Recruitment of immunocompetent cells after dentinal injuries in innervated and denervated young rat molars: an immunohistochemical study

Neuronal-immune axis alters pain and sensory afferent damage during dental pulp injury

ABSTRACT

Dental pulp tissue is densely innervated by afferent fibers of the trigeminal ganglion. When bacteria cause dental decay near the pulpal tissue, a strong neuronal and immune response occurs, creating pulpitis, which is associated with severe pain and pulp tissue damage. Neuroimmune interactions have the potential to modulate both the pain and pathological outcome of pulpitis. We first investigated the role of the neuropeptide calcitonin gene-related peptide (CGRP), released from peptidergic sensory afferents, in dental pain and immune responses by using Calca knockout (Calca -/- ) and wild-type (Calca +/+ ) mice, in a model of pulpitis by creating a mechanical exposure of the dental pulp horn. We found that the neuropeptide CGRP, facilitated the recruitment of myeloid cells into the pulp while also increasing spontaneous pain-like behavior 20% to 25% at an early time point. Moreover, when we depleted neutrophils and monocytes, we found that there was 20% to 30% more sensory afferent loss and increased presence of bacteria in deeper parts of the tissue, whereas there was a significant reduction in mechanical pain response scores compared with the control group at a later time point. Overall, we showed that there is a crosstalk between peptidergic neurons and neutrophils in the pulp, modulating the pain and inflammatory outcomes of the disease.

The Role of Dendritic Cells during Physiological and Pathological Dentinogenesis

The dental pulp is a soft connective tissue of ectomesenchymal origin that harbors distinct cell populations, capable of interacting with each other to maintain the vitality of the tooth. After tooth injuries, a sequence of complex biological events takes place in the pulpal tissue to restore its homeostasis. The pulpal response begins with establishing an inflammatory reaction that leads to the formation of a matrix of reactionary or reparative dentin, according to the nature of the exogenous stimuli. Using several in vivo designs, antigen-presenting cells, including macrophages and dendritic cells (DCs), are identified in the pulpal tissue before tertiary dentin deposition under the afflicted area. However, the precise nature of this phenomenon and its relationship to inherent pulp cells are not yet clarified. This literature review aims to discuss the role of pulpal DCs and their relationship to progenitor/stem cells, odontoblasts or odontoblast-like cells, and other immunocompetent cells during physiological and pathological dentinogenesis. The concept of “dentin-pulp immunology” is proposed for understanding the crosstalk among these cell types after tooth injuries, and the possibility of immune-based therapies is introduced to accelerate pulpal healing after exogenous stimuli.

Dental nerves: a neglected mediator of pulpitis

As one of the most densely innervated tissues, the dental pulp contains abundant nerve fibres, including sensory, sympathetic and parasympathetic nerve fibres. Studies in animal models and human patients with pulpitis have revealed distinct alterations in protein expression and histological appearance in all types of dental nerve fibres. Various molecules secreted by neurons, such as classical neurotransmitters, neuropeptides and amino acids, not only contribute to the induction, sensitization and maintenance of tooth pain, but also regulate non-neuronal cells, including fibroblasts, odontoblasts, immune cells and vascular endothelial cells. Dental nerves are particularly important for the microcirculatory and immune responses in pulpitis via their release of a variety of functional substances. Further, nerve fibres are found to be involved in dental soft and hard tissue repair. Thus, understanding how dental nerves participate in pulpitis could have important clinical ramifications for endodontic treatment. In this review, the roles of dental nerves in regulating pulpal inflammatory processes are highlighted and their implications for future research on this topic are discussed.

Deciduous autologous tooth stem cells regenerate dental pulp after implantation into injured teeth

Pulp necrosis arrests root development in injured immature permanent teeth, which may result in tooth loss. However, dental pulp regeneration and promotion of root development remains challenging. We show that implantation of autologous tooth stem cells from deciduous teeth regenerated dental pulp with an odontoblast layer, blood vessels, and nerves in two animal models. These results prompted us to enroll 40 patients with pulp necrosis after traumatic dental injuries in a randomized, controlled clinical trial. We randomly allocated 30 patients to the human deciduous pulp stem cell (hDPSC) implantation group and 10 patients to the group receiving traditional apexification treatment. Four patients were excluded from the implantation group due to loss at follow-up (three patients) and retrauma of the treated tooth (one patient). We examined 26 patients (26 teeth) after hDPSC implantation and 10 patients (10 teeth) after apexification treatment. hDPSC implantation, but not apexification treatment, led to regeneration of three-dimensional pulp tissue equipped with blood vessels and sensory nerves at 12 months after treatment. hDPSC implantation increased the length of the root (P < 0.0001) and reduced the width of the apical foramen (P < 0.0001) compared to the apexification group. In addition, hDPSC implantation led to regeneration of dental pulp tissue containing sensory nerves. To evaluate the safety of hDPSC implantation, we followed 20 patients implanted with hDPSCs for 24 months and did not observe any adverse events. Our study suggests that hDPSCs are able to regenerate whole dental pulp and may be useful for treating tooth injuries due to trauma.

