Trigeminal sensory nerve patterns in dentine and their responses to attrition in rat molars.

OBJECTIVE: Our goal was to define trigeminal nerve ending quantities and patterns in rat molar dentine, their responses to attrition (tooth wear), and their associated odontoblasts and connections with pulpal plexuses. DESIGN: Trigeminal ganglia were labeled for axonal transport of 3H-proteins to dentinal nerve endings in male rats (3-13 months old). Autoradiography detected radio-labeled dentinal tubules as indicators of nerve ending locations. Quantitative morphometry was done (ANOVA, t-tests), and littermates were compared for attrition and innervation. RESULTS: There were six dentinal patterns, only two of which had an associated neural plexus of Raschkow and cell-free zone (Den-1, Den-2). Other nerves entered dentin from bush-like endings near elongated odontoblasts (Den-B), as single fibers (Den-X), as networks in predentine (PdN), or as single fibers in tertiary dentine at cusp tips (Den-S). There were at least 186,600 innervated dentinal tubules within the set of three right maxillary molars of the best-labeled rat, and similar densities were found in other rats. Attrition levels differed among cusps and in littermates (t-test p < 0.02-0.0001), but the matched right/left cusps per rat were similar. Innervations of tertiary and enamel-free dentine (Den-S, Den-X) were preserved in all rats. Den-B and Den-2 coronal patterns were unchanged unless displaced by dentinogenesis. Den-1 losses occurred in older cusps, while Den-2 patterns increased near cervical and intercuspal odontoblasts. CONCLUSIONS: The extensive molar dentinal innervation had unique distributions per rat per cusp that depended on region (buccal, middle, palatal) and attrition, but only two of six patterns connected to a plexus of Raschkow.

Chewing causes rapid changes in immunoreactive nerve patterns in rat molar teeth: Implications for dental proprioception and pain.

OBJECTIVE: This study tests the hypothesis that normal use of teeth (chewing) causes changes in immunoreactive-(IR) patterns for endings of large Aß and CGRP axons in rat molar cusps. DESIGN: First, a new paradigm to test chewing in adult male rats was developed. Then IR patterns for large dental axons were analysed for a calcium-binding protein, parvalbumin (PV), heavy neurofilament protein-200 (NFP), and vesicle-release molecule synaptophysin (SYN) that all typify large dental axons and proprioceptors for comparison with endings of CGRP-IR neuropeptide axons. The behavior groups were: (1) daytime sleeping/fasting (Group:SF); (2) brief feeding after 8-11 h of daytime sleeping/fasting (Group:SF-C); (3) normal nocturnal feeding (Group:N); (4) nocturnal fasting (Group:NF); (5) brief feeding/chewing after nocturnal fasting (Group:NF-C). RESULTS: Nerve endings with NFP-, PV-, or SYN-IR were lost or altered in pulp and dentin in all chewing groups. Other endings with CGRP-IR were near those with PV-, NFP- and SYN-IR at the pulp-dentin border and in dentin, and they also lost immunoreactivity in all chewing groups. The special beaded regions along the crown pulp/dentin borders lost neural labeling in all chewing groups. Nerves of molar roots and periodontal ligament were not changed. CONCLUSIONS: Rapid neural reactions to chewing show extensive, reversible, non-nociceptive depletions of crown innervation. Those changes were rapid enough to occur during normal feeding followed by recovery during rest. The new dental paradigm related to chewing and fasting allows dissection of intradental proprioceptive-like mechanisms during normal tooth functions for comparison with nociceptive and mechanosensitive reactions after injury or inflammation.

Multiple complex somatosensory systems in mature rat molars defined by immunohistochemistry.

