Innervation of human periodontium I. Classification of periodontal receptors

A bstract — The neural tissue in human periodontium is associated with the terminal part of a norve trunk from which myelinated nerve fibres leave and in some instances divide into three or more nerve fibres.
Encapsulated myelinated nerve fibres lose their myelin sheaths and encircle the adjacent myelinated nerve fibres to form compound meehanoreceptors approximately 35 × 45 μm. Simple mechanoreceptors of approximately 10 × 10 μm consisted of single myelinated nerve fibres surrounded by cell bodies and terminated as encapsulated unmyelinated nerve fibres. A cluster of compound mechanoreceptors formed a complex approximately 100times 150 μm.
An arterial system appeared to supply nutrition for the compound receptors, whilst an arcade of veins surrounded the neural complex.     

Ultrastructure and degeneration analysis of the nerve fibres of the tooth pulp in the cat

An attempt was made to distinguish somatic sensory nerve fibres from autonomic postganglionic sympathetic nerves in tooth pulp by secondary degeneration. Pulps were compared after transection of the inferior alveolar nerve, after extirpation of the superior cervical sympathetic ganglion and after both operations performed at the same time (total neural isolation). About 15 per cent of the nerves in normal feline pulps were myelinated and about 85 per cent unmyelinated. Only 1.5 per cent contained granular vesicles 30–50 nm or 80–120 nm in diameter. After transection of the alveolar nerve, all myelinated as well as some unmyelinated fibres degenerated. Degenerated fibres contained no vesicles. After extirpation of the ganglion, only a few degenerating unmyelinated fibres were observed; some contained 80–100 nm diameter granular vesicles. Two months after total neural isolation, the pulp contained no nerve fibres.     

Quantitation of nerve fibres in the primary and permanent canine and incisor teeth in man.

Myelinated and unmyelinated nerve fibres were counted and myelinated axons were measured in juxta-apical cross-sections of human primary and permanent canines and incisors. Fully-developed human primary canines had significantly more myelinated axons than permanent canines, but the number of unmyelinated axons was similar. Permanent incisors had significantly more myelinated nerve fibres entering the apex than did primary incisors, but the number of unmyelinated nerve fibres was similar. Primary canines and incisors lost nerve fibres early during resorption; evidence of degenerating myelinated axons was scant. A significant linear correlation existed between numbers of myelinated and unmyelinated axons for primary incisors and canines. The myelinated axon circumference was similar for primary and permanent teeth. Permanent teeth tended to have smaller groups of unmyelinated axons.     

Enzyme-histochemical and morphological characteristics of muscle fibre types in the human buccinator and orbicularis oris

Human masticatory muscles, originating from the first branchial arch and innervated by the trigeminal nerve, have a fibre composition distinct from that of limb and trunk muscles. The zygomatic muscles, originating from the second branchial arch and innervated by the facial nerve, differ in fibre composition from either the masticatory or the limb and trunk muscles. To elucidate further the structural basis for function, and the influence of embryological origin and innervation on oro-facial muscles, the buccinator and orbicularis oris muscles, which originate from the second branchial arch and are innervated by the facial nerve, were investigated. Like the masticatory and zygomatic muscles, they have a large representation in the cerebral cortex. Both muscles were composed of type I, type IIA and a few type IIC fibres of about equal diameter. However, the type I fibres had a different myofibrillar ATPase reaction from those in masticatory, zygomatic, limb and trunk muscles; this was a moderate to strong staining at pH 9.4, indicating a special isomyosin composition. Whereas the buccinator was composed of 53% type I fibres, the orbicularis oris had a 71% predominance of type II fibres. In both muscles, the mean fibre diameter and its marked intramuscular variability were similar to earlier findings in the zygomatic muscles. No muscle spindles were found. The large number of type I fibres in the buccinator implies a capacity for endurance during continuous work at relatively low levels of force. The predominance of type II fibres in the orbicularis oris indicates that it is built up of fast-twitch motor units, related to properties such as rapid acceleration and high speed during intermittent oro-facial movements. The similarities and differences in fibre-type composition between the facial, masticatory and limb muscles imply that specific functional demands are of greater importance for muscle differentiation than embryological origin and nerve supply.     

