Mechanisms involved in the resistance of Enterococcus faecalis to calcium hydroxide

EDTA treatment diminishes the antibacterial and anti-adherence effect of calcium hydroxide on Enterococcus faecalis: an in vitro study

This study sought to understand the cell surface characteristics, viability and biofilm-forming potential ofEnterococcus faecaliscells sequentially exposed to EDTA and calcium hydroxide, as in endodontic treatment. Bacterial cells exposed to EDTA and calcium hydroxide were assayed for cell viability, membrane integrity, cell surface hydrophobicity and surface charge, while alteration in the surface topography ofE. faecaliscells was examined using atomic force microscopy (AFM). The bacterial adherence potential to type I collagen was also examined to assess the biofilm-forming capacity ofE. faecaliscells exposed to EDTA and calcium hydroxide. It was found that calcium hydroxide treatment reduced the viability ofE. faecalis. However, prior exposure to EDTA significantly reduced the antibacterial effect of calcium hydroxide (P< 0.05). Calcium hydroxide treatment resulted in impaired cell wall morphology, observed as increased surface roughness and pore formation under AFM. However, these topographical changes induced by calcium hydroxide were significantly reduced in EDTA pretreated cells (P< 0.05). Calcium hydroxide treatment caused reduction in hydrophobicity and adherence ofE. faecalisto type I collagen. These effects due to calcium hydroxide were also significantly altered in EDTA-pretreated cells (P< 0.001). The findings from this study showed that the antibacterial and anti-adherence effect of calcium hydroxide was diminished by prior exposure ofE. faecaliscells to EDTA.

In vitro evaluation of the effectiveness of the chemomechanical preparation against Enterococcus faecalis after single- or multiple-visit root canal treatment

The purpose was to assess the elimination of Enterococcus faecalis in vitro in human mandibular premolars after chemomechanical preparation with or without the use of a calcium hydroxide dressing. After 60 days of contamination with E. faecalis, the root canals were prepared using the Crown-Down technique combined with 2% chlorhexidine gel irrigation. Then, the specimens were divided into two experimental groups, treated in a single visit or in multiple visits, and two control groups. The multiple-visit group received a dressing with calcium hydroxide for 14 days (Calen) and the single-visit group did not receive any medication. In the two control groups, the canals were filled with BHI after chemomechanical preparation with 2% chlorhexidine gel or distilled water. Microbial samples were taken from the root canals for colony forming unit count for each phase of the treatment using sterile paper points inside the root canal lumen. Data were ranked and analyzed by the Kruskal-Wallis statistical test. The residual microbial colonies were then assessed. The results showed that chemomechanical preparation using 2% chlorhexidine gel with no intra-canal dressing reduced by 100% the E. faecalis contamination of the root canal lumen. The calcium-hydroxide group that received the 14-day intra-canal dressing allowed a small number of bacteria to grow between visits, but without statistical differences between groups.

Lipoteichoic acid partially contributes to the inflammatory responses to Enterococcus faecalis

Enterococcus faecalis, a pathogenic gram-positive bacterium, is closely related to refractory apical periodontitis. Because lipoteichoic acid (LTA) is considered a major virulence factor of gram-positive bacteria, in the present study, highly pure LTA from E. faecalis was prepared, and its ability to stimulate murine macrophages was investigated in comparison with those of the killed whole cells. Upon exposure to E. faecalis LTA, RAW 264.7 (a murine macrophage cell line) produced a significantly (p < 0.05) high level of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in a concentration-dependent manner. It is to note that the LTA was able to stimulate Toll-like receptor 2 (TLR2) but not TLR4. Concomitantly, LTA enhanced the DNA-binding activity of a transcription factor, nuclear factor-kappa B (NF-kappaB), which plays an important role in the transcriptional activation of genes encoding inflammatory mediators. In contrast, heat-killed E. faecalis stimulated both TLR2 and TLR4, whereas the killed E. faecalis whole cells induced significant (p < 0.05) levels of TNF-alpha and NO in RAW 264.7 cells as their LTA did. These results suggest that LTA partially contributes to E. faecalis-induced inflammatory responses.

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.

Octenidine in root canal and dentine disinfection ex vivo

AIM

The aim of the present study was to investigate the antimicrobial activity of octenidine on Enterococcus faecalis ATCC 29212 in a dentine block model.