OBJECTIVE: Intradental sensory receptors trigger painful sensations and unperceived mechanosensitivity, but the receptor bases for those functions are only partly defined. We present new evidence here concerning complex endings of myelinated axons in rat molars. DESIGN: We sectioned mature rat jaws in sagittal and transverse planes to analyze neural immunoreactivity (IR) for parvalbumin, peripherin, neurofilament protein, neurotrophin receptors, synaptophysin, calcitonin gene-related peptide (CGRP), or mas-related g-protein-receptor-d (Mrgprd). RESULTS: We found two complex sensory systems in mature rat molar dentin that labeled with neurofilament protein-IR, plus either parvalbumin-IR or peripherin-IR. The parvalbumin-IR system made extensively branched, beaded endings focused into dentin throughout each pulp horn. The peripherin-IR system primarily made unbeaded, fork-shaped dentinal endings scattered throughout crown including cervical regions. Both of these systems differed from neuropeptide CGRP-IR. In molar pulp we found peripherin- and parvalbumin-IR layered endings, either near special horizontal plexus arrays or in small coiled endings near tangled plexus, each with specific foci for specific pulp horns. Parvalbumin-IR nerve fibers had Aß axons (5-7µm diameter), while peripherin-IR axons were thinner Aδ size (2-5µm). Mechano-nociceptive Mrgprd-IR was only found in peripherin-IR axons. CONCLUSIONS: Complex somatosensory receptors in rat molars include two types of dentinal endings that both differ from CGRP-IR endings, and at least two newly defined types of pulpal endings. The PV-IR neurons with their widely branched, synaptophysin-rich, intradentinal beaded endings are good candidates for endodontic non-nociceptive, low threshold, unperceived mechanoreceptors. The complex molar dentinal and pulpal sensory systems were not found in rat incisors.

Prospective study of histomorphometry, biochemical bone markers and bone densitometric response to pamidronate in ß-thalassaemia presenting with osteopenia-osteoporosis syndrome.

This study aimed to evaluate bone remodelling disorders in thalassaemia by using pamidronate (PD) infusion with or without hormone replacement therapy (HRT) as a diagnostic-therapeutic tool. In this prospective study, 24 adult thalassaemia major (TM) and 10 thalassaemia intermedia (TI) patients received either PD and HRT or HRT only (controls) for 3 years. Eugonadal patients with TI had PD only. Bone remodelling was assessed by dual energy X ray absorptiometry (DXA scan), type 1-collagen biochemical bone markers (BBM) and histomorphometry of iliac crest biopsy before and after PD. As a group, thalassaemics had a significant improvement in spinal and femoral bone mineral density Z scores following PD (P < 0·01) compared to the controls. Although BBM were comparable pre-therapy, they were significantly lower in the PD cohort (P < 0·001) compared to the control group. All patients had osteopenia, diminished osteoid formation and bone volume on histomorphometry pre-therapy with high turnover bone disease (HTO) in TM and low-turnover disease (LTO) in TI. In TM, bone volume improved significantly, whereas TI patients showed little or no response to PD. In conclusion, histomorphometry data suggest that TM patients have a distinct pathology of high turnover bone disease compared to TI patients, who have low-turnover disease.

Odontoblasts in developing, mature and ageing rat teeth have multiple phenotypes that variably express all nine voltage-gated sodium channels.

OBJECTIVE: Our goal was to evaluate the expression patterns for voltage gated sodium channels in odontoblasts of developing and mature rat teeth. DESIGN: We analysed immunoreactivity (IR) of the alpha subunit for all nine voltage gated sodium channels (Nav1.1-1.9) in teeth of immature (4 weeks), young adult (7 weeks), fully mature adult (3 months), and old rats (6-12 months). We were interested in developmental changes, crown/root differences, tetrodotoxin sensitivity or resistance, co-localization with nerve regions, occurrence in periodontium, and coincidence with other expression patterns by odontoblasts such as for transient receptor potential A1 (TRPA1). RESULTS: We found that Nav1.1-1.9-IR each had unique odontoblast patterns in mature molars that all differed from developmental stages and from incisors. Nav1.4- and Nav1.7-IR were intense in immature odontoblasts, becoming limited to specific zones in adults. Crown odontoblasts lost Nav1.7-IR and gained Nav1.8-IR where dentine became innervated. Odontoblast staining for Nav1.1- and Nav1.5-IR increased in crown with age but decreased in roots. Nav1.9-IR was especially intense in regularly scattered odontoblasts. Two tetrodotoxin-resistant isoforms (Nav1.5, Nav1.8) had strong expression in odontoblasts near dentinal innervation zones. Nav1.6-IR was concentrated at intercusp and cervical odontoblasts in adults as was TRPA1-IR. Nav1.3-IR gradually became intense in all odontoblasts during development except where dentinal innervation was dense. CONCLUSIONS: All nine voltage-gated sodium channels could be expressed by odontoblasts, depending on intradental location and tooth maturity. Our data reveal much greater complexity and niche-specific specialization for odontoblasts than previously demonstrated, with implications for tooth sensitivity.

