Periapical inflammatory responses and their modulation

The role of Toll-like receptors 2 and 4 on reactive oxygen species and nitric oxide production by macrophage cells stimulated with root canal pathogens

INTRODUCTION

Periapical lesions arise as a result of the activation and interaction of the host immune responses against root canal infection. Recently identified Toll-like receptors (TLR) seem to be involved in the recognition and development of immune responses against a myriad of microorganisms. However, very little information is available on the role of TLR in the induction of periapical lesions.

METHOD

The role of TLR-2 and TLR-4 in the activation of murine macrophages stimulated using Fusobacterium nucleatum and Peptostreptococcus anaerobius was investigated. The production of nitric oxide (NO) and reactive oxygen species (ROS) was assessed.

RESULTS

The results demonstrate that TLR-2 and TLR-4 are involved in the production of ROS by activated macrophages. The microorganisms induced similar levels of NO production by TLR-2-competent and TLR-2-deficient macrophages, regardless of the addition of interferon-gamma (IFN-gamma), ruling out a role for TLR-2 in the NO production induced by these bacteria. Only P. anaerobius induced NO production by TLR-4-competent macrophages without the addition of IFN-gamma. However, after IFN-gamma addition, F. nucleatum induced macrophage NO production. Therefore, NO production stimulated by IFN-gamma and these microorganisms seems to be TLR-4-independent.

CONCLUSION

TLR-2 seems to be involved in the induction of ROS production by macrophages in response to prevalent root canal bacteria, while only F. nucleatum induced ROS production by TLR-4-competent macrophages. Both microorganisms significantly induced large amounts of NO independent of TLR-2 and TLR-4. We conclude that microorganisms may participate in the induction and progression of periapical lesions through NO and ROS production by activated macrophages.

T lymphocyte activation and cytokine expression in periapical granulomas and radicular cysts

INTRODUCTION

Radicular cysts (RCs) are periapical lesions resulting in jaw bone destruction. The inflammatory dental periapical granuloma (PG) is considered to be the origin of RC formation; however the mechanism of RC development remains unclear.

METHODS

Cell suspension from the surgically extirpated tissue of 27 RCs and 25 PGs was obtained. Bacteriological analysis of the PG tissue samples was performed in order to define two major groups of PG according to the prevailing causative bacterial infection: the streptococcal PG (PG-S, n=10) and the anaerobe PG (PG-A, n=9) group. The inflammatory response of tissue infiltrating lymphocytes was assessed by following T lymphocyte activation (HLA-DR expression) as well as interferon gamma (IFN-gamma) and interleukin 4 (IL-4) production which were evaluated by the flow cytometry.

RESULTS

In comparison to RC both types of PG contained a higher proportion of activated T cells (HLA-DR) and lower proportion of IL-4 producing cells. PG-A tissue contained increased percentage of CD3 cells and increased percentage of T helper 1 (Th1) cells in comparison with PG-S. In RC the IFN-gamma production is higher than in streptococcal PG-S but similar as in PG-A.

DISCUSSION

Tissue infiltration by Th2 cells and IL-4 production is likely to play an etiopathogenic role in RC formation.

Herpesviruses in endodontic pathoses: association of Epstein-Barr virus with irreversible pulpitis and apical periodontitis

Irreversible pulpitis and apical periodontitis are inflammatory diseases caused by opportunistic bacteria with possible co-infection with latent herpesviruses. The objectives of this study are to identify herpesviruses, including human cytomegalovirus (HCMV), Epstein-Barr virus (EBV), herpes simplex virus (HSV-1), and Varicella zoster virus (VZV) in patients with irreversible pulpitis (n = 29) or apical periodontitis, either primary (n = 30) or previously treated (n = 23). Using primary and nested polymerase chain reaction (PCR) and reverse transcription-PCR, EBV DNA and RNA were present in endodontic pathoses in significantly higher percentages (43.9% and 25.6%, respectively) compared with healthy pulp controls (0% and 0%, respectively). HCMV DNA and RNA were found in measurable numbers in both endodontic patients (15.9% and 29.3%, respectively) and in healthy pulp controls (42.1% and 10.5%, respectively). HSV-1 DNA was found in low percentages in endodontic patients (13.4%), and only one patient showed the presence of VZV. In conclusion, EBV may be associated with irreversible pulpitis and apical periodontitis.

Differential patterns of receptor activator of nuclear factor kappa B ligand/osteoprotegerin expression in human periapical granulomas: possible association with progressive or stable nature of the lesions

Receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) are expressed in apical periodontitis, suggesting a role for these molecules during lesion development. However, the profiles of RANKL/OPG expression in periapical lesions remain unknown. In this study we investigated the patterns of RANKL and OPG mRNA expression by real-time polymerase chain reaction in human periapical granulomas (N = 44) and compared them with sites presenting characteristic bone resorbing activity: healthy (n = 14) and orthodontically stretched and compressed periodontal ligament (n = 26), healthy gingiva (n = 24), chronic gingivitis (n = 32), and chronic periodontitis (n = 34) samples. Both RANKL and OPG mRNA expression was higher in periapical granulomas when compared with healthy periodontal ligament. Distinct patterns of RANKL and OPG expression ratio were found in the granulomas and in different physiologic and pathologic conditions, with characteristic bone resorption activity potentially being indicative of the stable or progressive nature of the lesions. Lesions with radiographic image smaller than 5 mm showed higher RANKL/OPG expression than images greater than 5 mm. Periapical granulomas presented heterogeneous patterns of RANKL and OPG expression, ranging from samples with RANKL/OPG ratio similar to that seen in sites with minimal or absent bone resorption to samples with RANKL/OPG expression pattern comparable with active bone resorption sites.

Interleukin-8 is increased in gingival crevicular fluid from patients with acute pulpitis

Irreversibly inflamed pulp (IIP) constitutes both a pathophysiologic and a diagnostic challenge. Gingival crevicular fluid (GCF) samples were obtained with Periopaper strips from IIP and adjacent and contralateral teeth for interleukin-8 (CXCL8) and tumor necrosis factor-alpha (TNF-alpha) measurements. Pain intensity was reported by using a verbal numeric scale (1-10). TNF-alpha (n = 25) was not detectable in GCF, whereas CXCL8 (n = 17) was significantly greater in IIP (302.1 +/- 164.9 pg/mL) compared with adjacent (139 +/- 138.58 pg/mL; P = .0072) or contralateral (173.8 +/- 166.4 pg/mL; P = .0231) teeth. A subgroup of high pain (>5) patients (n = 7) had CXCL8 IIP levels (323.6 +/- 148.4 pg/mL) that were significantly different from the contralateral teeth (P = .0262); however, they did not differ from the adjacent teeth (P = .1649), suggesting that neighboring teeth might also have inflammation. Another group of patients (n = 7) who had received local anesthesia before sampling had very low IIP CXCL8 levels. GCF CXCL8 levels might be a useful measurement for staging patients with acute pulpitis.