METHODOLOGY

Fifty-six root segments of extracted human teeth were infected with E. faecalis for 4 weeks. Octenidine-phenoxyethanol gel (1 : 1) was applied for different timing: 1 min, 10 min, 7 days and in a different formula (1 : 3) for 10 min. Three samples were chosen for the group with placebo gel and for the group without infection (negative control). Dentine samples were collected, and the total count of bacteria and colony-forming units were determined. In addition, for controls and the 10 min group with 1 : 1 gel, the proportion of viable bacteria (PVB) was assessed.

RESULTS

Octenidine was particularly effective after incubation periods of 10 min and 7 days. The mean PVB decreased significantly from 57.2% to 5.7% after 10 min application. After 7 days, only one of 10 samples showed positive culture.

CONCLUSION

The present study showed the effectiveness of octenidine against E. faecalis in dentine disinfection. Further laboratory and clinical studies are required.

Antimicrobial Effect of Triclosan and Triclosan with Gantrez on Five Common Endodontic Pathogens

Microbial control of the root canal system is one of the key objectives of root canal therapy. Triclosan is a widely accepted broad spectrum antimicrobial agent proven to be effective against many gram-positive and gram-negative bacteria. Triclosan acts by blocking bacterial fatty acid biosynthesis. The addition of Gantrez copolymer has been shown to enhance the antimicrobial activity of triclosan. The purpose of this study was to determine the minimum inhibitory and bactericidal concentrations of triclosan and triclosan with Gantrez against Prevotella intermedia, Fusobacterium nucleatum, Actinomyces naeslundii, Porphyromonas gingivalis, and Enterococcus faecalis. The minimum inhibitory concentration (MIC) of both test solutions was determined for each of the 5 microorganisms by using microtiter serial dilutions. Samples were streaked on 5% sheep blood agar plates and placed in an anaerobic incubator to determine the minimum bactericidal concentration (MBC). The MBC of triclosan ranged from 12-94 microg/mL. The MBC of triclosan with Gantrez ranged from <0.3-10.4 microg/mL. The addition of Gantrez enhanced the bactericidal activity of triclosan. Both triclosan and triclosan with Gantrez demonstrated bactericidal activity against the 5 specific endodontic pathogens.

A big role for the very small--understanding the endodontic microbial flora

Apical periodontitis, an inflammatory process around the apex of a tooth root, is primarily a sequel to microbial infection of the pulp space. The microbial flora is composed of a restricted group of the total oral flora, selected by environmental pressures of anaerobiosis, nutrition and competition with other species and inhabits the root canal as a biofilm of coaggregated communities in an extracellular matrix. The untreated infected canal is generally composed of a polymicrobial mix with approximately equal proportions of Gram-positive and Gram-negative species, dominated by obligate anaerobes. The type of microbial flora in the root-filled tooth with persistent apical periodontitis has very different characteristics. These infections are characterized by one or just a few species, predominantly Gram-positive micro-organisms with an equal distribution of facultative and obligate anaerobes. Enterococcus faecalis has been a conspicuous finding in most studies. Because the primary aetiological problem is infection, endodontic treatment is directed at control and elimination of the root canal flora by working in a sterile way. Based on current knowledge, the best available method for obtaining clean, microbe-free root canals is by instrumentation with antimicrobial irrigation reinforced by an intracanal dressing with calcium hydroxide.

Antimicrobial effect of nanometric bioactive glass 45S5

Most recent advances in nanomaterials fabrication have given access to complex materials such as SiO(2)-Na(2)O-CaO-P(2)O(5) bioactive glasses in the form of amorphous nanoparticles of 20- to 60-nm size. The clinically interesting antimicrobial properties of commercially available, micron-sized bioactive glass 45S5 have been attributed to the continuous liberation of alkaline species during application. Here, we tested the hypothesis that, based on its more than ten-fold higher specific surface area, nanometric bioactive glass releases more alkaline species, and consequently displays a stronger antimicrobial effect, than the currently applied micron-sized material. Ionic dissolution profiles were monitored in simulated body fluid. Antimicrobial efficacy was assessed against clinical isolates of enterococci from persisting root canal infections. The shift from micron- to nano-sized treatment materials afforded a ten-fold increase in silica release and solution pH elevation by more than three units. Furthermore, the killing efficacy was substantially higher with the new material against all tested strains.

