair et al . 43–45 , using light and electron microscopy showed that healthy human premolars receive an average of 312 (+− 149) myelinated nerve fibers and 2000 non-myelinated axons (range 534–3912) at the juxta-apical pulp. Taken together these numbers are significantly higher than the values found in our work, and a possible explanation is the fact that the CLARITY/Light sheet microscopy method with the PGP9.5 antibody was not always able to distinguish fibers from larger fiber bundles.…”