Bacteroides spp. in dental root canal infections

Prevalence of Enterococcus faecalis and Candida albicans in endodontic retreatment Cases: A comprehensive study

Introduction

Endodontic treatment failures often stem from the presence of microbial pathogens, particularly Enterococcus faecalis and Candida albicans. This study systematically assesses the prevalence of E. faecalis and C. albicans in endodontic retreatment cases, aiming to explore their impact on treatment outcomes.

Methods

Employing a systematic sampling approach, 30 patients with a history of previous endodontic treatment were selected. Rigorous clinical and radiographic assessments were conducted, following standardized protocols for root canal sample collection. Microbiological analysis, utilizing selective culture media, was employed to identify and quantify E. faecalis and C. albicans. Statistical analyses, including chi-square and logistic regression tests, were performed.

Results

The study involved 30 patients undergoing endodontic retreatment, with comprehensive clinical and radiographic evaluations for cases with and without periradicular lesions. Microbiological analysis unveiled a significant prevalence of E. faecalis and C. albicans, establishing a robust association between these pathogens and retreatment failure. These findings underscore the critical need for targeted antimicrobial interventions to enhance the overall success rates of endodontic retreatment procedures.

Conclusion

This study highlights the substantial prevalence of E. faecalis and C. albicans in endodontic retreatment cases, emphasizing the importance of identifying and effectively managing these pathogens for successful treatment outcomes. The notable association between these microbial agents and retreatment failure underscores the imperative for tailored antimicrobial strategies to enhance the efficacy of endodontic retreatment procedures.

Microbiological profile of root canals indicated for endodontic retreatment due to secondary endodontic infections or for prosthetic reasons

OBJECTIVE

The objective of this study was to evaluate the microbiological profile of root canals indicated for endodontic retreatment due to secondary endodontic infections evidenced by the presence of chronic apical periodontitis (G1) or for prosthetic reasons, without clinical and radiographic signs of endodontic reinfection (G2).

METHODS

Microbiological samples were collected from thirty teeth (N=30) out of which 15 were indicated for retreatment due to the presence of chronic apical periodontitis (G1) and 15 were indicated exclusively for prosthetic reasons (G2). Samples were collected from root canals before (S1), after chemomechanical preparation (S2), and after 30 days of intracanal medication composed of calcium hydroxide and 2% chlorhexidine gel (S3). The molecular analysis was performed using Nested-PCR for the detection of 17 bacterial species. The efficacy of each stage of the retreatment in reducing the microbial load was verified by counting colony-forming units (CFU). The statistical analysis considered a significance level of 5%.

RESULTS

The results showed that bacteria were detected in 100% of the cases in S1, in both groups, by Nested PCR. The most frequently found species in S1 in both groups were Enterococcus faecalis, Fusobacterium nucleatum, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Parvimonas micra. The microbial load of G1 was higher than G2 in the initial samples (S1). Endodontic retreatment was effective in reducing the microbial load in G1 and G2. Statistically significant associations were found between specific bacteria and clinical signs and symptoms.

CONCLUSION

It was concluded that the microbial community present in the root canal of teeth indicated for endodontic retreatment is mixed and heterogeneous. G1 and G2 differ in the number of species per case and microbial load.

CLINICAL RELEVANCE

Endodontic retreatment was effective in reducing the microbial load. Statistically significant associations were found between specific bacteria and clinical signs and symptoms.

Implant Periapical Lesion: Clinical and Histological Analysis of Two Case Reports Carried Out with Two Different Approaches

Periapical implantitis (IPL) is an increasingly frequent complication of dental implants. The causes of this condition are not yet entirely clear, although a bacterial component is certainly part of the etiology. In this case series study, two approaches will be described: because of persistent IPL symptoms, a patient had the implant removed and underwent histological analysis after week 6 from implantation. The histomorphometric examination revealed a 35% bone-implant contact area involving the coronal two-thirds of the implant. The apical portion of the fixture on the other hand was affected by an inflammatory process detectable on radiography as a radiolucent area. The presence of a probable root fragment, detectable as an imprecise radiopaque mass in the zone where the implant was later placed, confirms the probable bacterial etiology of this case of IPL. On the other hand, in case number 2, the presence of IPL around the fixture was solved by surgically removing the implant apical third as well as the adjacent tooth apex. It may be concluded from our histological examination that removal of the apical portion of the fixture should be considered an effective treatment for IPL since the remaining implant segment remains optimally osseointegrated and capable of continuing its function as a prosthetic abutment. Careful attention, however, is required at the implantation planning stage to identify in advance any sources of infection in the edentulous area of interest which might compromise the final outcome.

A critical analysis of research methods and experimental models to study the root canal microbiome

Endodontic microbiology deals with the study of the microbial aetiology and pathogenesis of pulpal and periradicular inflammatory diseases. Research in endodontic microbiology started almost 130 years ago and since then has mostly focussed on establishing and confirming the infectious aetiology of apical periodontitis, identifying the microbial species associated with the different types of endodontic infections and determining the efficacy of treatment procedures in eradicating or controlling infection. Diverse analytical methods have been used over the years, each one with their own advantages and limitations. In this review, the main features and applications of the most used technologies are discussed, and advice is provided to improve study designs in order to properly address the scientific questions and avoid setbacks that can compromise the results. Finally, areas of future research are described.

Etiologic role of root canal infection in apical periodontitis and its relationship with clinical symptomatology

Evidence shows the polymicrobial etiology of endodontic infections, in which bacteria and their products are the main agents for the development, progression, and dissemination of apical periodontitis. Microbial factors in necrotic root canals (e.g., endotoxin) may spread into apical tissue, evoking and supporting a chronic inflammatory load. Thus, apical periodontitis is the result of the complex interplay between microbial factors and host defense against invasion of periradicular tissues. This review of the literature aims to discuss the complex network between endodontic infectious content and host immune response in apical periodontitis. A better understanding of the relationship of microbial factors with clinical symptomatology is important to establish appropriate therapeutic procedures for a more predictable outcome of endodontic treatment.