On the pulpal nerve supply in primary human teeth: evidence for the innervation of primary dentine*

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 μm 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 μm but most terminated within 30 μm 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.     

Neurolytic effects of ampicillin on the rat infraorbital nerve

J Oral Pathol Med (2012) 41 : 268–271 Purpose: The aim of this study was to investigate the histomorphological changes of the infraorbital nerve of rats treated with ampicillin. Materials and Methods: The infraorbital nerve was approached through the infraorbital foramen, and 0.01 ml of ampicillin dissolved in distilled water was injected taking care not to damage the nerve. Saline solution was used in control animals. Nerves were dissected and after routine histology processing analysed by light microscopy. Results: Cross‐section of the nerve treated with ampicillin showed damaged axons with disintegration of heavily myelinated fibres, while thinly myelinated fibres remain unaffected. In the saline group, no damage was observed. The signs of regeneration of the damaged infraorbital nerves were detected on the fourth post‐operative week. Conclusion: Ampicillin can cause peripheral nerve damage when injected perineurally.     

Ultrastructural characteristics of axons in traumatic neuromas of the human lingual nerve

AIMS: To determine the ultrastructural characteristics of axons in traumatic neuromas of the human lingual nerve during the surgical removal of lower third molar teeth and to establish whether any characteristics were different between patients with dysesthesia and patients without dysesthesia. METHODS: Transmission electron microscopy was used to determine the ultrastructural morphological characteristics of human lingual nerve neuromas (n = 34) removed at the time of microsurgical nerve repair. From a sample population of myelinated and nonmyelinated fibers within the neuromas, fiber diameter, myelin thickness, g-ratio, and the number of mitochondria per axon were quantified. Comparisons were made with normal control lingual nerve specimens (n = 8) removed at the time of organ donor retrieval. RESULTS: Significant differences in ultrastructural morphology were found between the neuromas and control nerves. The neuromas contained a higher proportion of small (2- to 8-microm diameter) myelinated nerve fibers than controls, and the mean myelinated fiber diameter was significantly lower in neuromas than in controls. Mean myelin sheath thickness was significantly thinner in neuromas (0.6 +/- 0.1 microm) than in controls. However, the g-ratio, which is a measure of the myelination status of the nerve fibers in relation to their diameter, was found to be similar in each group, suggesting a normal process of myelination in the damaged axons. Nonmyelinated axon diameter was also significantly smaller in the neuromas than in the controls, and Schwann cells were found to sheathe more nonmyelinated axons in neuromas than in controls. The ratio of nonmyelinated to myelinated axons was significantly higher in neuromas than in controls. However, no significant differences were found between patients with dysesthesia and those without dysesthesia. CONCLUSION: Damage to the lingual nerve results in marked changes to axon diameter, myelin sheath thickness, and Schwann cell-axon relationships. These ultrastructural changes could contribute to the altered electrophysiological properties of axons trapped within neuromas. However, no significant differences in the ultrastructural characteristics studied were found between specimens from patients with or without symptoms of dysesthesia.     

The use of undifferentiated bone marrow stromal cells for sciatic nerve regeneration in rats