C5L2 Silencing in Human Pulp Fibroblasts Enhances Nerve Outgrowth Under Lipoteichoic Acid Stimulation

INTRODUCTION

We recently reported that caries-associated C5a receptor (C5aR) expression and activation result in up-regulation of brain-derived neurotropic factor secretion by pulp fibroblasts inducing prominent neurite outgrowth toward the carious site. Our data further showed a negative regulation of this brain-derived neurotropic factor secretion by C5L2, another C5aR. C5L2 was considered a nonfunctional receptor and thus has received much less attention than C5aR. The aim of this study was to identify the role of C5L2 in pulp fibroblast-mediated neurite outgrowth.

METHODS

In this study, lipoteichoic acid (LTA) was used to mimic dental caries-like inflammation. To evaluate the role of C5L2 in pulp neurite outgrowth, human pulp fibroblasts were C5L2 small interfering RNA silenced and cocultured with human neurons in a nerve growth assay system.

RESULTS

C5L2 silencing drastically increased the neurite outgrowth toward the LTA-stimulated pulp fibroblasts. The number of neurites detected was increased in the LTA-treated pulp fibroblasts.

CONCLUSIONS

Our results show that C5L2 constitutes a negative regulator of the neurite outgrowth under LTA stimulation. Of the events occurring during dentin-pulp regeneration, nerve regeneration is the key factor for maintaining tooth viability after infection or injury. Our study provides a foundation for creating therapeutic tools that target pulp fibroblasts during pulp/nerve regeneration.

Cytotoxic and biological effects of bulk fill composites on rat cortical neuron cells

The aim of this study was to investigate potential cellular responses and biological effects of new generation dental composites on cortical neuron cells in two different exposure times. The study group included five different bulk-fill flow able composites; Surefil SDR Flow, X-tra Base Flow, Venus Bulk Flow, Filtek Bulk Flow and Tetric-Evo Flow. They were filled in Teflon molds (Height: 4 mm, Width: 6 mm) and irradiated for 20 s. Cortical neuron cells were inoculated into 24-well plates. After 80% of the wells were coated, the 3 µm membrane was inserted and dental filling materials were added. The experiment was continued for 24 and 72 h. Cell viability measured by MTT assay test, total antioxidant and total oxidant status were examined using real assay diagnostic kits. The patterns of cell death (apoptosis) were analyzed using annexin V-FITC staining with flow cytometry. Β-defensins were quantitatively assessed by RT-PCR. IL-6, IL-8 and IL-10 cytokines were measured from the supernatants. All composites significantly affected analyses parameters during the exposure durations. Our data provide evidence that all dental materials tested are cytotoxic in acute phase and these effects are induced cellular death after different exposure periods. Significant cytotoxicity was detected in TE, XB, SS, FBF and VBF groups at 24 and 72 h, respectively.

Heterogeneity and Developmental Connections between Cell Types Inhabiting Teeth

Every tissue is composed of multiple cell types that are developmentally, evolutionary and functionally integrated into the unit we call an organ. Teeth, our organs for biting and mastication, are complex and made of many different cell types connected or disconnected in terms of their ontogeny. In general, epithelial and mesenchymal compartments represent the major framework of tooth formation. Thus, they give rise to the two most important matrix–producing populations: ameloblasts generating enamel and odontoblasts producing dentin. However, the real picture is far from this quite simplified view. Diverse pulp cells, the immune system, the vascular system, the innervation and cells organizing the dental follicle all interact, and jointly participate in transforming lifeless matrix into a functional organ that can sense and protect itself. Here we outline the heterogeneity of cell types that inhabit the tooth, and also provide a life history of the major populations. The mouse model system has been indispensable not only for the studies of cell lineages and heterogeneity, but also for the investigation of dental stem cells and tooth patterning during development. Finally, we briefly discuss the evolutionary aspects of cell type diversity and dental tissue integration.

Modulation of Dental Inflammation by the Sympathetic Nervous System

Recent findings have indicated that immune responses are subjected to modulation by the sympathetic nervous system (SNS). Moreover, the findings show that the SNS inhibits the production of pro-inflammatory cytokines, while stimulating the production of anti-inflammatory cytokines. The present review is an attempt to summarize the current results on how the SNS affects inflammation in dental tissues. In dental tissues, it has been found that the SNS is significant for recruitment of inflammatory cells such as CD 43+ granulocytes. Sympathetic nerves appear to have an inhibitory effect on osteoclasts, odontoclasts, and on IL-1α production. The SNS stimulates reparative dentin production, since reparative dentin formation was reduced after sympathectomy. Sprouting of sympathetic nerve fibers occurs in chronically inflamed dental pulp, and neural imbalance caused by unilateral sympathectomy recruits immunoglobulin-producing cells to the dental pulp. In conclusion, this article presents evidence in support of interactions between the sympathetic nervous system and dental inflammation.

