Periapical innervation of the ferret canine and the local retrograde neural changes after pulpectomy

A Case of Respiratory Epithelium-Lined Cyst with Enriched Nociceptor Innervation

Apical lesions of endodontic origin can be classified as either granulomas or cysts. In rare cases, respiratory epithelium can proliferate and encapsulate a lesion, forming a cyst. Moreover, the innervation of apical lesions has only been previously reported in animal models of apical periodontitis. This report demonstrates an unusual case in which tooth #15 was initially treated with nonsurgical root canal therapy. Still, the patient remained in moderate to severe pain for several days following the procedure. Next, an intentional replantation was performed in which a periapical cyst was curetted from the alveolus. The patient experienced immediate pain relief following the procedure. Histological analysis revealed that the periapical cyst was lined entirely with respiratory epithelium, and immunohistochemical analysis showed it to be densely innervated. In addition, these nerve fibers expressed the LPS receptor, TLR4. This is the first demonstration of the innervation pattern of a periapical cyst. Further studies are warranted to evaluate innervation in apical lesions and its correlation with pre- and intra-operative symptoms and their participation in the pathogenesis of apical periodontitis.

Animal Models for Stem Cell-Based Pulp Regeneration: Foundation for Human Clinical Applications

IMPACT STATEMENT

Animal models are essential for tissue regeneration studies. This review summarizes and discusses the small and large animal models, including mouse, ferret, dog, and miniswine that have been utilized to experiment and to demonstrate stem cell-mediated dental pulp tissue regeneration. We describe the models based on the location where the tissue regeneration is tested-either ectopic, semiorthotopic, or orthotopic. Developing and utilizing optimal animal models for both mechanistic and translational studies of pulp regeneration are of critical importance to advance this field.

Upregulation of Basic Fibroblast Growth Factor in Human Periapical Lesions

Basic fibroblast growth factor is one of a class of heparin-binding growth factors that stimulates endothelial cell proliferation and migration in vitro and angiogenesis in vivo. The purpose of this study was to investigate the expression of basic fibroblast growth factor in chronic periapical lesions of endodontic origin. Ten chronic inflammatory periapical lesions were examined using immunohistochemical staining. The experimental control group consisted of four specimens of uninflamed periodontal ligament tissue. Two independent observers graded the staining intensity for basic fibroblast growth factor. An immunopositive, cytoplasmic, and nuclear reaction for basic fibroblast growth factor, with varying degrees of upregulation was observed in all 10 chronic periapical lesions. We speculate that the formation of granulation tissue and the activation of epithelial cell rests in chronical apical lesions might be associated with a local rise in the tissue level of basic fibroblast growth factor. Therefore, this growth factor could play an important role in the pathogenesis of chronic apical periodontitis and periapical cysts.

Thermal sensitivity of endodontically treated teeth

CASE REPORTS

The problem of thermal sensitivity following non-surgical root-canal treatment is explored and case reports are presented. Possible causes for post-treatment discomfort from endodontic and restorative aetiologies are discussed, as are the mechanisms to explain the patients' painful experiences. Treatment of this problem may vary from the simple replacement of a defective restoration to a more extensive non-surgical retreatment of the case, despite radiographic evidence of an acceptable root filling and normal periradicular tissues.

Periapical inflammatory responses and their modulation

Periapical inflammatory responses occur as a consequence of bacterial infection of the dental pulp, as a result of caries, trauma, or iatrogenic insult. Periapical inflammation stimulates the formation of granulomas and cysts, with the destruction of bone. These inflammatory responses are complex and consist of diverse elements. Immediate-type responses--including vasodilatation, increased vascular permeability, and leukocyte extravasation--are mediated by endogenous mediators, including prostanoids, kinins, and neuropeptides. Non-specific immune responses--including polymorphonuclear leukocyte and monocyte migration and activation, and cytokine production--are elicited in response to bacteria and their products. Interleukin-1 and prostaglandins in particular have been implicated as central mediators of periapical bone resorption. Chronic periapical inflammation further involves specific T- and B-cell-mediated anti-bacterial responses, and activates a network of regulatory cytokines which are produced by Th1- and Th2-type T-lymphocytes. Various naturally occurring and genetically engineered models of immunodeficiency are beginning to help elucidate those components of the immune system which protect the pulpal/periapical complex. Both specific and non-specific responses interface with and are regulated by the neural system. The modulation of these responses by immune response modifies, cytokine antagonists, and other novel therapeutic agents is discussed. As an experimental model, periapical inflammation has many advantages which permit it to be used in studies of microbial ecology and pathogenesis, host response, neuroimmunology, and bone resorption and regeneration.

