Ultrastructure of the neuromuscular junction of vasomotor nerves in the microvasculature of human dental pulp

Vascular architecture regulates mesenchymal stromal cell heterogeneity via P53-PDGF signaling in the mouse incisor

Mesenchymal stem cells (MSCs) reside in niches to maintain tissue homeostasis and contribute to repair and regeneration. Although the physiological functions of blood and lymphatic vasculature are well studied, their regulation of MSCs as niche components remains largely unknown. Using adult mouse incisors as a model, we uncover the role of Trp53 in regulating vascular composition through THBS2 to maintain mesenchymal tissue homeostasis. Loss of Trp53 in GLI1+ progeny increases arteries and decreases other vessel types. Platelet-derived growth factors from arteries deposit in the MSC region and interact with PDGFRA and PDGFRB. Significantly, PDGFRA+ and PDGFRB+ cells differentially contribute to defined cell lineages in the adult mouse incisor. Collectively, our results highlight Trp53's importance in regulating the vascular niche for MSCs. They also shed light on how different arterial cells provide unique cues to regulate MSC subpopulations and maintain their heterogeneity. Furthermore, they provide mechanistic insight into MSC-vasculature crosstalk.

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

Direct visualization of the spatial relationships of the dental pulp tissue at the whole-organ has remained challenging. CLARITY (Clear Lipid-exchanged Acrylamide Tissue hYdrogel) is a tissue clearing method that has enabled successful 3-dimensional (3D) imaging of intact tissues with high-resolution and preserved anatomic structures. We used CLARITY to study the whole human dental pulp with emphasis on the neurovascular components. Dental pulps from sound teeth were CLARITY-cleared, immunostained for PGP9.5 and CD31, as markers for peripheral neurons and blood vessels, respectively, and imaged with light sheet microscopy. Visualization of the whole dental pulp innervation and vasculature was achieved. Innervation comprised 40% of the dental pulp volume and the vasculature another 40%. Marked innervation morphological differences between uni- and multiradicular teeth were found, also distinct neurovascular interplays. Quantification of the neural and vascular structures distribution, diameter and area showed that blood vessels in the capillary size range was twice as high as that of nerve fibers. In conclusion whole CLARITY-cleared dental pulp samples revealed 3D-morphological neurovascular interactions that could not be visualized with standard microscopy. This represents an outstanding tool to study the molecular and structural intricacies of whole dental tissues in the context of disease and treatment methods.

Human pulpal blood flow in different root formation stages measured with transmitted-light plethysmography

OBJECTIVES

To determine the pulp vitality after traumatic injury, dentists often use pulp sensitivity tests, which can be ambiguous in young permanent teeth with incomplete root formation. Transmitted-light plethysmography (TLP) is a non-invasive objective method that uses a 525-nm LED to detect blood volume change in the pulp. The present study aimed (1) to investigate pulpal blood flow with TLP and optical characteristics in healthy permanent maxillary incisors in different root formation stages, and (2) to assess the influences of body growth of the children and tooth color on the TLP amplitude.

DESIGN

Seventy-eight fully erupted maxillary central incisors were divided into four groups, according to the root formation stages. Group 1: root with wide-open apex, Group 2: root completed in length with open apex, Group 3: root with half-closed apex, Group 4: root with complete formation. The TLP amplitude, optical density, electric pulp testing, and cervical tooth color measurements of each group were compared using a one-way analysis of variance followed by the Bonferroni method. The correlation between the weights/heights of children and TLP amplitudes was analyzed using Pearson coefficient.

RESULTS

The TLP amplitude was significantly higher in Group 3 than in the other groups. The amplitude was correlated with the weights/heights of children, but not with the tooth color. Optical density and electric sensitivity increased with tooth maturation.

CONCLUSION

The amplitude of TLP and optical density may be affected by growth and development in children and indicate changes in the vascular dynamics of the pulp and hard tissue maturation during root formation stages.

Influence of occlusal stimuli on the microvasculature in rat dental pulp

OBJECTIVE

To examine the influence of occlusal stimuli on the vasculature in the dental pulp, using an occlusal hypofunction model.