Histological evaluation of the pulp in teeth from dogs with naturally occurring periodontal disease

The purpose of this investigation was to evaluate the pulp of dog teeth affected by advanced periodontal disease. Histological examination was done on demineralized teeth extracted during clinical treatment of mature, client owned small and medium-size breed dogs with either good periodontal health or with advanced naturally occurring periodontal disease. Routinely stained sections from 5 clinically normal teeth and 22 teeth with advanced periodontitis from dogs between 5 and 12-years of age were examined using light microscopy. The pulp cavities of most teeth were narrow with low cellularity and some fibrosis of the pulp. Findings specific to periodontally affected teeth included acute and chronic pulpitis, vascular congestion, and pulp necrosis. A glomus body was identified in the pulp of one tooth and areas of poorly mineralized cementum were seen in both normal and diseased teeth. Age related changes in dog teeth appear similar to those reported for man and the rat. In addition to age related changes, the pulp of dog teeth with advanced periodontal disease were frequently inflamed or necrotic. This may reflect the advanced periodontitis affecting these teeth or a mechanical effect related to excessive tooth mobility. Further study is required to determine the etiology and significance of these findings and to investigate pulp status in less severely diseased teeth.

Low-dose doxycycline inhibits bone resorption associated with apical periodontitis

AIM

To test the effect of low-dose doxycycline on bone resorption associated with apical periodontitis.

METHODOLOGY

Apical periodontitis was induced by occlusal pulp exposure in the mandibular first molars of 36 rats. Animals were divided into three groups of 12: group A received doxycycline in drinking water at a dose of 5.85 mg day(-1); group B received a dose of 1.48 mg day(-1) (one-quarter of the original dose); and group C received no medicament and served as the control. A bioassay determined the doxycycline serum levels. After 21 days, the mandibles were removed, radiographed and the radiographs scanned to generate digital images. These images were analysed morphometrically and the total area of the periapical bone resorption of the mesial and distal roots of each tooth was determined and used to compare the groups. Statistical analysis was completed using anova with repeated measures.

RESULTS

The mean doxycycline serum level in group A was 0.22(+/-0.03) microg mL(-1) and in group B below the detection level of the assay (<0.062 microg mL(-1)). The mean area of the periapical bone resorption in the control group C was 2.91(+/-0.61) mm(2). In animals treated with a low-dose doxycycline, the mean size of the bone resorption was significantly smaller at 1.59(+/-0.59) mm(2) (group A) and 1.72(+/-0.85) mm(2) (group B) (P = 0.001). No significant difference was found in the area of the bone resorption between these two groups A and B.

CONCLUSIONS

Low-dose doxycycline reduced the area of bone resorption associated with apical periodontitis in the mandibular first molar teeth of rats.

Localization of substance P-induced upregulated interleukin-8 expression in human dental pulp explants

AIM

To localize ex vivo expression of interleukin-8 (IL-8) induced by substance P (SP) in human dental pulps.

METHODOLOGY

Intact caries-free, freshly extracted third molars (n = 20) were collected from patients (15-25 years old). The teeth were split and pulpal tissue was obtained and stored in Dulbecco's modified Eagle medium. Human dental pulp tissue explants were stimulated with SP. Expression of IL-8 in pulp explants was detected and localized by immunohistochemistry.

RESULTS

Moderated IL-8 immunoreactivities were detected mainly in the cell-rich zone in pulp tissues 12 h after tumour necrosis factor alpha (TNF-alpha) stimulation (positive controls), whereas only weak IL-8 expression was observed in tissues stimulated with SP at the same time interval. These data did not differ from those in negative controls. Increased IL-8 expression in pulp explants after 24 h of SP stimulation was noted compared with negative controls and located in fibroblast-like cells, blood vessel-associated cells and extracellular matrix in the central zone and cell-rich zone of pulp explants. Tissues stimulated with TNF-alpha for 24 h (positive controls) revealed weak IL-8 immunoreactivities with altered cell morphology.

CONCLUSIONS

Substance P induces IL-8 expression and was located in fibroblast-like pulp cells, blood vessel-associated cells and extracellular matrix of human dental explants. These data support the hypothesis that neuropeptide (SP) coordinates the modulation of pulpal inflammation via up-regulating chemokine IL-8.

The effect of mineral trioxide aggregate on phagocytic activity and production of reactive oxygen, nitrogen species and arginase activity by M1 and M2 macrophages

AIM

To assess the influence of co-culture with mineral trioxide aggregate (MTA) on phagocytosis and the production of reactive oxygen intermediates (ROI) and nitrogen (NO) species and the arginase activity by M1 and M2 peritoneal macrophages.

METHODOLOGY

Cellular viability, adherence and phagocytosis of Saccharomyces boulardii were assayed in the presence of MTA. Macrophages were stimulated with zymosan for ROI assays and with Fusobacterium nucleatum and Peptostreptococcus anaerobius and IFN-gamma for NO production and arginase activity, when in contact with capillaries containing MTA. Data were analysed by T, anova, Kruskall-Wallis and Mann-Whitney tests.

RESULTS

M2 macrophages displayed greater cellular viability in polypropylene tubes, greater ability to ingest yeast and smaller production of ROI and higher arginase activity when compared with M1 macrophages. Both macrophages, M1 and M2, presented similar cell adherence and NO production. The addition of bacterial preparations to macrophages interfered with NO and arginase productions. MTA did not interfere with any of the parameters measured.

CONCLUSIONS

Phagocytosis and the ability of the two macrophage subtypes to eliminate microbes were not affected by MTA.

Correlation Between Platelet-derived Growth Factor B Chain and Bone Resorption in Rat Periapical Lesions

The purpose of this study was to examine the relationship between platelet-derived growth factor B chain (PDGF-B) and bone resorption in rat periapical lesions. Periapical lesions were induced in Sprague-Dawley 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 frontal sections were prepared for immunohistochemistry and enzymehistochemistry. PDGF-B-positive cells and osteoclasts could be observed on day 7. From day 7 to day 14, the number of PDGF-B-positive cells and osteoclasts were ascending, and a significant correlation was found between them; from day 21 to day 28, more PDGF-B-positive cells and fewer osteoclasts could be observed, and the positive expression of PDGF-B was negatively correlated with osteoclasts. These findings showed that PDGF-B could be observed, which might be associated with the bone resorption of periapical lesions.