Effects of prolonged exposure to alkaline pH on Enterococcus faecalis survival and specific gene transcripts

INTRODUCTION

The persistence of Enterococcus faecalis in treated root canals has been attributed to its resistance to the high pH of antimicrobial agents used during treatment, but the specific mechanisms are not clear. We investigated the survival and gene expression of E. faecalis maintained in alkaline media.

METHODS

E. faecalis JH2-2 was maintained in media at pH 7, 10, 11 and 12 at either 25 degrees C or 37 degrees C for 1 week (168 h). At 24, 48, 72, 120 and 168 h, cell viability was determined in parallel with real-time quantitative polymerase chain reaction analyses of stress response genes (dnaK, fba, ftsZ, GroEL, napA, pbp5, tsf and tuf).

RESULTS

After 1 week the E. faecalis showed survival levels of 100% in pH 7, 1% in pH 10, 0.001% in pH 11 and 0.00001% in pH 12 media. At 37 degrees C increased levels of gene transcripts occurred between 72 and 120 h in pH 7 media for ftsZ and dnaK, and in pH 10 media for ftsZ, pbp5, dnaK, napA, tsf, fba and GroEL. No increase in transcripts was observed at 37 degrees C in media at pH 11 or pH 12, nor at 25 degrees C in any media.

CONCLUSION

Transcripts of ftsZ, a gene involved in cell division, increased by 37-fold after 120 h at pH 10 at 37 degrees C. Overall, the greatest increase in levels of gene transcripts occurred in cultures maintained in pH 10 media at 37 degrees C. These data may assist in understanding the survival strategies of E. faecalis following prolonged exposure to alkaline pH levels.

Antimicrobial action of calcium hydroxide, chlorhexidine and their combination on endodontic pathogens

BACKGROUND

The common recovery of Candida albicans and Enterococcus faecalis from failed root canals of teeth in which previous treatment has failed is notable. These organisms have been shown to be resistant to antimicrobial action of calcium hydroxide but are sensitive to chlorhexidine gluconate. The aim of the present in vitro study was to investigate the antimicrobial efficacy of calcium hydroxide paste, 2% chlorhexidine gel and their combination against Candida albicans and Enterococcus faecalis.

METHODS

Inoculae of these organisms were used to make lawn cultures on Sabouraud's dextrose agar and blood agar plates. Wells were prepared with these lawn cultures and filled with calcium hydroxide paste, 2% chlorhexidine gel and their combination. The agar plates were kept overnight for incubation at 37 degrees C and the zone of inhibition was examined after 24 and 72 hours.

RESULTS

The results suggest that 2% chlorhexidine gel alone is more effective at 72 hours than calcium hydroxide paste alone or in combination with 2% chlorhexidine gel against both the organisms, even though calcium hydroxide showed better antifungal efficacy against Candida albicans at 24 hours.

CONCLUSION

In failed root canal treatments, 2% chlorhexidine gel may be a more effective intracanal medicament than calcium hydroxide paste or their combination against Candida albicans and Enterococcus faecalis.

An In Vitro Comparison of the Antimicrobial Effects of Various Endodontic Medicaments on Enterococcus faecalis

The purpose of this in vitro study was to investigate the antimicrobial action of Dermacyn (Oculus Innovative Sciences, Petaluma, CA), BioPure MTAD (Dentsply Tulsa Dental, Johnson City, TN), 2% chlorhexidine (CHX; Ultradent, West Jordan, UT), and 5.25% sodium hypochlorite (NaOCl) against Enterococcus faecalis (American Type Culture Collection 4082). Eighteen Petri dishes of BHI agar were inoculated with E faecalis. Each Petri dish had five saturated paper disks placed. Four of the disks were saturated with a different test solution, and the last paper disk served as the control and was saturated with sterile distilled water. The plates were randomly distributed into two groups. Group one (n=9) was incubated aerobically and group 2 (n=9) was incubated anaerobically for 48 hours at 37 degrees C. The largest diameter of the zones of microbial inhibition was measured in millimeters and recorded. Statistical analysis was performed with repeated-measures analysis of variance. BioPure MTAD showed significantly (p<0.05) more zones of microbial inhibition than 5.25% NaOCl, 2% CHX, and Dermacyn. Sodium hypochlorite and CHX showed significantly (p<0.05) more zones of microbial inhibition than Dermacyn. The zone of inhibition between NaOCl and CHX was not significant (p>0.05). The control group showed no microbial inhibition.

