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The purpose of this study is to observe the immunohistochemical localization of Receptor Activator of NF Kappa B Ligand (RANKL) in the rat periapical lesions. Periapical lesions were induced in Sprague-Dawley (SD) rats by occlusal exposure of the pulp of their mandibular first molars. Animals were sacrificed randomly at 0, 7, 14, 21, and 28 days after the exposure and their mandibles were removed, demineralized, and embedded in paraffin. Frontal sections in the region of the first molar were prepared for enzyme histochemistry and immunohistochemistry. Tartrate-resistant acid phosphatase (TRAP)-positive cells and RANKL-positive cells could be observed on day 7. From day 7 to day 14, increasing amounts of inflammatory infiltration and alveolar bone resorption were observed in the periapical region. The expression and number of TRAP-positive cells and RANKL-positive cells were climaxed on day 14. In the 21- and 28-day samples, the expression of RANKL decreased and fewer TRAP-positive cells could be observed. These findings demonstrated that RANKL could be observed, which may be associated with the pathogenesis of periapical lesions.

A novel protein known as receptor activator of NF-kappa beta ligand (RANK-L) has been identified as a potential osteoclast differentiation factor. However, comparatively little is known about the expression of RANK-L in the pathogenesis of periradicular lesions. In this study, RANK-L expression was evaluated in biopsy specimens from apical periodontitis. Tissue samples from 21 periapical lesions were collected. RANK-L mRNA was isolated by using the guanidinium isothiocyanate acid phenol method. This was followed by generation of cDNA using specific primer for RANK-L by reverse transcription polymerase chain reaction amplification. RANK-L expression in each periapical sample was assessed by agarose gel electrophoresis. Gel electrophoresis analysis showed a single band of 385 bp corresponding to RANK-L in every periapical lesion. By contrast, normal control tissue showed no detectable RANK-L mRNA expression. In conclusion, RANK-L may play a role in apical periodontitis-induced bone resorption.

Objective: To compare the endotoxin levels between acute and chronic periapical periodontitis with different clinical symptoms., Methods: 10 cases of acute periapical priodontitis(Group 1), 10 cases of chronic periapical periodontitis (group 2, the diameter of apical radiolucency area was less than 2 mm), 10 cases of chronic periapical periodontitis with sinus(group 3, the diameter of apical radiolucency area was greater than 2 mm), 10 cases of chronic periapical periodontitis without sinus (group 4, the diameter of apical radiolucency area was greater than 2 mm), were included in the study. Chromogenic substrate method of limulus amebocyte lysate(LAL) test was used to measure the endotoxin level., Results: Endotoxin concentrations in group 2 were significantly lower than those in group 1, group 3 and group 4(P < 0.01)., Conclusion: Endotoxin plays a very important role in the initiation and development of periapical periodotitis and is closely associated with clinical symptoms and apical radiolucency degree.

Objective: The purpose of this study was to quantify the cytokines interleukin (IL)-1 receptor antagonist (RA), IL-6, and transforming growth factor beta(1) found in extracts of inflammatory periapical tissues and to study the effect of a new antibiotic (linezolid) on the levels of these cytokines., Study Design: Twenty-two patients with root-filled teeth with persisting periapical pathoses were randomly divided into a control group or an antibiotic group. One tooth from each of the patients was resected at the root-end, and the periapical tissue was collected. IL-1RA, IL-6, and TGF-beta(1) were quantified in tissue extracts through the use of enzyme-linked immunosorbent assays., Results: Measurable amounts of all 3 cytokines were found in all extracts. A statistically significant reduction in IL-1RA per milliliter was observed in the linezolid group in comparison with the control group (P <.05). The difference in variation of IL-1RA in the treatment and control groups was also highly statistically significant (P <.001)., Conclusions: Although drawn from a limited sample size, the results indicate that IL-1RA is a sensitive indicator of the effect of antibacterial treatment on the immune response in periapical inflammatory tissues.

