Rat Periapical Lesions Research Articles

Periapical lesions in rats with streptozotocin-induced diabetes

The purpose of this study was to investigate histologically and histometrically the changes in pulpal periapical tissues after pulpal exposure in streptozotocin-induce diabetic rats. Control rats were injected with citrate buffer. Experimental rats were injected with streptozotocin dissolved in citrate buffer. All animals received a pulpal exposure in the left mandibular first molar. Blood glucose concentration was measured at, 0, 7, 14, 28, and 42 days. All animals were killed at 7, 14, 28, and 42 days after pulpal exposure, and their mandibles were evaluated histologically and histometrically. Blood glucose levels in the experimental rats were significantly higher than those in the control rats. In experimental rats, inflammation in the apical periodontal ligament and root resorption and alveolar bone resorption were more severe than that in control rats. This study also revealed histometrically that, in experimental rats, lesions in the periapical area were significantly larger than those in control rats.

Immunolocalization of bone‐resorptive cytokines in rat pulp and periapical lesions following surgical pulp exposure

The bone-resorptive cytokines interleukin 1 (IL-1) and tumor necrosis factor (TNF) have been implicated in the pathogenesis of many chronic inflammatory diseases, including pulpitis and apical periodontitis.To further elucidate their role in these disorders, we have identified cells that express IL-1 alpha and TNF alpha in infected pulps and in developing rat periapical lesions after surgical pulp exposure. As detected by immunohistochemistry, IL-1 alpha- and TNF alpha-positive cells were present as early as 2 days after pulp exposure in both the pulp and periapical region. The numbers of cytokine-expressing cells increased up to day 4 in the pulp and up to day 30 in the periapex. In contrast, cells expressing IL-1 beta and TNF beta, the homologous forms of these mediators, were not found in pulp or periapical lesions during this period. Cells expressing IL-1 alpha and TNF alpha were identified primarily as macrophages and fibroblasts, with occasional staining of polymorphonuclear leukocytes. Osteoblasts and osteoclasts were also positive, whereas lymphocytes were negative. In general, cytokine-expressing cells were located proximal to abscesses and the root apex. These findings demonstrate that cells that express bone-resorptive cytokines IL-1 alpha and TNF alpha are present immediately after pulp exposure in this model, which supports the hypothesis that these mediators play a key role in pulpal and periapical pathogenesis, including the concomitant bone destruction. They also indicate that both resident connective tissue cells as well as infiltrating cells express bone-resorptive cytokines in response to infection in these lesions.

Effect of traumatic occlusion on periapical lesions in rats

The effect of traumatic occlusion on periapical lesions in rats was investigated histologically and histometrically. Rats were divided equally into groups A to D. Rats in group A received no treatment; in group B, rats received pulpal exposure of the left mandibular first molar; in group C, a resin plate was cemented onto the occlusal surface of the corresponding maxillary molar; and in group D, the molar pulp was exposed and the resin plate was installed. At 1 and 2 wk, compression of the periodontal ligament and inflammation were less in group D than in group B. Lesions in the periapical periodontal ligament at 1, 2, and 4 wk in group D were significantly smaller than those in group B. This study suggests that traumatic occlusion delayed the enlargement of the periapical lesions in rats.

Detection of interleukin-1β mRNA in rat periapical lesions

Cells expressing interleukin-1 beta (IL-1 beta) mRNA were demonstrated by in situ hybridization in rat periapical lesions. A great number of osteoclasts with significant tartrate-resistant acid phosphatase activity were observed on the bone surfaces, and numerous IL-1 beta mRNA-expressing cells were widely distributed in the periodontal ligaments. IL-1 beta mRNA-expressing cells were mainly observed around the blood vessels in the vicinity of the bone resorption sites and occasionally found near the osteoblasts. Immunohistochemistry and enzyme histochemistry assays showed that IL-1 beta mRNA-expressing cells were not bone cells, but that they had the characteristic features of macrophages. These results suggested that macrophages may contribute to the production of IL-1 beta and play an important role in activation of osteoclastic bone resorption.