Is it really penetration? Locomotion of devitalized Enterococcus faecalis cells within dentinal tubules of bovine teeth

OBJECTIVE

The aim of the present study was to evaluate the penetration characteristics of devitalized and vital E. faecalis cells into root dentinal tubules.

DESIGN

Thirteen root canals were incubated with devitalized (4days, 7days, 14days, 28days) and vital (28days) E. faecalis strains (streptomycin-resistant strains) after root canal enlargement (size 80, taper 0.02) with 3 % NaOCl solution. The smear layer was intentionally removed with 20 % EDTA before inoculation. Samples were processed for analysis by scanning electron microscopy (SEM) and DAPI (4',6-diamidino-2-phenylindole) staining. DAPI was conducted for fluorescence microscopic visualization of the bacterial penetration into dentinal tubules. The penetration depth was calculated with the measurement tool of the Axio Vision program (Zeiss, Jena, Germany).

RESULTS

Devitalized E. faecalis strains were able to penetrate into dentinal tubules of the root canal. Apikal penetration depths of the devitalized cells were 100.67μm±26.54μm after 7days, 230.67μm±111.5μm after 14days and 266.5μm±92.63μm after 28days of incubation. The total number and penetration depth of E. faecalis cells was lower compared to a vital suspension of E. faecalis (1002.45μm) after 28days. It was noted that bacterial penetration was not common to all of the dentinal tubules in the vital E. faecalis control and especially in the devitalized control.

CONCLUSIONS

Increased exposure times of devitalized bacteria into root canals lead to an increased number of penetrated dentinal tubules as well as to a deeper penetration.

Antimicrobial peptide-based treatment for endodontic infections--biotechnological innovation in endodontics

The presence/persistence of microorganisms in the pulp and periapical area corresponds to the maintenance of an exacerbated immune response that leads to the start of periradicular bone resorption and its perpetuation. In endodontic treatment, the available intracanal medications do not have all the desirable properties in the context of endodontic infection and apical periodontitis; they need to include not only strong antimicrobial performance but also an immunomodulatory and reparative activity, without host damage. In addition, there are various levels of resistance to root canal medications. Thus, antimicrobial agents that effectively eliminate resistant species in root canals could potentially improve endodontic treatment. In the emergence of new therapies, an increasing number of studies on antimicrobial peptides (AMPs) have been seen over the past few years. AMPs are defense biomolecules produced in response to infection, and they have a wide spectrum of action against many oral microorganisms. There are some studies that correlate peptides and oral infections, including oral peptides, neuropeptides, and bacterial, fish, bovine and synthetic peptides. So far, there are around 120 published studies correlating endodontic microbiota with AMPs but, according to our knowledge, there are no registered patents in the American patent database. There are a considerable number of AMPs that exhibit excellent antimicrobial activity against endodontic microbiota at a small inhibitory concentration and modulate an exacerbated immune response, down-regulating bone resorption. All these reasons indicate the antimicrobial peptide-based endodontic treatment as an emerging and promising option.

Antimicrobial activity of essential oils and chloroform alone and combinated with cetrimide against Enterococcus faecalis biofilm

The Enterococcus faecalis bacteria have been identified as the most commonly recovered species from teeth with persistent endodontic infections. The antimicrobial activity of essential oils and chloroform (CHL), alone and in association with various concentrations of cetrimide (CTR), against biofilm of Enterococcus faecalis was investigated. Solutions of CHL, eucalyptus oil (EO) and orange oil (OO) associated with CTR at 0.3%, 0.2%, 0.1%, and 0.05% were used to determine antimicrobial activity by exposing treated bovine dentine blocks to E. faecalis. Biofilms grown in the dentine blocks for 7 days were exposed to solutions for 2 and 5 min. Biofilm reduction between OO and EO at 2 min did not show any significant differences; however, OO had a higher kill percentage of biofilms than did the eucalyptus oil at 5 min (p < 0.01). Combinations with CTR at all concentrations achieved a 100% kill rate at 2 and 5 min. The association of CTR with solvent agents achieved the maximum antimicrobial activity against E. faecalis biofilms in dentine.

Sonic extracts from a bacterium related to periapical disease activate gelatinase A and inactivate tissue inhibitor of metalloproteinases TIMP-1 and TIMP-2

AIM

To examine the effects of sonicated bacterial extracts (SBEs) from three related to periapical disease bacteria (Porphyromonas gingivalis, P. endodontalis and F. nucleatum) on the activation of matrix metalloproteinase (MMP-2) and the inactivation of tissue inhibitors of metalloproteinase (TIMP-1 and TIMP-2).

METHODOLOGY

Each SBE was added to cultures of human periodontal ligament (PL) cells or HT1080 cells and their supernatants were analysed by zymography for MMP-2. Each SBE was added to PL cell cultures, and the amount of TIMP-1 was determined by ELISA. P. gingivalis SBE was incubated with HT1080 cell culture supernatants, and the amounts of TIMP-1 and TIMP-2 were determined by ELISA. Statistical analysis was performed with the paired Student's t-test.

RESULTS

In extracts of PL cells that had been incubated in the presence of P. gingivalis SBE, one representing pro-MMP-2 (72 kDa) and a band corresponding to the active MMP-2 (66 kDa) were observed; but in the other extracts it was not detected. When HT1080 cells were treated with P. gingivalis SBE, the pro-MMPs was processed into 86- and 66-kDa fragments, but in the other extracts, the processing did not occur when the other SBEs were used. When PL cells were incubated with the same SBEs, the amount of TIMP-1 was markedly decreased (P < 0.01), but in the other extracts, it was not. The amounts of both TIMP-1 and TIMP-2 were decreased in a dose-dependent manner when HT1080 cell culture supernatant was incubated with P. gingivalis SBE.

CONCLUSIONS

These findings suggest that P. gingivalis SBE may cause connective tissue to be destroyed, contributing to the process of periapical disease, by activating pro-MMP-2 as well as by inactivating TIMP-1 and TIMP-2.

Bacterial diversity in persistent periapical lesions on root-filled teeth

BACKGROUND

The purpose of this study was to analyze the bacterial diversity in persistent apical lesions on root-filled teeth by using culture-independent molecular methods.

