Black-pigmented bacteria in coronal and apical segments of infected root canals

Apical root canal microbiome associated with primary and posttreatment apical periodontitis: A systematic review

BACKGROUND

Microorganisms colonizing the apical root canal system are conceivably the ones directly involved with the causation and maintenance of apical periodontitis.

OBJECTIVES

This article systematically reviews the reports on the microbiome occurring exclusively at the apical root canal of teeth with primary and posttreatment apical periodontitis.

METHODS

The electronic databases PubMed, Embase, Web of Science, Science Direct, and Proquest were searched up to August 2023. Clinical studies using culture and molecular microbiology methods to identify the microbial taxa present exclusively in the apical root canal segment of infected teeth with apical periodontitis were included. Studies were critically assessed using the Joanna Briggs Institute Critical Prevalence Assessment Checklist.

RESULTS

From 2277 articles initially detected, 52 were selected for full reading and 21 were eventually included in this review. Of these, molecular methods were used in 19 and culture in 2 studies. Ten studies evaluated primary infections, 8 evaluated posttreatment infections, and 3 included both. Cryopulverization of the apical root specimens was conducted in 11 studies. All studies evaluated the prevalence and diversity of bacteria, and only one also reported on fungi. Overall, the most frequent/abundant bacterial taxa found in the apical canal of primary infections were Pseudoramibacter alactolyticus, Olsenella uli, Fusobacterium species, Streptococcus species, Porphyromonas endodontalis, Prevotella species, Actinomyces species, Parvimonas micra, Treponema denticola, Synergistetes species, and an as-yet uncharacterized taxon. In posttreatment infections, the most prevalent/abundant bacterial taxa included species of Streptococcus, Enterococcus, Fusobacterium, Actinomyces, Pseudoramibacter, Pseudomonas, and Propionibacterium. At the phylum level, Firmicutes was the most represented. The average apical bacterial load ranged from 105 to 106 in primary infections and from 103 to 104 in posttreatment infections.

DISCUSSION

Microbial diversity in the apical part of the root canal system was examined encompassing data from both primary and posttreatment infections. Heterogeneity amongst the studies, especially in sample collection and microbial identification methods, is an important limitation that prevented a meta-analysis.

CONCLUSIONS

There is a pronounced bacterial diversity in the infected apical canal, with a high interindividual variability. Different microbiome compositions at the species/genus level are observed according to the infection type.

REGISTRATION

PROSPERO CRD42021275886.

Retrospective analysis of Porphyromonas gingivalis in patients with nasopharyngeal carcinoma in central China

Little is known about the presence and possible role of Porphyromonas gingivalis (P. gingivalis) in nasopharyngeal carcinoma (NPC), its co-infection with Epstein-Barr virus (EBV), or their association with clinical characteristics of patients with NPC in Central China, where NPC is non-endemic. A total of 45 NPC formalin-fixed paraffin-embedded (FFPE) tissues were retrospectively analyzed using immunohistochemistry (IHC) and a nested PCR combined with DNA sequencing to detect the presence of P. gingivalis, and using reverse transcription-quantitative PCR to detect the presence of EBV. Clinical data including EBV and P. gingivalis status were associated with overall survival (OS). All tumors were undifferentiated, non-keratinizing carcinomas, of which 40/45 (88.9%) were positive for EBV (EBV⁺), 26/45 (57.8%) were positive for P. gingivalis (by IHC), and 7/45 (15.6%) were positive for P. gingivalis DNA (P. gingivalis ⁺). All seven P. gingivalis DNA-positive NPCs were co-infected with EBV. The 5-year survival rates of the patients with EBV^-/P. gingivalis ^-, EBV⁺/P. gingivalis ^-, and EBV⁺/P. gingivalis ⁺ tumors were 60.0% (3/5), 39.4% (13/33) and 42.9% (3/7), respectively. No significant difference was found between the OS of NPC patients among the different infection groups (P=0.793). In conclusion, to the best of our knowledge, this is the first study to describe and confirm the presence of P. gingivalis in FFPE tissues from patients with NPC. P. gingivalis was found to co-exist with EBV in NPC tumor tissues, but is not etiologically relevant to NPC in non-endemic areas, such as Central China.

