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The presence of nerves in human tooth pulp has been recognized for over a hundred years, and the innervation of dentine for about 40 years. These observations have been made in permanent teeth. Very few studies have reported on the innervation of the primary pulp and dentine. The purpose of this study was to describe the innervation of the primary tooth pulp-dentine complex. Ten mature primary teeth (one incisor, six canines and three molars) were used. Immediately following extraction they were divided into three sections using a diamond disc and saline coolant. They were then immersion fixed in a solution of formaldehyde and picric acid dissolved in a phosphate buffer pH 7.4). The teeth were then demineralized for 1-3 weeks in formic acid. Following complete demineralization, 30 microns sections were cut on a freezing microtome. Neural tissue was stained using a specific antibody to calcitonin gene related peptide (CGRP). Sections were mounted on glass slides and examined using light microscopy. No individual nerve fibres were seen in the control sections, suggesting that the method used was specific for CGRP-containing nerve fibres. The primary teeth appeared to be well innervated. Myelinated and unmyelinated nerves were seen. There was a dense but variable subodontoblastic plexus of nerves (plexus of Raschkow) and nerve fibres were seen to leave this to travel towards the odontoblast layer. Most terminated here, but a few penetrated the odontoblast layer to enter predentine and the dentine tubules. The maximum penetration was 125 microns but most terminated within 30 microns of the dentinopulpal junction. The coronal region was more densely innervated than the root. Within the crown the cervical third was the most densely innervated region, followed by the pulp horn and the middle third. In conclusion, this study has demonstrated that mature primary tooth contains a pulp which is well innervated and has many nerve endings terminating in or near the odontoblast layer, with a small number penetrating into dentine.

The pulp chambers of 11 freshly extracted human third molars were exposed by cutting off the roots apical to the cervical margin and the pulps were either removed with forceps and discarded or left in situ. The teeth were fixed, demineralized, divided longitudinally, embedded in resin and 2-micron sections stained with toluidine blue were examined by light microscopy. In pulp-removed specimens the percentage retention of the odontoblast layer with the predentine varied near the longitudinal division but when sectioned deeper all six specimens displayed 100% retention. The intactness of the retained odontoblast layer was mostly good as judged by the mutual close apposition of the distal ends of the cell bodies and their relation to the predentine. The retention of the odontoblast layer with the predentine may be due to the distribution of fibronectin, which others have shown is present between odontoblasts, and between odontoblasts and predentine, but lacking beneath the odontoblast layer.

The innervation of pulp and dentine was studied in fully formed human deciduous teeth using antibodies to calcitonin gene related peptide (CGRP). Freshly extracted healthy teeth were divided, fixed, demineralised, cryosectioned and treated with antibodies to human CGRP which was then labelled with horseradish peroxidase. Bundles of nerve fibres passed from the apex of the root to the coronal region where a subodontoblast plexus was formed. In the cervical half of the root some nerve fibres branched away from the main bundles to supply both the odontoblast layer and the dentine. Branches from the coronal subodontoblast plexus also reached the odontoblast layer and the dentine. Most of the nerve fibres terminated in the odontoblast layer. In some areas a marginal plexus of nerves was observed between the odontoblasts and the predentine; intratubular nerve fibres arose either from this plexus or directly from the pulp. The dentine of the crown was more densely innervated than that of the root. In the crown the cervical one third had the most densely innervated dentine followed by the pulp horn and the middle third. The most densely innervated areas occurred in regions where the marginal plexus was present. Although many tubules contained a single nerve filament more complex patterns of termination were also observed. The maximum penetration of a nerve fibre into the dentine was 125 microns. The pattern of the deciduous innervation shows some similarities to the permanent dentition but among the differences is the high density of dentinal innervation in the cervical region. The latter point correlates with the clinical impression of greater sensitivity experienced by patients during invasive procedures performed without anaesthetic in the cervical area.