Eugenol suppressed the expression of lipopolysaccharide-induced proinflammatory mediators in human macrophages

Eugenol is commonly used as an analgesic agent during acute pulpitis and is a major component of root canal sealers. Despite the frequent applications of eugenol in the practice of dentistry, little is known about the role of eugenol under the status of inflammation. This study was aimed to investigate the influence of eugenol on human macrophages (U937) under the stimulation of lipopolysaccharide (LPS). Eugenol was shown to block the release of the bone resorbing mediators, including interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and prostaglandin E2 from LPS-stimulated macrophages. In contrast, eugenol alone did not alter the expression levels of these proinflammatory mediators in macrophages. Consistent with downregulation of bone-resorbing mediators, eugenol suppressed the messenger RNA expression of LPS-induced IL-1beta, TNF-alpha, and cyclooxygenase-2 in macrophages. The results suggest a potential anti-inflammatory effect of eugenol in the acute inflamed pulps and apical periodontitis.

Elevated expression of Cu, Zn-SOD and Mn-SOD mRNA in inflamed dental pulp tissue

AIM

To determine the mRNA expression levels of copper-zinc superoxide dismutase (Cu, Zn-SOD) and manganese SOD (Mn-SOD) in healthy and inflamed human dental pulp tissue.

METHODOLOGY

Sixteen patients with symptomatic irreversible pulpitis (eight females and eight males) were selected for study. Normal healthy pulps were removed from extracted mandibular third molar teeth from 10 systemically healthy individuals (six females and four males). QRT-PCR analysis of Cu, Zn-SOD and Mn-SOD mRNA expression was carried out in 16 cases of irreversible pulpitis and in 10 cases of systemically healthy donors. The Shapiro-Wilk's test was used to test the normality of data, whereas the Mann-Whitney U-test was used to evaluate the significance of the differences between groups. Differences in the expression levels were considered to be statistically significant for P-values <0.05.

RESULTS

A significant increase (P < 0.05) occurred in both Cu, Zn-SOD and Mn-SOD mRNA expression in cases of irreversible pulpitis. The increase in Mn-SOD level was significantly higher (P < 0.05) than the change observed for Cu, Zn-SOD.

CONCLUSIONS

The development of pulpitis is associated with elevated transcription of both Cu, Zn-SOD and Mn-SOD; pulp tissue inflammation generated higher Mn-SOD transcription compared with Cu, Zn-SOD.

RANKL in human periapical granuloma: possible involvement in periapical bone destruction

OBJECTIVES

The cytokine receptor activator of nuclear factor kappaB-ligand (RANKL) has been involved in both the physiological and pathological regulation of osteoclast life span and bone metabolism. Periapical granuloma is a periradicular lesion characterized by periapical bone destruction. The aims of this study were to associate the RANKL mRNA levels to periapical granulomas using the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) technique and to determine the specific cell involved in RANKL synthesis.

METHODS

In eight periapical granuloma and eight periodontal ligament samples from periodontally healthy volunteers, RANKL mRNA was detected by real-time RT-PCR. Expression of RANKL on infiltrate leukocytes was further investigated by flow cytometry in six periapical granulomas.

RESULTS

Receptor activator of nuclear factor kappaB-ligand mRNA levels were higher in periapical granulomas than in healthy periodontal ligament as its RANKL mRNA cycle threshold (Ct) and DeltaCt were significantly lower than that of controls (33.07 +/- 1.24 vs 36.96 +/- 1.69 and 11.58 +/- 3.02 vs 15.60 +/- 3.31, respectively). A 16.2-fold (2.0-131.6) higher RANKL gene expression was detected in the granulomas compared with the control tissues. We determined by flow cytometry that lymphocytes were the predominant leukocyte cells (53.31%), and monocytes and dendritic cells were the main RANKL synthesizers in granuloma lesions.

CONCLUSIONS

These data indicate that monocytes synthesized RANKL in periapical granulomas and suggest that RANKL is involved in bone loss associated with periapical lesions.

Antimicrobial susceptibility and molecular analysis of Enterococcus faecalis originating from endodontic infections in Finland and Lithuania

BACKGROUND/AIMS

Enterococcus faecalis strains with multiple antibiotic resistances can cause infections that are difficult to treat. The microbial flora in treatment-resistant apical periodontitis is dominated by E. faecalis, and is a potential source of infections at other sites.

MATERIAL AND METHODS

Sensitivities to a range of antibiotics were determined for 59 endodontic E. faecalis isolates from Finland and Lithuania. The DNA sequence of the gene responsible for the species' intrinsic quinupristin-dalfopristin resistance, lsa, was determined from two isolates with diminished resistance. Four pairs of isolates from the same root canal were typed by pulsed-field gel electrophoresis.

RESULTS

A high prevalence of resistance to rifampicin was found, whereas all isolates were susceptible or showed intermediate susceptibility to penicillin and ampicillin and four isolates were unusually susceptible to cefotaxime. No vancomycin or high-level gentamicin resistance was detected. Nine of 59 isolates were susceptible to quinupristin-dalfopristin. A fully quinupristin-dalfopristin-susceptible isolate also susceptible to clindamycin produced a truncated Lsa polypeptide, and an isolate with borderline quinupristin-dalfopristin-susceptibility had mutations proximal to the predicted ribosomal binding site. Pulsed-field gel electrophoresis showed that the same root canal could harbor two different strains of E. faecalis during the course of the same infection.

CONCLUSION

Despite the differing antibiotic usage in Finland and Lithuania, E. faecalis from endodontic infections in these countries showed similar susceptibility patterns with levels of resistance considered typical for the species, and decreased resistance to clindamycin and quinupristin-dalfopristin as well as lesions in the lsa gene which were similar to those described in other clinical isolates.

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.

Receptor activator NFkappaB-ligand and osteoprotegerin protein expression in human periapical cysts and granulomas

OBJECTIVE

The purpose of this study was to determine the expression of receptor activator of NFkappaB ligand (RANKL) and osteoprotegerin (OPG) associated with bone destruction in periapical cysts and granulomas.

STUDY DESIGN

Forty human dental chronic periapical lesions were collected after periapical surgery. The lesions collected were fixed in 10% buffered formalin and histologically processed. At least 2 sections of each specimen were stained with hematoxylin and eosin for microscopic diagnosis. After that, 10 human periapical granulomas and 10 cysts were selected for immunohistochemical analysis for RANKL, OPG, and CD68+.

RESULTS

Polymorphonuclear neutrophils, macrophages, endothelial cells, and lymphocytes were stained for RANKL and OPG in both lesions. Epithelial cells were also stained for RANKL and OPG in periapical cysts. Quantitative analysis was conducted and the results were expressed as a ratio of the number of immunostained cells over the total number of cells in the field (n = 100). The ratio of RANKL+/total cells was higher than OPG+/total cells in periapical granulomas (0.553 +/- 0.153 and 0.483 +/- 0.189, respectively; P < .0012; paired t test) and in cysts (0.519 +/- 0.09 and 0.339 +/- 0.117, respectively; P < .0001; paired t test). The ratios of OPG+/total cells (P < .0001; paired t test) and RANKL+/total cells (P < .0322; paired t test) were greater in granulomas than in cysts. However, the ratio RANKL+/OPG+ in granulomas (1.336 +/- 0.723) and cysts (1.404 +/- 0.385) was not significantly different. The ratio of CD68+/total cells was significantly higher in granulomas (0.381 +/- 0.040) than in cysts (0.307 +/- 0.068) (P < .0001; unpaired t test with Welch correction).