Present status and future directions - microbiology of endodontic infections

Apical periodontitis has a microbial aetiology and is one of the most common inflammatory diseases that affect humans. Fungi, archaea and viruses have been found in association with apical periodontitis, but bacteria are by far the most prevalent and dominant microorganisms in endodontic infections. Bacterial infection of the root canal system only occurs when the pulp is necrotic or was removed for previous treatment. In some specific cases, including acute and chronic abscesses, the bacterial infection may reach the periradicular tissues. Intracanal bacteria are usually observed as sessile multispecies communities (biofilms) attached to the dentinal root canal walls. Infection in the main root canal lumen can spread to other areas of the root canal system. Although more than 500 bacterial species have been detected in endodontic infections, a selected group of 20 to 30 species are most frequently detected and may be considered as the core microbiome. There is a high interindividual variability in the endodontic microbiome in terms of species composition and relative abundance. Obligate anaerobic species are more abundant in the intraradicular bacterial communities of teeth with primary apical periodontitis, while both anaerobes and facultatives dominate the communities in post-treatment apical periodontitis. Bacterial interactions play an essential role in determining the overall virulence of the community, which has been regarded as the unit of pathogenicity of apical periodontitis. This article reviews the microbiologic aspects of endodontic infections and provides perspectives for future research and directions in the field.

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.

Systemic and Extraradicular Bacterial Translocation in Apical Periodontitis

Apical periodontitis is an inflammatory disease of microbial etiology. It has been suggested that endodontic bacterial DNA might translocate to distant organs via blood vessels, but no studies have been conducted. We aimed first to explore overall extraradicular infection, as well as specifically by Porphyromonas spp; and their potential to translocate from infected root canals to blood through peripheral blood mononuclear cells. In this cross-sectional study, healthy individuals with and without a diagnosis of apical periodontitis with an associated apical lesion of endodontic origin (both, symptomatic and asymptomatic) were included. Apical lesions (N=64) were collected from volunteers with an indication of tooth extraction. Intracanal samples (N=39) and respective peripheral blood mononuclear cells from apical periodontitis (n=14) individuals with an indication of endodontic treatment, as well as from healthy individuals (n=14) were collected. The detection frequencies and loads (DNA copies/mg or DNA copies/μL) of total bacteria, Porphyromonas endodontalis and Porphyromonas gingivalis were measured by qPCR. In apical lesions, the detection frequencies (%) and median bacterial loads (DNA copies/mg) respectively were 70.8% and 4521.6 for total bacteria; 21.5% and 1789.7 for Porphyromonas endodontalis; and 18.4% and 1493.9 for Porphyromonas gingivalis. In intracanal exudates, the detection frequencies and median bacterial loads respectively were 100% and 21089.2 (DNA copies/μL) for total bacteria, 41% and 8263.9 for Porphyromonas endodontalis; and 20.5%, median 12538.9 for Porphyromonas gingivalis. Finally, bacteria were detected in all samples of peripheral blood mononuclear cells including apical periodontitis and healthy groups, though total bacterial loads (median DNA copies/μL) were significantly higher in apical periodontitis (953.6) compared to controls (300.7), p<0.05. Porphyromonas endodontalis was equally detected in both groups (50%), but its bacterial load tended to be higher in apical periodontitis (262.3) than controls (158.8), p>0.05; Porphyromonas gingivalis was not detected. Bacteria and specifically Porphyromonas spp. were frequently detected in endodontic canals and apical lesions. Also, total bacteria and Porphyromonas endodontalis DNA were detected in peripheral blood mononuclear cells, supporting their plausible role in bacterial systemic translocation.

On the dynamics of root canal infections-what we understand and what we don't

Infections of the root canal space and their sequelae can be extremely painful and potentially dangerous, yet they do not necessarily have to be. Chronic, asymptomatic inflammatory lesions around the apex of a tooth with a necrotic dental pulp or an insufficient root canal treatment can develop unnoticed by the patient, and remain so for years. The course of disease is modulated by both the virulence of the microbiota established in the root canal space and the capacity of the immune system to curb the infection. To both ends, highly convincing investigations to help us understand when and why the tissues around an endodontically involved tooth become acutely inflamed are missing. We will discuss how recent advances in molecular identification of microorganisms have altered our understanding of root canal infections, and which information is currently missing to link clinical experience with observations from experimental research.