MATERIALS AND METHODS

Twenty 7-week-old male Sprague-Dawley rats were divided into two groups. To produce occlusal hypofunction, the appliances were attached to the maxillary and mandibular incisors. Untreated rats served as controls. Serial horizontal paraffin sections of the mandibular first molar were processed by conventional methods. To evaluate the microvasculature in the dental pulp, sections of each specimen were stained with hematoxylin-eosin.

RESULTS

In the experimental group, the arterioles in the tooth pulp tissue ran convergently, and their inside diameter was significantly smaller than that of the control group.

CONCLUSION

This study suggests that occlusal stimuli influence the periodontal ligament throughout the microvasculature of the dental pulp.

Vascular status in human primary and permanent teeth in health and disease

The present study sought to compare the vascular status of human primary teeth with that of human permanent teeth, and to determine whether caries or painful pulpitis was associated with changes in vascularity. Coronal pulps were removed from 62 primary and 62 permanent mandibular molars with a known pain history. Teeth were categorized as intact, moderately carious or grossly carious. Pulp sections were labelled with Ulex europaeus I lectin (UEIL), which is a marker of human vascular endothelium. Image analysis was then used to quantify the percentage area of UEIL-labelled tissue (vascularity) and the number of blood vessels present within three regions: the pulp horn, the subodontoblastic region, and the mid-coronal pulp. Only the mid-coronal region of the primary tooth pulp was found to be significantly more vascular than the corresponding area of the permanent tooth pulp. Both dentitions showed a significant increase in vascularity within the pulp horn region with caries progression, but this was not accompanied by an increase in vessel number. There was no correlation between vascularity and pain symptoms. These findings suggest that the primary tooth pulp is more vascular than its successor within the mid-coronal region. However, the functional and clinical significance of this finding remains speculative.

Immunocytochemical investigation of neurovascular relationships in human tooth pulp

This study sought to explore the anatomical relationships between peptidergic nerves and blood vessels within human primary and permanent teeth. Extracted primary and permanent molars (n = 120) were split longitudinally, placed in Zamboni's fixative and the coronal pulps were processed for indirect immunofluorescence. Ten-micrometre-thick serial frozen pulp sections were triple-labelled using combinations of the following antisera: (1) protein gene-product 9.5 (PGP 9.5), a general neuronal marker; (2) one of the neuropeptides, calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal polypeptide (VIP) or neuropeptide Y (NPY); and (iii) the lectin Ulex europeus, a label for vascular endothelium. The mid-coronal pulp region was examined, using fluorescence microscopy, to determine the proportion of blood vessels showing a positive innervation (recorded when PGP 9.5-labelled nerves appeared to intersect the vessel wall). In addition, the percentage of these vascular-related nerves expressing each of the above neuropeptides was recorded. Overall, 20% of pulpal blood vessels appeared to have a positive innervation. In the main these were thick-walled arterioles. Capillaries, venules and lymphatics were mostly devoid of an associated innervation. Ninety-two per cent of vascular-related nerves expressed CGRP, 87% expressed SP, 15% expressed VIP and 80% expressed NPY. There were no significant differences in overall innervation or peptide-related innervation between primary and permanent teeth (P < 0.05, ANOVA), indicating that pulpal blood flow is likely to be subject to similar neurological control mechanisms in both dentitions.

Odontoblast morphology and dental repair

OBJECTIVES

To investigate the changes in morphology and activity of pulp odontoblasts in response to cavity restoration variables and patient factors.

METHODS

Class V non exposed cavities were prepared in the intact 1st or 2nd premolar teeth of 27 patients, aged between 9 and 17 years-old. Following tooth extraction, the area of reactionary dentine and the area of the odontoblasts were measured using computerised histomorphometry.

RESULTS

The cytoplasm to nucleus ratio of the odontoblasts was found to increase beneath cut dentinal tubules, following the secretion of reactionary dentine. However, none of the patient or preparation variables were found to be correlated with changes in the odontoblast cytoplasm to nucleus ratio.

CONCLUSIONS

Morphological changes in human odontoblasts is directly related to their capacity to repair dentine injuries and provide pulp protection. Changes in odontoblast morphology reflect secretory activity.