In recent years, cell transplantation has become a focus of attention and reliable outcomes have been achieved in regeneration of the sciatic nerve. The effect of undifferentiated bone marrow stromal cells (BMSCs) on peripheral nerve regeneration was studied using a rat sciatic nerve regeneration model. A 10-mm sciatic nerve defect was bridged using an inside-out vein graft (IOVG) filled with undifferentiated BMSCs (2 × 10(7)cells/ml). In the control group, the vein was filled with phosphate buffer saline alone. The regenerated fibres were studied 4, 8 and 12 weeks after surgery. Assessment of nerve regeneration was based on functional (walking track analysis), histomorphometric and immunohistochemical (Schwann cell detection by S100 expression) criteria. The functional study confirmed significant recovery of regenerated axons in the IOVG/BMSC group (P<0.05). Quantitative morphometric analyses of regenerated fibres showed the number and diameter of myelinated fibres in the IOVG/BMSC group were significantly higher than in the control group (P<0.05). This demonstrates the potential for using undifferentiated BMSCs in peripheral nerve regeneration without the limitations of donor-site morbidity associated with isolation of Schwann cells. It also reduces costs because the interval between tissue collection and cell injection is reduced and the laboratory procedures are simpler compared to undifferentiated BMSCs.     

Enzyme-histochemical differences in fibre-type between the human major and minor zygomatic and the first dorsal interosseus muscles

Human masticatory muscles, innervated by the trigeminal nerve, differ in fibre-type composition from limb and trunk muscles, but the anterior and the posterior belly of the human digastric muscle, innervated by the trigeminal and facial nerves, respectively, do not. The major and minor zygomatic muscles from adult males, which originate from the second branchial arch and are supplied by the facial nerve, were analysed enzyme-histochemically and compared with the first dorsal interosseus hand muscle, which has spinal innervation and, like the masticatory and facial muscles, a large cortical representation. Both zygomatic muscles had a marked predominance of type II fibres, the minor one having the largest proportion (89.1 per cent) ever reported in human skeletal muscle. Besides type I, IIA, IIB, and a few type IIC fibres, there was a large group with an ATPase reaction at pH 4.6, between that of type IIA and type IIB, and termed IIAB. This fibre-type profile may reflect a special isomyosin composition. Type I and II fibres were of about equal diameter, corresponding to that of type I fibres in the masticatory muscles. Individual and intra-muscular variability in fibre size and shape was considerable. The unusually high frequency of type II fibres in the zygomatic muscles suggest that they have fast-contraction properties and relatively large motor units, and therefore are poorly adapted to finely-graded movements. The absence of muscle spindles supports this view. The hand muscle had a chequer-board pattern of type I, IIA and IIB fibres, similar to that of large limb and trunk muscles, with no difference between its two heads.(ABSTRACT TRUNCATED AT 250 WORDS)     

Scanning electron microscopy of organic structures on the root surface of human teeth

abstract – The surface morphology of fibers, vessels, nerves and cells located on the surface of 29 human teeth was studied in the scanning electron microscope. The length of the torn principal fibers was about 250 μm. They tapered with the widest diameter near the cementum. The principal fiber bundles were composed of smaller elements with a diameter of 4–5 μm which were composed of fibrils with a diameter up to about 5,000 Å. Adjacent to the cementum the principal fiber bundles interlaced with thin fibrous elements, and thus a fibrous coating covered the root surface. The size of the interlacing fibrils varied, and those with a diameter of 500 Å exhibited a cross-striation with a periodicity of 600 Å. The surface of the vessels had a dense appearance. Nerve fibers and nerve endings were observed. In one case there was a peculiar branching of structural elements that could be identified as nerve tissue. Cell cultures of chicken fibroblasts were studied for comparison with cells from the root surface with regard to shape and size. Both had a rough surface, a central nuclear region and long, fairly straight celltails.     

Uncultured undifferentiated adipose-derived nucleated cell fractions combined with inside-out artery graft accelerate sciatic nerve regeneration and functional recovery