The pH changes of calcium hydroxide mixed with six different vehicles

OBJECTIVE

The aim of this study was to determine the pH values of calcium hydroxide mixed with sterile saline, glycerin, Xylocaine pump spray, Citanest Octapressin, 0.2% chlorhexidine solution, and Ultracaine DS.

STUDY DESIGN

pH values of all vehicles were measured by a pH microelectrode before calcium hydroxide powder was added to 2 mL of the vehicle until the solutions were saturated (n = 10). After all the saturated samples were prepared, pH was remeasured at 0, 10, 20, 30, and 45 minutes; 1, 24, and 48 hours; and 7 days.

RESULTS

When pH changes over the time course were compared, there were no statistically significant differences among mean pH values of 0, 10, 20, 30, 45 minutes, 1 hour, and 24 hours (P = .754) and mean pH values of these groups were significantly lower than the mean pH value of 48 hours and 7 days (P < .05). The highest mean pH value was observed at day 7. When different vehicles were compared, the lowest mean pH value was observed in sterile saline. The mean pH value of Xylocaine was the highest (P < .05).

CONCLUSION

The result of this study indicated that when calcium hydroxide powder was mixed with glycerin, Xylocaine pump spray, Citanest Octapressin, 0.2% chlorhexidine solution, Ultracaine DS, and sterile saline solution, the mixtures became very highly alkaline. However, the pH values of the mixtures increased significantly after 24 hours. When one of these vehicles is used for root canal medication, a calcium hydroxide mixture might be left in place at least 7 days.

Response to alkaline stress by root canal bacteria in biofilms

AIM

To determine whether bacteria isolated from infected root canals survive alkaline shifts better in biofilms than in planktonic cultures.

METHODOLOGY

Clinical isolates of Enterococcus faecalis, Lactobacillus paracasei, Olsenella uli, Streptococcus anginosus, S. gordonii, S. oralis and Fusobacterium nucleatum in biofilm and planktonic cultures were stressed at pH 10.5 for 4 h, and cell viability determined using the fluorescent staining LIVE/DEAD BacLight bacterial viability kit. In addition, proteins released into extracellular culture fluids were identified by Western blotting.

RESULTS

Enterococcus faecalis, L. paracasei, O. uli and S. gordonii survived in high numbers in both planktonic cultures and in biofilms after alkaline challenge. S. anginosus, S. oralis and F. nucleatum showed increased viability in biofilms compared with planktonic cultures. Alkaline exposure caused all planktonic cultures to aggregate into clusters and resulted in a greater extrusion of cellular proteins compared with cells in biofilms. Increased levels of DnaK, HPr and fructose-1,6-bisphosphate aldolase were observed in culture fluids, especially amongst streptococci.

CONCLUSIONS

In general, bacteria isolated from infected roots canals resisted alkaline stress better in biofilms than in planktonic cultures, however, planktonic cells appeared to use aggregation and the extracellular transport of specific proteins as survival mechanisms.

Antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in infected human root canals

AIM

To determine the antimicrobial efficacy of ozonated water, gaseous ozone, sodium hypochlorite and chlorhexidine in human root canals infected by Enterococcus faecalis.

METHODOLOGY

Thirty human maxillary anterior teeth were prepared and inoculated with E. faecalis for 60 days. Eppendorf tubes were connected to the coronal portion of the teeth. Urethane hoses were attached to the tubes and to the entrance of a peristaltic pump. The exit of the apparatus corresponded to the apical portion of the root canals. The test irrigating solutions were ozonated water, gaseous ozone, 2.5% sodium hypochlorite (NaOCl), 2% chlorhexidine that circulated at a constant flow of 50 mL min(-1) for 20 min. Samples from the root canals were collected and immersed in 7 mL Letheen Broth (LB), followed by incubation at 37 degrees C for 48 h. Bacterial growth was analysed by turbidity of the culture medium and subculture on a specific nutrient broth. A 0.1 mL inoculum obtained from LB was transferred to 7 mL of brain heart infusion and incubated at 37 degrees C for 48 h. Bacterial growth was checked by turbidity of the culture medium carried out in triplicate.

RESULTS

No solution used as an irrigant over a 20-min contact time demonstrated an antimicrobial effect against E. faecalis.

CONCLUSION

The irrigation of infected human root canals with ozonated water, 2.5% NaOCl, 2% chlorhexidine and the application of gaseous ozone for 20 min was not sufficient to inactivate E. faecalis.