Trigeminal injury causes kappa opioid-dependent allodynic, glial and immune cell responses in mice.

BACKGROUND: The dynorphin-kappa opioid receptor (KOR) system regulates glial proliferation after sciatic nerve injury. Here, we investigated its role in cell proliferation following partial ligation of infraorbital nerve (pIONL), a model for trigeminal neuropathic pain. Mechanical allodynia was enhanced in KOR gene deleted mice (KOR-/-) compared to wild type mice. Using bromodeoxyuridine (BrdU) as a mitotic marker, we assessed cell proliferation in three different areas of the trigeminal afferent pathway: trigeminal nucleus principalis (Vp), trigeminal root entry zone (TREZ), and trigeminal ganglion (TG). RESULTS: In KOR-/- mice or norBNI-treated mice, the number of proliferating cells in the Vp was significantly less than in WT mice, whereas cell proliferation was enhanced in TREZ and TG. The majority of the proliferating cells were nestin positive stem cells or CD11b positive microglia in the Vp and macrophages in the TG. GFAP-positive astrocytes made a clear borderline between the CNS and the PNS in TREZ, and phosphorylated KOR staining (KOR-p) was detectable only in the astrocytes in CNS in WT mice but not in KOR-/- or norBNI-treated mice. CONCLUSIONS: These results show that kappa opioid receptor system has different effects after pIONL in CNS and PNS: KOR activation promotes CNS astrocytosis and microglial or stem cell proliferation but inhibits macrophage proliferation in PNS. The trigeminal central root has a key role in the etiology and treatment of trigeminal neuralgia, and these newly identified responses may provide new targets for developing pain therapies.

Dexamethasone effects on Na(v)1.6 in tooth pulp, dental nerves, and alveolar osteoclasts of adult rats.

Dexamethasone causes extensive physiologic reactions including the reduction of inflammation and pain. Here, we asked whether it also affected dental or periodontal cells or dental innervation by altering voltage-gated sodium channel Na(v)1.6 immunoreactivity (IR) or neural synaptophysin. Daily dexamethasone (0.2 mg/kg) given for 1 week to rats caused 12-fold increased intensity of Na(v)1.6-IR in dendritic pulpal cells of normal molars and incisors compared with vehicle treatment. These cells also co-localized monocyte (ED-1) or dendritic cell (CD11b/Ox42) markers, and their location in molars expanded during dexamethasone treatment to include deeper pulp. Furthermore, dexamethasone caused a 10-fold decrease in the number of Na(v)1.6-immunoreactive multinucleate osteoclasts along the alveolar bone of molar root sockets. No changes occurred for neural Na(v)1.6 at axonal nodes of Ranvier, even though IR for calcitonin gene-related peptide was greatly decreased, as expected, and neural synaptophysin-IR was decreased 59% by dexamethasone. At 4 days after tooth injury, pulpal vasodilation and increased Na(v)1.6-immunoreactive pulp cells were similar for all groups. Thus, dexamethasone changes dental pulp cell and alveolar osteoclast Na(v)1.6-IR in normal teeth, but different mechanisms occur after tooth injury when tissue reactions were similar for dexamethasone- and vehicle-treated rats. Steroid-induced alterations of dental pain and inflammation coincide with altered exocytic capability in dental nerve fibers as shown by synaptophysin-IR and with altered pulp cell Na(v)1.6-IR and osteoclast number, but not with any changes in Na(v)1.6-IR for nodes of Ranvier in myelinated dental axons.

Endothelin receptors and endothelin-1 in developing rat teeth.