CONCLUSION

Taking into account the limitations of the experimental approach employed, our findings indicate the presence of RANKL and OPG in cysts and granulomas, strongly suggesting the involvement of these gene products in the development of periapical lesions.

Human cytomegalovirus, Epstein-Barr virus and bone resorption-inducing cytokines in periapical lesions of deciduous teeth

BACKGROUND

A connection of herpesvirus periapical infection with symptomatic and large-size periapical lesions has been recognized in adult patients, but no data exist about a possible involvement of herpesviruses in severe periapical pathosis in children. Herpesviruses have the potential to elicit potent bone resorption-inducing cytokines in mammalian cells.

AIM

This study aimed to determine the occurrence of human cytomegalovirus and Epstein-Barr virus DNA, and mRNA transcripts of receptor activator of nuclear kappa B ligand (RANKL), osteoprotegerin, core binding factor alpha-1, colony stimulating factor-1, transforming growth factor-beta, and monocyte chemoattractant protein-1 in periapical symptomatic pathosis of deciduous teeth.

MATERIAL AND METHODS

Twelve deciduous molar teeth from patients aged 2-8 years were extracted due to severe periapical infection, and granulomatous tissue adherent to the root tip of the extracted teeth was collected using a surgical knife. Non-diseased pulpal tissue, obtained from 12 teeth extracted for orthodontic reasons, served as negative control. Polymerase chain reaction assays were employed to identify herpesvirus DNA and cytokine gene expression, using established polymerase chain reaction primers and procedures.

RESULTS

Seven (58%) of the periapical lesions yielded human cytomegalovirus and eight (67%) Epstein-Barr virus. Only one (8%) periapical lesion showed neither human cytomegalovirus nor Epstein-Barr virus. In healthy pulpal tissue, one (8%) specimen demonstrated human cytomegalovirus and another (8%) specimen revealed Epstein-Barr virus. Of the cytokines examined, RANKL expression showed significantly higher occurrence in periapical pathosis than in healthy pulpal tissue (P < 0.040). No relationship was identified between the type of herpesvirus and cytokine expression in the periapical lesions studied.

CONCLUSIONS

The present findings provide evidence of a putative role of human cytomegalovirus and Epstein-Barr virus in the pathogenesis of symptomatic periapical pathosis in deciduous teeth. Increased RANKL expression in periapical lesions may be of pathogenetic significance.

NF-kappaB activation in human dental pulp stem cells by TNF and LPS

Post-natal human dental pulp stem cells (DPSCs) represent a unique precursor population in the dental pulp, which has multipotential and can regenerate a dentin/pulp-like structure. Because the dental pulp is frequently infected by oral bacteria due to dental decay, in this study, we examined whether lipopolysaccharide (LPS) and tumor necrosis factor (TNF) activated the immunologic transcription factor nuclear factor kappa B (NF-kappaB) in DPSCs. We found that both TNF and LPS activated the I-kappa B kinase complex (IKK) in DPSCs to induce the phosphorylation and degradation of IkappaBalpha, resulting in the nuclear translocation of NF-kappaB. Consistently, both TNF and LPS rapidly induced the expression of the NF-kappaB-dependent gene interleukin-8 (IL-8). However, unlike in monocytes, we found that LPS could not induce the phosphorylation of the NF-kappaB active subunit p65 in DPSCs. In summary, our studies suggest that DPSCs may be involved in immune responses during pulpal infection through activating NF-kappaB.

Effect of mineral trioxide aggregate on cytokine production by peritoneal macrophages

AIM

To test the effect of two commercial brands of grey mineral trioxide aggregate (ProRoot and MTA-Angelus) on cytokine production by M1 and M2 inflammatory macrophages.

METHODOLOGY

M1 (from C57BL/6 mice) and M2 peritoneal inflammatory macrophages (from C57BL/6 IL12p40-/- mice) were obtained and cultured in vitro in the presence of MTA. The cellular viability and the production of tumour necrosis factor-alpha, interleukin (IL)-12 and IL-10 in response to stimulation with interferon-gamma and Fusobacterium nucleatum or Peptostreptococcus anaerobius were evaluated. Data were analysed by Mann-Whitney, Kruskal-Wallis and anova tests.

RESULTS

The cements did not interfere with cellular viability or with cytokine production by either type of macrophage. However, M2 macrophages produced higher levels of IL-10 when stimulated with F. nucleatum than M1 macrophages (P < 0.05).

CONCLUSIONS

The brands of MTA evaluated did not interfere in the cytokine response by M1 or M2 macrophages to the two bacteria tested. However, a difference in cytokine production between the two types of macrophages was found.

Effect of E. faecalis on the release of serine proteases elastase and cathepsin G, and collagenase-2 (MMP-8) by human polymorphonuclear leukocytes (PMNs)

AIM

To measure the release of hydrolytic enzymes [elastase, cathepsin G and collagenase-2 (MMP-8)] from human polymorphonuclear leukocytes (PMNs) during interaction with strains of Enterococcus faecalis isolated from endodontic infections.

METHODOLOGY

Six E. faecalis strains isolated from treatment resistant cases of apical periodontitis were included in the study. Overnight cultures of the microbes were used for the experiments. PMNs were isolated using the Ficoll Paque technique, and their vitality was assessed throughout the experiments by the Trypan Blue exclusion test. A known amount of microbes and PMNs were mixed in PBS at +37 degrees C in air, and the release of elastase, cathepsin G and MMP-8 was measured at 0, 20, 60 and 120 min after initiation of incubation. The activities of elastase and cathepsin G were analysed by spectrophotometer assays using specific synthetic peptide substrates, and MMP-8 by western immunoblotting quantitated by computer densitometry. PMNs incubated in buffer without any added microbes served as negative controls, cells incubated with 5 ng mL(-1) phorbol myristic acetate (PMA) served as a positive control. The 95% confidence interval was used to compare the relative amount of elastase and cathepsin G released from the samples.

RESULTS

One E. faecalis strain induced a similar or higher elastase, cathepsin G and MMP-8 release than the positive control, whereas the other five strains induced only moderate or no release of the three enzymes examined as compared with the negative and positive controls. Western immunoblot revealed that released MMP-8 had molecular sizes of 60 and 75 kDa representing active and latent forms of MMP-8. In addition, >110 kDa high molecular size and a fragmented 20-30 kDa MMP-8 species could be observed.