Periapical neural changes after pulpectomy

Pulpectomy and pulpal necrosis result in severance of the nerves that supply the pulp as well as loss of their target organ. Inflammatory changes commonly extend into the periapical region to involve those nerves. The neural response to pulpal loss combined with periapical inflammation is a derangement of the periodontal plexus normally located in the center of the periodontal space around the apical third of the root; the result is the formation of a disorganized group of sprouting and branching axons that have some features in common with neuromas. The inflammatory and neural responses continue for at least a year even when pulpectomy is followed by canal debridement and obturation. Then the responses are reduced but not eliminated by steroids. Root canal therapy with techniques that do not leave residual inflammation still results in increased periapical innervation; the increase seems to be an organized addition to the normal periradicular plexus.

A histological comparison of periapical inflammatory and neural responses to two endodontic sealers in the ferret

Previous studies have shown that there is a proliferation of nerves beneath the apices of pulpectomized teeth. This may be due to the inflammation induced after the procedure, resulting, perhaps, from the irritant nature of the materials used to fill the root canal. The experiment reported here was conducted to determine whether this inflammation was induced by the sealer rather than arising as a result of tissue damage and whether, if inflammation is eliminated or reduced, the neural changes are also reduced. In 12 young adult ferrets under general anaesthesia the pulps of the lower canine teeth were removed and replaced with gutta percha and sealer. A sealer of Grossman's formulation with eugenol as the liquid phase was used on one side and a calcium hydroxide sealer that contained no eugenol on the other. Three months later the animals were, again under general anaesthesia, perfused with a fixative mixture. The mandibles were removed and the presence and size of any periapical inflammatory lesions and the density of periapical innervation determined histologically. All 12 teeth sealed with the Grossman's sealer had inflammatory lesions at their apices. Three of the 12 teeth treated with the calcium hydroxide sealer showed similar lesions. In all the teeth with inflammatory lesions the normal arrangement of nerves in a periodontal 'plexus' was disrupted but there was no statistically significant difference between the overall innervation density in inflamed and non-inflamed periapical areas nor between areas beneath teeth sealed with Grossman's sealer and with calcium hydroxide. The incidence of periapical inflammation is related to the nature of endodontic sealer used.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral microflora of the ferret at the gingival sulcus and mucosa membrane in relation to ligature-induced periodontitis

The aim of this study was to describe, in the domestic ferret, the composition of the normal gingival sulcus and the near related mucosa microflora and the shift in the composition during an acute periodontal breakdown induced by the placement of ligatures. Five animals were used. At the start of the experiment (day 0) and before the placement of the ligatures, 2 microbiological samples were obtained from the gingival sulcus and the related mucosa at the mid-buccal surface of the right upper P4. The same sites were sampled on the left side, serving as control sites. On day 28, new microbiological samples were taken from the same 4 sites. The samples were analyzed with darkfield microscopy and with viable counts. In the darkfield analysis, on day 0, the predominant bacterial morphotype was cocci, ranging from 88-92%. The viable counts showed that nearly 100% of the total cultivable flora was composed of facultative anaerobic gram-negative and gram-positive rods. Pasteurella spp., Corynebacterium spp. and Rothia spp. were the major components of these bacterial groups. No anaerobic bacteria were detected. On day 28, cocci decreased to approximately 75% in the experimental gingival sulcus sample, and filaments and rods increased significantly. Spirochetes remained largely unchanged during the experiment. The composition of the experimental site samples changed. There was a decrease in the mean numbers of facultative anaerobic gram-positive rods, and approximately one third of the microflora comprised anaerobic gram-negative rods, mainly Porphyromonas gingivalis and Fusobacterium spp. Although the composition of the microflora of the ferret presented few similarities to that described in dogs and monkeys, the anaerobic portion of the gingival sulcus and oral mucosa microflora related to ligature-induced periodontitis presented microorganisms observed in experimental periodontitis both in dogs and monkeys as well as in human periodontal diseases.

Normal histologic features of domestic ferret periodontium

The normal histologic features of the periodontal tissues in 17 domestic ferrets (10 male and 7 female) are described. The following teeth were histologically evaluated: canines, the maxillary third premolar (P3), the mandibular fourth premolar (P4), the carnassial teeth (P4 in the maxilla and the first molar, M1, in the mandible) and the next molar after the carnassials (M1 in the maxilla and M2 in the mandible). After histologic preparation for light microscopy, the sections were analyzed at magnifications of x 20 and x 100. The histometric measurements performed were 1) distance between the cementoenamel junction (CEJ) and the alveolar bone crest, 2) distance between CEJ and the most coronal connective tissue, 3) root length, 4) width of the periodontal ligament at three different locations along the root surface, and 5) cementum layer thickness at the most apical portion of the root. The number of sections exhibiting root resorption was counted. The results gave the normal values of some common periodontal variables and suggested a possible future use of the domestic ferret as an alternative experimental animal in periodontology.