Objective: The aim of this study was to examine the levels of prostaglandin E2 in periapical exudates before and after root canal treatment., Methods: Periapical exudates specimens were quantitatively sampled from root canals of 25 teeth at consecutive treatment visits, and the concentration of prostaglandin E2 in each sample was determined using a commercial kit., Results: The mean prostaglandin E2 levels significantly decreased after the endodontic therapy. Significant correlations between the levels of prostaglandin E2 and the clinical features of periapical periodontitis were also found in this study., Conclusion: The results suggest that the level of prostaglandin E2 in periapical exudates reflects the state of periapical periodontitis.

Bacterial infection of the pulp and root canal system leads to the recruitment of immunocompetent cells in the periapex and stimulates inflammatory cell responses to produce a variety of inflammatory mediators. Cytokines, reactive oxygen intermediates, and reactive nitrogen intermediates are frequently found at sites of acute inflammation. In this study, we measured the levels of interleukin (IL)-8 and nitric oxide (NO) in the periapical exudate (PE) from human periapical lesions and investigated the association of these mediators with the clinical symptoms of periapical periodontitis. PE samples were collected from root canals during routine endodontic treatments. The IL-8 concentration was measured by the enzyme-linked immunosorbent assay, and the NO level was measured as nitrite/nitrate concentration assayed by the Griess reaction. Detectable levels of IL-8 and nitrite/nitrate were found in 24 and 19 of 27 PE-samples, respectively. Although PE-IL-8 and nitrite/nitrate concentration showed a broad range, a significantly positive correlation was found between both mediators. Also, significantly higher IL-8 levels were found in PE from lesions that had painful symptoms at the sampling visit. However, there was no relationship between elevated NO levels and clinical symptoms. These results suggest that the up-regulation of IL-8 may have a critical role in the development of the symptoms of periapical disease.

Apical periodontitis was induced in Wistar rats by exposing the pulp chamber of right mandibular first molars to the oral environment. Animals were killed 0, 5, 10, 15, 20, 30, 60, and 80 days after lesion induction. Microradiographic and automated image analysis showed that the lesions expanded significantly in a time-dependent manner from day 0 to day 20 (0.039 mm2/day, p < 0.05, active phase) and stabilized thereafter (chronic phase). A linear regression test revealed a positive correlation between the numbers of ED-1 positive macrophage per microscopic high power field and the periapical lesion size during the active phase (r = 0.98, p < 0.01). Immunohistochemical studies showed that transforming growth factor-beta 1 positive macrophages distributed around the root apex and areas showing bone resorption during active lesion phase, whereas TGF-beta 1-positive osteoblasts were detected during the chronic stage (days 30, 60, and 80 after pulp exposure). Histologically TGF-beta 1 positive osteoblasts possessed a large, round nucleus as well as an abundant cytoplasm and located in close vicinity to areas exhibiting reparative bone formation. These results suggest that macrophages may play important role(s) in the initiation and development of periapical lesions and TGF-beta 1 may play dual roles in both bone resorption and deposition in induced rat periapical lesions.

We examined the induction of the cytokines interleukin (IL)-1 beta, IL-6, and IL-8 by lipopolysaccharides (LPSs) from several species of possible endodontopathic black-pigmented bacteria. Studies were conducted in human whole blood cultures from six patients (two from each group) with differing numbers of periapical periodontitis lesions (i.e. patients with radiographically clear periapical lesions in 10 or more teeth (high-lesion group, n = 4), in one or two teeth (low-lesion group, n = 6), and six healthy volunteers with no periapical lesions (no lesion group)). LPS from Prevotella intermedia ATCC 25611, Porphyromonas gingivalis 381, and Prophyromonas endodontalis ATCC 27067 induced a higher IL-8 response in the subjects of the high-lesion group, compared with the subjects of the other two groups. To ascertain the degree of sensitization by test bacteria, we examined the reactivities of antibodies in serum and saliva from the subjects to different bacterial species. LPS from P. gingivalis reacted strongly with sera from the high-lesion group. Thus, LPS from black-pigmented bacteria may be involved in multilesional periapical periodontitis by inducing particular cytokines and/or humoral immune responses.