Pathogenesis of induced rat periapical lesions

Studies of the mechanisms of pathogenesis of periapical lesions were undertaken using a rat model of surgical pulp exposure. In this model, periapical lesions develop rapidly between days 0 and 15 (active phase) and more slowly thereafter (chronic phase). A Gram-negative anaerobic flora, similar to that seen in human beings, are quickly established. Lesions contain a mixed inflammatory cell infiltrate consisting of T cells, neutrophils, B cells, macrophages, and plasma cells. Helper T cells predominate during the active phase, whereas suppressor T cells are more frequent in the chronic phase. Extracts of periapical lesions contain bone-resorbing activity, the highest levels of which are present when lesions are actively expanding. Most bone-resorbing activity is mediated by the cytokine interleukin-1α, as determined by biochemical criteria and antibody neutralization studies. Prostaglandin 2 accounts for 10% to 15% of resorptive activity. Cells that express interleukin-1α were identified in pulp beginning on day 2 after exposure and in periapical tissue beginning on day 7, as determined by in situ hybridization and immunostaining. Macrophages, fibroblasts, neutrophils, and osteoclasts were positive for interleukin-1α mRNA and protein. Cells that express tumor necrosis factor α were also detected, whereas cells expressing interleukin-1β or tumor necrosis factor β were absent. Finally, periapical bone destruction was inhibited by 60% by treatment with interleukin-1 receptor antagonist. These studies establish a key role for interleukin-1α in the pathogenesis of periapical lesions in the rat model.

Effect of methotrexate-induced neutropenia on rat periapical lesion

We investigated the effect of methotrexate-induced neutropenia on periapical lesions in rats. Periapical lesions were prepared in all animals by pulpal exposure. The animals were injected with methotrexate three times a week 4 weeks before or after the pulpal exposure. The periapical lesion of each animal was examined histologically, histometrically, and immunohistochemically. The total leukocyte count and neutrophil count in the peripheral blood decreased after the injection. The methotrexate-induced neutropenia elicited after pulpal exposure did not change the status of the periapical lesion, whereas the neutropenia before the exposure inhibited the development of the lesion. Moreover, the neutropenia before pulpal exposure resulted in an inhibition of infiltration of neutrophils into the lesion.

Immnohistochemical examination on the localization of macrophages and plasma cells in induced rat periapical lesions

To investigate the role of plasma cells and macrophages in the development of periapical lesions, we immunohistochemically examined the distribution of these inflammatory cells in experimental induced rat periapical lesions after pulpectomy. The number of ED1-positive mononuclear cells increased rapidly, reached a plateau which remained stable between days 10 and 60, and subsequently decreased. Immunoglobulin (Ig)-bearing plasma cells appeared after 60 days, and, of these, IgG-bearing plasma cells were predominant after 90 days. The radiographic and histopathological findings indicated the development of bone destruction at 10 days which continued until 60 days; tissue repair began to take place after 90 days. The results suggested that macrophages had a close relation to bone destruction and that plasma cells might participate in tissue repair rather than the development of periapical lesions.

Endotoxin and Gram-negative bacteria in the rat periapical lesions

The purpose of this study was to measure the amount of endotoxin as well as to identify Gram-negative bacteria in experimental periapical lesions in rats. Molar pulps were exposed and infected and the amount of endotoxin in the periapical tissue of the right mandibular first molar was measured by Endospecy, while the colony number of Gram-negative bacteria was determined in the same region of the left mandibular first molar. In the control animals, the amount of endotoxin in the periapical tissues did not change at all during the experimental period, and no Gram-negative bacteria were isolated. In the experimental animals, the amount of endotoxin in the periapical tissues increased gradually from 1 to 70 days, and its level was significantly greater than that of control animals after 7 days. Gram-negative bacteria were isolated from the periapical tissues and their number gradually increased from 1 to 14 days (26 to 82%), but decreased at 21 days. It was approximately 60% from 28 to 70 days. The results of this study showed that the amount of endotoxin in the periapical tissues gradually increased with increasing time and that Gram-negative bacteria were isolated from the same region but did not increase in number concurrently with the increase in the amount of endotoxin.