CONCLUSIONS

The majority of the E. faecalis strains induced little or no release of hydrolytic enzymes from the PMN cells. The finding may partly explain the clinical observation that root canal infections dominated by E. faecalis are usually symptom free.

Effect of root canal filling/sealer systems on apical endotoxin penetration: a coronal leakage evaluation

Endotoxin, elaborated by gram-negative organisms, is an important factor in apical periodontitis. The objective of this study was to evaluate the magnitude of endotoxin penetration through root canal treated teeth using a dual chamber model system. Forty-four maxillary anterior teeth were prepared endodontically and canals filled either by lateral condensation or a warm thermoplasticized technique in combination with either Roth's 801 or AH 26 sealer. Teeth were suspended in the model system with a mixed anaerobic bacterial suspension in the upper chamber and HBSS in the lower chamber. The QCL-1000 LAL assay was used to measure endotoxin at 0, 1, 7, 14, and 21 days. Response feature analysis using trapezoidal area under the curve was performed; the four treatment groups were compared using nonparametric methods. Groups differed (p = 0.028), with thermoplasticized root canal filling/Roth's 801 sealer permitting the least apical endotoxin penetration. Results suggest that Roth's 801 sealer may have a role in inhibiting endotoxin penetration.

Immunolocalization of Receptor Activator of NF Kappa B Ligand in Rat Periapical Lesions

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.

Pulp-dentine complex changes and root resorption during intrusive orthodontic tooth movement in patients prescribed nabumetone

Pulpitis, external root resorption, and pain may be experienced during orthodontic movement. The use of nonsteroidal anti-inflammatory drugs (NSAIDs) has been suggested to control these changes. The purpose of this study was to observe pulp-dentinal reactions, root resorption, tooth pain, and tooth movement after the application of a 4-ounce intrusive orthodontic force to human maxillary first premolars in patients given the NSAID nabumetone. Thirty-four maxillary first premolars were evaluated. A placebo was prescribed to 17 patients after an intrusive force was activated and reactivated for an 8-week period on the right side. The same procedure was repeated on the left side after patients were given nabumetone. Pulp-dentinal reactions and external root resorption were evaluated by histology. Pain and movement were also evaluated. Nabumetone was found to be useful in reducing pulpitis, external root resorption, and pain caused by intrusive orthodontic movement, without altering tooth movement in response to the application of orthodontic force.

Conservative endodontic management of teeth associated with extensive periapical pathology: report of two cases

Traditionally, long-term calcium hydroxide dressings have been recommended for the conservative management of large periapical lesions. However, calcium hydroxide therapy has some disadvantages such as variability of treatment time, difficulties with patient follow-up and prolonged treatment periods that increase the risk of root canal contamination via microleakage and crown fractures. This paper reports the healing of large periapical lesions following conservative non-surgical treatment with calcium hydroxide dressings.

State of the art and science of endodontics

BACKGROUND

Advances in the art and science of endodontics have facilitated better understanding of disease processes and have led to development of treatment modalities aimed to restore health to the pulp and periradicular tissues. This article presents a summary of both basic and clinical breakthroughs in endodontics.

RESULTS

The author indicates that, on the basis of the reviewed literature, pulp and periradicular diseases are primarily microbial. Basic research has led to development of methodologies that have allowed for specific and accurate identification of pathogens that are likely to cause persistent infections. Close examination of clinical data shows that meticulous débridement of the infected root canal system will result in a high probability of successful treatment outcome. Progress in visualization, mechanical and chemical disinfection, and biological seal of portals of entry will improve quality of care further.

CONCLUSIONS AND CLINICAL IMPLICATIONS

A better understanding of the pathogenesis of pulp and periradicular diseases, inflammation and healing, as well as of pain pathways, will improve patient care and result in preservation of natural tissues.

Factors affecting the outcome of orthograde root canal therapy in a general dentistry hospital practice

OBJECTIVE

The goal of this study was to weigh the impact of patient-related, tooth-related, and treatment-related factors on therapy outcome in a series of consecutive patients.

STUDY DESIGN

Eighty-four patients were included. Of these, 66 (79%) were available for recall after > or = 30 months (mean = 46 months). Root canal treatments were performed using a standard protocol. At recall, teeth were scored by means of the periapical index (PAI), which was the dependent variable (dichotomized to sound/ unsound). Explanatory variables were patient age, integrity of the nonspecific immune system, smoking status, dichotomized PAI score before treatment, initial treatment versus retreatment, prior exposition of the root canal to saliva, stainless-steel hand versus NiTi rotary instrumentation, and quality of root filling. Unit of observation was the patient-individual. Data were analyzed using univariate tests and backward stepwise logistic regression analysis.

RESULTS

After 5 steps with elimination of the least significant independent variable, status of the immune system (P = .05), initial PAI (P = .04), and root filling quality (P = .01) were found to be the indispensable predictors for treatment outcome. Using these 3 explanatory variables, the logistic regression model had a predictive value of 87%, compared to 91% with all 8 variables. Success rate at recall (PAI < or = 2 without symptoms) was 88% (95% CI = 78, 94).

CONCLUSION

The integrity of a patient's nonspecific immune system, which has been neglected in earlier investigations, is a significant predictor for endodontic treatment outcome, and should receive more attention in future studies.

Pathogenesis of apical periodontitis and the causes of endodontic failures

Apical periodontitis is a sequel to endodontic infection and manifests itself as the host defense response to microbial challenge emanating from the root canal system. It is viewed as a dynamic encounter between microbial factors and host defenses at the interface between infected radicular pulp and periodontal ligament that results in local inflammation, resorption of hard tissues, destruction of other periapical tissues, and eventual formation of various histopathological categories of apical periodontitis, commonly referred to as periapical lesions. The treatment of apical periodontitis, as a disease of root canal infection, consists of eradicating microbes or substantially reducing the microbial load from the root canal and preventing re-infection by orthograde root filling. The treatment has a remarkably high degree of success. Nevertheless, endodontic treatment can fail. Most failures occur when treatment procedures, mostly of a technical nature, have not reached a satisfactory standard for the control and elimination of infection. Even when the highest standards and the most careful procedures are followed, failures still occur. This is because there are root canal regions that cannot be cleaned and obturated with existing equipments, materials, and techniques, and thus, infection can persist. In very rare cases, there are also factors located within the inflamed periapical tissue that can interfere with post-treatment healing of the lesion. The data on the biological causes of endodontic failures are recent and scattered in various journals. This communication is meant to provide a comprehensive overview of the etio-pathogenesis of apical periodontitis and the causes of failed endodontic treatments that can be visualized in radiographs as asymptomatic post-treatment periapical radiolucencies.