Background: The recognition that periodontal diseases are associated with specific pathogens has led to interest in the use of antibacterial drugs for inhibition of these microorganisms. On these bases, the present study was aimed at evaluating the tissue distribution of the new macrolide antibiotic azithromycin in patients subjected to oral surgery for chronic inflammatory diseases of both marginal and periapical periodontium., Methods: Thirty-two patients were treated with azithromycin 500 mg/day orally for 3 consecutive days, and drug concentrations in plasma, saliva, normal gingiva, and pathological periodontal tissues were evaluated. For this purpose, samples of blood, saliva, normal gingiva, granulation tissue, and radicular granuloma or cyst wall (from dentigerous cyst) were collected during oral surgery or 0.5, 2.5, 4.5, and 6.5 days after the end of pharmacological treatment; then, azithromycin levels were measured by a microbiological plate assay, using Micrococcus luteus NCTC 8440 as the indicator organism., Results: The concentrations of azithromycin in plasma, saliva, normal gingiva, and pathological tissues reached the highest values 12 hours after the last dose (0.37+/-0.05 mg/l, 2.12+/-0.30 mg/l, 6.30+/-0.68 mg/kg, and 11.60+/-1.50 mg/kg, respectively) and then declined gradually. Consistent levels of the drug in normal gingiva and pathological tissues could be detected, however, up to 6.5 days, indicating that azithromycin was retained in target tissues for a long time after the end of treatment. Moreover, azithromycin levels in both normal gingiva and pathological tissues exceeded the minimum inhibitory concentrations of most pathogens involved in the pathophysiology of chronic inflammatory periodontal diseases. Notably, azithromycin levels in pathological tissues were significantly higher than those in normal gingiva 0.5, 2.5, and 4.5 days after the last dose., Conclusions: The present results indicate a marked penetration of azithromycin into both normal and pathological periodontal tissues, suggesting that azithromycin represents a promising option in both adjunctive and prophylactic treatments of chronic inflammatory periodontal diseases.

Aim: In this study, the interaction of interferon-gamma-(IFN-gamma) and inducible nitric oxide synthase (iNOS)-producing cells in human radicular cysts were investigated., Methodology: Inflamed periapical tissues were obtained from patients at the time of endodontic surgical treatments and were cut into two pieces. After fixing with acetone or 4% paraformaldehyde in phosphate-buffered saline, 5-m-thick paraffin and cryostat sections were prepared. The paraffin sections of the inflamed tissues were evaluated histologically with haematoxylineosin stains. The specimens diagnosed as radicular cysts were then examined by immunostaining. Immunohistochemistry for iNOS and fluoresence microscopy for IFN-gamma using the cryostat sections were performed with a mixture of affinity purified human iNOS antiserum and human IFN-gamma monoclonal antibodies., Results: The results revealed that iNOS-gamma producing cells localized adjacent to IFN-gamma-producing cells. In addition, some of iNOS-producing cells exhibited immunoreactive IFN-gamma. On the other hand, epithelial cells showed significant levels of iNOS production, but not IFN-gamma., Conclusions: The data would suggest the possibility that iNOS production could be precisely controlled by autocrine or paracrine effects of IFN-gamma producing cells in radicular cysts and might play a pivotal role in periapical lesions. These findings are consistent with a hypothesis suggesting that NO inhibitors could be used through the root canals as a pharmacological treatment for periapical lesions.

Pulpal and periapical diseases are characterized by inflammation. The cytokine IL-6 is a major mediator of the host response to tissue injury and infection. This study examined the level of interleukin-6 (IL-6) in six inflamed human pulps and six human periapical lesions of endodontic origin using ELISA. Pulp samples from eight clinically impacted teeth were used as controls. The periapical samples exhibited significant levels of IL-6 (mean = 78.1 +/- 9 pg/mg protein) as did inflamed pulpal tissues mean = 36 +/- 3.9 pg/mg protein) compared to healthy pulp mean = 0.01 +/- 0.02 pg/mg protein). These data indicated that IL-6 was produced and released locally in the inflamed pulpal and periapical lesions.