DESIGN

Twenty surgically removed apical lesions from therapy-resistant teeth were examined for the presence of bacterial DNA using PCR targeting the 16s ribosomal RNA gene, followed by cloning and sequencing.

RESULTS

Bacterial DNA was detected in 17 of the 20 samples (85%). A total of 236 clones were analyzed. Seven different bacterial phyla were represented and a total of 75 different bacterial taxa were identified; 36% of the species have not yet been cultivated. Commonly detected bacterial species included Fusobacterium spp., Prevotella spp., Tannerella forsythia, Porphyromonas endodontalis, Treponema denticola, Bacteroidetes spp., Peptostreptococcus spp., and Streptococcus spp.

CONCLUSIONS

A wide range of bacteria was identified in periapical lesions on therapy-resistant teeth. These bacteria may contribute in the etiology of periapical infection and impede healing of these lesions.

Presence of bacteria in dentinal tubules

This study demonstrated that a significant number of bacteria is present in the radicular dentinal tubules of periodontally diseased human teeth. Ten periodontally diseased teeth were prepared and stained by Brown and Brenn technique for histological examination. Bacteria were detected in all teeth. It is suggested that bacteria may invade dentinal tubules exposed to periodontal pocket and are very hard to be eliminated by conventional mechanical and chemical periodontal therapy. Contaminated dentinal tubules of periodontally diseased teeth can thus act as active bacterial reservoirs to promote recolonization of mechanically treated root surfaces, which could interfere with the periodontal healing and progression of the disease.

Microbiological evaluation of primary endodontic infections in teeth with and without sinus tract

AIM

To examine the microbiological status of primary endodontic infections in teeth with and without a sinus tract.

METHODOLOGY

Samples were collected by means of a size 15 H-type file and two sterile paper points from 30 cases of primary endodontic infections with (n = 15) or without (n = 15) a sinus tract. The presence of 40 bacterial species was determined by the checkerboard DNA-DNA hybridization method.

RESULTS

The species found at the highest levels and prevalence were Fusobacterium nucleatum sp. vincentii, Porphyromonas gingivalis, Veillonella parvula, Enterococcus faecalis, Campylobacter gracilis and Neisseria mucosa. Total bacterial counts were similar between teeth with (44 x 10(5)) and without (50 x 10(5)) a sinus tract (t-test: P > 0.05). E. faecalis, Streptococcus anginosus, Capnocytophaga sputigena and Capnocytophaga gingivalis had significantly higher counts in the absence of sinus tract (Mann-Whitney test, P < 0.05). Higher levels of P. gingivalis and Fusobacterium nucleatum sp. nucleatum were observed in cases with a sinus tract. Leptotrichia buccalis (OR = 1.83; CI 95%) and Porphyromonas endodontalis (OR = 2.15; CI 95%) were associated with an increased chance of subjects having a sinus tract.

CONCLUSIONS

Primary endodontic infections were associated with a large variety of bacterial species. Specific differences between the composition of the microbiota of primary root canal infections were observed in cases with or without a sinus tract.

Determination of the minimum inhibitory concentration of four medicaments used as intracanal medication

The aim of this study was to determine the minimum inhibitory concentration (MIC) of iodoform, calcium hydroxide, IKI (iodine potassium iodine) and CFC (ciprofloxacin, Flagyl (metronidazole) and calcium hydroxide) required to kill S. aureus, Pseudomonas aeruginosa, Enterococcus faecalis and B. fragilis. In the experiment, medicaments were added to bacterial species into test tubes, in 10 different concentrations. The MIC was the lowest concentration of the drug at which bacterial growth could not be observed. In this investigation, CFC was the most effective medicament against all bacteria. All drugs were able to eliminate E. faecalis and B. fragilis, while IKI was not effective against S. aureus. IKI and calcium hydroxide were not able to eliminate P. aeruginosa as well.

Duration-dependent susceptibility of endodontic pathogens to calcium hydroxide and chlorhexidene gel used as intracanal medicament: an in vitro evaluation

The aim of this study was to evaluate the effective duration of antimicrobial activity of a calcium hydroxide-based medicament (Apex Cal) and 2% chlorhexidene gluconate gel against selected endodontic pathogens (Enterococcus faecalis, Candida albicans, Porphyromonas gingivalis, and Prevotella intermedia). The agar diffusion test was used to determine the antimicrobial activity. Chlorhexidene gluconate gel showed the largest inhibitory zones. The antimicrobial action of both medicaments decreased significantly with time, with calcium hydroxide showing no antimicrobial action after 72 hours. In conclusion, 2% chlorhexidene gel showed better antimicrobial activity than calcium hydroxide, and the effective antimicrobial action of both medicaments decreased after 48 hours.

Use of multiple-displacement amplification and checkerboard DNA-DNA hybridization to examine the microbiota of endodontic infections

Multiple-displacement amplification (MDA) has been used to uniformly amplify bacterial genomes present in small samples, providing abundant targets for molecular analysis. The purpose of this investigation was to combine MDA and checkerboard DNA-DNA hybridization to examine the microbiota of endodontic infections. Sixty-six samples were collected from teeth with endodontic infections. Nonamplified and amplified samples were analyzed by checkerboard DNA-DNA hybridization for levels and proportions of 77 bacterial taxa. Counts, percentages of DNA probe counts, and percentages of teeth colonized for each species in amplified and nonamplified samples were computed. Significance of differences for each species between amplified and nonamplified samples was sought with Wilcoxon signed-rank test and adjusted for multiple comparisons. The amount of DNA in the samples ranged from 6.80 (+/- 5.2) ng before to 6.26 (+/- 1.73) mug after MDA. Seventy of the 77 DNA probes hybridized with one or more of the nonamplified samples. All probes hybridized with at least one sample after amplification. Most commonly detected species at levels of >10(4) in both amplified and nonamplified samples were Prevotella tannerae and Acinetobacter baumannii at frequencies between 89 and 100% of samples. The mean number of species at counts of >10(4) in amplified samples was 51.2 +/- 2.2 and in nonamplified samples was 14.5 +/- 1.7. The endodontic microbiota was far more complex than previously shown, although microbial profiles at teeth with or without periradicular lesions did not differ significantly. Species commonly detected in endodontic samples included P. tannerae, Prevotella oris, and A. baumannii.