Reactionary Dentinogenesis and Neuroimmune Response in Dental Caries

Reactionary dentin formation is an adaptive secretory response mediated by odontoblasts to moderate dentin injury. The implications of this process for neuroimmune interactions operating to contain pathogens have not been fully appreciated. The purpose of the present study was to describe the relationship between reactionary dentinogenesis, the neurogenic changes of dental pulp innervation, and dendritic cell recruitment to caries progression, using a comparative immunohistochemical approach in human teeth from young adult individuals. Reactionary dentin formation during dentin caries progression is associated with changes in the integrity of junctional complexes within the odontoblast layer. Diminished coexpression of Cx43 and zonula occludens 1 implies a reduced level of intercellular connectivity between odontoblasts. Dentin caries also causes overexpression of growth-associated protein 43, a modulator of neural plasticity that promotes extensive sprouting of nerve endings into the reactionary dentin matrix. At the same time, an elevated number of HLA-DR-positive dendritic cells infiltrate the odontoblast layer and subsequently invade reactionary dentin formed underneath the early caries-affected regions. Simultaneous odontoblast layer remodeling, nerve fiber sprouting, and activation of dendritic cells during caries progression suggest a coordinated neuroimmune response to fight caries pathogen invasion and to promote dentin-pulp healing. We propose that reactionary dentin formation hinders pathogen invasion and supports defensive neuroimmune interactions against infection. The eventual understanding of this complex scenario may contribute to the development of novel approaches to dental caries treatment.

Stress-induced neurogenic inflammation in murine skin skews dendritic cells towards maturation and migration: key role of intercellular adhesion molecule-1/leukocyte function-associated antigen interactions

The skin continuously serves as a biosensor of multiple exogenous stressors and integrates the resulting responses with an individual's central and peripheral endogenous response systems to perceived stress; it also acts to protect against external challenges such as wounding and infection. We have previously shown in mice that stress induces nerve growth factor- and substance P-dependent neurogenic inflammation, which includes the prominent clustering of MHC class II(+) cells. Because the contribution of dendritic cells (DCs) in response to stress is not well understood, we examined the role of DCs in neurogenic inflammation in murine skin using a well-established murine stress model. We show that sound stress increases the number of intradermal langerin(+) and CD11c(+) DCs and induces DC maturation, as indicated by the up-regulated expression of CD11c, MHC class II, and intercellular adhesion molecule-1 (ICAM-1). Blocking of ICAM-1/leukocyte function-associated antigen-1 interactions significantly abrogated the stress-induced numeric increase, maturation, and migration of dermal DCs in vivo and also reduced stress-induced keratinocyte apoptosis and endothelial cell expression of ICAM-1. In conclusion, stress exposure causes a state of immune alertness in the skin. Such adaptation processes may ensure protection from possible infections on wounding by stressors, such as attack by predators. However, present-day stressors have changed and such adaptations appear redundant and may overrun skin homeostasis by inducing immune dermatoses.

Innate Immune Responses of the Dental Pulp to Caries

Various cells and inflammatory mediators are involved in the initial pulpal responses to caries. This review focuses on the cellular, neuronal, and vascular components of pulpal innate responses to caries. Discussion will include dentinal fluid, odontoblasts, neuropeptides, and neurogenic inflammation, which are not classic immune components but actively participate in the inflammatory response as the caries progress pulpally. Summaries of innate immune cells as well as their cytokines and chemokines in healthy and reversible pulpitis tissues are presented.

Immunoglobulin producing cells in the rat dental pulp after unilateral sympathectomy

Recent studies show that sympathetic nerves participate in immunomodulation. We investigated the effects of unilateral sympathectomy on recruitment of cells expressing kappa and lambda (kappa and lambda) light chains in the rat dental pulp. Superior cervical ganglion was removed in experimental rats (n=10) while control rats (n=8) received sham surgery. Following perfusion 18 days later, mandibular jaws were processed for immunohistochemistry and electron microscopy. Sympathectomy results in recruitment of cells expressing kappa and lambda light chains into the dental pulp (P=0.005). Electron microscopy revealed these cells to be mainly plasma cells and Mott cells. We conclude that neural imbalance caused by unilateral sympathectomy recruits immunoglobulin producing cells in the dental pulp. Our results are in agreement with a model of immune regulation in which the sympathetic nervous system exerts a tonic regulatory effect over lymphocyte proliferation and migration.

Effect of electrical tooth stimulation on blood flow and immunocompetent cells in rat dental pulp after sympathectomy

Previous experiments show that nerves have effect on the emigration of immunocompetent cells during acute neurogenic inflammation. The present study aims to determine whether the sympathetic or sensory nerves are responsible for emigration of CD43+ and I-A antigen-expressing cells in the dental pulp after electrical tooth stimulation. Wistar rats were used. Experimental rats (n = 6) had the right superior cervical ganglion removed (SCGx), whereas control rats (n = 6) had sham surgery. Fourteen days later, electrical stimulation of the right maxillary 1st molar was performed in both groups for 20-25 s every 5th min for a total period of 4 h. Changes in pulpal blood flow (PBF) were recorded with a laser Doppler flowmeter. All rats were transcardiacally perfused and processed for immunohistochemistry using antibodies against neuropeptides and immune cells. Intermittent electrical stimulation consistently increased PBF and depleted sympathetic and sensory neuropeptides in the dental pulp. The increase in PBF gradually decreased and approached control values at the end of the 4 h stimulation period. A significant increase in the number of I-A antigen-expressing dendritic cells was found in both the SCGx (P < 0.001) and control rats (P < 0.007). In contrast, tooth stimulation did not increase the number of CD43+ cells in the SCGx rats compared to the unstimulated contralateral control molar. Significantly more CD43+ PMN cells (P < 0.01) were found in the control rats after stimulation. It is concluded that stimulation of sympathetic nerves causes recruitment of CD43+ PMN cells, whereas stimulation of sensory nerves causes emigration of I-A antigen-expressing dendritic cells in the dental pulp.