INTRODUCTION: The endothelins are a family of small peptides with multiple roles in a variety of tissues. Signaling is mediated through two receptor subtypes, the endothelin A receptor (ET(A)) specific for Et-1 and the non-specific endothelin B receptor (ET(B)). OBJECTIVE: Our goal was to determine the location of immunoreactivity (IR) for ET(A) and ET(B) in developing and mature rat teeth as indicators of endothelin (Et) regulatory sites and to compare this to the Et-1 (ligand)-IR expression patterns. DESIGN: We used immunohistochemistry to study developing and mature rat molars and continuously developing incisors. RESULTS: We demonstrate ET(A), ET(B), and Et-1 expression patterns in teeth, for the first time. ET(A) was found in developing molar root pulp, pulpal vasculature, and preodontoblasts, and then persisted in odontoblasts or cellular cementocytes at the root apices of mature teeth. ET(B) was found at the molar (Hertwig's) root sheath during root formation and in molar ameloblasts, nerve fibers and odontoblasts of immature and mature teeth. In incisors, ET(B)-IR was associated with ameloblasts and the stem cell niche of the cervical loop while ET(A) was located in the substratum layer. Et-1 was found throughout the dental and periodontal tissues with higher concentrations associated with odontoblasts, nerves and incisor layers that expressed ET(B). CONCLUSION: The patterns of ET(A) and ET(B) in teeth differ from each other and from those of adjacent tissues suggesting multiple tooth-specific functions for endothelin during development and mature dental function.

Peripherin- and CGRP-immunoreactive nerve fibers in rat molars have different locations and developmental timing.

UNLABELLED: Developing rat molars gain mature sensitivity to electric stimulation at 4-5 weeks after eruption, but the related mechanisms are incompletely understood. Preliminary studies showed weak co-localization of calcitonin gene-related peptide (CGRP) immunoreactivity (IR) with peripherin (PER) or neurofilament protein (NF) in rat molar nerve fibers, while the latter two co-localized extensively. OBJECTIVE: Our goal was to compare timing and location of PER-IR and CGRP-IR innervation in rat first molars during tooth maturation. METHODS: We used single and double immunocytochemistry to study molars of rats aged 10 days to 1 year. Neural patterns were compared with odontoblast maturation stages, dentinogenesis, formation of cell-free and cell-rich zones, and root closure. RESULTS: Spatial and temporal patterns showed that most CGRP-IR and PER-IR have different terminal domains in teeth. PER-IR fibers were well established among immature odontoblasts prior to tooth eruption, but CGRP-IR fibers were absent. Two weeks after eruption of first molars, many CGRP-IR beaded fibers entered dentin, the larger PER-IR fibers began shifting away from odontoblasts towards the pulp, and the symmetrical PER-IR pulpal pattern was being established. The CGRP-IR fibers continued to increase their asymmetric dentinal innervation until root growth was completed, during which time odontoblasts matured, the cell-free and cell-rich zones appeared, and roots closed. CONCLUSIONS: Sensory maturation of rat molars coincides with closed root apices, extensive innervation of dentin by CGRP-IR nerve fibers, and the appearance of the mature avascular odontoblast layer next to cell-free and cell-rich zones in the pulp horns.

Behavioural responses following tooth injury in rats.

Early changes in spontaneous behaviour (exploration, grooming, freezing, rearing, jaw motion, yawning) and body weight were measured at two and three days after pulp exposure injury and implantation of Fluorogold (FG) into molar teeth of rats. Rats with FG and injuries to three teeth gained weight less rapidly, explored less frequently and froze more often than sham-operated rats. Yawning was not observed in any rats prior to surgery and it was seen more frequently in tooth-injured rats than in sham-operated rats. These results suggest that careful observation of spontaneous behaviour after tooth injuries can be used to assess dental pain in rats and may provide behavioural markers to correlate with anatomical changes after injury. The dental nerve cell bodies that had accumulated transported FG were medium to large, and they only co-localized calcitonin gene-related peptide (CGRP) in a subset of the medium neurons. Chromatolytic or moribund FG-labelled neurons were also found.

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.

GFAP immunoreactivity and transcription in trigeminal and dental tissues of rats and transgenic GFP/GFAP mice.

