Neuropeptide expression and morphometric differences in crushed alveolar inferior nerve of rats: Effects of photobiomodulation.

Inferior alveolar nerve (IAN) injuries may occur during various dental routine procedures, especially in the removal of impacted lower third molars, and nerve recovery in these cases is a great challenge in dentistry. Here, the IAN crush injury model was used to assess the efficacy of photobiomodulation (PBM) in the recovery of the IAN in rats following crushing injury (a partial lesion). Rats were divided into four experimental groups: without any procedure, IAN crush injury, and IAN crush injury with PBM and sham group with PBM. Treatment was started 2 days after surgery, above the site of injury, and was performed every other day, totaling 10 sessions. Rats were irradiated with GaAs Laser (Gallium Arsenide, Laserpulse, Ibramed Brazil) emitting a wavelength of 904 nm, an output power of 70 mWpk, beam spot size at target ∼0.1 cm2, a frequency of 9500 Hz, a pulse time 60 ns, and an energy density of 6 J/cm2. Nerve recovery was investigated by measuring the morphometric data of the IAN using TEM and by the expression of laminin, neurofilaments (NFs), and myelin protein zero (MPZ) using Western blot analysis. We found that IAN-injured rats which received PBM had a significant improvement of IAN morphometry when compared to IAN-injured rats without PBM. In parallel, all MPZ, laminin, and NFs exhibited a decrease after PBM. The results of this study indicate that the correlation between the peripheral nerve ultrastructure and the associated protein expression shows the beneficial effects of PBM.

Microstructural and ultrastructural assessment of inferior alveolar nerve damage following nerve lateralization and implant placement: an experimental study in rabbits.

PURPOSE: The present study assessed damage to the inferior alveolar nerve (IAN) following nerve lateralization and implant placement surgery through optical and transmission electron microscopy (TEM). MATERIALS AND METHODS: IAN lateralization was performed in 16 adult female rabbits (Oryctolagus cuniculus). During the nerve lateralization procedure, one implant was placed through the mandibular canal, and the IAN was replaced in direct contact with the implant. The implant was placed in the right mandible, and the left side was used as a control (no surgical procedure). After 8 weeks, the animals were sacrificed and samples were prepared for optical and TEM analysis of IAN structural damage. Histomorphometric analysis was performed to determine the number and cross-sectional dimensions of nerve fascicles and myelin sheath thickness between experimental and control groups. The different parameters were compared by one-way analysis of variance at the 95% significance level. RESULTS: Alterations in the perineural and endoneural regions of the IAN, with higher degrees of vascularization, were observed in the experimental group. TEM showed that the majority of the myelinated nerve fibers were not affected in the experimental samples. No significant variation in the number of fascicles was observed, significantly larger fascicle height and width were observed in the control group, and significantly thicker myelin sheaths were observed in the experimental samples. CONCLUSION: IAN lateralization resulted in substantial degrees of tissue disorganization at the microstructural level because of the presence of edema. However, at the ultrastructural level, small amounts of fiber degeneration were observed.

Dynorphin-A immunoreactive terminals on the neuronal somata of rat mesencephalic trigeminal nucleus.

Dynorphin-A-like immunoreactivity was investigated in the rat mesencephalic trigeminal nucleus (Mes 5) at the light and electron microscopic levels. Dynorphin-A immunoreactive fibers and puncta, likely representing nerve terminals, were observed throughout rostrocaudal extension of the Mes 5 at the light microscopic level. Within the rostrocaudal extension, more abundant fibers and puncta were localized in the midbrain-pontine junction and pontine areas than in the midbrain area. At the electron microscopic level, dynorphin-A immunoreactive synapses were observed on the somata of Mes 5. Dynorphin-A-like immunoreactivity tended to be restricted to dense-cored vesicles in the synapses. These results suggest that dynorphin-A-containing fiber systems affect mastication through the Mes 5.

Synaptic contacts established by inferior alveolar nerve fibres in the paratrigeminal nucleus: an electron microscopic study in the rat.