Kinetics of immune cell and bone resorptive responses to endodontic infections

Infection of the dental pulp stimulates a host immune response in the periapical region (the periapical "lesion") with the concomitant resorption of bone. The cell composition of human or rat periapical lesions is mixed, consisting of T, B, and "null" lymphocytes, plasma cells, macrophages, polymorphonuclear leukocytes, and mast cells. Cells are thus present which mediate a broad spectrum of immunological phenomena. In order to determine which of these mechanisms contribute to periapical bone resorption, a rat model system has been used in which periapical lesions are induced by pulp exposure and infection from the oral environment. In this model, a rapid period of lesion expansion and bone destruction occurs between days 1 and 15 after exposure (active phase), with a chronic phase characterized by lesion stabilization commencing thereafter. Phenotypic analysis of the cellular infiltrate has shown that T helper cells predominate during the active phase, whereas increased numbers of T suppressor cells are associated with chronicity. Extracts of periapical lesions contain bone-resorbing activity, as determined by the release of 45Ca from prelabeled a rat long bones in organ culture. Higher levels of bone-resorbing activity are present during the active than in the chronic phase. Characterization of bone-resorbing activity indicates the presence of resorptive mediators which are heat labile and protease sensitive and which are distinct from lipopolysaccharide. Preliminary biochemical fractionation indicates that resorptive mediators fractionate in the 15,000- to 60,000-dalton molecular mass range, presumably cytokines such as interleukin 1 and tumor necrosis factor. These studies demonstrate the utility of the rat model for studying mechanisms of periapical lesion pathogenesis and implicate T helper cell-mediated activities, in particular those leading to macrophage activation and cytokine production, in periapical lesion expansion.

T Helper and T Suppressor Cell Reversal During the Development of Induced Rat Periapical Lesions

T helper (TH) and T suppressor (TS) cells were enumerated in developing rat periapical lesions in order to identify the cell type associated with the active phase of lesion formation. Experimental pulp exposures were made in all molar teeth of 29 Sprague-Dawley rats, and teeth were left open to the oral environment. On days 15, 20, 30, and 90 after induction, inflammatory cells were isolated from periapical lesions, and T helper (W3/25+), T suppressor (OX8+), and total T cells (W3/13+) were enumerated by reactivity with monoclonal antibodies. During the early, most active phase of lesion development (day 15), TH cells outnumbered TS cells (TH/TS = 1.7). However, by day 20, when lesion expansion had slowed, the TH/TS ratio was reversed (0.9) and remained so for up to 90 days after induction (TH/TS = 0.7). Total T cell numbers did not change over the period of observation. TH cells thus predominated during the active phase of lesion development, whereas TS cells were associated with the chronic phase. This dynamic TH/TS reversal indicates that immune responses which occur within periapical lesions are highly regulated. In addition, the predominance of TH during the active phase of lesion development suggests that TH-mediated activities may be involved in the bone destruction and immune cell activation within periapical lesions.

The effect of indomethacin on experimental dental periapical lesions in rats

The role of prostaglandins in the pathogenesis of dental granulomas and associated bone loss was studied by testing the ability of indomethacin, a potent inhibitor of prostaglandin synthesis, to influence bone resorption in experimentally induced dental granulomas. The cusps of maxillary first molar teeth of Sprague-Dawley rats were ground away, exposing the dental pulps to the oral environment. Daily i.p. injections of 0.1 to 0.2 ml of indomethacin (10 mg per kg) dissolved in 95% ethyl alcohol were administered to one group of the rats while the other group received i.p. injections of 0.1 to 0.2 ml of 95% ethyl alcohol. The rats were killed after 6 wk and specimens of the molar teeth and surrounding jaw bone were taken for routine histopathological processing. The specimens from indomethacin-treated rats demonstrated milder inflammatory changes and a significantly lower degree of periapical alveolar bone resorption. These results support the suggestion that prostaglandins are involved in the events leading to bone resorption in dental periapical lesions.

Identification of inflammatory cells in developing rat periapical lesions

In a time-course study, cells isolated from developing rat periapical lesions were characterized to determine the inflammatory cell type(s) associated with active lesion formation. Experimental pulp exposures were made in all molar teeth of 40 Sprague-Dawley rats, and teeth were left open to the oral environment. On days 15, 20, 30, and 90 after induction, inflammatory cells from periapical lesions were isolated and enumerated by morphological and phenotypic criteria. At all time points, lymphocytes were found to be the predominant cell type (50 to 60%), followed by polymorphonuclear leukocytes (25 to 40%), macrophage-monocytes, plasma cells, and blasts (10 to 15%). No significant time-related differences in morphological types were found. Phenotyping with monoclonal antibodies specific for all T cells (W3/13) and la antigen-positive cells (OX4) revealed that T cells constituted the major non-polymorphonuclear leukocyte inflammatory cell component and outnumbered la-positive B cells at all time points. T cells rather than B cells may therefore play an important role in the pathogenesis of periapical lesions in this model system.