Three-dimensional wall structure and the innervation of dental pulp blood vessels

The involvement of neural components in plasma extravasation and blood flow in the dental pulp has been established by pharmacological and physiological studies. We review here the segmental constitution of pulp vessels and the possible involvement of neural components in both the contractility and permeability of the pulp vessels from a morphological viewpoint. Six vascular segments can be identified based on the morphology of peri-endothelial cells, such as smooth muscle cells and pericytes. These are: muscular arterioles, terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and collecting or muscular venules. The perivascular nerve forms a mesh with numerous terminal varicosities, some of which attach directly to arteriolar smooth muscle cells. This mesh can be seen by scanning electron microscopy, and indicates the important role of neural components in regulating the pulpal circulation. After administering norepinephrine (0.2 mg/kg/dog), the surface texture of the smooth muscle cells of pulp arterioles reveals marked irregularities, which are correlated with arteriolar contraction. The pericytes in larger postcapillary venules (diameter 20 microm or larger) also show irregularities, whereas no changes are seen in the pericytes of either smaller postcapillary venules or capillaries. The intercellular spaces of pericytes in the postcapillary venules are wide enough for leukocytes to pass through, and the occasional extravasation of leukocytes through venule walls can be seen under electron microscopy. The microvessels of healthy human dental pulp react weakly to selectins, indicating that apparently healthy dental pulp may be weakly inflamed. In rat dental pulp, CGRP-immunoreactive nerves and nerve terminals containing many granular vesicles supply the postcapillary venules more densely than the arterioles, which suggests the involvement of postcapillary venules in neurogenic inflammation in the dental pulp.

Human odontoblast cell numbers after dental injury

OBJECTIVES

The purpose of this study was to measure the changes in odontoblast cell numbers in response to cavity restoration variables and patient factors, and the effect these factors have on dental repair by tertiary dentinogenesis. The number of vital odontoblasts is a critical factor for pulpal repair following restorative surgery, and yet little information is available on these cell numbers.

METHODS

Class V non-exposed cavities were prepared in the buccal surface of intact first or second premolar teeth of 27 patients, between 9 and 17 years of age. Following tooth extraction (28-163 days) the area of reactionary dentine and the area of the odontoblasts were measured histomorphometrically.

RESULTS

Patient factors, as well as cavity preparation and restoration variables, had little effect on the numbers of odontoblasts per pulpal unit area. However, the age of the patient did appear to have an effect on the reactionary dentine secretory capacity of odontoblasts per unit area, and on the relative number of odontoblasts beneath cut dentinal tubules.

CONCLUSIONS

Odontoblast cell numbers were maintained following the preparation of cavities cut into dentine with a 0.5mm residual dentine thickness. The repair capacity of the pulp-dentine complex would appear to be age dependent, this may explain differences in the success of various restorative treatments between patients.

Immunohistochemical demonstration of exocytosis-regulating proteins within rat molar dentinal tubules

No morphologically defined synaptic structures have so far been detected between nerve terminals and the dentine-producing odontoblasts. Recent studies of the molecular mechanisms in neuronal exocytosis have identified several proteins that participate in synaptic-vesicle exocytosis. By localizing these proteins with immunohistochemical methods, information about the capacity for synaptic exocytosis should be obtained. Here, antibodies directed against some of the exocytosis-related proteins were used to investigate whether they are present in nerve fibers within the dentinal tubules in rat molars. Antibodies against synaptosome-associated protein of 25 kDa, Rab 3, synaptotagmin and synapsin all produced a punctuate staining pattern, suggesting that the proteins are accumulated in bouton-like elements. The results demonstrate that a set of exocytosis-related proteins is accumulated in the dentinal tubules, most probably within the intradentinal nerves. This finding is consistent with the hypothesis that intradentinal nerves can mediate efferent signals.

Scanning electron microscopy and immunohistochemical observations of the vascular nerve plexuses in the dental pulp of rat incisor

BACKGROUND

The innervation of rat incisors, which are continuously erupting teeth, is quite unique. Although many reports have documented the neural control of the pulpal blood flow, only a few studies have examined the structure and distribution of vascular nerves in the rat incisors. This study examined the nerve plexuses and the spatial relationship of nerve terminals to smooth muscle cells of the pulp vessels of rat incisors.