Cells expressing interleukin-1 (IL-1) were examined in rat periapical lesions using immunohistochemical methods. During the acute phase, both IL-1 alpha- and IL-1 beta-expressing cells were observed adjacent to many osteoclasts that contained large cytoplasms, and consequently the periapical lesions tended to expand. However, the number of IL-1 beta-expressing cells was about twice that of IL-1 alpha-expressing cells during the same period. On the other hand, there were significantly less IL-1 beta-expressing cells during the chronic phase and consequently a significant expansion of the periapical lesions was not seen. Furthermore, IL-1 alpha- and IL-1 beta-expressing cells were located far from the bone surfaces, whereas a fibroblastic cell layer lay between the IL-1-expressing cells and the bone surfaces. Both IL-1 alpha and IL-1 beta were mainly expressed by macrophages. In addition, after the percolated application of formocresol to experimentally induced periapical lesions, numerous macrophages expressing IL-1 beta became conspicuous within the vicinity of the extensive bone resorption sites. These results suggest that macrophages expressing IL-1 beta may play an important role in the activation and recrudescence of osteoclastic bone resorption, and this may be due to their localization close to the bone resorption sites noted within experimental periapical lesions.

Exudate is often found in the root canal of teeth requiring endodontic therapy. The aim of this study was to evaluate the relationship of sequential changes of different host mediators in endodontic exudates to clinical and radiographic findings. Thirty-two nonvital teeth with periapical symptoms were evaluated. Exudates were collected with filter paper strips every 3 min after opening of the pulp chamber. The concentrations of beta-glucuronidase, IgG, IgA, IgM, and interleukin-1 beta in the exudates were analyzed. In general, the concentration of the mediators in exudates from less involved lesions did not change over time. The exception was an increase in the IgM concentration when patients presented with percussion or palpation sensitivity. In contrast, in the more involved lesions, the concentrations of IgA and IgM increased as sampling progressed. The concentrations of beta-glucuronidase and interleukin-1 beta decreased over time in the more involved lesions. These data suggest that the amount of proinflammatory mediators in the canal and periapical lesion is limited. Furthermore, IgM seemed to be a marker for the severity of periapical lesions. This may relate to vascular permeability that allows passage of this larger molecule into the extravascular environment.

Multimicrobial infection of the dental pulp triggers inflammatory responses and ultimately causes bone destruction in the periradicular tissues. Besides bacteria, noxious substances such as degraded protein components and cholesterol could also act as antigens and elicit a host response, which can be harmful to periradicular tissues. Histologically, a dense infiltration of immunocompetent cells is seen in periradicular lesions and their host reactions may induce bone resorption. Polymorphonuclear leucocytes (PMN) and macrophages migrate to the periapical lesions and phagocytose pathogens as a first line of defence. Dead PMN are quickly phagocytosed by macrophages and this disposal system plays a role in maintaining chronicity of the lesions. The pathological roles of periradicular T cells have been assessed through analysing phenotypic markers of cell types, especially CD antigens, but the results are still controversial. Recently, technical developments in immunology and molecular biology have made it possible to investigate the pathogenesis of many diseases at molecular level. The investigation of functional analysis of the immune cells and their regulatory molecules such as apoptosis-associated molecules and adhesion molecules, will lead to a better understanding of the pathogenesis of periradicular lesions. The role of inflammatory mediators including antibodies, cytokines, matrix metalloproteinases, growth factors and arachidonic metabolism is becoming known for these lesions. Knowledge from these investigations improve the understanding of the pathological mechanisms of periradicular infections.