Detection of Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia, and Prevotella nigrescens in chronic endodontic infection

Black-pigmented anaerobic rods such as Prevotella spp. and Porphyromonas spp. are involved in the etiology and perpetuation of endodontic infections. The aim of this study was to evaluate the prevalence of these species in chronic endodontic infections by using culture and polymerase chain reaction (PCR) techniques. Samples of 100 patients with root canals displaying chronic endodontic infections were obtained by sterilized paper points. Bacterial identification was performed by using culture and PCR techniques. By culture, in 33% of the samples, P. intermedia-P. nigrescens (75.8%), P. gingivalis (27.3%), and P. endodontalis (9.1%) were identified, and by PCR 60% of the samples harbored P. nigrescens (43.3%), P. gingivalis (43.3%), P. intermedia (31.7%), and P. endodontalis (23.3%). The presence of these black-pigmented anaerobic rods alone or in association in chronic endodontic infections seems to be frequent. PCR is a very sensitive technique for detecting DNA from bacterial cells. Culturing is only able to reveal living bacteria and is less sensitive for the identification of low numbers of bacterial cells.

Co-production of vascular endothelial cadherin and inducible nitric oxide synthase by endothelial cells in periapical granuloma

AIM

To clarify the mechanisms of inflammatory cell migration in human periapical granulomas by examining vascular endothelial (VE) cadherin and inducible nitric oxide synthase (iNOS)-producing cells.

METHODOLOGY

Periapical tissues were obtained from patients during endodontic surgery and were divided into two portions. After fixing the tissues with acetone or 4% paraformaldehyde in phosphate-buffered saline, 5-microm-thick paraffin or cryostat sections were prepared, respectively. The paraffin sections of the inflamed tissues were evaluated histologically with haematoxylin-eosin stains. Cryostat sections of the tissue, diagnosed as periapical granulomas, were then examined by either immunohistochemistry using anti-human VE-cadherin or iNOS antibodies (Abs) for the characterization of infiltrating cells. In addition, co-localization of VE-cadherin and iNOS production was also analysed by two-colour immunofluorescence image analysis.

RESULTS

Endothelial cells were strongly stained with iNOS Abs. Macrophages, lymphocytes, polymorphonuclear leucocytes and fibroblasts also exhibited iNOS production. These iNOS-positive cells accumulated around the blood vessels. On the other hand, VE-cadherin production was exhibited in only endothelial cells. Two-colour immunofluorescence image analysis using VE-cadherin and iNOS Abs demonstrated that iNOS-producing endothelial cells also showed VE-cadherin production.

CONCLUSIONS

Vascular endothelial-cadherin produced by endothelial cells could be regulated by iNOS-producing cells in periapical granulomas and might play a pivotal role in vascular permeability.

Uncultivated phylotypes and newly named species associated with primary and persistent endodontic infections

Endodontic infections have been traditionally studied by culture methods, but recent reports showing that over 50% of the oral microbiota is still uncultivable (B. J. Paster et al., J. Bacteriol. 183:3770-3783, 2001) raise the possibility that many endodontic pathogens remain unknown. This study intended to investigate the prevalence of several uncultivated oral phylotypes, as well as newly named species in primary or persistent endodontic infections associated with chronic periradicular diseases. Samples were taken from the root canals of 21 untreated teeth and 22 root-filled teeth, all of them with radiographic evidence of periradicular bone destruction. Genomic DNA was isolated directly from each sample, and 16S rRNA gene-based nested or heminested PCR assays were used to determine the presence of 13 species or phylotypes of bacteria. Species-specific primers had already been validated in the literature or were developed by aligning closely related 16S rRNA gene sequences. Species specificity for each primer pair was confirmed by running PCRs against a panel of several oral bacteria and by sequencing DNA from representative positive samples. All species or phylotypes were detected in at least one case of primary infections. The most prevalent species or phylotypes found in primary infections were Dialister invisus (81%), Synergistes oral clone BA121 (33%), and Olsenella uli (33%). Of the target bacteria, only these three species were detected in persistent infections. Detection of uncultivated phylotypes and newly named species in infected root canals suggests that there are previously unrecognized bacteria that may play a role in the pathogenesis of periradicular diseases.

Neuropeptide release from dental pulp cells by RgpB via proteinase-activated receptor-2 signaling

Dental pulp inflammation often results from dissemination of periodontitis caused mostly by Porphyromonas gingivalis infection. Calcitonin gene-related peptide and substance P are proinflammatory neuropeptides that increase in inflamed pulp tissue. To study an involvement of the periodontitis pathogen and neuropeptides in pulp inflammation, we investigated human dental pulp cell neuropeptide release by arginine-specific cysteine protease (RgpB), a cysteine proteinase of P. gingivalis, and participating signaling pathways. RgpB induced neuropeptide release from cultured human pulp cells (HPCs) in a proteolytic activity-dependent manner at a range of 12.5-200 nM. HPCs expressed both mRNA and the products of calcitonin gene-related peptide, substance P, and proteinase-activated receptor-2 (PAR-2) that were also found in dental pulp fibroblast-like cells. The PAR-2 agonists, SLIGKV and trypsin, also induced neuropeptide release from HPCs, and HPC PAR-2 gene knockout by transfection of PAR-2 antisense oligonucleotides inhibited significantly the RgpB-elicited neuropeptide release. These results indicated that RgpB-induced neuropeptide release was dependent on PAR-2 activation. The kinase inhibitor profile on the RgpB-neuropeptide release from HPC revealed a new PAR-2 signaling pathway that was mediated by p38 MAPK and activated transcription factor-2 activation, in addition to the PAR-2-p44/42 p38MAPK and -AP-1 pathway. This new RgpB activity suggests a possible link between periodontitis and pulp inflammation, which may be modulated by neuropeptides released in the lesion.

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.