Molecular characterization of the microbial flora residing at the apical portion of infected root canals of human teeth

INTRODUCTION

This study investigated the bacterial communities residing in the apical portion of human teeth with apical periodontitis in primary and secondary infections by using a culture-independent molecular biology approach.

METHODS

Root canal samples from the apical root segments of extracted teeth were collected from 18 teeth with necrotic pulp and 8 teeth with previous endodontic treatment. Samples were processed for amplification via polymerase chain reaction and separated with denaturing gradient gel electrophoresis. Selected bands were excised from the gel and sequenced for identification.

RESULTS

Comparable to previous studies of entire root canals, the apical bacterial communities in primary infections were significantly more diverse than in secondary infections (P = .0003). Interpatient and intrapatient comparisons exhibited similar variations in profiles. Different roots of the same teeth with secondary infections displayed low similarity in bacterial composition, whereas an equivalent sample collected from primary infection contained almost identical populations. Sequencing revealed a high prevalence of Fusobacteria, Actinomyces species, and oral Anaeroglobus geminatus in both types of infection. Many secondary infections contained Burkholderiales or Pseudomonas species, both of which represent opportunistic environmental pathogens.

CONCLUSIONS

Certain microorganisms exhibit similar prevalence in primary and secondary infection, indicating that they are likely not eradicated during endodontic treatment. The presence of Burkholderiales and Pseudomonas species underscores the problem of environmental contamination. Treatment appears to affect the various root canals of multirooted teeth differently, resulting in local changes of the microbiota.

An investigation of a potential confounder in ex vivo microbiological studies--the bulk flow of fluid through apical foramina during tooth extraction

AIMS

To investigate the factors affecting bulk flow of dye and bacterial suspensions into and out of apical foramina during simulated tooth extraction, using an ex vivo model.

METHODOLOGY

Sixty extracted, single-rooted, human teeth were accessed, root canals located and in 50 the pulps dissolved; 10 teeth with attached periapical lesions were preserved. The size of apical foramina was determined digitally. The teeth were mounted in vials with polyvinylsiloxane impression material. Part 1: different dyes were inoculated in the coronal half of root canals or cervical 'gingival' margin, respectively, in separate experiments using the same teeth. Tooth extraction movements were simulated and apical penetration of the dye solutions with and without coronal restorations were examined in each case (20 teeth re-used 4 × ). Part 2: the same procedures were repeated on 30 more teeth but using a standard inoculum of Acidovorax sp. Part 3: 10 teeth with attached periapical lesions were inoculated with Acidovorax sp. in the absence of coronal restorations. Bacterial leakage into the periapical lesions was assessed.

RESULTS

Coronal restorations significantly reduced the flow of dyes (P=0.002) or bacterial suspension (P=0.001) out of the canals and bacterial suspension into (P=0.02) the canals during simulated tooth extraction. The 'size of apical foramina' were positively correlated with passage of bacterial suspension out of the canal (P=0.04) and from the gingival trough into the canal (P=0.008), in the presence of a coronal restoration.

CONCLUSIONS

The presence of coronal restorations, the size of apical foramina and presence of native canal contents with attached periapical lesions, all influenced fluid flow into and out of canals during simulated tooth extraction movements.

Application of a chairside anaerobic culture test for endodontic treatment

Periapical lesions are caused by bacterial infections. The fundamental objective of endodontic treatment is to eliminate bacteria present in the root canal system because they play an important role in the development and maintenance of periapical lesions. Therefore, confirming the absence of bacteria before filling root canals is important. Anaerobic culture tests have been used in many endodontic cases, and they have brought about good treatment outcomes. These tests, however, require specific apparatuses and bacteriological techniques. Here, we report a chairside anaerobic culture test that does not require any specialized apparatuses or techniques. We also report two endodontic cases in which this simple test was used. Both patients were diagnosed with chronic purulent periapical lesions. After confirming the absence of bacteria in the root canals, they were filled with gutta-percha points. At followup, the radiolucencies showed recovery, although longterm observation is under way. From these results, the authors conclude that this simple chairside anaerobic culture test is effective for evaluating periapical lesion treatment procedures.

