Rat Molar Pulp Research Articles

Effect of traumatic occlusion on CGRP and SP immunoreactive nerve fibre morphology in rat molar pulp and periodontium.

Traumatic occlusion provides a trauma that affects the whole tooth and its supporting tissues. To study the effect of this trauma on CGRP and SP immunoreactive nerve morphology in pulp and periodontium, traumatic occlusion was induced in 2-months-old rats. The occlusal surface of the first maxillary molar in 30 rats were unilaterally raised 1 mm with a composite material. At different observation periods up to 30 days, the rats were transcardiacally perfused, the jaws demineralized, sectioned and processed for immunohistochemistry with the avidin-biotin-peroxidase method. Changes in nerve morphology, distribution and density in first and second molars and their supporting tissues were analyzed and compared in experimental (n = 30) and control rats (n = 14). Already after 5 days with traumatic occlusion, 22% of the experimental teeth had increased density of CGRP and SP immunoreactive nerves locally in gingiva, the periodontal ligament and the pulp, while in 15%, axonal proliferation and changed nerve morphology were found in the whole pulp (severe reaction). During a 20-day period, the pulpal nerve reactions progressed and included the whole pulp in 46% of the experimental teeth. The periodontal nerve responses were still localized only to the cervical and apical regions, and they remained local in these areas throughout the experimental periods. After 20 days the number of teeth with severe nerve changes seemed to decrease. The study shows that an unilateral change in occlusion of the first molar initiate nerve responses in the total molar dentition. In this experimental model the pulpal axons containing CGRP and SP reacted more serious to occlusal trauma than the nerves in the periodontium. The results indicate that the nerve changes in some cases might be transient.

Immunoelectron microscopic observation of calcitonin gene-related peptide (CGRP)-positive nerves in the dental pulp of rat molars.

The ultrastructure of nerves containing immunoreactivity for calcitonin gene-related peptide (CGRP) was investigated in the dental pulp of rat molars. The immunoreactivity was recognized predominantly in unmyelinated nerve fibers, and sparsely in a few myelinated fibers. It was localized throughout the axoplasm, as well as in the large cored vesicles. Small clear vesicles and mitochondria were free of the immunoreaction. The CGRP-immunoreactive nerves were frequently observed to terminate, being devoid of Schwann cell investment, in the vicinity of blood vessels in the coronal pulp, suggesting that CGRP may be involved in the regulation of pulpal blood flow. Moreover, CGRP-immunoreactive axon terminals containing numerous small clear vesicles, a few large cored vesicles and mitochondria were recognized in contact with the cell bodies of odontoblasts and their processes in the dentinal tubules. Although specialized synaptic ultrastructures were not recognizable, a functional association of CGRP nerves and odontoblasts was suggested. Thus, CGRP in the dental pulp appears to have multiple functions, including vascular regulation and sensory transduction.

Inflammation of rat molar pulp and periodontium causes increased calcitonin gene-related peptide and axonal sprouting.

We have studied the response of nerve fibers containing calcitonin gene-related peptide immunoreactivity (CGRP-IR) to inflammation using a rate dental experimental system. Inflammation was induced by drilling tooth cusps to create pulpal exposures; the induced pulpitis and subsequent periapical lesions were studied 1-35 days later using standard CGRP immunohistochemistry and the avidin-biotin peroxidase method. The injury and resulting inflammation caused a disruption of CGRP-IR nerve fiber location and arborization that varied depending on whether the initial injury was limited to the pulp tip or extended throughout the pulp horn. At shorter survival periods (24 hr, 3 days) nerve fibers were either decreased or bundled into the center of the pulp with sprouting along the wound border. At 6 days necrosis and acute inflammation had advanced to varying degrees, and CGRP-IR fibers were extensively sprouted in the surviving pulp; the pulp also stained specifically for CGRP within 1-2 mm of the inflamed tissue at 6 days. At 35 days, we found total pulp necrosis in most teeth and the development of periapical bone loss, granulomatous tissue, and periapical abscesses. There was also an extensive increase in CGRP-IR nerve fibers in the tissues surrounding sites of severe periodontal inflammation and necrosis. In some cases, macrophage-like cells staining specifically for CGRP were near the abscesses. The results show important interactions between peptidergic nerve fibers and inflammatory cells, and are discussed in terms of the role of nerve fibers containing CGRP in neurogenic inflammation, mechanisms for intensification of CGRP immunoreactivity in affected fibers or neighboring cells, and implications for chronic inflammatory conditions, dental pain, and anesthesia.

Development of the vascular supply in the dental pulp of rat molars--scanning electron microscope study of microcorrosion casts.

Development of the vascular supply in the dental pulp of rat molars--scanning electron microscope study of microcorrosion casts.