Sensory mechanisms in teeth are not well understood and may involve pulpal-neural interactions. Tooth cells that proliferate in vitro have polyclonal immunoreactivity (IR) for glial fibrillary acidic protein (GFAP), growth-associated protein (GAP-43), and vimentin, plus glial-like ion channels. Here, we analyzed GFAP-IR patterns in dental and trigeminal tissues of rats, for comparison with green fluorescent protein (GFP) associated with GFAP transcription in transgenic mice, in order to better characterize glial-like cells in dental tissues. Astrocytes, ganglion satellite cells, and epineurial Schwann cells were demonstrated by anti-GFAP antibodies and GFP-GFAP, as expected. Odontoblasts did not stain by any of these methods and cannot be the glial-like cells. Fibroblasts and undifferentiated mesenchymal cells in pulp had polyclonal GFAP-IR and vimentin-IR, while nerve fibers reacted only with polyclonal antibody. Some Schwann cell subtypes in trigeminal nerve and oral mucosa were positive for GFP and for polyclonal anti-GFAP, but not for monoclonal antibody. In pulp almost all Schwann cells were unstained, but many Schwann cells in periodontal ligament had polyclonal GFAP-IR. These results show greater heterogeneity for Schwann cells than expected, and suggest that the glial-like pulp cells are fibroblasts and/or undifferentiated mesenchymal cells or stem cells. We also found that polyclonal GFAP revealed intermediate filaments in preterminal sensory nerve fibers, thereby providing a useful marker for that neural subregion. GFP transcription by some Schwann cell subtypes in oral mucosae and trigeminal nerve, but not trigeminal root was a novel finding that reveals more complexity in peripheral glia than previously recognized.

Dental neuroplasticity, neuro-pulpal interactions, and nerve regeneration.

This review covers current information about the ability of dental nerves to regenerate and the role of tooth pulp in recruitment of regenerating nerve fibers. In addition, the participation of dental nerves in pulpal injury responses and healing is discussed, especially concerning pulp regeneration and reinnervation after tooth replantation. The complex innervation of teeth is highly asymmetric and guided towards specific microenvironments along blood vessels or in the crown pulp and dentin. Pulpal products such as nerve growth factor are distributed in the same asymmetric gradients as the dentinal sensory innervation, suggesting regulation and recruitment of those nerve fibers by those specific factors. The nerve fibers have important effects on pulpal blood flow and inflammation, while their sprouting and cytochemical changes after tooth injury are in response to altered pulpal cytochemistry. Thus, their pattern and neuropeptide intensity are indicators of pulp status, while their local actions continually affect that status. When denervated teeth are injured, either by pulp exposure on the occlusal surface or by replantation, they have more pulpal necrosis than occurs for innervated teeth. However, small pulp exposures on the side of denervated crowns or larger lesions in germ-free animals can heal well, showing the value of postoperative protection from occlusal trauma or from infection. Current ideas about dental neuroplasticity, neuro-pulpal interactions, and nerve regeneration are related to the overall topics of tooth biomimetics and pulp/dentin regeneration.

Trigeminal ganglion neuronal activity and glial fibrillary acidic protein immunoreactivity after inferior alveolar nerve crush in the adult rat.

Nerve injury to the mandibular division of the trigeminal nerve has been shown to cause satellite cell reactions that extend beyond the mandibular division of the trigeminal ganglion into the maxillary and ophthalmic divisions. The goal of this study was to determine whether any physiological abnormalities correlated with this dispersal of satellite cell reaction. We investigated the electrophysiological and satellite cell glial fibrillary acidic protein immunoreactivity (GFAP-IR) changes that occur within the trigeminal ganglion 3, 10 and 59 days after a crush injury of the inferior alveolar nerve (IAN). At 3 days after IAN crush, there were no mechanically-evoked responses to ipsilateral stimulation of the skin and intraoral structures (e.g., mandibular incisor, lower lip and rostral mandibular gingiva) innervated by the IAN. However, the peripheral representations of the auriculotemporal, mylohyoid, lingual and maxillary nerve were intact and no abnormal responses to mechanical stimulation were detected to stimulation of tissue innervated by these nerves. By 10 days after the IAN crush, mandibular neurons responded to mechanical and electrical stimuli of the peripheral receptive field of the IAN, but with slower conduction velocities and higher electrical thresholds compared to control values. These abnormal electrophysiological response characteristics persisted 59 days following nerve injury. At 3, 10 and 59 days after IAN crush, 3-4% of the recorded mandibular neurons displayed spontaneous activity that was never observed in rats without nerve injury. Spontaneous activity was also never observed in neurons recorded in the maxillary or ophthalmic divisions of the trigeminal ganglion. Intense GFAP-IR in satellite cells was observed surrounding a mean of 131.7 neurons/section within the mandibular division of the trigeminal ganglion 3 days after nerve injury and around 50.3 neurons/section at 10 days. GFAP-IR was also present surrounding 16.5 and 10.3 neurons/section in the maxillary division of the trigeminal nerve at 3 and 10 days, respectively. At 59 days after IAN crush, GFAP-IR satellite cells were found around 22.9 neurons/section in the mandibular division of the trigeminal nerve, but were not found elsewhere in the trigeminal ganglion. The more extensive distribution of neurons encircled by satellite cell GFAP-IR compared to the trigeminal ganglion region containing abnormal electrophysiological responses demonstrates that abnormal neuronal signaling may not be characteristic of trigeminal ganglion neurons that are surrounded by GFAP injury reactions. However, the persistence of GFAP-IR 59 days after nerve injury suggests that satellite cell GFAP is involved in the long-term recovery of injured neurons.