Photo-Activated Disinfection Of The Root Canal: A New Role For Lasers In Endodontics

Because micro-organisms play a crucial role in the development of pulpal and periapical disease, the prognosis of endodontic therapy is intimately related to the presence of bacteria within the root canal system. Micro-organisms may persist in the apical region of the root canal system despite chemomechanical preparation. The usefulness of Class IV lasers (such as Nd:YAG, diode, KTP and Er:YAG) for photo-thermal disinfection of the root canal has been demonstrated in numerous studies. An alternative approach to microbial killing in the root canal system by laser light involves the use of low-power lasers to drive a photochemical reaction that produces reactive oxygen species, a technique termed photo-activated disinfection (PAD). By using exogenous photosensitisers such as tolonium chloride, killing of all types of bacteria can be achieved. In vitro studies of PAD have demonstrated its ability to kill photosensitised oral bacteria (such as E. faecalis), and more recently microbial killing in vivo in the root canal system has been demonstrated. While PAD can be undertaken as part of the routine disinfection of the root canal system, it also has potential use for eradicating persistent endodontic infections for which conventional methods have been unsuccessful.

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.

Selected Endodontic Pathogens in the Apical Third of Infected Root Canals: A Molecular Investigation

Bacteria located at the apical portion of the root canals are conceivably in a strategic position to induce damage to the periradicular tissues and resulting inflammatory diseases. This study sought to investigate the prevalence of 11 selected putative endodontic pathogens in the apical third of infected root canals associated with periradicular lesions. The apical root portion of 23 extracted teeth with carious pulpal exposures and attached periradicular lesions was sectioned, and the root canals were sampled for microbiological investigation. DNA was extracted from the samples and analyzed for the presence of 11 bacterial species using a nested polymerase chain reaction assay. The results showed that Pseuramibacter alactolyticus occurred in 10 cases (44%), Treponema denticola in 6 (26%), Fusobacterium nucleatum in 6 (26%), Porphyromonas endodontalis in 4 (17%), Filifactor alocis in 2 (9%), Dialister pneumosintes in 1 (4%), Porphyromonas gingivalis in 1 (4%), and Tannerella forsythensis in 1 (4%). No sample yielded Prevotella intermedia, Prevotella nigrescens, or Campylobacter rectus. Of the samples examined, 17 were positive for at least 1 of the target species. Occurrence of these bacterial species in the apical third of infected root canals suggests that they can be involved in causation of periradicular lesions.

Geographical Differences in Bacteria Detected in Endodontic Infections Using Polymerase Chain Reaction

The polymerase chain reaction (PCR) is an innovative nucleic acid-based assay that has the highest sensitivity of any microbiological technique for the detection of bacteria. The purpose of this study was to use PCR to detect the presence of specific species of bacteria in samples collected from two geographical locations. Microbial samples from abscesses of endodontic origin were collected from patients in Portland, Oregon, and Rio de Janeiro, Brazil. PCRs with species-specific oligonucleotide primers for the 16S ribosomal RNA gene were used for detection of the bacteria after DNA extraction from each clinical sample. Statistical analysis revealed that there was a significant difference in detection of the bacteria between the two geographical locations for Prevotella intermedia, Prevotella nigrescens, Prevotella tannerae, Fusobacterium nucleatum, and Porphyromonas gingivalis, but not for Porphyromonas endodontalis, Fusobacterium necrophorum, and Enterococcus faecalis. These results suggest that differences in bacteria detected or cultured in studies can be associated with geographical location.

Clinical and Radiographic Evaluation of Root-canal Obturation with Obtura II

This study evaluated clinical and radiographic healing of 236 root-canal treatments in 131 cases obturated with the Obtura II system. One operator performed all canal preparation and obturation with sealer. A standardized apical-coronal preparation technique instrumented all canals. Clinical symptoms, periodontal condition, and radiographic findings were evaluated at 3, 6, and 12 months. Radiographs taken immediately postobturation were compared to recall radiographs. The level of the final root filling was classified as short (more than 2 mm short of the apex), flush (within 2 mm), or over (beyond) in 12.7%, 81.4%, and 5.9% of cases, respectively. More than 96% of cases were treated successfully by the Obtura II system. Where roots were filled flush, over, or short, lesions healed in 97%, 93%, and 93% of cases, respectively, with no significant differences (p < 0.05). Root filling excess had no impact on the healing process.

Invasion of dentinal tubules by oral bacteria

Bacterial invasion of dentinal tubules commonly occurs when dentin is exposed following a breach in the integrity of the overlying enamel or cementum. Bacterial products diffuse through the dentinal tubule toward the pulp and evoke inflammatory changes in the pulpo-dentin complex. These may eliminate the bacterial insult and block the route of infection. Unchecked, invasion results in pulpitis and pulp necrosis, infection of the root canal system, and periapical disease. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria is involved in the invasion of dentinal tubules and subsequent infection of the root canal space. Gram-positive organisms dominate the tubule microflora in both carious and non-carious dentin. The relatively high numbers of obligate anaerobes present-such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp.-suggest that the environment favors growth of these bacteria. Gram-negative obligate anaerobic rods, e.g., Porphyromonas spp., are less frequently recovered. Streptococci are among the most commonly identified bacteria that invade dentin. Recent evidence suggests that streptococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra-tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate the invasion of dentin by select bacterial groupings. An understanding the mechanisms involved in dentinal tubule invasion by bacteria should allow for the development of new control strategies, such as inhibitory compounds incorporated into oral health care products or dental materials, which would assist in the practice of endodontics.

Yeasts in apical periodontitis

Microbiological reports of apical periodontitis have revealed that yeasts can be isolated from approximately 5-20% of infected root canals. They occur either in pure cultures or together with bacteria. Almost all isolated yeasts belong to the genus Candida, and the predominant species is C. albicans. Pheno- and genotypic profiles of C. albicans isolates show heterogeneity comparable with those of isolates from other oral sites. C. albicans expresses several virulence factors that are capable of infecting the dentin-pulp complex, including dentinal tubules. This causes, consequentially, an inflammatory response around the root apex, which suggests a pathogenic role for this organism in apical periodontitis. Yeasts are particularly associated with persistent root canal infections that do not respond favorably to conservative root canal therapy. This may be due to the resistance of all oral Candida species against a commonly used topical medicament, calcium hydroxide. However, other antimicrobial agents may offer alternative therapeutic approaches and improve the treatment of these persistent cases of apical periodontitis.