Periradicular tissue samples were recovered from patients undergoing endodontic surgery. Immunohistochemical procedures were used to identify interleukin-6 (IL-6) present in the neutrophils associated with these lesions. Using specific polyclonal antibody, 15 to 20% of the neutrophils associated with the periradicular tissue lesions were positive for IL-6. IL-6-positive plasma cells and histiocytes were also abundant. Cytokine production by neutrophils from the peripheral blood of nondiseased individuals was also evaluated. The cells were stimulated with lipopolysaccharides and bacterial extracts of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Significant levels of IL-6 were produced by cells stimulated with Escherichia coli lipopolysaccharide B5 (933 pg/ml/10(7) neutrophils) and E. coli lipopolysaccharide B12 (791 pg/ml/10(7) neutrophils) when compared with unstimulated cells (39.31 pg/ml/10(7) cells). There was a dose-dependent increase in IL-6 production when cells were stimulated for 24 h with 6 and 12 micrograms/ml of A. actinomycetemcomitans extract. Less stimulation occurred with P. gingivalis, but it was also dose-dependent. Neutrophils resident in periradicular lesions may, therefore, provide a source of IL-6 in addition to that produced by tissue histiocytes and plasma cells.

Objective: To further study the mechanisms of damages and resorption of bone in chronic periapical periodontitis., Methods: The quantities and distribution of PGE2 and TXB2 in apical granuloma of chronic periapical periodontitis were analyzed using radio immunization analysis., Results: The quantities of PGE2 and TXB2 in apical granuloma of chronic periapical periodontitis were significantly (P < 0.05) higher than those in controls., Conclusion: The PGE2 has the close relation with the bone resorption of chronic periapical periodontitis during the whole process. Meanwhile, TXB2 also has certain relation with the bond absorption. The quantities of PGE2 and TXB2 are imbalanced.

To determine if nitric oxide (NO) is produced by chronically infected human polymorphonuclear leucocytes (PMNs) in vivo, inflamed exudates (periapical exudates: PE) collected from periapical periodontitis patients were examined. Cell-free supernatants and cells were separated by centrifugation. Significant levels of nitrite concentrations were observed in the supernatants. The production of inducible NO synthase (iNOS) in highly purified PMNs derived from PEs was then immunocytochemically determined using rabbit anti-human iNOS antiserum. In vitro, human peripheral blood PMNs (PB-PMNs) isolated from patients were cultured with a combination of Esherichia coli-lipopolysaccharide (LPS), recombinant human interferon-gamma (rhIFN-gamma) and/or interleukin-1 beta (rhIL-1 beta). The stimulated PB-PMNs showed steady-state levels of nitrite. The stimulation of LPS, rhIFN-gamma and rhIL-1 beta showed more NO induction than that of LPS with either IFN-gamma or IL-1 beta, suggesting the synergistic effects of cytokines. Cryostat sections of surgically removed periapical tissues were also immunohistochemically examined for iNOS, IFN-gamma and IL-1 beta. Two-colour immunohistochemistry revealed the interaction of iNOS-producing PMNs and IFN-gamma- or IL-1 beta-producing mononuclear cells. On the basis of these data, we concluded that with the stimulation of inflammatory cytokines derived from mononuclear cells, PMNs can spontaneously produce NO at the site of chronic infection. The present studies are consistent with a hypothesis suggesting that PMNs could be regulated and delicately balanced to produce NO by mononuclear cell-derived cytokines in vivo. NO-producing cells may play a pivotal role in chronic inflammation.

We have previously demonstrated that detectable levels of prostaglandin E2 exist in periapical exudates (PE-PGE2) from root canals of periapical periodontitis. Our data from a cross-sectional study also suggested the association of PE-PGE2 concentrations with the active phase of periapical lesions. The objective of this study was to investigate the longitudinal changes of PE-PGE2 levels during root canal treatment. Periapical exudate specimens were quantitatively sampled from root canals of 20 nonvital teeth at consecutive treatment visits to measure PGE2 concentrations. The mean PE-PGE2 levels significantly decreased following the endodontic therapy (158.0 +/- 54.1 pg/microliter in the first samples versus 48.4 +/- 37.9 pg/microliter in the second samples). A significant correlation was also found between the changes in PE-PGE2 levels and the clinical disease expression of periapical periodontitis (p < 0.01). Decreased PGE2 production is considered to reflect the remission of disease activity. These results suggest the central roles of PGE2 in regulatory mechanisms for the expression of periapical disease.