Apical root canal microbiota as determined by reverse-capture checkerboard analysis of cryogenically ground root samples from teeth with apical periodontitis

INTRODUCTION

Bacteria located in the apical root canal system potentially participate in the pathogenesis of apical periodontitis. Detection and identification of apical bacteria can be compromised because of limitations in conventional sampling and identification procedures. This study identified several bacterial taxa in the apical and middle/coronal segments of primarily infected root canal system by using pulverized root segments and a culture-independent molecular method.

METHODS

Seventeen extracted teeth with attached apical periodontitis lesions were sectioned to obtain 2 root fragments (apical and middle/coronal segments). Root fragments were cryogenically ground, and DNA was extracted from samples. After multiple displacement amplification, DNA from samples was used as template in a reverse-capture checkerboard hybridization assay targeting 28 bacterial taxa.

RESULTS

Bacterial DNA was detected in all samples. The most prevalent taxa in the apical root canal system were Olsenella uli (76.5%), Prevotella baroniae (71%), Porphyromonas endodontalis (65%), Fusobacterium nucleatum (53%), and Tannerella forsythia (47%). O. uli, P. endodontalis, and Propionibacterium acnes were as frequently detected in apical samples as they were in middle/coronal samples. P. baroniae, T. forsythia, and F. nucleatum were found more frequently in the apical part of the canal as compared with matched coronal segments. Streptococcus species were more prevalent in middle/coronal samples. The median and mean of shared bacterial taxa between matched apical and middle/coronal segments were 27% and 41%, respectively.

CONCLUSIONS

Several candidate endodontic pathogens were very prevalent in the apical root canal system. The apical microbiota was usually complex and differed in species composition when compared with the microbiota of middle/coronal samples from the same tooth.

Distinctive features of the microbiota associated with different forms of apical periodontitis

Microorganisms infecting the dental root canal system play an unequivocal role as causative agents of apical periodontitis. Although fungi, archaea, and viruses have been found in association with some forms of apical periodontitis, bacteria are the main microbial etiologic agents of this disease. Bacteria colonizing the root canal are usually organized in communities similar to biofilm structures. Culture and molecular biology technologies have demonstrated that the endodontic bacterial communities vary in species richness and abundance depending on the different types of infection and different forms of apical periodontitis. This review paper highlights the distinctive features of the endodontic microbiota associated with diverse clinical conditions.

Bacterial community profiling of cryogenically ground samples from the apical and coronal root segments of teeth with apical periodontitis

Bacteria located at the apical part of infected root canals are arguably directly involved in the pathogenesis of apical periodontitis. This study was conducted to profile and further compare the bacterial communities established at the apical and middle/coronal segments of infected root canals. Extracted teeth with attached apical periodontitis lesions were sectioned so as to obtain two root fragments representing the apical third and the coronal two thirds. Root fragments were subjected to a cryogenic grinding approach. DNA was extracted from root powder samples and used as a template for bacterial community profiling using a 16S ribosomal RNA gene-based seminested polymerase chain reaction/denaturing gradient gel electrophoresis approach. The mean number of bands in apical samples from teeth with primary infections was 28, ranging from 18 to 48, whereas in the middle/coronal samples, it was also 28, ranging from 19 to 36. Findings showed that the profile of bacterial community colonizing the apical third of infected root canals is as diverse as that occurring at the middle/coronal thirds. A high variability was observed for both interindividual (samples from the same region but from different patients) and intraindividual (samples from different regions of the same tooth) comparisons. The methodology used to prepare and analyze samples was highly effective in disclosing a previously unanticipated broad diversity of endodontic bacterial communities, especially at the apical part of infected root canals.

Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia and Prevotella nigrescens in endodontic lesions detected by culture and by PCR

he aim of this study was to investigate the presence of four black-pigmented bacteria, Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia and Prevotella nigrescens, in endodontic infections by culture and polymerase chain reaction (PCR) analyses. Microbial samples were obtained from 50 teeth with untreated necrotic pulps (primary infection) and from 50 teeth with failing endodontic treatment (secondary infection). Microbiological strict anaerobic techniques were used for serial dilution, plating, incubation, and identification. For PCR detection, the samples were analyzed using species-specific primers of 16S rDNA and the downstream intergenic spacer region. Culture and PCR detected the test species in 13/100 and 50/100 of the study teeth, respectively. The organisms were cultured from 11/50 (22%) of primarily infected root canal samples and from 2/50 (4%) of secondary root canal samples. PCR detection identified the target species in 32/50 (64%) and 18/50 (36%) of primary and secondary infections, respectively. P. gingivalis was rarely isolated by culture methods (1%), but was the most frequently identified test species by PCR (38%). Similarly, P. endodontalis was not recovered by culture from any tooth studied, but was detected by PCR in 25% of the sampled teeth. PCR-based identification also showed higher detection rates of P. intermedia (33%) and P. nigrescens (22%) than culture (13%). In conclusion, P. gingivalis, P. endodontalis, P. intermedia, and P. nigrescens were identified more frequently in teeth with necrotic pulp than in teeth with failing endodontic treatment. Also, a higher frequency of black-pigmented species was detected by PCR than by culture.

Endodontic Therapy Associated with Calcium Hydroxide As an Intracanal Dressing: Microbiologic Evaluation by the Checkerboard DNA-DNA Hybridization Technique

This study evaluated the predominant microbiota of infected necrotic pulps and the effects of calcium hydroxide therapy on these microorganisms by the checkerboard DNA-DNA hybridization technique. Conventional endodontic therapy associated with calcium hydroxide as intracanal dressing was performed in 12 single-rooted teeth with pulp necrosis and periradicular bone lesion. Samples were collected from the canal at baseline and 14 days after therapy, and the presence of 44 bacterial species was determined by the checkerboard method. Significant differences in the microbiota from baseline to post-therapy were sought by the paired-samples t test. The most prevalent species included F. nucleatum ss. vincentii, C. sputigena, C. ochracea, S. constellatus, V. parvula, P. gingivalis, P. melaninogenica, and S. sanguis. Most of the microorganisms were reduced after treatment, particularly A. gerencseriae, A. israelii, A. naeslundii, C. gingivalis, C. ochracea, P. gingivalis, S. noxia, S. sanguis, and S. oralis (p < 0.05). Conversely, A. actinomycetemcomitans, C. sputigena, and E. corrodens increased in numbers after therapy. These results indicate that conventional endodontic therapy with calcium hydroxide results in the reduction of pathogenic species associated with pulp necrosis. However, its use is limited, because it did not eliminate the whole spectrum of microorganisms.

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.

Microbiological analysis of infected root canals from symptomatic and asymptomatic teeth with periapical periodontitis and the antimicrobial susceptibility of some isolated anaerobic bacteria

The purpose of the present study was to investigate the correlation between the composition of the bacterial flora isolated from infected root canals of teeth with apical periodontitis with the presence of clinical signs and symptoms, and to test the antibiotic susceptibility of five anaerobic bacteria mostly commonly found in the root canals of symptomatic teeth against various substances using the E-test. Microbial samples were taken from 48 root canals, 29 symptomatic and 19 asymptomatic, using adequate techniques. A total of 218 cultivable isolates were recovered from 48 different microbial species and 19 different genera. Root canals from symptomatic teeth harbored more obligate anaerobes and a bigger number of bacterial species than the asymptomatic teeth. More than 70% of the bacterial isolates were strict anaerobes. Statistical analysis used a Pearson Chi-squared test or a one-sided Fisher's Exact test as appropriate. Suggested relationships were found between specific microorganisms, especially gram-negative anaerobes, and the presence of spontaneous or previous pain, tenderness to percussion, pain on palpation and swelling amoxicillin, amoxicillin + clavulanate and cephaclor were effective against all the strains tested. The lowest susceptibility rate was presented by Prevotella intermedia/nigrescens against Penicillin G. Our results suggested that specific bacteria are associated with endodontic symptoms of infected teeth with periapical periodontitis and the majority of the anaerobic bacterial species tested were susceptible to all antibiotics studied.