Effects of an inducible nitric oxide synthase inhibitor on experimentally induced rat pulpitis

Nitric oxide (NO) is a biological effector molecule involved in a large variety of reactions and, as synthesized by inducible nitric oxide synthase (iNOS), has many important roles in inflammatory conditions. This study aimed to evaluate the anti-inflammatory effects of an iNOS-specific inhibitor, N-(3-(aminomethyl)benzyl)acetamidine (1400W), on experimentally induced rat pulpitis in the upper incisors of 6-wk-old male Wistar rats. 1400W (1 mg kg(-1)), the non-specific NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 50 mg kg(-1)), or sterile saline (control) were administered before the application of lipopolysaccharide (LPS). Rats were killed 3, 6, 9, 12, 24, 48, and 72 h after LPS application, and immunocompetent cells were detected immunohistochemically. The numbers of granulocytes infiltrating into the pulp were significantly depressed in the 1400W group compared with the saline and L-NAME groups. The kinetics of the macrophages and Ia(+) cells in the 1400W group were similar to those in the L-NAME group, while the maximum numbers in both groups were significantly reduced compared with those in the saline group. These results suggest that NO may be responsible for the infiltration of immunocompetent cells in the progress of pulpitis, and that 1400W is a promising candidate for controlling pulpal inflammatory reactions.

Induction of vascular endothelial growth factor expression in human pulp fibroblasts stimulated with black-pigmented Bacteroides

AIM

To investigate the effect of black-pigmented Bacteroides on the expression of vascular endothelial growth factor (VEGF) gene in human pulp fibroblasts.

METHODOLOGY

The supernatants of Porphyromonas endodontalis, Porphyromonas gingivalis and Prevotella intermedia were used to evaluate VEGF gene expression in human pulp fibroblasts. The levels of mRNAs were measured by the quantitative reverse-transcriptase polymerase chain reaction analysis.

RESULTS

Black-pigmented Bacteroides induced significantly high levels of VEGF mRNA gene expression in human pulp fibroblasts (P < 0.05). In addition, the expression of VEGF depended on the bacteria tested.

CONCLUSIONS

Black-pigmented Bacteroides may be involved in developing pulpal disease through the stimulation of VEGF production that would lead to the expansion of the vascular network coincident to progression of the inflammation.

Cytotoxicity and sealing properties of four classes of endodontic sealers evaluated by succinic dehydrogenase activity and confocal laser scanning microscopy

The objectives of this study were to evaluate the cytotoxicity and sealing properties of four classes of endodontic sealers (PCS/Kerr, RoekoSeal/Roeko, TopSeal/Dentsply, and EndoREZ/Ultradent). For cytotoxicity testing (MTT method), the materials were either placed immediately in contact with cultured cells or 24 h after setting, then evaluated at three subsequent time points (24 h, 48 h, or 1 wk). For the leakage study, extracted human roots were obturated with acrylic cones and sealers and immersed for 48 h into rhodamine-labeled lipopolysaccharide. The roots were then observed under a confocal laser scanning microscope to estimate (semiquantitatively) the presence of the rhodamine-lipopolysaccharide (LPS) inside the canal. The results showed that cytotoxicity generally increased with time, and that most materials pose significant cytotoxic risks, particularly in the freshly mixed condition. Further, all materials showed significant leakage although there was large variation among teeth. Overall, the silicon-based material (Roeko Seal) was less cytotoxic and more effective in sealing root canals against LPS leakage than other materials.

Role of substance P and calcitonin gene-related peptide in the regulation of interleukin-8 and monocyte chemotactic protein-1 expression in human dental pulp

AIM

To determine whether leucocyte infiltration during neurogenic inflammation in the pulp is regulated by neuropeptides via inducing the release of proinflammatory chemokines interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) from human dental pulp.

METHODOLOGY

Cultured primary pulp cells and pulp tissue explants were stimulated with substance P (SP) and/or calcitonin gene-related peptide (CGRP). IL-8 or MCP-1, secreted from cultured cells or produced in pulp explants, was analysed by enzyme-linked immunosorbent assay.

RESULTS

Substance P induced IL-8 secretion from cultured pulp cells (approximately threefold increase over control, P < 0.05) and from pulp tissue explants (two- to three fold). SP only minimally to moderately induced MCP-1 (approximately two fold) in cultured pulp cells. While MCP-1 induction in cultured pulp cells was detected after 24 h of SP stimulation, no induction was observed in pulp tissue. CGRP did not induce IL-8, but moderately increased MCP-1 production (approximately three fold) in cultured pulp cells. There was no synergistic induction of MCP-1 by SP plus CGRP stimulation of pulp cells.

CONCLUSIONS

Substance P is a stronger inducer of IL-8 production in dental pulp than CGRP. IL-8 is more strongly induced than MCP-1 by SP, suggesting a more important role for IL-8 than MCP-1 in leucocyte infiltration during neurogenic inflammation in dental pulp.

Identification of γδT lymphocytes in human periapical lesions

Endodontic (root canal) therapy is required when the pulp of a tooth becomes necrotic due to a bacterial infection or trauma. A proportion of patients who receive endodontic therapy subsequently have periapical (around the tooth root) lesions detected by radiolucency. Currently, there are no means to identify susceptible patients. Although tissue from periapical lesions has been described as inflammatory, inflammatory cell types and their functions have been poorly characterized. For example, T lymphocytes were identified using pan specific anti-CD3 mAb, which recognizes both alphabeta and gammadeltaT cells. Using the current model of gammadeltaT cells as immunoregulatory cells; gammadeltaT cells can mediate protective or destructive milieus. We postulated that patients who have a periapical lesion, as identified by radiographic bone loss, mount a gammadeltaT cell response. We collected specimens removed by surgery from both periapical lesions and other oral tissues, generated total RNA and performed reverse-transcriptase polymerase chain reaction to identify rearranged delta genes. Results were confirmed with semi-nested polymerase chain reaction. In addition, we demonstrate that these lesions contain a population of CD3+ cells that are alphabetaT cell receptor negative, implying that these cells are gammadeltaT cells. Here we show that 36/37 of periapical lesions and only 2/11 of other lesions contain gammadeltaT cells (P<0.0001). Vdelta2+ T cells were the most common subtype identified (30/36) in these samples. This is the first report in the literature of the presence of gammadeltaT cells in human periapical lesions.