Dexamethasone treatment reduces sensory neuropeptides and nerve sprouting reactions in injured teeth.

Dental injuries have been shown to generate extensive structural and cytochemical changes in sensory fibers that contain neuropeptides such as calcitonin gene-related peptide (CGRP) or substance P (SP). The present study was designed to test whether the anti-inflammatory drug dexamethasone (DEX) can alter neural responses to dental injuries. DEX (20 micrograms/100 g body weight) was given to adult rats (n = 10) prior to dental surgery and daily thereafter for 4 days. Control animals received sterile saline vehicle (n = 6) or no injection (n = 1). Each rat was then anesthetized for dental surgery and a cavity was drilled partway through dentin on the anterior side of the right maxillary first molar. Pulp exposure injuries were also made on two right mandibular molars in 14 of 17 rats. After 4 days of daily drug treatment, the rats were anesthetized and fixed by perfusion with formaldehyde-picric acid, and their jaws were prepared for immunocytochemistry. Neural CGRP immunoreactivity near the maxillary cavity injury site of DEX-treated rats was reduced more than 50% compared to controls, as determined both qualitatively and by digital analysis. The SP immunoreactive (IR) fibers in molar pulp also had extensive inhibition of neural reactions to cavity injury. DEX also reduced the immunoreactivity for CGRP and SP in normal contralateral rat molars of all treated rats, and it caused a postoperative loss of weight. Pretreatment for 1-5 days prior to the 4 day injury gave the same results as pretreatment for 1 h. The mandibular pulp exposure injuries induced a chronic abscess and advancing pulpal necrosis but did not show differences in nerve reactions between DEX-treated rats and the controls. In conclusion, the synthetic steroid dexamethasone suppressed the CGRP and SP neuropeptide immunoreactivity in normal dental nerves and it reduced nerve-sprouting responses to dentin cavity injuries; however, sensory nerve reactions to pulpal exposure injuries were not affected by DEX in these experiments.

Dental sensory receptor structure in human teeth.

Electron microscopy was used to study normal human extracted teeth in order to define the junctions between sensory nerve endings and other cells in external pulp and inner dentin at the crown tip. Two sets of associated cells were found: (1) Connective tissue cells. The pulpal fibroblast newtork made occasional desmosome junctions with the odontoblast newtork, and the cells of each network formed many gap junctions and desmosomes with one another. (2) Nerve endings. The terminal axons formed a succession of appositions with each other or with Schwann cells in the plexus of Raschkow and the cell-free zone, possibly with fibroblasts in the cell-free zone and odontoblast layer, and with odontoblasts in the odontoblast layer, predentin and dentin. The appositions between nerve endings and their companion cells at all levels usually maintained a regular intercellular spacing of at least 15-20 nm. In predentin and dentin, axons could be easily identified by their distinctive vesicles and mitochondria, and they often occurred within clusters of adjacent dentinal tubules; in the odontoblast layer axon identification was much more difficult. Axo-axonic appositions were found in the plexus of Raschkow, the cell-free zone, predentin and dentin; in many cases, bare axons were separated from each other only by a 5-10 nm extracellular space. Dental sensory mechanisms are discussed in relation to these observations.