Bacteriological study of root canals associated with periapical abscesses

OBJECTIVE

The aim of this study was to identify microorganisms from root canals with periapical abscesses and to ascertain the susceptibility of Peptostreptococcus prevotii and Fusobacterium necrophorum to antimicrobials. Study design Thirty root canals were microbiologically sampled by using sterile paper points. The concomitant microorganisms were identified through the use of established methods. The susceptibility of P prevotii and F necrophorum to antimicrobials was evaluated by using the E test method.

RESULTS

A total of 117 different bacterial strains were recovered, including 75 strict anaerobes or microphilic species. The most frequently isolated strict anaerobes were P prevotii, Peptostreptococcus micros, and F necrophorum. Facultative bacteria such as Gemella morbillorum and Streptococcus mitis were also found, albeit less frequently. The data revealed that P prevotii and F necrophorum were susceptible to the tested antibiotics.

CONCLUSIONS

Gram-positive anaerobic bacteria predominate in the mixed microbiota of root canals with periapical abscesses. Moreover, P prevotii and F necrophorum are susceptible to the tested antibiotics.

An in vitro evaluation of the antibacterial properties of barriers used in guided tissue regeneration

The inhibition of growth of Prevotella nigrescens and Enterococcus faecalis by three barriers membrane, (a) polylactic acid (Atrisorb), (b) laminar bone, and (c) calcium sulfate, was compared using an agar diffusion test. The first group of 20 plates were inoculated with P. nigrescens in a prereduced anaerobically-sterilized brain-heart infusion broth, while the second group of 20 plates were inoculated with E. faecalis in a brain-heart infusion broth. On each plate, a 5.0-mm section of each barrier was placed such that every plate had all three barriers. The plates in the P. nigrescens group were incubated in an anaerobic chamber for 7 days. The plates in the E. faecalis group were incubated at 37 degrees C for 2 days. No zones of inhibition were observed with laminar bone or calcium sulfate. Zones of inhibition were observed with the Atrisorb barrier membrane in both groups. The zone of inhibition of P. nigrescens was significantly greater than the zone of inhibition of E. faecalis. The hydrophobicity of Atrisorb and its N-methyl-2-pyrolidine component were suggested as the sources of its antibacterial activity.

Scanning electron microscopy study of the adhesion of Prevotella nigrescens to the dentin of prepared root canals

The purpose of this study was to evaluate the effect of the presence or absence of amorphous, irregular smear layers on the adhesion of Prevotella nigrescens, to the dentin of the root canal by using scanning electron microscopy (SEM). Human incisors extracted within 7 days, with no cavities, no fractures, and no evidence of calcification of the canal, were selected. After cutting the crown portion at the CEJ, root canal preparation was undertaken by using a modified crown-down technique with Profile and Gates Glidden drills. Ten milliliters of physiologic saline solution (groups 1 and 4), 10 ml of 3.5% NaOCl (groups 2 and 5), or 10 ml of NaOCl and 10 ml of 0.5 M EDTA (groups 3 and 6) were used as irrigation solution while preparing the canal. After vertical sectioning and ethylene oxide gas sterilization, samples (groups 1, 2, and 3) were immersed in brain-heart infusion broth with yeast extract, hemin, and menadione, inoculated with P. nigrescens (ATCC 33563), and incubated for 3 h at 37 degrees C. All samples were prepared for and observed with SEM. The data were analyzed by using t test and one-way ANOVA. Smear layer was observed to cover the entire root canal surface after root canal preparation. Smear layer was removed and the entrances of dentinal tubules opened widely after applying 3.5% NaOCl and 0.5 M EDTA. A significantly greater number of bacteria were found to adhere to those teeth in which a smear layer was present (p < 0.05). Given that the smear layer produced during root canal preparation promoted adhesion and colonization of P. nigrescens to the dentin matrix, it might also increase the likelihood of canal reinfection.