Expression of MHC Class II, CD70, CD80, CD86 and pro-inflammatory cytokines is differentially regulated in oral epithelial cells following bacterial challenge

Oral epithelium may play a regulatory role in local immune responses when interacting with bacteria. The present study was undertaken to investigate the effects of selected bacterial pathogens found in periodontal and endodontic infections on oral epithelial cells. Expression of cell surface molecules (major histocompatibility complex (MHC) Class II, CD54, CD70, CD80 and CD86) and secretion of inflammatory cytokines (interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha) in response to selected bacterial challenge were examined on an immortalized oral epithelial cell line, HOK-18A and a skin epithelial cell line, HaCaT. Actinomyces viscosus, Actinomyces israelii, Fusobacterium nucleatum lipopolysaccharide (LPS) or primary human periradicular exudate from a granuloma were co-cultured with epithelial cells for 4 or 24 h. Subsequently, cell surface expression of MHC Class II, CD54, CD70, CD80 and CD86, along with pro-inflammatory cytokine levels were determined using flow cytometry, ELISA and RT-PCR. Results indicated that the selected oral bacteria have greater effects on oral versus skin epithelial cells. F. nucleatum increased MHC Class II and CD54 (ICAM-1) cell surface expression on HOK-18A and HaCaT cells. A. israelii also had enhancing effects on the expression of CD54 and MHC Class II. A. israelii and LPS induced a 2.8-fold (P < 0.001) and 4.4-fold (P < 0.005) TNF-alpha secretion, respectively, while F. nucleatum and LPS induced a 10-fold (P < 0.0004) and 6-fold (P < 0.01) IL-1beta secretion, respectively by HOK-18A. Interestingly, CD70, CD80, and CD86 were generally decreased upon bacteria and LPS challenge on HOK-18A. The effects of increased MHC Class II and decreased CD70 were also evident with challenge of human periradicular exudate on HOK-18A. The implications of the study are unique in that oral epithelial cells may play both activating and inhibitory roles in the host immune response towards infection by oral bacteria. We introduce a concept of 'dormancy' where the differential expression of key cell surface antigens on oral epithelial cells may keep the recruited immune effector cells in a state of unresponsiveness, thus contributing to the long term quiescent period observed in many periodontal and endodontic lesions.

Cytokines in periradicular lesions: the effect of linezolid treatment

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.

Substance P induces interleukin-8 secretion from human dental pulp cells

OBJECTIVE

The role of neuropeptides in recruiting leukocytes in dental pulps is not known; therefore, we investigated whether interleukin-8 (IL-8) secretion from human pulp cells is increased after stimulation with substance P (SP) or calcitonin gene-related peptide (CGRP).

METHODS

Primary pulp cells exhibiting a fibroblast-like phenotype and an endothelial cell line were stimulated with various doses of SP or CGRP, and IL-8 secretion was measured by enzyme-linked immunosorbent assays.

RESULTS

IL-8 secretion from pulp cells increased significantly at 10(-8) to 10(-4) mol/L of SP stimulation (5- to 13.8-fold; P <.05); however, no significant IL-8 increase with CGRP (up to 10(-4) mol/L) stimulation was observed, nor was there synergistic induction of IL-8 with SP plus CGRP. The IL-8 increase reached its maximum at 8 hours after SP stimulation of the pulp cells. SP at a concentration of 10(-4) mol/L created minimal IL-8 induction in the endothelial cells and no synergistic induction by SP and CGRP.

CONCLUSIONS

Pulp cells may up-regulate IL-8 secretion by SP stimulation, which suggests that SP released in dental pulp may play a role in the influx of leukocytes, attracted by IL-8, into the pulp tissue.

Inflammatory infiltrate of chronic periradicular lesions: an immunohistochemical study

AIM

To determine the cellular profile of human chronic periradicular lesions using immunohistochemical methods in order to study the differences in the cell infiltrate of periradicular granulomas and cysts.

METHODOLOGY

The study population consisted of 45 individuals without any systemic disease. Biopsies were obtained during periradicular surgery. Paraffin-embedded sections were stained by the avidin-biotin complex method (ABC), whilst cryostat tissue sections were stained using the alkaline phosphatase antialkaline phosphatase assay (APAAP). These methods are highly valid and sensitive using a panel of specific monoclonal antibodies: CD4, CD8, CD3, CD10, HLADR, CD20, CD45RO, CD68 and CD57. The 45 specimens were characterized by the use of both techniques.

RESULTS

The 45 specimens were histologically diagnosed as: 25 periradicular granulomas, 17 periradicular cysts and 3 scar tissues. No statistically significant differences were detected in the inflammatory infiltrate between periradicular granulomas and cysts. Observation of the sections showed that the majority of inflammatory cells consisted of T and B lymphocytes and macrophages. T and B lymphocytes were equally distributed in 60% of the cases. The T4/T8 ratio ranged approximately from 1 to 3 and greater, being consistent with inflammation of periradicular tissues. The final differentiation of B lymphocytes to plasma cells was also detected, whilst natural killer (NK) cells were found in only 10 cases (22%). Moreover, antigen presenting cells and T suppressor/cytotoxic cells were found to be associated with both pre-existing and newly formed epithelium.

CONCLUSIONS

Periradicular granulomas and cysts represent two different stages in the development of chronic periradicular pathosis as a normal result of the process of immune reactions that cannot be inhibited.

Cytokine gene expression--part of host defence in pulpitis

Analyses of cytokines mediating inflammatory reactions are key to understanding the etiopathology of various diseases. This study investigated differences in cytokine gene expression between pulps from healthy virgin teeth and from symptomatic vital teeth with severe caries lesions in a group of young, healthy individuals. The mRNA levels of IL-1alpha, IL-1beta, IL-6, IL-8, and IL-18 were measured concomitantly by quantitative real-time RT-PCR. IL-1alpha and IL-1beta were not expressed at significantly higher levels in symptomatic versus clinically healthy pulps, while the difference was significant for the other cytokines (log-rank test, P<0.05). A concordance test for independence revealed significant correlation between IL-1alpha and IL-1beta, and between IL-6, IL-8, and IL-18 mRNA levels (P<0.05). The cytokine-specific differences revealed a differential significance of gene expression in cytokine regulation. The hypothesis that increase of cytokine mRNA expression is part of host reaction in pulpitis was corroborated by our observation.

Three-dimensional quantitation of periradicular bone destruction by micro-computed tomography

We have previously shown that two-dimensional, high-resolution, micro-computed tomography is a rapid, reproducible, and noninvasive method for measuring periradicular bone resorption in mice, giving results virtually identical to histology. In this study, we determined whether a three-dimensional volumetric quantitation of bone resorption could be achieved and whether this correlates with two-dimensional measurements. Periradicular lesions were induced in the lower first molars of mice by pulp exposure and infection; unexposed teeth served as controls. Mandibles were harvested on day 21 and subjected to: (a) three-dimensional micro-computed tomography imaging; and (b) conventional histology. Using a three-dimensional model and a semiautomatic contouring algorithm, we determined three-dimensional void volume, void surface, void thickness, and the standard deviation of the thickness distribution. The results showed a significant correlation between lesion void volume and two-dimensional lesion area by histology (r2 = 0.73), as well as high correlations between void volume and void thickness (r2 = 0.86) and standard deviation of the void thickness (r2 = 0.87), but no relationship with void surface. These results show that three-dimensional analysis of micro-computed tomography images is highly correlated with two-dimensional cross-sectional measures of periradicular lesions. Nevertheless, micro-computed tomography allows assessment of additional microstructural features as well as sub-regional analysis of lesion development.