Effects of transplantation of adipose-derived nucleated cell fractions (ADNCs) on sciatic nerve regeneration were studied. A 10-mm sciatic nerve defect was bridged using artery graft filled with ADNCs. In control group, artery graft was filled with saline alone. Regenerated nerve fibres were studied for 12 weeks. In sham-operated group, sciatic nerve was only exposed and manipulated. Behavioural and functional studies confirmed faster recovery of regenerated axons in ADNCs transplanted animals than in control group (P < 0.05). At the end of study period, animals in ADNCs transplanted group achieved a sciatic functional index (SFI) value of −31.6 ± −3.14, whereas in control group a value of −42.5 ± −3.7 was found. Gastrocnemius muscle mass in ADNCs transplanted animals was found to be significantly higher than that in control group (P = 0.001). Morphometric indices of regenerated fibres showed the number and diameter of myelinated fibres to be significantly higher in ADNCs transplanted animals than in control group (P = 0.001). On immunohistochemistry, there was more positive staining of S100 in the ADNCs transplanted animals than in control group. ADNCs transplantation into an artery graft could be considered a readily accessible technique that improves functional recovery of sciatic nerve.     

Peripheral nerve regeneration using a three dimensionally cultured schwann cell conduit

The use of artificial nerve conduit containing viable Schwann cells is one of the most promising strategies to repair peripheral nerve injury. To fabricate an effective nerve conduit whose microstructure and internal environment are more favorable in nerve regeneration than those currently existing, a new three-dimensional (3D) Schwann cell culture technique using Matrigel and dorsal root ganglion (DRG) was developed.Nerve conduit of 3D arranged Schwann cells was fabricated using direct seeding of freshly harvested DRG into Matrigel-filled silicone tubes (inner diameter 1.98 mm, 14 mm length) and in vitro rafting culture for 2 weeks. The nerve regeneration efficacy of 3D cultured Schwann cell conduit (3D conduit group, n = 6) was assessed using an Sprague-Dawley rat sciatic nerve defect of 10 mm and compared with that of a silicone conduit filled with Matrigel and Schwann cells prepared with the conventional plain culture method (two-dimensional [2D] conduit group, n = 6). After 12 weeks, sciatic function was evaluated with sciatic function index (SFI) and gait analysis, and histomorphology of nerve conduit and the innervated tissues of sciatic nerve were examined using image analyzer and electromicroscopic methods.The SFI and ankle stance angle in the functional evaluation were -60.1 +/- 13.9, 37.9 degrees +/- 5.4 degrees in the 3D conduit group (n = 5) and -87.0 +/- 12.9, 32.2 degrees +/- 4.8 degrees in the 2D conduit group (n = 4). The myelinated axon was 44.91% +/- 0.13% in the 3D conduit group and 13.05% +/- 1.95% in the 2D conduit group. In the transmission electron microscope study, the 3D conduit group showed more abundant myelinated nerve fibers with well-organized and thickened extracellular collagen than the 2D conduit group, and the gastrocnemius muscle and biceps femoris tendon in the 3D conduit group were less atrophied and showed decreased fibrosis with less fatty infiltration than the 2D conduit group. A new 3D Schwann cell culture technique was established, and nerve conduit fabricated using this technique showed much improved nerve regeneration capacity than the silicone tube filled with Matrigel and Schwann cells prepared from the conventional plain culture method.     

Innervation of the human periodontium. IV. Fine structure of the complex mechanoreceptors and free nerve endings

A bstract — The complex consists of encapsulated nerve fibres and end rings, exposed and lacunar endings, and a metarteriole. The myelinated nerve fibre and metarteriole are closely associated in the capsule.     

The epithelial proprial relations of Meissner''s corpuscles in buccal mucosa. An electron microscopic study

A bstract — Meissner's corpuscles were seen in specimens obtained from the buccal mucosa of three patients. The corpuscles arose mainly from myelinated nerve fibres although some unmyelinated fibres were involved. The myelin sheath terminated where the fibres entered the capsules. Axons were invested by lamella cell processes and terminated digitately in desmosome-like contacts with one another and the basal lamina of the basal epithelial cells. The corpuscles were encapsulated by collagen fibres and the cell processes of fibroblasts.     

Innervation of the Human Periodontium II. Fine Structure of Simple Mechanoreceptors

A bstract — The fine structure of myelinated nerve fibres and of the proximal, central and distal portions of the simple mechanoreceptors are described and discussed.     