A quantitative evaluation of the types of synaptic contacts from afferent fibres in the paratrigeminal nucleus after partial pulpectomy was compared with that after transection of the inferior alveolar nerve (IAN), using transganglionic degeneration. Degenerating terminals with a marked increase in axoplasmic electron opacity were observed bilaterally in the paratrigeminal nucleus of rats submitted to either partial pulpectomy or IAN transection. The total number of degenerating terminals observed after partial pulpectomy was 53% of that for IAN transection. This suggests a considerable contribution of tooth pulp afferent fibres in the total number of synaptic contacts in the intermediate and caudal parts of the paratrigeminal nucleus. In both the partial pulpectomy and IAN-transected groups, the majority of these synapses formed single asymmetric contacts with intermediate and distal dendritic segments, and accounted for 74% of all classified contacts. The remaining 26% of contacts occurred with proximal dendritic segments, dendritic spines, perikaryon, normal terminals and double post-synaptic elements. There was no statistically significant difference in the number of synaptic contacts for each type of synapse, with the exception of contacts with dendritic spines in the contralateral side, between the partially pulpectomised and IAN-transected groups.

Mesenchymal stem cells modified with nerve growth factor improve recovery of the inferior alveolar nerve after mandibular distraction osteogenesis in rabbits.

Distraction osteogenesis is widely used in the treatment of bony deformities and defects. However, injury to the inferior alveolar nerve is a concern. Our aim was to investigate the feasibility of using lentiviral-mediated human nerve growth factor beta (hNGFß) of the inferior alveolar nerve in mandibular distraction osteogenesis in rabbits. To achieve this, mesenchymal stem cells (MSC) from the bone marrow of rabbit mandibles were isolated and genetically engineered using recombinant lentiviral vector containing hNGFß. Twenty New Zealand white rabbits underwent mandibular distraction osteogenesis, and 5 million MSC transduced with hNGFß-vector or control vector were transplanted around the nerve in the gap where the bone had been fractured during the operation (n=10 in each group). After gradual distraction, samples of the nerve were harvested for histological and histomorphometric analysis. We found that the genetically engineered MSC transduced by the lentiviral vector were able to secrete hNGFß at physiologically relevant concentrations as measured by ELISA. Histological examination of the nerve showed more regenerating nerve fibres and less myelin debris in the group in which hNGFß-modified MSC had been implanted than in the control group. Histomorphometric analysis of the nerve showed increased density of myelinated fibres in the group in which hNGFß-modified MSC had been implanted than in the control group. The data suggest that implantation of hNGFß-modified MSC can accelerate the morphological recovery of the inferior alveolar nerve during mandibular distraction osteogenesis in rabbits. The use of lentiviral-mediated gene treatment to deliver hNGFß through MSC may be a promising way of minimising injury to the nerve.

Immunoelectron microscopic study on neuropeptide Y in the periodontal ligament of the incisor following peripheral nerve injury to the inferior alveolar nerve in the rat.

Immunoelectron microscopic analysis was carried out to examine whether neuropeptide Y (NPY)-like immunoreactivity (-LI) is localized in mechanoreceptors in the lingual periodontal ligament of the rat incisor following peripheral nerve injury to the inferior alveolar nerve (IAN). In the lingual periodontal ligament of normal animals, no NPY-like immunoreactive (-IR) primary afferents were observed, except for a very few sympathetic perivascular nerve fibers which showed NPY-LI. Fourteen days following chronic constriction injury to the IAN combined with sympathectomy of the superior cervical ganglion, thick NPY-IR nerve fibers showing tree-like raminifications were detected in the shear zone between the tooth-related part and alveolus-related part as well as in the alveolus-related part. Immunoelectron microscopy revealed that expanded NPY-IR nerve terminals were covered with several Schwann sheaths and that a part of the axoplasm expanded to the surrounding tissues. These ultrastructural features of NPY-IR structures were identical to those of periodontal Ruffini endings, categorized as slowly adapting mechanoreceptors. Thick (6-8 microns in diameter) NPY-IR axons were also observed without any apparent myelin sheath. The present results provide further evidence that NPY is closely associated with thick axons, probably myelinated nerves and Ruffini endings, following peripheral nerve injury.

Effects of peripheral axotomy of the inferior alveolar nerve on the levels of neuropeptide Y in rat trigeminal primary afferent neurons.