Detection of vascular endothelial growth factor/ vascular permeability factor in periapical lesions

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF), is a multifunctional cytokine. It is overexpressed in several conditions, which are characterized by vascular hyperpermeability and angiogenesis. In this investigation, we have evaluated the possibility that VEGF/VPF could be expressed in periapical lesions. We studied 17 periapical granulomas and 6 periapical cysts by immunohistochemistry. An immunopositive reaction for VEGF/VPF was observed in all 23 periapical lesions; however, the intensity of immunostaining by anti-VEGF antibody varied according to histopathological findings. In periapical granulomas without epithelium, almost all of the inflammatory cells were immunoreactive to anti-VEGF/VIP antibody. In periapical granulomas, which had rests of Malassez in them, some inflammatory cells were stained. On the other hand, epithelial cells always were stained by VEGF/VPF antibody, both in periapical lesions with epithelium and in radicular cysts. This study demonstrated that periapical lesions express VEGF/VPF, although with some differences in cell immunolabeling, which correlated to the lesions' stages of development. Initially, VEGF/VPF would assure angiogenesis and vascular hyperpermeability, resulting in accumulation of inflammatory cells, later it could be involved in cyst fluid accumulation. We hypothesize, therefore, that VEGF/VPF expression plays an important role in the pathogenesis of periapical granulomas and enlargement of radicular cysts by several mechanisms.

Calcium hydroxide reduces lipopolysaccharide-stimulated osteoclast formation

OBJECTIVE

The purpose of this study was to determine the direct effects of lipopolysaccharide (LPS) on osteoclastogenesis and to assess the ability of calcium hydroxide-Ca(OH)(2)-to inhibit the osteoclast formation stimulated by LPS.

STUDY DESIGN

RAW 264.7 cells were cultured with 50 ng/mL recombinant receptor activator of NF-kappaB ligand (RANKL) for 72 hours. RANKL was then removed, and the cells were treated with 0, 1, 10, or 100 ng/mL of LPS, Ca(OH)(2)-treated LPS, or 50 ng/mL of RANKL as a positive control for an additional 48 hours. Cells were fixed and stained with fluorescein isothiocyanate-conjugated phalloidin to detect actin ring formation, and histochemistry was performed to detect multinucleated cells expressing tartrate-resistant acid phosphatase activity.

RESULTS

LPS induced osteoclast-like cell (OCL) formation in a dose-dependent manner when osteoclast precursor RAW 264.7 cells were pretreated for 72 hours with RANKL. Ca(OH)(2) significantly inhibited the ability of LPS to stimulate OCL formation.

CONCLUSION

This study shows that LPS directly stimulates OCL formation. The detoxification of LPS by treatment with Ca(OH)(2) significantly reduced its ability to trigger the differentiation of OCLs.

Nitric oxide promotes infectious bone resorption by enhancing cytokine-stimulated interstitial collagenase synthesis in osteoblasts

This experiment was undertaken to determine the role of macrophage-derived nitric oxide (NO) in mediating lipopolysaccharide (LPS)-induced bone resorption by using an in vitro co-culture system and an in vivo model of infectious bone resorption. Our results demonstrated that LPS stimulated the expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)-a mRNAs and nitrite synthesis in the J774 mouse macrophage cell line but not in the UMR-106 (rat) and MC3T3-E1 (mouse) osteoblast cell lines. Conditioned media (CM) from LPS-stimulated J774 triggered only low to moderate levels of iNOS mRNAs in MC3T3-E1 and a trivial effect in UMR-106. On the other hand, CM induced matrix metalloproteinase-1 (MMP-1) gene expression in both osteoblast cell lines. The NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) did not alter this effect in MC3T3-E1 and UMR-106, whereas TNF-a antibody diminished the CM-induced MMP-1 gene expression in both cell lines. Interestingly, SNAP, a NO donor, although by itself is not a MMP-1 stimulator for UMR-106, augmented the TNF-alpha-stimulated MMP-1 mRNA production in UMR-106. In a J774/UMR-106 co-culture system, LPS stimulated significant MMP-1 gene expression in UMR-106, and this upregulation was abolished by L-NMMA and TNF-alpha antibodies. Immunohistochemical analysis in a rat model of infectious bone resorption (periapical lesion) showed co-distributions of iNOS+ macrophages and MMP-1+ osteoblasts around the osteolytic areas. Administration of L-NMMA markedly reduced the extent of bone loss and the percentage of MMP-1-synthesizing osteoblasts. These data suggest that NO derived from macrophages after LPS stimulation may enhance bone loss by augmenting the cytokine-induced MMP-1 production in osteoblasts.

Cytokine production in response to endodontic infection in germ-free mice

This study evaluated the cytokine profiles (type 1 or type 2) that are triggered by and modulate endodontic periapical infections in the root canal system of germ-free mice. Microorganisms isolated from two patients with pulpal necrosis were inoculated into two groups of experimental animals: group I (Gemella morbillorum) and group II (Bifidobacterium adolescentis, Fusobacterium nucleatum and Clostridium butyricum). In vitro, G. morbillorum induced type 1 cytokine synthesis, while the modulation processed in vivo seemed to have the opposite effect, with a reduction in the basal levels of IL-12 and IFN-gamma, IL-4-independent down-modulation. In vitro, microorganisms from group II, in poly-infection, induced a reduction of type 1 cytokine levels from day 10 to day 20, which seemed to be modulated via IL-4. In vivo, however, a predominance of the immune response to one species over the others occurred.

Evaluating IL-2 levels in human pulp tissue

In murine and human CD4+ T cell populations, there are three subpopulations of T helper cell types. Hahn et al. demonstrated the ratio of CD4/ CD8 + cells significantly increases in inflamed dental pulps compared with normal pulps. Elevated levels of interleukin (IL)-2 have been detected in inflamed dental pulps and the level of IL-2 could be used as a marker for inflammation. In this study, levels of IL-2 were evaluated by using a human IL-2 cytokine assay kit on 80 samples of freshly extracted human pulp tissue. Applying standard diagnostic procedures, the tissue samples were clinically categorized into one of three experimental groups. The results demonstrated that there were no significant differences between the concentrations of IL-2 in any of the experimental groups. Our findings are different from results reported previously. Further investigation is warranted to determine if a correlation exists between the concentration of IL-2 or other interleukins and the degree of inflammation present in the dental pulp.