Large melanosome complexes in the human gingival epithelium

The morphology of melanosome complexes (MC) in gingival epithelium from smokers and non-smokers was studied by electron microscopy. The cross-cut diameter was measured on 770 complexes within keratinocytes. In pigmented smokers and non-smokers the average diameter was between 0.51 and 0.63 μm, which is larger than those observed in clinically non-pigmented non-smokers and compared to those previously reported from clinically non-pigmented Caucasians. The diameter of 95% of all complexes was less than 1.0 μm, but 40 large melanosome complexes (LMC) were also found. LMC could reach a diameter of 3.2 μm, and contain more than 100 melanin granules. The presence of LMC in oral mucosa has not been reported previously, but they have been observed in pigmented human skin disorders. Our finding of LMC in the gingival epithelium of pigmented individuals among smokers and non-smokers, but not in non-pigmented non-smokers, indicate that this entity is related to melanosome packaging in situations of high melanin production and not necessarily only to pathological conditions.     

Effect of particle diameter on air polishing of dentin surfaces

We examined the abrasiveness of glycine powders with particle diameters of 63 and 100 μm by measuring the depth and volume of defects produced during air polishing of human dentin. A total of 36 extracted human teeth were embedded in acrylic resin. The resin blocks were polished until the dentin surfaces were exposed. The nozzle of an air polisher was mounted 4 mm from the dentin surface, and the dentin surface was treated for 5 s at one of two angles of incidence (45° or 90°). Three materials were used in the polishing process: NaHCO₃ powder with a mean particle diameter of 100 μm (Handy Jet Powder), glycine powder with a mean particle diameter of 63 μm (Handy Jet Powder PMTC), and glycine powder with a mean particle diameter of 100 μm (Handy Jet Powder Recall). The defect depth at both angles was significantly deeper after treatment with Handy Jet Powder or Handy Jet Powder PMTC. The defect volume was the greatest with Handy Jet Powder, followed by Handy Jet Powder PMTC, and Handy Jet Powder Recall. The larger diameter glycine powder resulted in less damage to the dentin.     

Morphometric analysis of sural nerve in elderly diabetes mellitus

Biopsy specimens of the sural nerve obtained from 28 middle-aged and elderly diabetics suffering from neuropathy were studied morphometrically. Myelinated nerve fiber density, especially large fibers, was decreased, and the bimodal distribution of myelinated fiber diameter shifted to unimodal distribution containing only a small fiber peak and the mean diameter of myelinated fiber was decreased. An insulin-treated group and a group with severe retinopathy showed a prominent decrease of myelinated fiber density; the severity and duration of diabetes may be a factor in this decrease. Large unmyelinated nerve fibers were also decreased and the mean diameter of unmyelinated fibers was reduced. Three patients with prominent autonomic nervous system symptoms showed a significant reduction of total unmyelinated fibers. The linear correlation between the square root of the transverse axis cylinder area and the number of myelin lamellae was obscured, and the plots were towards two directions, axonal atrophy and remyelination in diabetes. The latter process tended to be dominant in the middle-aged patients, but the importance of these two processes was reversed with age. To discuss the morphological changes of the sural nerve in diabetic neuropathy, the influence of aging as well as the duration, severity and clinical symptoms should be considered.     

The presence of nerve fibres in the coronal odontoblast layer of teeth at various stages of root development

Summary. Many studies have investigated the presence of nerve fibres in the coronal odontoblast layer of mature teeth. However, little information is available on the presence of these structures in immature human teeth. The pulps of 18 human maxillary and mandibular third molars at various stages of development were collected, sectioned, and stained by the immunoperoxidase technique. The results showed the presence of numerous myelinated nerve fibres in the coronal odontoblast layer of teeth with fully formed roots. Similar observations were made in teeth with half formed roots, and in those without roots. On the basis of these results, it appears that a lack of response to vitality tests in teeth with incompletely formed roots is not wholly due to the absence of nerve fibres in the coronal odontoblast layer.