The effects of peripheral axotomy of the inferior alveolar nerve (IAN) on the presence and distribution of neuropeptide Y (NPY)-like immunoreactivity (IR) in the trigeminal sensory nuclear complex (TSNC) and trigeminal ganglion were investigated in the rat by immunohistochemistry. In the normal trigeminal ganglion, there were no NPY-IR cells, and some perivascular nerve fibres exhibited NPY-IR. In normal TSNC, many NPY-IR axons and nerve terminals were observed in the superficial layers of the subnucleus caudalis (SpVc) and paratrigeminal nucleus (paraV), but were sparse in the other subnuclei of the TSNC. Fourteen days following peripheral axotomy of the IAN, many large- and medium-sized cells in the trigeminal ganglion displayed NPY-IR, and marked increases in the numbers and staining densities of NPY-IR were observed in deeper laminae (laminae III-V) of the dorso-medial region of the SpVc and other nuclei, in addition to the dorso-medial region of the spinal trigeminal tract. Degrees of alterations of the levels of NPY were most marked in the SpVc. The present results indicate that peripheral axotomy of the IAN evokes the appearance of NPY-IR in the trigeminal ganglion and alterations of NPY-IR in the entire IAN projection areas of the TSNC.

Graphic digitizer analysis of the myelinated axon spectrum in the inferior alveolar nerve of the cat.

The diameter spectrum and other parameters indicating size and shape of myelinated axons were established in a cross-section of the inferior alveolar nerve obtained at the mandibular foramen. The spectrum is bimodal with approximately equal numbers of axons in the Aalpha and Adelta-range, in contrast to unimodal spectra of certain branches contributing to the inferior alveolar nerve.

Coexpression of vasoactive intestinal polypeptide and substance P in reinnervating pulpal nerves and in trigeminal ganglion neurones after axotomy of the inferior alveolar nerve in the rat.

The effect of this axotomy on the expression of vasoactive intestinal polypeptide (VIP) in trigeminal ganglion neurones and nerve fibres in the first molar was examined immunohistochemically 3 weeks postsurgically in rats. A distinct upregulation of VIP-like immunoreactivity was found in 3 to 4% of the neurones (mean dia., 20.9 +/- 0.45 microns; mean cross-sectional area, 367 +/- 13.2 microns 2) in the mandibular region after axotomy. An almost complete coexpression was registered in neurones upregulated for VIP and growth-associated protein 43. Coexpression of VIP and substance P (SP) was found in a small number of the immunoreactive (IR) small-sized neurones, mainly in those in which VIP and SP were both weakly immunoreactive. In the uninjured ganglion, weakly labelled VIP-positive granules were frequently traced at high magnification in the cytoplasm of small neurones. No VIP-IR fibres were found in the control molar pulp, except for a few in the root pulp near the apex. However, 3 weeks after axotomy, a number of VIP-containing nerve fibres were found in the molar pulp and apical periodontium. Coarse VIP-IR fibres directed towards the odontoblast layer were a common finding. In some of these fibres VIP was shown to colocalize with SP. These results indicate that VIP is clearly expressed and transported in regenerating primary afferent neurones after axotomy of the inferior alveolar nerve.

Histomorphometric results after late microsurgical nerve grafting of the inferior alveolar nerve of the rabbit.

An experimental study was conducted to evaluate the regenerative potential of the inferior alveolar nerve after nerve transection and microsurgical reconstruction at different intervals. Histomorphometric parameters of regenerating axons were assessed using a computer-assisted image analysis system. A continuous decrease in axon density and a reduction in axon diameter was noted in all groups. The average regeneration rate ranged from 42% to 60%. The results of this study indicate that microsurgical reconstruction of the inferior alveolar nerve is even possible 12 months after nerve transection.

Expanded polytetrafluoroethylene entubulation of the rabbit inferior alveolar nerve.

OBJECTIVE: The purpose of this study was to evaluate the use of an expanded polytetrafluoroethylene conduit in the treatment of a 6. 0-mm gap in the rabbit inferior alveolar nerve and compare the results with those of an autogenous interpositional tibial nerve graft. STUDY DESIGN: The inferior alveolar nerves of 5 adult New Zealand White female rabbits (10 nerves) were exposed bilaterally, and a 6-mm segment of each nerve was resected. On one side, chosen at random, the gap was immediately bridged through use of an 8.0 x 2. 0-mm expanded polytetrafluoroethylene conduit; on the other side, the gap was grafted with an autogenous tibial nerve graft. Two randomly selected nerves served as sham-dissected controls. At 15 weeks after surgery, the animals were killed and the entire nerve segments were harvested and prepared according to standard fixation and embedding techniques. The sections were examined histomorphometrically to quantify the degree of axonal regeneration through definition of fascicular number, total fascicular surface area, axonal density, and mean axonal diameter at 3 locations along the repair site. RESULTS: Light microscopic examination revealed the presence of disorganized neural tissue in both groups, with slightly more fibrovascular interfascicular tissue in the expanded polytetrafluoroethylene group. Histomorphometric analysis revealed no significant differences between groups for most of the measured variables. The mean axonal diameter varied between groups, and the fascicular number was greater in the expanded polytetrafluoroethylene group at the middle site. CONCLUSIONS: This study demonstrates that regeneration of the inferior alveolar nerve can occur across a 6.0-mm gap through an expanded polytetrafluoroethylene tube with results comparable to those of an autogenous nerve graft, significant donor site morbidity being avoided. The significant differences between groups were probably due to greater containment of regenerating axonal fibers in the expanded polytetrafluoroethylene group.