Comparison of antibacterial and toxic effects of various root canal irrigants

AIM

To compare the antibacterial properties and toxicity of 5.25% sodium hypochlorite (NaOCl), 2% chlorhexidine gluconate and 0.2% chlorhexidine gluconate plus 0.2% cetrimide (Cetrexidin); Vebas, San Giuliano, Milan, Italy).

METHODOLOGY

The antibacterial effects of the irrigants in vitro were examined after 5 min and 48 h in freshly extracted human teeth with single roots, whose canals were infected by Enterococcus faecalis ATCC 29212. In a separate in vivo study, bacterial culture samples were collected before treatment from the infected root canals of deciduous teeth containing necrotic pulp tissue. Irrigants were used to clean the canals which were then left empty for 48 h. Aerobic/facultative anaerobic and anaerobic bacterial growth were compared before and 48 h after irrigation. Finally, the toxic effects of the irrigants were assessed by injecting them into the subcutaneous tissues of rats. The inflammatory reactions that occurred 2 h, 48 h and 2 weeks after the injections were evaluated.

RESULTS

In the laboratory study, the 2% chlorhexidine gluconate and Cetrexidin were significantly more effective on E. faecalis than the 5.25% NaOCl at 5 min (P < 0.05). Similarly, in the in vivo study, 2% chlorhexidine gluconate and Cetrexidin were significantly more effective on anaerobic bacteria than the 5.25% NaOCl at 48 h (P < 0.05). At the end of 2 weeks, the toxicity of the NaOCl solution was greater than that of the other irrigants (P < 0.05).

CONCLUSIONS

Cetrexidin and 2% chlorhexidine gluconate were more effective, and had more residual antibacterial effects and lower toxicity than 5.25% NaOCl solution.

Cytomegalovirus and Epstein-Barr virus active infection in periapical lesions of teeth with intact crowns

Herpesviruses seem to play an important role in the pathogenesis of aggressive periodontitis and may also contribute to periapical pathosis. This study determined the presence of human cytomegalovirus, Epstein-Barr virus, and herpes simplex virus productive infection in five symptomatic periapical lesions of teeth having intact crowns and calcified necrotic pulps. Periapical samples were collected in conjunction with periapical surgery and kept frozen until virological examination. Reverse transcription-polymerase chain reaction was used in herpesviral identification. RNA was isolated from periapical tissue by a guanidinium isothiocyanate-acid phenol procedure. cDNAs were generated from highly conserved regions of the test viruses using a preamplification kit. Sensitivity and validity of the PCR-primers were determined according to established methods. Amplification products were identified using gel electrophoresis. Human cytomegalovirus and Epstein-Barr virus dual transcription was detected in all five periapical lesions studied. Herpes simplex virus transcript was not identified in any lesion. The present data suggest that human cytomegalovirus or Epstein-Barr virus activation participate in the pathogenesis of symptomatic periapical lesions. We hypothesize that periapical active herpesvirus infection impairs local defenses, thereby inducing overgrowth of endodontopathic bacteria and the clinical flare-up of inflammation.

Cytomegalovirus and Epstein-Barr virus DNA transcription in endodontic symptomatic lesions

OBJECTIVES

Productive Herpesviridae infections are implicated in the etio-pathogenesis of aggressive periodontitis. However, virtually nothing is known about a possible role of herpesviruses in pulpal and periapical pathosis. This study employed a cDNA analysis to determine transcription of human cytomegalovirus (HCMV), Epstein-Barr virus (EBV) and herpes simplex virus (HSV) in 14 recalcitrant periapical lesions and in 2 periapical healthy control sites.

METHODS

Periapical samples were collected in conjunction with periapical surgery and kept frozen until virologic examination. RNA was isolated from periapical tissue by using a guanidinium isothiocyanate-acid phenol procedure (TRIZOL LS Reagent, GIBCO BRL, Rockville, MD). cDNAs were amplified by means of oligonucleotides targeting highly conserved regions of the test viruses and the RT-PCR-100 amplification kit (Sigma-Aldrich, St Louis, MO). Standardization of PCR primer sensitivity and validation was carried out according to established methods. Amplification products were identified by agarose gel electrophoresis.

RESULTS

HCMV transcript was detected in 12 of 13 symptomatic and in 1 asymptomatic periapical lesion. EBV transcript was demonstrated in 8 of the 13 symptomatic lesions but not in the asymptomatic periapical lesion. HCMV and EBV dual transcription occurred at higher frequency in periapical lesions showing radiographic bone destruction of 5 mm x 7 mm or larger than in smaller size lesions (P = 0.03; Chi-squared test). No HCMV or EBV transcription was identified in the 2 healthy control sites. HSV transcript was not detected in any study site.

CONCLUSION

The present data suggest that HCMV or EBV infections participate in the pathogenesis of periapical symptomatic lesions. Herpesviruses may produce periapical pathosis as a direct result of viral infection and replication, or as a consequence of virally induced impairment of the host defense and subsequent increased virulence of resident bacterial pathogens.

Dialister pneumosintes can be a suspected endodontic pathogen

OBJECTIVE

Dialister pneumosintes is a nonmotile, nonfermentative, non-spore-forming, obligately anaerobic, gram-negative bacillus that has been associated with some infections in the human body. A species-specific nested polymerase chain reaction assay was used to investigate the occurrence of D pneumosintes in primary root canal infections.

STUDY DESIGN

Samples were collected from 32 teeth with carious lesions, necrotic pulps, and radiographic evidence of periradicular bone destruction. Twenty-two teeth were asymptomatic, and 10 cases were diagnosed as acute apical periodontitis. DNA extracted from the samples was initially amplified with universal 16S ribosomal DNA primers. A second round of amplification used the first polymerase chain reaction products to specifically detect D pneumosintes.

RESULTS

This bacterial species was detected in 17 of 22 asymptomatic cases (77.3%) and in 4 of 10 root canals associated with acute apical periodontitis (40%). No relationship was found between the presence of this bacterial species and the occurrence of symptoms. In general, D pneumosintes was detected in 21 of 32 root canal samples (65.6%).