Effect of Intracanal Medication with Calcium Hydroxide and 1% Chlorhexidine in Endodontic Retreatment Cases with Periapical Lesions: An In Vivo Study

BACKGROUND/PURPOSE

Calcium hydroxide (Ca(OH)(2)) has been widely used as an intracanal medicament for endodontic retreatment, but very few studies used both Ca(OH)(2) and 1% chlorhexidine (CHX) as intracanal medicaments. The purpose of this study was to assess the in vivo effectiveness of a combination of Ca(OH)(2) and 1% CHX as intracanal medicaments in endodontic retreatment cases with periapical lesions.

METHODS

Previous cases of endodontically treated teeth with periapical pathosis in 70 patients (36 men and 34 women, age range 18-60 years) were included. Of these teeth, 59 had received root canal treatment and 11 had been subjected to previous apical surgery, indicating endodontic failure. Following the routine procedures, including canal reshaping and irrigation with 2% CHX, a canal medication material containing Ca(OH)(2) powder and a 1% CHX solution was placed into the root canals. Over a 6-week period, the intracanal medication was periodically changed until the teeth became asymptomatic. Patients were recalled at 3-month intervals for radiographic and clinical examination.

RESULTS

Our clinical and radiographic assessment of retreatment cases showed complete healing in 41 (64%) teeth, incomplete healing in 9 (14%) teeth, and failure in 14 (22%) teeth. For complete healing teeth, the healing time varied from 6 to 36 months. The size of the periapical lesions and previous surgical treatment had no influence on the prognosis.

CONCLUSION

Our results suggest that a combination of Ca(OH)(2) and 1% CHX can be successfully used as intracanal medicament for disinfection in endodontic retreatment cases with periapical lesions.

Susceptibility of Enterococcus faecalis biofilm to antibiotics and calcium hydroxide

The purpose of this study was to investigate the antimicrobial efficacy of six groups of antibiotics and calcium hydroxide against Enterococcus faecalis biofilm in a membrane filter model. Two-day-old E. faecalis (ATCC 29212) biofilm was exposed to ampicillin, co-trimoxazole, erythr omycin, oxytetracycline, vancomycin, vancomycin followed by gentamicin, Ca(OH)(2), and phosphate-buffered saline (control). After 1 h of exposure, the antimicrobial activity was neutralized by washing each disc five times in PBS, and then the colony-forming units of the remaining viable bacteria on each disc were counted. The results revealed that only erythromycin, oxytetracycline and Ca(OH)2 showed 100% biofilm kill. An ANOVA with a Bonferroni post hoc test (P < 0.05) detected significant differences among the test agents, except in the ampicillin group versus the co-trimoxazole group. It is concluded that erythromycin, oxytetracycline and Ca(OH)2 are 100% effective in eliminating E. faecalis biofilm, whereas ampicillin, co-trimoxazole, vancomycin, and vancomycin followed by gentamicin are ineffective.

Resistance to acidic and alkaline environments in the endodontic pathogen Enterococcus faecalis

BACKGROUND/AIMS

This study aimed to investigate the biochemical mechanisms employed by the endodontic pathogen Enterococcus faecalis to confer acid- and alkali-resistance and to compare these with the mechanisms of representative oral streptococci.

METHODS

E. faecalis JCM8728, Streptococcus mutans NCTC10449 and Streptococcus sanguinis ATCC10556 were used to assess both acid- and alkali-resistance by examining: (i) growth in complex media; (ii) stability of intracellular pH (pH(in)); (iii) cell durability to leakage of preloaded BCECF (2',7'-bis-(2-carboxyethyl)-5,6-carboxy-fluorescein); and (iv) cell permeability to SYTOX-Green.

RESULTS

Growth was initiated by E. faecalis at pH 4.0-11.0, by S. mutans at pH 4.0-9.0 and by S. sanguinis at pH 5.0-9.0. The pH(in) was similar to the extracellular pH in S. mutans and S. sanguinis at pH 5-10, while the pH(in) of E. faecalis was maintained at approximately 7.5-8.5 when extracellular pH was 7.5-10 and was maintained at levels equivalent to the extracellular pH when pH < 7.5. Cell membranes of E. faecalis were resistant to BCECF leakage when extracellular pH was 2.5-12 and to SYTOX-Green permeability at pH 4-10. The cell membrane durability to extracellular pH in E. faecalis was higher than that observed in the Streptococcus strains.