Revisión bibliográfica de la anatomía del nervio dentario inferior y su implicancia en la cirugía implantológica de los sectores posteriores mandibulares / A review of the literature on inferior alveolar nerve anatomy and its involvement with implant surgery of the posterior mandibular sectors

El nervio dentario inferior es una de las estructuras anatómicas más importantes a considerar previo a la colocación de implantes dentales en la mandíbula. La lesión de este nervio es una situación temida por los pacientes y los profesionales por la posibilidad de daño permanente en su conducción nerviosa. Es fundamental para todos los odontólogos que realicen maniobras quirúrgicas próximas a la entidad nerviosa, conocer ampliamente su recorrido, distribución y características normales, para prevenir la injuria del mismo y sus indeseables consecuencias. El objetivo de esta publicación es brindar información actualizada del conocimiento del nervio dentario inferior y su relación con la implantología oral...

Evaluación de la anatomía mandibular relacionada con la osteotomía sagital de la rama / Evaluation of mandibular anatomy related to sagittal split ramus osteotomy

La osteotomía sagital de la rama mandibular (SSRO) es una de las técnicas quirúrgicas más frecuentes para corregir las deformidades de la mandíbula. Con el fin de prevenir problemas anatómicos y quirúrgicos, los cirujanos requieren una mayor investigación sobre las estructuras anatómicas relacionadas con la SSRO. El objetivo de este estudio fue investigar las posiciones de la antilingula (AL), la entrada al nervio alveolar inferior (NAI) en la mandíbula y otros puntos de referencia anatómicos en relación con la língula mandibular (L). Fueron estudiadas 70 hemimandíbulas secas. La AL y los demás puntos de referencia y, la posición correspondiente de la L se marcaron en la cara medial y lateral de la rama mandibular respectivamente. Fueron medidas las distancias de la AL, NAI y L en los planos anterior-posterior y superior-inferior con un caliper, y se estableció su relación geométrica. Los resultados mostraron que la AL era perceptible en el 100 por ciento de las caras laterales mandibulares. La mayoría de las ALs se encuentran anterior a la L, con una distancia media de 0,66+/-2,43mm y 0,92+/-2,56 mm y, 4,23+/-2,97 mm y 3,62 +/- 3,14 mm superior a ella (lados derecho-izquierdo respectivamente) (ambos con un valor de p <0,001). Valores similares se observaron en relación con el NAI. No se encontraron diferencias significativas entre los lados derecho e izquierdo, para la mayoría de los parámetros. Los parámetros estudiados pueden asistir a los cirujanos maxilofaciales a determinar la proximidad anatómica del NAI, y reducir al mínimo el riesgo de dañar el nervio y vasos sanguíneos. No recomendamos el uso de la AL como única referencia anatómica cuando se realiza un procedimiento de SSRO.

Sagittal split ramus osteotomy (SSRO) of the mandible is one of the most common surgical techniques to correct mandibular deformities. In order to prevent many surgical anatomical problems, surgeons have found that further investigation of the anatomical structures related to SSRO is needed. This study aims to investigate positions of the antilingula (AL), inferior alveolar nerve (IAN) and other anatomic landmarks in relation to the lingula of dried mandibles. 70 Chilean dried hemimandibles were studied. The AL, others landmarks and the corresponding position of the L were marked on the internal and external aspect of the mandibular ramus respectively. The distances from the AL, IAN and L were measured in the anterior­posterior and the superior­inferior planes using a digital caliper and geometric relationship was established. The results showed the AL was discernible in 100 percent of lateral mandibular rami studied. The most of the AL was found anteriorly to the L with a mean distance of 0.66+/-2.43mm and 0.92+/-2.56mm, and 4.23 +/- 2.97mm and 3.62+/-3.14mm superiorly (right-left sides respectively) (both with p value <0.001). Similar values were seen in relation with IAN. No significant differences were found between the right and left sides, for the majority of parameters. The studied parameters will assist clinicians to determine the anatomical proximity to the IAN, and, minimize the risk of damaging nerver and vessels. We do not recommend the use of antilingula as only anatomical landmark when performing a SSRO procedure.