Molecular detection of black-pigmented bacteria in infections of endodontic origin

A 16S rDNA-directed polymerase chain reaction method was used to assess the occurrence of four black-pigmented anaerobic rods in root canal infections. Samples were obtained from 54 infected teeth. Ten cases were diagnosed as acute periradicular abscesses. DNA was extracted from the samples and analyzed using a polymerase chain reaction-based identification assay. The method allowed detection of black-pigmented bacteria anaerobes in 59.3% of the examined teeth. Twelve cases yielded more than one black-pigmented species. In general Porphyromonas endodontalis was found in 42.6%, Porphyromonas gingivalis in 27.8%, Prevotella nigrescens in 7.4%, and Prevotella intermedia in 5.6% of the cases. P. endodontalis was found in 70% of the pus samples, P. gingivalis in 40%, and P. intermedia in 10%. P. gingivalis was always found associated with P. endodontalis in abscessed teeth. P. nigrescens was not found in any pus sample. The high prevalence of P. endodontalis and P. gingivalis suggests that they can play an important role in the pathogenesis of periradicular diseases.

Antimicrobial effectiveness of electro-chemically activated water as an endodontic irrigation solution

AIM

The aim of this in vitro study was to evaluate the antimicrobial effectiveness of electro-chemically activated water (ECA) as an endodontic irrigation solution.

METHODOLOGY

The root canals of 60 caries-free, single-rooted, adult, maxillary, anterior human teeth were instrumented and irrigated in a similar method to that used for in vivo root canal treatment. The external root surface of each tooth was sealed, maintaining the access cavities patent and the root canals were inoculated with a suspension containing four bacteria. The teeth were randomly divided into four groups (n = 15). Each group was irrigated ultrasonically with one of the following solutions: distilled water (control), NaOCl (3.5%), and ECA, the latter at pHs 7.0 and 9.0. Antimicrobial effectiveness was established directly after irrigation and again 7 days later, by counting colony-forming units on blood agar plates and by spectrophotometric analysis.

RESULTS

Large numbers of bacteria were present in the canals of teeth irrigated with distilled water. No bacteria were observed following irrigation with NaOCl. Neither of the ECA solutions were found to be effective against all the bacteria. Although some reduction in the number of bacteria was evident in the ECA groups, this was not statistically significant (P > 0.05) when compared to sodium hypochlorite.

CONCLUSION

Within the confines of this study ECA did not demonstrate antimicrobial effectiveness.

A comparative evaluation of three root-end filling materials: an in vitro leakage study using Prevotella nigrescens

This study used Prevotella nigrescens to evaluate the sealing ability of Geristore, Super-EBA, and ProRoot when used as root-end filling materials. One hundred single-canal, extracted, human teeth were cleaned and shaped with Gates-Glidden burs and .04 Taper (ProFile Series 29) rotary instruments. The root-ends were resected, and a 3-mm deep root-end preparation was made with ultrasonic tips. After steam sterilization, the teeth were randomly divided into three groups of 30. Each group was root-end-filled with a different material. Five root-end cavities were left open and served as positive controls; another five root-end cavities filled with sticky wax and covered with two layers of nail polish acted as negative controls. The teeth were attached to presterilized snap-on plastic caps; the root-ends submerged into 12-ml vials of chopped meat carbohydrate broth and placed in an anaerobic chamber. Twice a week, a sterile micropipette was used to inoculate 0.1 ml of a broth culture of Prevotella nigrescens into the root canal of each tooth. Results after 47 days indicated there were no significant differences between the three root-end filling materials against penetration of Prevotella nigrescens.

Prevalence OfPrevotella IntermediaAndPrevotella NigrescensIn Infected Root Canals From A Brazilian Population

The purpose of the present study was to evaluate the prevalence of Prevotella intermedia and Prevotella nigrescens in symptomatic and asymptomatic endodontic infections from a Brazilian population. DNA extracted from samples obtained from 28 cases of endodontic infection were examined by the 16S rDNA-directed Polymerase Chain Reaction (PCR) method. PCR detected P. intermedia in 7.1% of the cases (2 out of 28 teeth) and P. nigrescens in only one sample (3.6%). The low prevalence of P. intermedia and P. nigrescens as reported in the present study is probably justified for geographical reasons.