IL-1 beta is synthesized as an inactive precursor, which is subsequently processed by IL-1 beta converting enzyme (ICE) and found extracellularly as a mature biologically active polypeptide. Also, IL-1 beta has been detected in necrotic and inflamed dental pulp. We examined the IL-1 beta production in human dental pulp (HDP) cells treated with lipopolysaccharide (LPS) from Porphyromonas endodontalis (P. e.) isolated from root canals and radicular cyst fluids. We demonstrated that P. e. LPS stimulated IL-1 beta release from HDP cells in a time- and dose-dependent manner. However, ICE activity was not increased by P. e. LPS. Northern blot hybridization analysis revealed that the IL-1 beta mRNA level in HDP cells was increased by P. e. LPS. These results suggest that stimulation of IL-1 beta release from HDP cells by P. e. LPS may have an important role in the progression of inflammation in pulpal and periapical disease.

In this study the relationship of prostaglandin E2 (PGE2) concentrations in periapical exudates with clinical findings of teeth with periapical periodontitis is discussed. Periapical exudate samples were obtained from root canals of 77 endodontically involved teeth during routine root canal treatment by the quantitative sampling method using paper points. PGE2 concentrations in periapical exudates (PE-PGE2) were determined by radioimmunoassay. Significantly higher levels of PGE2 were found in periapical exudates from teeth with radiolucent areas than from teeth without radiolucent areas (236.8 +/- 521.3 pg/microliter vs. 14.9 +/- 23.1 pg/microliter, respectively). The elevated PE-PGE2 levels were associated with the presence of clinical symptoms that reflected an acute inflammation in the periapical lesion. In contrast, a significantly negative association of decreased PE-PGE2 levels with increasing size of radiolucent areas was demonstrated. These results suggested that PGE2 was produced locally in periapical lesions and that the PGE2 concentration in periapical exudate could reflect the state of the disease activity in periapical periodontitis.

In order to establish whether tissues damaged by Chronic Periapical Pathology (CPP) of endodontic origin produced heat shock protein (HSP) capable of attracting reactive lymphocytes, paraffin sections of samples from the oral cavity of 10 patients with CPP were incubated with commercially available anti-HSP monoclonal antibodies. Antibodies were evidenced employing the alkaline phosphatase immunoenzymatic method (DAKO). HSP was found in the lamina propria infiltrated by lymphocytes, in six of the ten samples. These results suggest that HSP may be one of the lymphocyte recruiting factors in the damaged area and opens new possibilities for further research.

The purpose of this study was to determine the concentration of leukotriene C4 (LTC4), a potent inflammatory mediator, in human symptomatic and asymptomatic periradicular lesions. Periradicular lesions from each of six asymptomatic and symptomatic patients were obtained. Six pulps from unerupted third molars served as the negative controls, six samples of chronically inflamed gingival tissues served as the positive controls. All samples were immediately frozen in liquid nitrogen. The concentration of LTC4 was determined by reverse-phase high-pressure liquid chromatography. Representative samples from each group were fixed in formalin, sectioned and stained with haemotoxylin and eosin. The concentrations of LTC4 found in the periradicular lesions were significantly higher than those in uninflamed pulpal tissue (P = 0.027). However, no statistically significant difference was found between the concentration of LTC4 in the periradicular lesions of the symptomatic patients and those found in the asymptomatic patients and in the samples of the chronically inflamed gingival tissue (P > 0.05). This data would suggest that among other inflammatory mediators, LTC4 participates in the pathogenesis of human periradicular lesions.