Glial cell line-derived neurotrophic factor (GDNF) from adult rat tooth serves a distinct population of large-sized trigeminal neurons

Glial cell line-derived neurotrophic factor (GDNF) mediates trophic effects for specific classes of sensory neurons. The adult tooth pulp is a well-defined target of sensory trigeminal innervation. Here we investigated potential roles of GDNF in the regulation of adult trigeminal neurons and the dental pulp nerve supply of the rat maxillary first molar. Western blot analysis and radioactive 35S-UTP in situ hybridization revealed that GDNF in the dental pulp and its mRNAs were localized with Ngf in the coronal pulp periphery, in particular in the highly innervated subodontoblast layer. Retrograde neuronal transport of iodinated GDNF and Fluorogold (FG) from the dental pulp indicated that GDNF was transported in about one third of all the trigeminal dental neurons. Of the GDNF-labelled neurons, nearly all (97%) were large-sized (> or =35 microm in diameter). Analysis of FG-labelled neurons revealed that, of the trigeminal neurons supporting the adult dental pulp, approximately 20% were small-sized, lacked isolectin B4 binding and did not transport GDNF. Of the large-sized dental trigeminal neurons approximately 40% transported GDNF. About 90% of the GDNF-accumulating neurons were negative for the high-temperature nociceptive marker VRL-1. Our results show that a subclass of large adult trigeminal neurons are potentially dependent on dental pulp-derived GDNF while small dental trigeminal neurons seems not to require GDNF. This suggests that GDNF may function as a neurotrophic factor for subsets of nerves in the tooth, which apparently mediate mechanosensitive stimuli. As in dorsal root ganglia both small- and large-sized neurons are known to be GDNF-dependent; these data provide molecular evidence that the sensory supply in the adult tooth differs, in some aspects, from the cutaneous sensory system.

Comparison of the effects of 1,25 dihydroxycholecalciferol and prostaglandin E2 on orthodontic tooth movement

This study compared the effects of local administrations of prostaglandin E2 (PGE2) and 1,25-dihydroxycholecalciferol (1,25-DHCC) on orthodontic tooth movement in rats. Thirty-seven 6-week-old male Sprague-Dawley rats, weighing 160 +/- 10 g were used. Five rats served as the baseline control group. A fixed appliance system exerting 20 g of distally directed force was applied on the maxillary incisors of 32 animals for 9 days. Eight rats served as the appliance control group; 8 received a 20-microL injection of dimethyl sulfoxide (solvent for 1,25-DHCC) on days 0, 3, and 6; 8 received 20 microL of 10(-10) mol/L 1,25-DHCC on days 0, 3, and 6; 8 received a single injection of 0.1 mL of 0.1 microg PGE2 only on day 0. There was no significant difference in tooth movement between the PGE2 and the 1,25-DHCC groups. Both PGE2 and 1,25-DHCC enhanced the amount of tooth movement significantly when compared with the control group. The numbers of Howship's lacunae and capillaries on the pressure side were significantly greater in the PGE2 group than in the 1,25-DHCC group. On the other hand, the number of osteoblasts on the external surface of the alveolar bone on the pressure side was significantly greater in the 1,25-DHCC group than in the PGE2 group. Thus, 1,25-DHCC was found to be more effective in modulating bone turnover during orthodontic tooth movement, because its effects on bone formation and bone resorption were well balanced.

Occlusion of dentinal tubules and selective block of pulp innervation prevent the nociceptive behaviour induced in rats by intradental application of irritants

OBJECTIVES

Application of irritants on the exposed dentine of the incisors has been shown to produce aversive behaviour in awake rats. This study aims to demonstrate that the observed aversion is due to the infiltration of irritants through the dentinal tubules and the activation of capsaicin sensitive fibres in the tooth pulp.

METHODS

Different groups of rats were subjected, under anaesthesia, to cutting of the distal 2 mm of their lower incisors and the fixation of an artificial crown that allows the application of 10-15 microl of solution. Several procedures were followed to prevent the action of the irritants including occlusion of the dentinal tubules, local application of lidocaine, selective ablation of the capsaicin sensitive primary afferents (CSPA) or incisor pulpectomy; the reactions to intradental application of either capsaicin (1%) or formalin (2.5%) were tested using a newly designed behavioural score.

RESULTS

Occlusion of dentinal tubules produced significant attenuation of the nociceptive behaviour induced by dentinal application of either capsaicin or formalin. Similar results were observed following either local block with lidocaine (2%), selective ablation of capsaicin sensitive afferents or total denervation by pulpectomy.

CONCLUSIONS

The present results confirm the hypothesis of infiltration of irritants to the incisor pulp through the dentinal tubules and suggest that the reported inflammatory reaction and hyperalgesia are mediated, to a large extent, by capsaicin sensitive primary afferents.