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.

Association of black-pigmented bacteria with endodontic infections

Black-pigmented bacteria (BPB) have been associated with endodontic infections. The purpose of this study was to evaluate further the presence of BPB with the clinical signs and symptoms associated with endodontic infections. Microbial samples were collected from the root canals of 40 intact teeth with necrotic pulps and apical periodontitis. Conventional laboratory methods were used for identification of the strains of BPB isolated in pure culture. In addition, the polymerase chain reaction and specific primers for 16S r-RNA genes were used to differentiate Prevotella nigrescens from Prevotella intermedia. Twenty-two (55%) samples were positive for the growth of BPB. Of those, 11 of 22 (50%) were identified as P. nigrescens, 8 of 22 (36%) were P. intermedia, 2 of 22 (9%) were Porphyromonas gingivalis, and 1 of 22 (5%) was Prevotella melaninogenica. Sixteen of the 22 root canals positive for the growth of BPB were associated with purulent drainage either from the root canal or an associated sinus tract. Statistical analysis did not show a significant relationship for the presence of BPB with clinical signs and symptoms.

Black-pigmented anaerobic rods in closed periapical lesions

AIM

This study determined the frequency of Porphyromonas endodontalis, Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens in 20 closed periapical lesions associated with symptomatic and asymptomatic refractory endodontic disease.

METHODOLOGY

To deliniate possible oral sources of P. endodontalis, the presence of the organism was assessed in selected subgingival sites and saliva in the same study patients. Periapical samples were obtained by paper points during surgical endodontic procedures using methods designed to minimize contamination by non-endodontic microorganisms. Subgingival plaque samples were obtained by paper points from three periodontal pockets and from the pocket of the tooth associated with the closed periapical lesion. Unstimulated saliva was collected from the surface of the soft palate. Bacterial identification was performed using a species-specific polymerase chain reaction (PCR) detection method.

RESULTS

P. endodontalis was not identified in any periapical lesion, even though subgingival samples from eight patients (40%) revealed the P. endodontalis-specific amplicon. P. gingivalis occurred in one periapical lesion that was associated with moderate pain. P. nigrescens, P. endodontalis and P. intermedia were not detected in any periapical lesion studied.

CONCLUSIONS

Black-pigmented anaerobic rods appear to be infrequent inhabitants of the closed periapical lesion.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and polymerase chain reaction for differentiation of Prevotella intermedia and Prevotella nigrescens

Isolates previously thought to be Prevotella intermedia have been shown to be a closely related species now known as Prevotella nigrescens. The purpose of this study was to determine the efficacy of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and polymerase chain reaction (PCR) to differentiate endodontic isolates of P. nigrescens from P. intermedia. Fifty-six strains of black-pigmented bacteria isolated from endodontic infections and conventionally identified as P. intermedia were used in this study. Using SDS-PAGE, novel polypeptide bands were used to differentiate P. nigrescens from P. intermedia. PCR was accomplished with specific primers for the 16S ribosomal RNA gene of both strains. Of 56 endodontic isolates, 41 (73%) strains were identified by SDS-PAGE as P. nigrescens and 15 (27%) strains as P. intermedia. Of the 41 strains of P. nigrescens identified by SDS-PAGE, PCR identified 37 strains as P. nigrescens. Restriction endonuclease digestion of amplified 16S ribosomal RNA genes indicated that the remaining four strains originally identified by SDS-PAGE as P. nigrescens were actually strains of Prevotella distinct from P. nigrescens and P. intermedia. Of 15 strains of P. intermedia identified by SDS-PAGE, PCR identified 14 strains as P. intermedia; but, one strain was identified as P. nigrescens. The results indicated that PCR was a more precise method than SDS-PAGE to differentiate P. intermedia from P. nigrescens. This study confirms that P. nigrescens is more commonly isolated in pure culture from endodontic infections than P. intermedia.