CONCLUSION

This study is the first to report a high prevalence of D pneumosintes in root canal infections of humans. Because of this high prevalence and the apparent pathogenicity of the microorganism, we suggest the inclusion of D pneumosintes in the selected group of putative endodontic pathogens.

PCR-based identification of bacteria associated with endodontic infections

PCR primers that target the bacterial 16S rRNA genes (or the tuf gene for the genus Enterococcus) were used to identify 10 putative bacterial pathogens in root canals with necrotic pulp. In addition, the associations of these microorganisms with symptoms and a history of diabetes mellitus were investigated. Microbial samples from the root canals of 24 teeth with necrotic pulp were included in the study. PCR with universal bacterial primers identified bacterial DNA in 22 specimens; the remaining 2 specimens were from intact teeth that had been traumatized 6 months prior to treatment. PCR with specific primers showed that preoperative symptoms were significantly associated with the presence of Streptococcus spp. (P < 0.001 by chi-square analysis). There was also a nonsignificant trend for symptoms to be associated with Fusobacterium nucleatum and Porphyromonas gingivalis (odds ratio, >2) and for diabetes mellitus to be associated with P. gingivalis and Porphyromonas endodontalis (odds ratio, >2). Cloning and sequencing of the universal PCR product in one specimen revealed the presence of an organism related to the genus Olsenella, which has not previously been described in endodontic infections.

Pathologic interactions in pulpal and periodontal tissues

Both endodontic and periodontal disease are caused by a mixed anaerobic infection. The pathways for the spread of bacteria between pulpal and periodontal tissues have been discussed with controversy. This article is an attempt to provide a rational approach to the perio-endo/endo-perio question based on a review of the relevant literature. In the light of evidence, clinical concepts for the diagnosis and treatment of lesions involving both periodontal and pulpal tissues are discussed.

Combinations of bacterial species in endodontic infections

AIM

This study was undertaken to investigate combinations of bacteria found in root-canal infections of teeth with periapical bone destruction without clinical signs and symptoms.

METHODOLOGY

Endodontic samples from 58 root canals were cultured anaerobically and microorganisms were counted and identified. Eighty-one combinations of microorganisms were found and tested for a symbiotic relationship using the Fisher's exact test and Odds ratio calculation.

RESULTS

All samples contained microorganisms with a median CFU mL(-1) of 8x10(4) per sample. Strict anaerobic species accounted for 87% of the microflora. The most prevalent bacteria were Prevotella intermedia, Peptostreptococcus micros and Actinomyces odontolyticus, present in 33, 29 and 19%, respectively, of the cultured canals. A significant relationship (P<0.05) and an Odds ratio >2 were found between P. intermedia and P. micros, P. intermedia and P. oralis, A. odontolyticus and P. micros, Bifidobacterium spp. and Veillonella spp.

CONCLUSIONS

These results indicate that endodontic pathogens do not occur at random but are found in specific combinations.

Comparison of temporal changes in components of formalin guaiacol under several storage conditions

This study examined the effects of storage conditions such as time course, temperature, fluorescent light, and darkness on the components and antibacterial activity of formalin guaiacol (FG) used in endodontic treatment. We measured the quantities of formaldehyde and guaiacol in FG and antibacterial activities against Staphylococcus aureus, Porphyromonas gingivalis, and Porphyromonas endodontalis. The components and antibacterial activity of FG in the brown or transparent tightly sealed containers were not affected by temperature or fluorescent light throughout the 4 week test. However, in the loosely sealed containers, formaldehyde and guaiacol in FG sample decreased remarkably within one week, not only in a temperature- and time-dependent manner, but also under fluorescent light at 20 degrees C. Furthermore, the antibacterial activities in the FG sample were significantly attenuated in parallel with the decrease in formaldehyde levels. Fluorescent light caused color changes and crystallization of FG samples in the transparent containers. These results suggest that it is important to replace fresh FG every 5 to 7 days for endodontic treatment and that, in the dental office, it is advisable to store fresh FG in tightly sealed containers every 2 weeks to maintain its efficacy.

Invasion of vascular cells in vitro by Porphyromonas endodontalis

AIM

The objective of this study was to determine whether laboratory strains and clinical isolates of microorganisms associated with root canal infections can invade primary cultures of cardiovascular cells.

METHODOLOGY

Quantitative levels of bacterial invasion of human coronary artery endothelial cells (HCAEC) and coronary artery smooth muscle cells (CASMC) were measured using a standard antibiotic protection assay. Transmission electron microscopy was used to confirm and visualize internalization within the vascular cells.

RESULTS

Of the laboratory and clinical strains tested, only P. endodontalis ATCC 35406 was invasive in an antibiotic protection assay using HCAEC and CASMC. Invasion of P. endodontalis ATCC 35406 was confirmed by transmission electron microscopy.

DISCUSSION

Certain microorganisms associated with endodontic infections are invasive. If bacterial invasion of the vasculature contributes to the pathogenesis of cardiovascular disease, then microorganisms in the pulp chamber represent potential pathogens.

Effect of occlusal trauma on healing of periapical pathoses: report of two cases

AIM

To present two clinical cases and demonstrate that occlusal trauma may affect healing of periapical pathoses.

SUMMARY

Two teeth with periradicular disease did not respond successfully to conventional root canal treatment or endodontic surgery. Occlusal adjustment was finally performed on both cases. After occlusal adjustment, uncomplicated healing and periapical repair occurred in both cases. The findings in these two cases suggest that occlusal trauma may play a role in the healing of periapical pathoses.

KEY LEARNING POINTS

Occlusal trauma is positively correlated with changes in periodontal tissues. Although experiments in animals have shown that application of forces to teeth will not induce further periodontal destruction, we believe that some failures of root canal treatment may be due to the presence of occlusal trauma modulating the responses of inflamed periapical tissues or apical pathoses with persistent infection.

Identification of oral spirochetes at the species level and their association with other bacteria in endodontic infections

OBJECTIVES

Recent molecular approaches have revealed that fastidious organisms such as Bacteroides forsythus and oral treponemes were frequently found in root canals with apical periodontitis. The purpose of this study was to identify the isolates of oral spirochetes at the species level in endodontic infections and to determine their association with B forsythus and Porphyromonas gingivalis.