NK1, NK2, NK3 and CGRP1 receptors identified in rat oral soft tissues, and in bone and dental hard tissue cells

The distribution of the tachykinin receptors neurokinin-1 (NK1), neurokinin-2 (NK2) and neurokinin-3 (NK3), and the calcitonin gene-related peptide-1 (CGRP1) receptor were examined in rat teeth and tooth-supporting tissues by immunohistochemical methods and light and confocal microscopy. Western blot analysis was performed to identify the NK1- and the CGRP1-receptor proteins in the dental pulp. The results showed that odontoblasts and ameloblasts, cementoblasts and cementocytes, osteoblasts and osteocytes are all supported with the tachykinin receptors NK1 and NK2, but a distinct, graded cellular labeling pattern was demonstrated. The ameloblasts were also positive for CGRP1 receptor. Blood vessels in oral tissues expressed the tachykinin receptors NK1, NK2 and NK3, and the CGRP1 receptor. Both gingival and Malassez epithelium were abundantly supplied by NK2 receptor. Pulpal and periodontal fibroblasts demonstrated NK1 and NK2 receptors. Western blot analysis identified both the NK1- and the CGRP1-receptor proteins in the dental pulp. These results clearly indicate that the neuropeptides substance P, neurokinin A, neurokinin B and CGRP, released from sensory axons upon stimulation, directly modulate the function of the different types of bone and dental hard tissue cells, and regulate functions of blood vessels, fibroblasts and epithelial cells in oral tissues.

Immunohistochemical study on pulpal response in rat molars after cavity preparation by Er:YAG laser

While Er:YAG laser systems are in extensive use for caries removal and cavity preparation, the effects of such treatment on pulp tissue remain unclear. This study evaluates these systems using immunohistochemical methods and compares the results with information gained from treatment using conventional burs. Cervical cavities were prepared in the upper first molars of rats, using either an Er:YAG laser or a conventional tungsten-carbide bur. At intervals of 5 min, 6 h, 12 h, 1 d, 3 d and 7 d after cavity preparation, the teeth were processed for immunohistochemical analyses of tissue non-specific alkaline phosphatase, OX6-positive major histocompatibility complex class II antigen-expressing cells and PGP 9.5-immunoreactive nerve fibers. DNA fragmentation was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Tissue non-specific alkaline phosphatase was observed mainly in the subodontoblastic layer under the cavity lesion, from 5 min, in both groups. The immunoreactivity was more pronounced in the laser group, but by 7 d no significant differences were recognizable. At 12 h, TUNEL-positive cells were detected around the odontoblastic layer in both groups. From 3 d to 7 d, a limited number of positive cells were still visible in the group that underwent standard treatment. Clear similarities in the distribution patterns of OX6-immunopositive cells and PGP 9.5-immunoreactive nerve fibers were also noted. From 12 h to 1 d, OX6-positive cells accumulated along the pulp-dentin border, extending their processes into the dentinal tubules. Numerous bead-like PGP 9.5-immunoreactive nerve fibers were observed under the odontoblastic layer at 7 d. These results demonstrated that there was no appreciable difference in the manner in which pulp tissue responded to treatment with either Er:YAG laser or a conventional drill. This would seem to indicate the usefulness of the Er:YAG laser system in the removal of caries and cavity preparation.

Nociceptive behaviour induced by dental application of irritants to rat incisors: a new model for tooth inflammatory pain

Animal models simulating acute human pulpitis are still lacking. The rat incisors present a particular situation where most of their innervation is considered to be unmyelinated and concentrated mainly in the tooth pulp. This study reports on a new model for dental pain induced by inflammatory agents applied to the tooth pulps of incisors. In different groups of rats, artificial crowns were fixed on the lower incisors, after cutting 1-2mm of their distal extremities. A volume of 7-10 microl of solutions of saline, capsaicin (1-10mg/ml) or formalin (2.5% or 5%) was injected in the crown cavity, and the nociceptive behaviour was quantitated following a devised scoring method of four scales. Intradental application of capsaicin produced nociceptive scores in the form of one plateau for 1-2h depending on the concentration used. Similar results were obtained with intradental application of formalin 2.5%. The one plateau of nociceptive scores obtained with formalin contrasts with the biphasic aspect of nociceptive behaviour described with the intradermal formalin test. This discrepancy could be attributed to a difference in the types of afferent fibres involved in each situation. Pretreatment with morphine (2 mg/kg) attenuated, in a naloxone-reversible manner, the nociceptive behaviour observed following intradental application of capsaicin. Pretreatment with meloxicam (a cyclo-oxygenase-2 inhibitor) exerted a less pronounced attenuation of the nociceptive scores when compared with morphine. These results provide evidence for the validity of the described model for the simulation of tooth pulp inflammatory pain in awake animals.