METHODS

The innervation of the pulp vessels of rat incisors was studied using immunohistochemical evaluations of calcitonin gene-related peptide (CGRP) and neuropeptide-Y (NPY). The three-dimensional ultrastructure of nerve meshworks and terminals on smooth muscle cells of pulp arterioles were examined by scanning electron microscopy (SEM) with a KOH digestion method.

RESULTS

The blood vessels were associated with many nerve fibers immunoreactive for CGRP and NPY. Some NPY and frequent CGRP-immunoreactive nerve fibers were observed in the labial odontoblast layer. Three different morphologies of nerve fibers could be distinguished: fine nerve fibers with numerous terminal varicosities, medium-sized fibers associated with occasional or much scarcer varicosities, and thick fibers that had no varicosity and sometimes ran apart from blood vessels. The SEM observations identified five vascular segment types: terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and muscular venules. Nerve meshworks were observed around the large terminal arterioles; these meshworks were very comparable to those revealed by immunohistochemistry. The vascular smooth muscle cells were closely attached by one or more terminal varicosities.

CONCLUSIONS

It has become evident that the large terminal arterioles in the rat incisors receive a dense nerve supply and provide well-developed wall architecture, suggesting an important role of neuronal regulation on the vessels.

Ultrastructural relation between nerve terminals and dentine bridge formation after pulpotomy in human teeth

Close association between nerve terminals and preodontoblasts, odontoblasts and predentine was observed during healing after pulpotomy. The nerve terminals frequently contained large numbers of synaptic vesicles. Terminals with many vesicles tended to be fewer in the predentine than in the odontoblastic layer. The distribution of terminals was more dense at the stage before the regenerated odontoblasts became arranged regularly beneath the predentine. It is suggested that these terminals have some efferent role(s), especially during collagen synthesis at the early stage of dentinogenesis. The nerves may release their abundant synaptic vesicles, in addition to serving a sensory role for monitoring the increased sensitivity in the injured areas.

Immunohistochemical study on the immunocompetent cells of the pulp in human non-carious and carious teeth

The condition of the pulp tissue was classified into seven groups according to the depth of carious lesions from stage (S) 0 (non-carious teeth) to S6 (exposed pulp). A substantial change in the infiltration of immunocompetent cells occurred between S3 and S4; all types were markedly increased in S4 as compared to S3, with a remarkable increase in the number of helper T lymphocytes, B-lineage cells, neutrophils and macrophages. Therefore, the pulpal immune reaction to carious stimuli could be classified into early (S1-S3) and advanced phases (S4-S6). In the early phase a cellular immunoresponse would be induced by T-lineage cells, and in the advanced phase the humoral immunoresponse is furthered by B-lineage cells concomitant with the destruction of pulp tissue by proteolytic enzymes released from infiltrating neutrophils and macrophages. Human dental pulp is thus equipped with a functional immune response that is sufficient as a biodefensive mechanism. Dental caries should be treated before S4.

An immunohistochemical and ultrastructural study of vasomotor nerves in the microvasculature of human dental pulp

Immunohistochemical methods for S-100 protein and neurone-specific enolase showed two types of nerve endings around the pulp microvasculature: the free endings, which comprise the major neural component and are distributed in all types of microvessel such as arterioles, venules and capillaries; and the varicose endings. The varicose ending was a less frequent, minor component observed only in the arterioles. Both immunohistochemical and ultrastructural observations confirmed that the varicose endings were the terminal axons of efferent vasomotor nerves. Further extensive ultrastructural examinations on the vasomotor nerves added the following new findings to our previous reports. Vasomotor nerves sometimes ramified into more than two terminal axons around arterioles, and most of these ramified axons ended in the adventitia-media junction of the arteriolar wall; however, nerve endings occasionally penetrated into the media. These findings suggest an intimate structural association between vasomotor nerves and arterioles in regulating the arteriolar microcirculation in human dental pulp by stimulating smooth-muscle cells not only of the outermost but also of the inner layers. Furthermore, the deep penetration of terminal axons into the arteriolar wall seems to provide effective regulation of pulpal blood flow under physiological and pathological conditions.