Bacterial contamination as a factor influencing the toxicity of materials to the exposed dental pulp

Three materials, which had been previously found to be toxic when applied as pulp-capping agents in conventional rat molar pulps, were retested in germ-free rats. All produced much more favorable responses in the pulp, with a lack of inflammation and the presence of dentine bridges in the majority of teeth. It appears that much of the pulp damage previously attributed to the chemical toxicity of materials may be caused by the presence of bacteria. The design of studies intended to evaluate the response of the pulp to materials should include staining techniques that will detect the presence of bacteria on the floors of test cavities.

Immunohistochemical study on regeneration of substance P-like immunoreactivity in rat molar pulp and periodontal ligament following resection of the inferior alveolar nerve

Using an indirect immunofluorescence method, after 14 days, regenerated SP-containing nerve fibres first appeared around the blood vessels in apical and coronal regions of the pulp and apical and middle regions of the periodontal ligament. Penetration of regenerated SP-positive fibres into the dentine and predentine was observed 25 days after operation. The number of regenerated SP-containing fibres recovered to nearly to the same level as in intact controls by 35 days. They had a similar distribution in the tissues.

Response of exposed pulp to composite resin in germ-free rat molars

The response of the pulp to the composite resin (Clearfil F) was histopathologically investigated in 23 germ-free rats. The upper first molar pulp was exposed with a #1/2 round bur through the mesial surface of the tooth and the cavity was arranged with a #33 1/2 inverted cone bur, and the composite resin was applied to the surface of the exposed pulp. The observation period was 2, 4, 7, 10 and 14 days postoperatively. The results indicated that the pulpal response to the composite resin was characterized by the initial weak inflammatory cell infiltration at 2, 4 and 7 days, followed by the reduced responses with evidence of newly formed calcified tissues at 10 and 14 days. However, moderate to severe circulatory disturbance was observed throughout the experimental period. From these findings, the composite resin proved to have an irritating potential on the rat molar pulp. The germ-free rats could be used as an excellent model to investigate the exposed pulp responses to the composite resin.

Scanning electron microscopic observations of the vascular system of rat molar pulps.

Scanning electron microscopic observations of the vascular system of rat molar pulps.

Terminal arborization of individual sensory axons in dentin and pulp of rat molars

Single sensory arbors labeled by axonal transport of [ 3H]proline were identified in rat molars and reconstructed from serial autoradiograms. Some axons ended in pulp, others made numerous endings in both dentin and pulp. Receptive fields in dentin varied from narrow (40–60 μm diameter) to elongated areas (80 × 350 μm). Sensory arbors had brush-like or fan-like shapes, the largest innervated more than 100 dentinal tubules.

The distribution and origin of substance P-like immunoreactivity in the rat molar pulp and periodontal tissues

Rat mandibles were fixed in Zamboni fixative and demineralized in a mixture of EDTA and fixative. Substance P-like immunoreactivity was demonstrated by indirect immunofluorescence in molar pulp, periodontal ligament and gingiva. Substance P (SP) containing nerve fibres with varicosities were observed in the pulp horn and root pulp in general located around blood vessels. Some SP-containing fibres penetrated into the predentine and dentine. In the periodontal ligament, SP fibres were localized along the blood vessels in the middle and apical regions. Many SP-containing fibres were associated with the blood vessels in the lamina propria of gingiva. After inferior alveolar nerve section, SP-positive nerve fibres in the pulp and periodontal ligament disappeared completely. In gingiva the number of SP fibres decreased but not all fibres disappeared. Removal of the superior cervical ganglion did not affect the distribution of SP-containing nerve fibres.

Primary mineralization of dentin in rats after pulp capping with calcium-hydroxide.

It has been previously reported that short term application of calcium-hydroxide to the dental pulp resulted in the formation of a dentin bridge with matrix vesicle calcification. The present study deals with the induction of reparative dentin in rat molar pulps by direct capping with calcium-hydroxide. The teeth were examined after 21 and 35 days. Transmission electron microscopy (TEM) revealed that the calcification process in the newly formed dentin was characterized by apatite deposition in matrix vesicles and the occurrence of calcifying nodules in the matrix. The persistence of these features of primary mineralization, during the experimental period, was associated with the continuous calcium hydroxide contact with pulp tissue, producing changes in its metabolic state.

Histologic study of pulp capping in rat molars using calcitonin

Calcitonin, a calcium regulating hormone, has been found to affect bone formation and resorption. In this study a calcitonin preparation and a calcium hydroxide preparation for comparison were applied to both exposed and unexposed rat molar pulps. Histologic examinations were conducted after periods of 1 day to 28 days. Calcium hydroxide pulp caps produced varying amounts of secondary dentin and inflammation. Calcitonin applied as an indirect agent had a similar effect. When calcitonin was applied to exposed pulp, a large amount of dense fibrous connective tissue reminiscent of scar tissue was formed. With increased time this connective tissue exhibited signs of progressive, orderly calcification continuing through a large portion of the coronal pulp.