Effect of denervation on healing after tooth replantation in the ferret

Studies have shown that the sensory nerves participate in inflammation and immune responses and possess trophic-facilitating wound healing in general. Tooth avulsion represents a pulpal and periodontal injury, and the mechanisms involved in the healing responses subsequent to replantation of teeth are still unclear. The objective of this study was to investigate the healing responses after denervation and replantation of teeth. Unilateral denervation was performed in 15 ferrets by axotomy of the inferior alveolar nerve, 5 days before extraction of the first lower premolars. Six weeks later the mandibles were excised and processed for histological evaluation. Immunohistochemistry was performed using antibodies against the sensory neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), and measurements of root resorption and ankylosis were performed in four sections from each replanted tooth. After 6 weeks substantial reinnervation was observed in the jaws. Immunoreactivity in the pulp was observed in only two replanted teeth on the denervated side, compared with four on the innervated side. Total pulp necrosis appeared in 10 replanted teeth on the denervated side and in 5 on the innervated, indicating that sensory nerves promote survival of the pulp after replantation. SP-immunoreactive (IR) fibers were more frequently observed in the resorptive lacunae than CGRP-IR fibers. However, resorptive areas lacking IR fibers were frequently found along the root surface. Root resorption averaged 0.062 +/- 0.029 mm2 on the innervated side compared to 0.016 +/- 0.0043 mm2 on the denervated (P< 0.02). Ankylosis was observed in four of the replanted teeth on the innervated side (169.3 +/- 49.7 microm) and in six on the denervated side (332.56 +/- 193.2 microm) (P = 1). It is concluded that the sensory nerves promote root resorption after pulpoperiodontal injuries but have less influence on the osteoblastic activity expressed by ankylosis.

A perfusion technique for the determination of pro-inflammatory mediators induced by intradental application of irritants

INTRODUCTION

Several morphological and functional features contribute to the consideration of the tooth as a separate compartment having special type of innervation and special immune mechanisms. This study describes a new method allowing the intradental perfusion of rat incisors for the in vivo assessment of pulpal reaction to inflammatory agents.

METHODS

Under deep anesthesia, the distal 2-3 mm of each of the rat lower incisors was cut and wrapped in a polyethylene tubing connected to a perfusion chamber made of tigone tubing (ID 1/8 in., volume 100-150 microl). Several groups of rats (n=5 each) were used for intradental application of either saline, capsaicin (100 microg in 100 microl), or endotoxin (ET, 20 microg in 100 microl) for a period of 40 min followed by filling the tooth chamber with saline and collecting the perfusate every 40 min for a period of 8 h. The collected perfusates were stored at -70 degrees C for subsequent determination of the concentration of prostaglandin E(2) (PGE(2)) and nerve growth factor (NGF) by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Dentinal injury produced a moderate increase in the levels of NGF and PGE(2) in incisors perfused with saline. Application of ET or capsaicin, however, produced a highly significant increase in the levels of both mediators. These effects peaked at 1.5-3 h for PGE(2) and at 5 h for NGF. Capsaicin showed the most significant effects.

DISCUSSION

The reported results cannot be attributed to any factor other than the inflammation of the incisor's pulp, because the described chamber does not allow any spread or leak of the applied irritants. Further studies using other reagents can allow the determination of the variation of the levels of the various pro-inflammatory mediators and their modulation by treatment with anti-inflammatory drugs.

The effect of unilateral sympathectomy and cavity preparation on peptidergic nerves and immune cells in rat dental pulp

Recent evidence suggests interactions between primary afferent nociceptors and postganglionic sympathetic efferents in the pathogenesis of inflammation. The effect of unilateral removal of the superior cervical ganglion on the innervation pattern of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), and neuropeptide Y (NPY), as well as the occurrence of immune cells in the injured and uninjured rat molar pulp, was investigated. Light microscopic immunocytochemistry demonstrated that the molar pulps contralateral to the sympathectomy contained a NPY-IR nerve fiber network more dense and heavily stained than unoperated control rats. The NPY-IR fibers showed, however, no sprouting after deep cavity preparation. There was no compensatory increase in CGRP- and SP-IR nerve fibers in the dental pulp after unilateral sympathectomy, although a significant increase in cells IR to CGRP and SP was found in the ipsilateral trigeminal ganglion. Unilateral sympathectomy induced a significant increase in immune cell density both in the inflamed and in the uninflamed dental pulp bilaterally. Our results demonstrate, for the first time, a trophic effect of the sympathetic nerves on immune cells in the dental pulp, indicating that an imbalance of sympathetic nerves may induce inflammation and pain in teeth.

Course and composition of the nerves that supply the mandibular teeth of the rat

The rodent dentition has become an important model for investigations of interactions between dental tissues and peripheral neurons. Although experimental nerve injury has been widely used for such studies, there is uncertainty about the courses of nerve fibers supplying the mandibular teeth. In order to clarify this, we used a mixture of monoclonal antibodies against neurofilament proteins to enhance demonstration of nerve fibers so that small nerves could be readily traced in serial frozen sections of mandibles of Sprague Dawley rats ranging in age from embryonic day (E) 18 to postnatal day (P) 90. The 1st molar and anterior portion of the 2nd molar were innervated by small nerves that emerged as distinct branches of the IAN trunk at or near the mandibular foramen. In contrast, the nerve supply to the 3rd molar and posterior part of the 2nd molar was a branch of the lingual nerve that bypassed the mandibular canal altogether. The IAN trunk split into the mental nerve and a large branch to the incisor about 2 mm anterior to the mandibular foramen. Thick branches of the incisor nerve descended into the incisor socket to form a dense plexus of nerve fiber bundles extending along the length of the incisor periodontium. The sparse pulpal innervation of the incisor was provided by a few thin fascicles that emerged from the caudal portion of the periodontal plexus to enter the incisor apex. The dental branches of the IAN and lingual nerve seen in the adult were well established and readily identifiable at age E18 even though their targets were limited to the follicles of the developing teeth. These studies show that the trigeminal branches that supply the mandibular teeth can be identified at a wide range of ages as distinct nerves at a considerable distance proximal to their targets. This detailed information on the courses taken by the dental nerves can provide an anatomical basis for increased precision in characterization and perturbation of neural pathways from the molars and incisor.