To identify the mediators that stimulate periapical bone resorption following infection, a rat model system was used in which active (rapid) and chronic (slow) phases of bone destruction can be distinguished. Extracts of inflammatory tissues from active lesions contained high levels of bone-resorbing activity, which was destroyed by proteinase K and heat (70 degrees C), but was unaffected by polymyxin B, indicating the presence of protein mediator(s) rather than lipopolysaccharide. Fast-performance liquid chromatography gel filtration of extracts of active lesions demonstrated that most activity was associated with macromolecules of MW 30-60 kDa and 15-20 kDa, consistent with bone resorptive cytokines, including interleukin 1 (IL-1) and tumor necrosis factor (TNF). Inhibition with cytokine-specific antisera demonstrated that resorbing activity in active lesions was significantly neutralized by anti-IL-1 alpha, whereas anti-IL-1 beta, anti-TNF alpha and anti-TNF beta had only slight effect. A lower amount of resorbing activity was present in extracts of chronic lesions, which was also neutralized only by anti-IL-1 alpha. Inflammatory tissue explants produced more IL-1 alpha than IL-1 beta in vitro, confirming findings with extracts, and high levels of IL-1 alpha were present in active lesions by radioimmunoassay. These data indicate that bone resorption stimulated by bacterial infection is primarily mediated by IL-1 alpha in this model. The similarity of cytokines in active and chronic lesions suggests that quantitative rather than qualitative differences in these mediators may account for lesion progression.

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.

The authors, thanks to the application of monoclonal antibodies, as well as the immunohistochemical technique of APAAP, have traced the qualitative and quantitative features of inflammatory cells implied in periapical lesions. Moreover ten patients, of whom 6 males and 4 females aged between 20 and 60 have been tested. The immunohistochemical reactions revealed a heterogeneous population of B and T (T4-T8) lymphocytes, together with myeloid trunk cells (granulocytes and histiocytes). The B lymphocytes form nearly 31.5% of all the inflammatory cell, whereas the T types form about 55.8. The granulo-histiocyte part implies 11.1% of all the inflammatory cells themselves. The average percentages of the roted inflammatory cells have been compared with two diagnostic categories of periapical granuloma and periapical cyst. However, by comparing the obtained results with the ones described by other authors, we notice agreement as for as qualitative analysis is concerned, while as for quantitative analysis, some differences are proved. Finally, this situation shows that the quantitative demonstration of inflammatory cell populations is only a moment in the development of immune reactions in the inflammatory tissue.

Leukotrienes play an important role in inflammation and its sequelae such as pain, swelling, and bone resorption. This review covers, their history, structure, synthesis, metabolism, biological effects, inhibitors, antagonists, and their possible role in pathogenesis of pulpal and periapical disease.

Samples were collected from the root canals of 30 teeth of patients with apical periodontitis and assayed for endotoxin content. The detection rates of endotoxin and endotoxin content were higher in symptomatic teeth, teeth with radiolucent areas, and teeth with exudation than in those without them.

Prostaglandins (PG) have been implicated in the genesis of periapical lesions. Periapical specimens from patients with clinical signs and symptoms of chronic and acute apical periodontitis were obtained and immediately frozen in liquid nitrogen. Periradicular tissues from unerupted third molars were frozen and used as controls. The concentration of PGE2 was determined by radioimmunoassay. Low levels of PGE2 were found in the control tissues as compared with those detected in chronic and acute lesions. Significantly higher levels of PGE2 were found in acute lesions than those found in chronic lesions. The results show that acute lesions have higher concentrations of PGE2 than chronic lesions and confirm the role of prostaglandins in the pathogenesis of human periapical lesions.

A model of traumatic periodontitis was created in 36 mongrel dogs and effects of periapical inflammation focus on trigeminal ganglia neurone structure were studied 1, 2, 3, 6, 12, and 24 months after experimental exposure of the animals. Histologic study was carried out by routine methods. In the first months after the intervention the morphologic shifts in the neurones represented drastic irritation and destruction. Later focal and diffuse inflammatory infiltrates and glial element growth were detectable in the ganglial stroma; reduced biopolymer levels were observed in the neurones and accumulation of their level in ganglial stroma. These data evidence an unfavorable effect of periapical focus on trigeminal ganglion elements.