Electron microscopy of pterygopalatine ganglion in starved rats.

The ultrastructure of rat's pterygopalatine ganglionic neurocytes after starvation was investigated. The following changes of cell organelles were observed. The mitochondria display altered internal structures--lack of matrix, swellings, and myelin structures. Rough endoplasmic reticulum and free ribosomes were reduced. Strong plication of nuclear membrane, diminution of nucleoli, increased number of lysosomes and lipofuscin granules were also noticed. The extent of these changes is variable and depends on the time period of starvation. The smallest changes were observed in the groups starved for 24-48 hrs, the largest--in the groups starved 120-144 hrs.

Fibre numbers and sizes in the inferior alveolar nerve of the cat.

Previous studies with the light microscope of paraffin-embedded, metal-impregnated sections have probably underestimated the narrow fibre components of the inferior alveolar nerve in the cat. In this study the inferior alveolar nerve of a young adult cat was fixed in situ with glutaraldehyde, post-fixed in osmium and embedded in plastic. A 1 micrometer section of the whole nerve, and an ultrathin section of its largest bundle were cut. Montage micrographs were made from both sections, and from tracings the number and size distribution of the nerve fibres were measured. The entire nerve contained 6856 myelinated nerves whose diameters were distributed bimodally with peaks at 3--4 and 9--10 micrometers. This total is higher than all previously published counts of this nerve, the increase being due to the detection of a greater number of narrower myelinated fibres. In the bundle examined electron microscopically 51.4% of the fibres counted were non-myelinated, four times as many as found in previous studies. The number and distribution of myelinated fibres found by electron microscopy was very similar to that found by light microscopy. The size distribution of myelinated nerves was similar in all the bundles examined. Apart from a lower incidence of non-myelinated fibres, the population of the core of the larger bundle was similar to that of the periphery.

Innervation of the pulp-predentin border zone of the cat following denervation and reinnervation.

Under general anesthesia the inferior alveolar nerves of 8 cats were transected unilaterally and the cut ends reapposed. Two of these animals were, under general anesthesia, perfused with fixative 2 days later and 6 animals 12 or 15 weeks later, and the crowns of the mandibular canine teeth were prepared for ultrastructural examination. The distribution of axons at the pulp-predentin border and in the predentinal tubules was measured on the operated and control sides. In unoperated teeth the innervation at the pulp-predentin border paralleled that in the predentinal tubules being denser more coronally. The axons at the pulp-predentin border had disappeared by 2 days after denervation but had returned by 12 weeks and later with a density and distribution similar to that of the control sides.

Structural development of the feline mental nerve.

The qualitative and quantitative structural development of the feline mental nerve (MN), a branch of the inferior alveolar nerve (IAN), was studied by electron microscopy from 40 days postconception (dpc) (about 2 weeks before birth) to 11 years after birth. Myelination was initiated at 40-45 dpc. At 2 months after birth de novo myelination was completed, and the larger myelinated axons had achieved a fully differentiated nodal-paranodal morphology. Size growth of myelinated axons continued until 6 months, when a bimodal size distribution between 1 and 12 months was established. When compared to the IAN, the MN contained a higher proportion of unmyelinated axons. Age-related signs of axon degeneration, which previously were recorded in the IAN, were lacking in the MN. This suggests that senescent IAN axon degeneration is related to dental rather than to cutaneous MN branches.

Degenerative changes of primary neurons following tooth extraction.

In summarizing the present experimental results of tooth extraction, it can be emphasized that the disturbance of the sensory input units from the teeth resulted in a definite degeneration of the primary neurons. On this ground, it is suggested that the lesion of the sensory input units in the masticatory computer system, according to the individual age affected, may become a large factor in impeding the masticatory activity and accelerating the aging of the masticatory function.