Co-increase of nerve fibers and HLA-DR- and/or factor-XIIIa-expressing dendritic cells in dentinal caries-affected regions of the human dental pulp: an immunohistochemical study

Neuro-immune interaction has been suggested to play some modulatory role in the immunodefense of the dentin/pulp complex. In this study, we performed a simultaneous immunohistochemical observation of neural elements and pulpal dendritic cells (PDCs) on human carious teeth, to obtain morphological evidence for neuro-immune interaction in response to dentinal tubule-derived carious stimuli. Human third molars bearing a pulp-exposure-free caries lesion were studied. Immunoperoxidase staining was performed with anti-HLA-DR, anti-coagulation factor XIIIa, and anti-CD14 as PDC markers, and anti-low-affinity nerve growth factor receptor (NGFR), anti-protein gene products 9.5, and anti-calcitonin gene-related peptide as nerve markers. The carious teeth usually exhibited localized accumulation of both PDCs and nerve fibers immunoreactive to each marker, in the para-odontoblastic region corresponding to the pulpal end of carious dentinal tubules. Semi-quantitative digital densitometry revealed that pixel numbers corresponding to factor-XIIIa- and NGFR-immunoreactivity were significantly higher in the carious regions than those in the non-carious regions of the same teeth as well as those in the corresponding regions of intact teeth. Classification of specimens with respect to caries depth showed that the co-increase was most apparent in teeth with superficial caries. The increase of PDCs was less pronounced in carious teeth with reparative dentin. These findings suggest that both pulpal nerves and PDCs respond promptly and actively to dentinal tubule-derived carious stimuli. The synchronized accumulation of the two structures suggests an increased opportunity for neuro-immune interaction that may be of significance in the modulation of pathological processes in the dental pulp.

Delayed recruitment of immunocompetent cells in denervated rat periodontal ligament following experimental tooth movement

It has previously been shown that the number of mononuclear phagocytic cells in the periodontal ligament (PDL) of orthodontically moved rat molars is significantly increased (p < or = 0.05) at 3, 7, and 14 days compared with the controls. Since these changes coincide with increased density of peptidergic nerve fibers, it was of particular interest to investigate a possible relation between the immunocompetent cells and sensory nerve fibers in the PDL of experimentally moved and denervated rat molars. Twenty-two young animals had the first right mandibular molar moved mesially, 7, 14, and 21 days after ipsilateral inferior alveolar nerve axotomy. The left side served as unoperated control. An immunohistochemical procedure was carried out on alternate, serial, cryostat sections with antibodies against CDllb (macrophages, dendritic cells) and class II major histocompatibility complex (MHC) molecules (RT1B). At 7 and 14 days, the number of CD11b+- and RT1B-expressing cells in the denervated PDL showed no significant difference compared with the contralateral side. However, at 21 days, when periodontal tissue re-innervation is established, the number of the investigated immunocompetent cells in the PDL of the denervated and experimentally moved mandibular molars demonstrated a significant difference compared with the contralateral and control molars (p < or = 0.05). It can be concluded that axotomy of the inferior alveolar nerve delays the recruitment of macrophage-like and class II MHC molecule-expressing cells in the PDL of orthodontically moved rat molars. The results further indicate that sensory nerve fibers interact with immunocompetent cells and participate in their mobilization to locally inflamed tissues.

Neurokinin-1 receptor expression in the mature dental pulp of rats

Substance P induces inflammatory reactions in peripheral tissues including the dental pulp, but its regulatory effects in target tissues are dependent on receptor signalling. Here the expression of the substance-P receptor neurokinin-1 (NK1) in the mature molar pulp of the rat was examined in order to localize the main target areas for substance P. A polyclonal antibody directed against the C-terminal of the receptor was used, and immunohistochemistry was performed by the avidin-biotin peroxidase complex method. The results showed that the NK1 receptor was intensely expressed along vessel-like structures in the odontoblast and subodontoblast layer. A granulated and diffusely distributed NK1-receptor labelling was found along larger blood vessels in the root pulp and pulp proper. NK1 receptor-positive cells were frequently observed in the cell-rich zone beneath the odontoblast layer. The results indicate that, in the mature rat molar pulp, the main targets for substance P acting through the NK1 receptors are tissues related to blood vessels in the odontoblast and subodontoblast area. Furthermore, the expression of NK1 receptors on cells located in the subodontoblast area could indicate that substance P also affects cell functions in this area.