Inflammatory lesions of periodontal and periapical connective tissue were studied by in situ hybridization to detect cells responsible for type I and type III collagen production. Formalin-fixed and paraffin-embedded tissue specimens from patients with oral lesions of various stages of inflammation were hybridized with cDNA probes specific for human pro alpha 1(I) and pro alpha 1(III) collagen mRNAs, and with bacteriophage lambda DNA as a control probe. This technique permitted us to localize fibroblasts active in type I collagen synthesis in the vicinity of inflammatory infiltrates in all the samples studied. Cells containing high levels of type III collagen mRNA were seen in early abscess formation and they were particularly abundant in pyogenic granuloma and irritation fibroma. Type I collagen mRNA was prominent in gingival fibrosis. In the infrabony lesions with active inflammatory infiltrations the production of collagen was confined mostly to the periphery of the lesions. These findings give indirect evidence that cytokines liberated during the early stages of the inflammatory process stimulate expression of the type III collagen gene by fibroblasts. In chronic lesions a gradual switch from type III to type I collagen gene expression occurs. The change in collagen types appears to underlie the observed isolation of the inflammation by a collagenous capsule. In all the samples studied fibroblasts exhibited marked variation in their levels of procollagen mRNAs, supporting previous views about their heterogeneity in connective tissues. The approach presented here offers new possibilities to study cellular interactions and metabolic activities in inflammatory lesions.

In 86 patients with chronic granulomatous and granulating periodontitis in the absence of other pathology the lipid peroxidation products levels were increased as indicated by accumulation of malonic dialdehyde and diene conjugates in the whole blood. The relative content of disulphide groups in the red blood cells was increased and that of sulfhydryl groups decreased. The findings correlate with those detected in granulomas.

An asymptomatic abscessed maxillary premolar, which had undergone previous endodontic treatment, was retreated. The initial attempt to remove the silver cone seal was unsuccessful. Early the next morning, the patient appeared with a severe cellulitis exacerbation. The silver cone was now loose: a lateral "blowout." Specific cultures of the silver cone and exudate revealed three aerobic microbes: a Streptococcus sp and two obligate Pseudomonas spp. Anaerobes were shown to be absent with anaerobic subcultures. This case would appear to substantiate the alteration of the tissue oxidation-reduction potential as the major factor in endodontic cellulitis exacerbations, as previously reported.

The Part 1 report revealed the microbiologic etiology and introduced the oxidation-reduction potential (Eh) as a major factor in acute cellulitis exacerbations during endodontic therapy. Facultative streptococci were the predominant group of microbes specifically isolated. This Part 2 study revealed a 9.5% incidence of cellulitis exacerbations in patients during endodontic treatment of 168 primarily intact nonvital teeth. These teeth were usually asymptomatic, manifesting radiographic periapical lesions without fistulous tracts and necrotic canals. This category of pulpal periapical inflammation is virtually the only type of tooth that is predisposed to cellulitis exacerbations. A frequency distribution of the 34 permanent teeth studied revealed a spectrum of mandibular and maxillary molars, premolars, and anterior teeth involved with the exacerbations. Sex and age did not appear to be factors. Further clinical evidence is cited, which support the concept of altering the tissue oxidation-reduction potential as the prime etiologic factor in favoring the growth of aerobic microbial pathogens.

A statement has been made by Sundqvist that it has not been possible to isolate the specific bacteria that is responsible for acute exacerbations during endodontic treatment of existing periapical inflammation. This clinical study presents specific microbial isolates from 34 intact nonvital teeth involved with acute cellulitis exacerbations during endodontic therapy. No obligate anaerobes were isolated. Forty-seven aerobic and facultative microbes were isolated. Streptococci, primarily facultative, were the major group of microbes isolated (80%); alpha hemolytic streptococci and the group D enterococcus were predominant as mixed and pure culture specimens. Gram-negative microbes as strict aerobic and facultative microbes were also reported as specific isolates. The biological role of anaerobes were discussed in primary pulpal-periapical infections. The alteration of the tissue oxidation-reduction potential, (Eh) is proposed as an etiologic factor in cellulitis exacerbations during endodontic treatment. This is further substantiated in the Part 2 report. Attention is drawn to the pathogenic potential of streptococci and other microbes isolated in this study.