Migration of materials and microorganisms in the dental pulp of dogs and rats

Data from a wide range of studies on pulp response to materials in rats and dogs and a series of gnotobiotic experiments designed to investigate pulp response to caries have been reviewed for evidence of migration of materials and bacteria within the pulp. Migration of materials after direct pulp capping was unusual in the rat molar pulp. In the dog, by contrast, migration of materials from direct pulp capping sites was frequently observed. When material particles were contained within phagocytic cells, there was little evidence of any pulp response; free material within the tissues was frequently associated with inflammation or necrosis. In the gnotobiotic studies, phagocytosis of strains of Streptococcus mutans by the pulp in carious teeth was seen.

A fine-structural investigation on the extent of perineurial investment of the nerve supply to the pulp in rat molar teeth

The fine structure of the tissues immediately adjacent to nerve fibres supplying the rat molar pulp has been examined and compared with that of perineurium of other peripheral nerves. In the periapical region, almost all nerve fibres were invested with typical perineurium; only a few Schwann cell units (unmyelinated axons) lacked perineurium. In the pulp at the apex of the distal root, most fibres were invested by less typical perineurium but some were not invested at all. In the pulp at the coronal end of the root, nerve fibres were completely invested or incompletely invested with attenuated perineurium or lacked investment altogether. In the coronal pulp, there was virtually no perineurium at all. Thus rat molar pulp nerve fibres lack perineurium for distances of about 0.5-3.0 mm, distances greater than in situations such as skin or muscle. In normal peripheral nerves, the perineurium behaves as a barrier to the passage of substances from the immediate environment of the nerve fibres (endoneurium) to the surrounding environment (epineurium) and vice versa. Its absence around pulp nerve fibres raises questions about the nature of the pulp environment and may help to explain the sensitivity of pulp nerves to chemical, osmotic and other stimuli.

A comparison of pulp responses to two different materials in the dog and the rat

A study is described in which the exposed pulps of dog and rat molars were capped with Dycal or zinc oxide and water. Favorable responses to both materials were observed in the rat molar pulp. Less favorable responses were observed in the dog. Detailed testing of pulp response to operative procedures and materials in different species is necessary.

The effect of buffer molarity on axonal exposure and axoaxonal apposition in the rat molar pulp.

Axons in the rat molar pulp have been examined morphometrically to determine axonal size and the degree of axonal exposure and axoaxonal apposition in tissue fixed by perfusion using 2% glutaraldehyde in cacodylate buffers ranging in molarity form 0.025 M to 0.4 M. Between 31.2% and 45.0% of the axons were incompletely ensheathed. This proportion of axons exposed was linearly related to the buffer molarity (P less than 0.05) and was approximately double that found in more central axons. Between 32.3% and 45.0% of the axons were in contact with other axons. This proportion was not linearly related to buffer molarity but was least ten times higher than that observed in more centrally positioned nerve fibers in the inferior alveolar nerves. Increasing buffer molarity reduced the size of the axons, a relationship not found in the more central axons. It is suggested that axonal exposure and axoaxonal apposition are constant, significant features of pulpal nerve fibers that may be related to the onset and spread of nociceptive activity. The permeability properties of pulpal axons may differ from those of more centrally placed axons.

Transmission electron microscopy of reparative dentin in rat molar pulps. Primary mineralization via extracellular matrix vesicles.

A reparative dentin bridge was induced in rat molar teeth by pulp exposure and capping with calcium hydroxide. Transmission electron-microscopic examination after 10 days revealed the presence of odontoblastic cells and collagenous matrix with focal calcifications. The calcifying fronts were composed of hydroxyapatite crystals. Numerous extracellular matrix vesicles were scattered between the forming cells and the calcifying fronts. Some of the vesicles contained electron-dense material and in others, apatite crystals were detected. Matrix vesicles could not be identified in normal, mature calcifying dentin matrix. In view of the present observations and studies on surgical manipulations in articular cartilage, it is concluded that matrix vesicle calcification may result from alterations in the metabolic state of mesenchymal tissues. These changes can be induced surgically or chemically.

Reaction of rat molar pulp tissue to Formocresol, formaldehyde, and cresol

The maxillary molars of rats were exposed and treated for five minutes with either Formocresol, formaldehyde, cresol, or glycerol—a control solution-and then covered with zinc oxide-eugenol and amalgam. After the treatment, the animals were killed at weekly intervals for four weeks. Analysis of histolgic sections showed that formaldehyde did not inhibit or enhance pulpal recovery when compared with the control solution. Cresol greatly hindered healing, as indicated by the lack of dentin bridge formation within the time span of this experiment. Formocresol treatment slowed, but did not prevent, the resolution of the defensive reaction.

The reaction of the rat molar pulp to various materials.

The reaction of the rat molar pulp to various materials.

Pulpal studies. I. Passage of 3H-tetracycline into circulatory system through rat molar pulps

Rats were used to study the fate of a radioactive antibiotic placed on injured pulpal tissue. Radioactivity found in the general circulation within 10 minutes after application was shown to be due to protein-bound, native, tritiated antibiotic.