Immune defense mechanisms of the dental pulp

Defense reactions of the dentin/pulp complex involve a variety of biological systems, in which the immune system plays a pivotal role. The knowledge of the organization and function of pulpal immunocompetent cells has been sparse, but in recent years a significant body of information of immune mechanisms in general has provided a footing for substantial new knowledge of the immune mechanisms of the dental pulp. The identification of pulpal dendritic cells (DCs) has generated research activities which have led to a concept of how an antigenic challenge may evoke a pulpal inflammatory response. Although DCs are not able to identify foreign antigens specifically, they provide necessary signals to activate T-lymphocytes which in turn will orchestrate other immunocompetent cells to mount the local immune defense of the dental pulp. The purpose of this review is to accent the organization and function of pulpal DCs and other tissue and cellular components and to provide a basis for how they may interact to instigate pulpal defense mechanisms.

An evaluation of after-office-hour dental trauma in Singapore

The purpose of this study was to assess the post-traumatic sequelae and treatment outcome and the corresponding prognostic factors at the initial emergency visit. Over a 5-year period, the authors collected case records from 129 dental trauma patients. These patients had been referred subsequent to receiving emergency treatment after office hours at the Accident and Emergency Department of Singapore General Hospital. After the exclusion of 31 cases with concomitant fracture of maxilla and/or mandible and cases with insufficient documentation, the final study sample consisted of 98 patients (41 males, 57 females) who had sustained injuries to 264 permanent teeth. The main cause of dental trauma was falls (56%), and the main type of injuries was periodontal tissue injuries with or without concomitant injuries to hard tissue, including root fracture (73%). For the final evaluation, teeth with insufficient recall period were excluded before univariate and multivariate stepwise logistic regression analysis. It was found that for 100 teeth with luxation type of injuries, the presence of concomitant hard tissue injuries retained prognostic significance for pulpal outcome (p < 0.001) after adjusting for severity of luxation, while the severity of luxation was the only significant factor for periodontal outcome (p < 0.001). For 34 avulsed teeth, the stage of root development was the major factor associated with the pulpal outcome (p = 0.003), while extra-alveolar storage media were found to be significantly related to the periodontal outcome (p < 0.001). For 72 teeth with hard tissue injuries, first-visit interval played a significant role in the outcome (p = 0.03). Although the sample size in the root fracture group was too small for such statistical analysis, the results indicated that patient education on dental trauma was an important factor. Thorough standardized documentation was also recommended to facilitate optimal follow-up management and future research as well as medico-legal purposes.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Immunocompetent cells in rat periodontal ligament and their recruitment incident to experimental orthodontic tooth movement

The aims of this study were to evaluate the number and distribution of immunocompetent cells in normal rat periodontal ligament (PDL) and to quantify their recruitment incident to experimental tooth movement. 27 young animals had the 1st right maxillary molar moved mesially by an orthodontic appliance for 1, 3, 7 and 14 days, respectively. 4 animals served as untreated controls. An immunohistochemical procedure was carried out on alternate serial cryostat sections, and monoclonal antibodies against CD11b (macrophages, dendritic cells), CD43 (lymphocytes, polymorphs), CD4 (helper T-lymphocytes), and class II MHC molecules were used. Mean counts of the immunolabeled cells in the control group showed the highest number of CD11b+ and class II molecule expressing cells, while CD4+ and CD43+ cells were scarcely found. Significant increase in the number of CD11b+, CD43+ cells and class II molecules was found in the PDL of the experimentally moved 1st molars compared with the contralateral side and the control group, while CD4+ cells showed no significant increase. CD11b+ and cells expressing class II molecules were found around hyalinized tissue, between dentin and cellular cementum and close to Malassez' epithelial cells. In conclusion, normal rat PDL has high number of macrophage and dendritic-like cells, but few lymphocytes and granulocytes. Furthermore, experimental tooth movement leads to significant recruitment of cells belonging to the mononuclear phagocytic system, but has no significant effect on the number of lymphocytes and granulocytes in the rat PDL.

Effect of capsaicin treatment or inferior alveolar nerve resection on dentine formation and calcitonin gene-related peptide- and substance P-immunoreactive nerve fibres in rat molar pulp

The aim of this study was to investigate whether decreased sensory innervation induced by capsaicin treatment or axotomy of the inferior alveolar nerve has an effect upon dentine formation in the rat first molar. Dentine formation was visualized by intravital injection of Procion brilliant Red H8BS and denervation was verified immunohistochemically for the neuropeptides calcitonin gene-related peptide (CGRP) and substance P. The observation times were 6 weeks for the capsaicin-treated group and 11 days for the axotomized group. Capsaicin injections caused a consistent reduction in numbers of CGRP- and substance P-immunoreactive fibres in the pulps and a somewhat smaller reduction in the periodontal tissues. Unilateral axotomy of the inferior alveolar nerve induced an almost complete loss of immunoreactive fibres in the pulp and in the mesial gingiva of the first molar. Dentine formation at the mesial pulp horn and at the central pulp floor was significantly reduced in both groups compared to controls. The results suggest that sensory neuropeptides such as CGRP and substance P may play a part in dentine formation.