The reinnervation of healing extraction sockets in the ferret

The objective of this study was to describe the pattern of healing of pulpal and periodontal nerve fibers following tooth extraction. The mandibular canine teeth were, under general anesthesia, removed from one side of nine young ferrets. One week (two animals), one month (four animals), and three months (three animals) later, again under general anesthesia, the animals were perfused with fixative. The mandibles were decalcified, paraffin-embedded, and serially sectioned. Sample sections were stained with hematoxylin and eosin, the remainder with a silver stain for nerves. Serial reconstructions were made of the innervation in control teeth and in the extraction sockets. A grid sampling technique was used for the estimation of the innervation density in different regions at various levels in the healing socket. One week after extraction, although osteoid material was beginning to fill the socket, the pattern of innervation remained similar to that of controls in being restricted to the former location of the periodontal ligament and being densest in the apical third of the socket. One month after extraction, the innervation consisted of many fine axons or small bundles distributed throughout the healing osteoid tissue though still most dense in the periphery of the socket. The overall innervation density increased between one week and one month post-extraction. At three months, as the margins of the socket were becoming obscured, the innervation consisted largely of one or two organized nerve trunks running from the apical to the coronal aspect in either the central or lateral aspects of the socket. At no time was there evidence of neuroma formation.

Neural changes in periapical lesions after systemic steroids in the ferret

This study was intended to clarify the relationship between the neural changes which occur around the apex of the ferret canine after pulpectomy and the inflammatory process induced by the procedure. In 12 young adult ferrets, under general anesthesia, the pulps in the mandibular canine teeth were removed and replaced with gutta percha and Grossman's sealer. Six of the animals were treated with dexamethasone to reduce the inflammatory response. Three months later, the animals, again under general anesthesia, were perfused with a fixative mixture. Three unoperated animals that had not been treated with dexamethasone were also perfused. The mandibular canine teeth and their supporting tissues were removed, processed, and serially sectioned. Three-dimensional reconstructions of the periapical lesions in each animal were assembled and their volumes measured. The density of innervation in the periapical region was estimated. The mean lesion volume in the pulpectomized animals not treated with dexamethasone was 3.54 (+/- 2.27) mm3 and in the dexamethasone-treated animals 1.33 (+/- 1.31) mm3. The differences were statistically significant when tested by the Mann-Whitney U test (p < 0.01). Bacteria were not seen within any of the lesions. The innervation density beneath the canines in the pulpectomized animals not treated with dexamethasone was 164 units per mm2 (+/- 80) and in the steroid-treated animals 151 +/- 68 units per mm2. In the control, untreated animals, the innervation density was 22 +/- 10 units per mm2. The difference between the steroid-treated pulpectomized animals and the untreated pulpectomized animals was not statistically significant (p > 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Trigeminal nuclear complex of the ferret: anatomical and immunohistochemical studies

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroanatomical istribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs.

Healing of induced periapical lesions in ferret canines

A previous study showed that the ferret canine is an appropriate model for inducing periapical lesions. Ferret canines were used in this study to study changes in periapical lesions after root canal treatment (RCT). After periapical pathosis was induced in the maxillary and mandibular canines of six ferrets, RCT was performed on three of the four canines in each animal. Each ferret received periodic intraperitoneal injections of Procion red dye. Two animals were killed at each of 4, 8, and 12 wk after RCT. Apices and surrounding lesions were evaluated radiographically, histologically, and by fluorescent microscopy. Periapical radiolucencies increased in size during induction but showed no changes after RCT. Lesions in untreated teeth showed features of granulomatous inflammation, mainly the presence of macrophages and lymphocytes. After RCT, there was histological evidence of healing in the form of cementum deposition, increased vascularity, and increased fibroblastic and osteoblastic activity. Fluorescent staining showed cementum deposition of variable thickness in the treated specimens.

Induced periapical lesions in ferret canines: histologic and radiographic evaluation

Ferrets have been utilized in endodontic research to study periapical responses. However, various aspects of induction and healing of periapical pathosis in ferrets are unclear. This study evaluated the radiographic and histopathologic features of induced periapical lesions. Periapical pathosis was consistently produced in 8 canines of 2 ferrets by extirpating the pulp, leaving the cavities open for a week, then sealing for 12 weeks. The resulting lesions were evaluated radiographically every two weeks. The animals were then killed and the induced lesions evaluated histologically and histobacteriologically. Four untreated canines from 2 other ferrets were used as controls. Results showed that periapical rarefactions were visible in all teeth in the experimental group within 4 weeks. Histologically, the induced lesions consisted principally of a mononuclear inflammatory infiltrate, dominated by macrophages but with numerous lymphocytes. With Brown & Brenn staining, bacteria were demonstrated in the pulp space of teeth in which the lesions were induced and in the apical arborization of the canal system. Only one specimen had bacteria within the periapical lesion.