The pulpal innervation of rabbit premolars and molars has been studied in transverse sections of perfusion-fixed, demineralised specimens using light microscopy and transmission electron microscopy. A mixed population of small myelinated and unmyelinated axons enters the apical foramen to supply the mesial and distal laminae of these continuously growing teeth. The nerve fibres are remote from the preodontoblasts and odontoblasts near the apical end, but in their passage to the occlusal end the pulp becomes progressively narrower and nerve fibres come to lie subjacent to the odontoblasts and postodontoblasts. Counts of myelinated fibres near the apical end and in the occlusal pulp suggested that the myelin is shed near the occlusal end. Most of the dentine in these teeth is tubular and migrates occlusally with supporting odontoblasts. Near the occlusal end, postodontoblasts deposit an atubular tissue which closes the pulpal ends of the tubules. Nearer the occlusal tip the pulpal contents degenerate and become embedded in the forming atubular tissue. Evidence of axon profiles was found near the occlusal end in the pulp, passing through the odontoblast layer and in the dentine tubules adjacent to odontoblast processes. However, many of the tubules contained an odontoblast process only and the atubular tissue was not innervated. Since innervated tubules eventually become closed by atubular tissue it is assumed that the nerve fibres retract from the tubules before their closure. In common with other teeth the function of the pulpal nerve supply is likely to be mostly nociceptive.(ABSTRACT TRUNCATED AT 250 WORDS)

Fluid movement in the pulp depends largely upon the physiology of the blood vessels; normally there is a net efflux of fluid and proteins from the capillaries into the extracellular environment. Most pulp capillaries lie close to the odontoblast layer and in order to see whether fluid can pass between the odontoblasts into the predentin we have perfused the vessels of molar tooth germs in anesthetized piglets with the electron dense tracer lanthanum. The results show that the tracer permeates the capillaries but encounters a barrier to permeability at the apical (predentinal) ends of the odontoblasts. The completeness of the barrier to the tracer lanthanum is discussed together with structural evidence of tight junctions between odontoblasts in both pigs and humans and the presence of collagen fibers through the tight junctional zone. It is concluded that there is little or no evidence that pulp fluid is normally confluent with predentin. An advantage of this arrangement may be that by maintaining an enclosed microenvironment it permits regulation of the orderly process of matrix deposition and mineralization of predentin to dentin. In order to maintain constant vascular and extracellular fluid pressures the capillary efflux has to be balanced by fluid removal; recent work in cats has shown that lymphatic vessels are available to transport fluid out of the pulp. In this paper the differences in the intrapulpal distribution of these vessels have been extrapolated to human teeth in an attempt to explain certain variations in the symptoms and progress of pulpal inflammatory conditions.

The collagenous fibers of von Korff pass from the dentin matrix between the odontoblasts into the dental pulp. Although collagen fibrils are known to be present between odontoblasts, the existence of von Korff fibers has remained controversial. This may be because their continuity between the dentin matrix and the pulp has not been demonstrated ultrastructurally. In this study we have examined the odontoblast layer in the middle to apical regions of perfusion-fixed permanent canine teeth of cats by using transmission electron microscopy. Ultrathin sections of demineralized specimens revealed frequent bundles of collagen fibrils 1) entering the odontoblast layer from the predentin, 2) present between odontoblast cell bodies, and 3) passing from between the odontoblasts into the pulp. The question of continuity of these bundles from the predentin, across the odontoblast layer into the pulp was examined in ultrathin serial sections. Unbroken continuity of a collagen bundle from the predentin between the odontoblasts into the pulp was established in a reconstruction of one series of 22 serial sections and was very strongly suggested by a number of other series in which the numbers of available sections restricted their full visibility. This investigation has shown, therefore, that classical von Korff fibers are present and that these fibers are present in fully erupted teeth with closed apices, i.e., at a time when secondary circumpulpal dentinogenesis is in progress. The findings call for a reexamination of the question of von Korff fibers during mantle dentinogenesis and primary circumpulpal dentinogenesis. Resolution of their existence at the earlier stages of dentinogenesis should be possible by using the ultrathin serial-sectioning technique.