STUDY DESIGN

Seventy-nine teeth with apical periodontitis were selected for this study. After sampling from the root canals aseptically, polymerase chain reaction amplification for the 16S rRNA gene was performed with eubacterial universal primers. Subsequently, dot-blot hybridization was performed with 8 species-specific oligonucleotide probes. The microbial associations were analyzed by using the odds ratio.

RESULTS

The most frequently found species was P gingivalis (27.4%), followed by Treponema maltophilum (26%), B forsythus (16.4%), and Treponema socranskii (2.7%). Other treponemes, including Treponema denticola, were not detected in our samples. Significant microbial associations were identified between T maltophilum, B forsythus, and P gingivalis by performing analysis with the odds ratio.

CONCLUSION

Our results indicate that T maltophilum should be included in etiologic studies of endodontic diseases.

Microorganisms isolated from root canals presenting necrotic pulp and their drug susceptibility in vitro

The knowledge about causative agents involved in endodontic infections is increasing, especially due to the improvement of culture techniques for anaerobic bacteria, showing that these microorganisms are predominant in this pathology. In this study, 31 canals with pulp necrosis were microbiologically analyzed before and after manipulation. Obligate and facultative anaerobes, microaerophilic bacteria and yeasts were recovered from 24, 14, 5 and 2 clinical specimens, respectively. The most frequent genera were Prevotella, Fusobacterium, Lactobacillus, Streptococcus, Clostridium and Peptostreptococcus for bacteria and Candida and Saccharomyces for yeasts. Strong positive associations, using an odds ratio system, were found between Clostridium and Prevotella and between Peptostreptococcus and Fusobacterium. Even after the instrumentation and the use of Ca(OH)2, facultative anaerobes were detected in two root canals and yeasts in three. Microorganisms were isolated from seven canals at the end of the endodontic treatment: facultative anaerobes from five and yeasts from one. The microbiological evaluation of root canals with pulp necrosis suggests the presence of polymicrobial infections, mainly involving obligate anaerobes, and shows that the infection may persist after treatment.

Detection of Porphyromonas endodontalis in infected root canals by 16S rRNA gene-directed polymerase chain reaction

Porphyromonas endodontalis has been isolated from the endodontic infections mainly in symptomatic teeth. This study evaluated the occurrence of P. endodontalis in both symptomatic and asymptomatic endodontic infections using 16S rRNA gene-directed polymerase chain reaction. P. endodontalis was detected in 39.5% of the cases (17 of 43 teeth). It was present in 4 of the 6 cases with acute periradicular abscess (66.7%) and in 13 of the 37 other cases (35.1%). The presence of P. endodontalis was associated with an asymptomatic periradicular lesion in 6 cases (25%) and in 10 teeth with tenderness to percussion (52.6%). P. endodontalis was also found in one asymptomatic case without evidence of periradicular pathosis. Our results indicated that, although P. endodontalis is commonly detected in symptomatic cases, it can be present in asymptomatic root canal infections. Further studies should determine if this bacterial species is really an important endodontopathogen.

Molecular epidemiology and association of putative pathogens in root canal infection

The purpose of this study was to investigate the epidemiology of putative pathogens in root canals with apical periodontitis and to determine the associations among the putative pathogens. Eighteen symptomatic and 20 asymptomatic teeth from 36 subjects were studied. This research was performed with polymerase chain reaction and hybridization using rRNA-based oligonucleotide probes. The most frequently found species was Fusobacterium sp. (68.4%), followed by Peptostreptococcus micros (44.7%) and Porphyromonas gingivalis (26.3%). Sixteen teeth (42.1%) contained one or more species of the selected black-pigmented bacteria. Bacteroides forsythus and Treponema sp. were detected in 8 teeth and 6 teeth, respectively. Among the analyzed bacteria, significant relationships were shown in the combination of B. forsythus/P. gingivalis and Treponema sp./P. gingivalis. There was no significant association between any bacteria and any symptoms.

Isolation of Enterococcus faecalis in previously root-filled canals in a Lithuanian population

The occurrence of Enterococcus faecalis in root canals of previously root filled teeth with apical periodontitis requiring retreatment was studied in Lithuanian patients. Twenty-five asymptomatic teeth were included in the study. Avoiding contamination microbiological samples were taken from the canals before and after preparation and irrigation with sodium hypochlorite and EDTA. Microbes were isolated from 20 of 25 teeth. E. faecalis was isolated from 14 of those 20 culture positive teeth, usually in pure culture or as a major component of the flora. Second samples taken after preparation revealed growth in 7 of the 20 teeth. Five of the seven cases were E. faecalis in pure culture. Isolation of E. faecalis was not related to the use of any particular root filling material in the original root filling. The results indicate that, rather than previous chemical treatment, it is the ecological conditions present in the incompletely filled root canal that are important for the presence of E. faecalis in these teeth.

Protective and destructive immune reactions in apical periodontitis

Apical periodontitis is initiated primarily by the mixed microflora of infected root canals. Continuous flow of bacteria and their products through the apical foramen induces influx, activation and coordinated interaction of immune-inflammatory cells within the periapical area. Successful mobilization of host defense mechanisms prevents abundant extraradicular bacterial invasion. However, anti-infective effector mechanisms are not restricted to killing the invading microorganisms but also destroy normal tissue components and induce bone absorption, resulting ultimately in the loss of the affected teeth. Moreover, autocrine and paracrine loops of stimulation may lead to the perpetuation of the local inflammatory lesion and may also alter the function of remote tissues and organs. This review attempts to summarize current knowledge about the pathogenic mechanism of apical periodontitis, focusing on the formation of a special granulation tissue that effectively fights bacteria originated from the infected pulp chamber and, by exerting this protective function, also contributes to harmful local and distant events. The dynamic equilibrium between defensive and destructive mechanisms may provide a pathobiological basis for better understanding of clinical signs and symptoms of various forms of apical periodontitis lesions and influence treatment strategy and practice.