Periapical innervation of the ferret canine one year after pulpectomy

Previous studies have shown that, following removal of the dental pulp and its replacement with a filling material, the nerves in the periapical region proliferate within an area of chronic inflammation. This study examined these responses in the ferret in more detail, both quantitatively and in three dimensions, 12 months after pulpectomy which was followed by obturation with gutta percha and zinc oxide and eugenol sealer. The results were compared with the responses after three months. The basic patterns, in terms of both inflammation and neural proliferation, were similar at the two time periods. Both the sizes of the inflammatory lesions and the degree of neural proliferation were lower at 12 months than at three, although the differences were not significantly different in the small number of specimens examined. Bacterial stains failed to show bacteria either in the apical root canal delta or in the periapical area. It is possible that the persistent inflammation was due to the irritant nature of the obturating materials used but not due to the original tissue damage, since extraction sites, by comparison, healed very quickly. Apparently, following endodontic treatment, chronic periapical inflammation and concomitant neural proliferation can continue for long periods.

Distribution and morphological characteristics of axons in the periodontal ligament of cat canine teeth and the changes observed after reinnervation

The distribution and morphological characteristics of myelinated and non-myelinated axons innervating the lower canine periodontal ligament (PDL) in adult cats have been analysed. After perfusion fixation and decalcification, the teeth were slit transversely, divided into segments, and embedded in plastic. Ultrathin sections of each segment were examined in the electron microscope and used to reconstruct the whole PDL at 1, 4, 7, and 9 mm from the tooth apex. One millimeter from the tooth apex there were a mean of 920 myelinated axons and 1,415 non-myelinated axons. The numbers of axons declined toward the tooth crown. Bundles of myelinated and small non-myelinated axons lay adjacent to the blood vessels midway between the bone and cementum. Isolated myelinated axons appeared to have split away from these main nerve bundles and entered the avascular zone of the ligament, where they lost their myelin sheaths to become large non-myelinated axons rich in mitochondria. These non-myelinated axons sometimes appeared to be linked to collagen fibres and were thought to be the mechanoreceptor terminals. Twelve weeks after sectioning and inferior alveolar nerve, the total number of axons innervating the periodontal ligament was 50% of that found in the contralateral controls. The large non-myelinated axons had smaller mean diameters and contained fewer mitochondria, a change which may be consistent with a reduction in mechanoreceptor excitability.

Anterograde horseradish peroxidase tracing and immunohistochemistry of trigeminal ganglion tooth pulp neurons after dental nerve lesions in the rat

The peripheral reorganization of pulpal nerves after tooth injury was studied, in the rat, with anterograde horseradish peroxidase tracing techniques, and combined retrograde Fluorogold tracing and immunohistochemistry was employed to examine the effects of inferior alveolar nerve lesions or tooth injury on some cytochemical characteristics of pulpal trigeminal ganglion nerve cells, namely content of substance P, calcitonin gene-related peptide and the ganglioside GM1 (binding subunit of cholera toxin), as well as affinity to RT 97 (antibody to neurofilament protein) and the lectin Griffonia simplicifolia isolectin I-B4. Anterograde horseradish peroxidase tracing demonstrated that pulpal nerves either disappear or reinnervate novel targets after loss of pulpal tissue. There were no obvious signs of neuroma formation. Retrograde Fluorogold labelling with immunohistochemistry showed that after inferior alveolar nerve lesions with subsequent regeneration, a much higher proportion of Fluorogold cells (15%) were substance P-positive compared to normal (2%). In addition, 3% of the cells were Griffonia simplicifolia isolectin I-B4-positive. Such cells were very rare in controls. Proportions of calcitonin gene-related peptide-, GM1- and RT-97-positive cells were normal. After tooth lesions, the proportions of Fluorogold-positive substance P-, Griffonia simplicifolia isolectin I-B4-, GM1- and RT 97-labelled cells were similar to controls, while the proportion of calcitonin gene-related peptide-positive neurons was reduced. The results show that pulpal deafferentation may change the long-term cytochemical characteristics of affected trigeminal ganglion neurons.

The effect of pulpectomy on the longitudinal distribution of nerve fibres in the periodontal ligament of the ferret

The innervation density of the periodontal ligament was measured at a series of levels around the mandibular canines of 6 ferrets, in 5 of the which the pulp of one of each of these pairs of teeth had been removed 3 months earlier. In control (unoperated) teeth the density of innervation was greatest in the apical third and lowest in the coronal third. The pattern around the pulpectomized teeth was similar. There was no statistically significant difference between density values for control and operated teeth. Pulpectomy thus does not affect the incidence or distribution pattern of nerves in the periodontal ligament.