CONCLUSION

Compared to S. mutans, E. faecalis was found to be equally resistant to acid and more resistant to alkalis. The results suggest that pH-resistance in E. faecalis is attributed to membrane durability against acid and alkali, in addition to cell membrane-bound proton-transport systems. These characteristics may account for why E. faecalis is frequently isolated from acidic caries lesions and from persistently infected root canals where calcium hydroxide medication is ineffective.

Bactericidal effect of Nd:YAG laser irradiation on some endodontic pathogens ex vivo

AIM

To define the role of neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers in root canal disinfection along with a minimally invasive treatment concept.

METHODOLOGY

The hypothesis was tested ex vivo that Nd:YAG laser irradiation has a bactericidal effect on endodontic pathogens inoculated in root canals. Resultant colony-forming unit counts were associated with observations of bacterial cell structural changes using conventional scanning electron microscopy (CSEM) and environmental scanning electron microscopy (ESEM) on inoculated dentine surfaces, following indirect and direct Nd:YAG laser irradiation, respectively.

RESULTS

The Nd:YAG laser irradiation (1.5 W, 15 Hz, four times for 5 s) of Enterococcus faecalis inoculated canals resulted in a significant reduction (P < 0.05, Wilcoxon signed rank test) of the bacterial load, meaning a 99.7% kill, but no sterilization. The CSEM procedure verified that the extent of radiation damage was in line with the total amount of laser energy applied. After 2 h of incubation and three cycles of indirect laser treatment (i.e. through a 1-mm-thick dentine disc), no morphologically intact bacteria of Actinomyces naeslundii or Streptococcus anginosus were discernible. However, when micro-colonies of S. anginosus and specially biofilms of E. faecalis were present after 2 days, the in situ experiment using ESEM and direct laser treatment showed that bacterial eradication was reduced in deep layers.

CONCLUSIONS

The Nd:YAG laser irradiation is not an alternative but a possible supplement to existing protocols for canal disinfection as the properties of laser light may allow a bactericidal effect beyond 1 mm of dentine. Endodontic pathogens that grow as biofilms, however, are difficult to eradicate even upon direct laser exposure.

Identification of Enterococcus faecalis in Root-filled Teeth With or Without Periradicular Lesions by Culture-dependent and—Independent Approaches

Enterococcus faecalis is the most commonly found species in root-filled teeth evincing recalcitrant periradicular lesions and as a consequence, a role in causation of endodontic treatment failure has been suggested. The purpose of this study was to evaluate the prevalence of this bacterial species in root-filled teeth with or without periradicular lesions. Identification of E. faecalis was carried out by polymerase chain reaction (PCR) or conventional culture procedures. Overall, E. faecalis was detected by species-specific 16S rRNA gene-based PCR in 40/50 teeth (80%), while culture revealed the occurrence of this species in 8/50 teeth (16%). PCR was significantly more effective than culture in detecting this bacterial species (p < 0.001). Of 27 root-filled teeth with no periradicular lesions, E. faecalis was found in 22 cases (81.5%) by PCR and in five cases (18.5%) by culture. Of 23 root-filled teeth with periradicular lesions, E. faecalis was identified in 18 cases (78%) by PCR and in three cases (13%) by culture. Regardless of the identification technique used, no significant difference was observed when comparing the occurrence of E. faecalis in root-filled teeth with and without periradicular lesions (p > 0.05). Although these findings apparently put into question the status of E. faecalis as the main species causing endodontic treatment failure, other related factors still need to be clarified before this assumption turns into certainty.

In vitro assessment of the effectiveness of chlorhexidine gel and calcium hydroxide paste with chlorhexidine against Enterococcus faecalis and Candida albicans

OBJECTIVE

The purpose of this study was to compare the effectiveness of various medicaments, including Ca(OH)2/2% chlorhexidine, 2% chlorhexidine gel, and Ca(OH)2 alone, against Enterococcus faecalis and Candid albicans in vitro.

STUDY DESIGN

Eighty extracted single-rooted human maxillary teeth were used. After removing the crown, each root was instrumented up to size 50 by using a conventional technique. The root canal was irrigated with ethylenediamine tetra-acetic acid (EDTA) solution to remove smear layer. Then, roots were infected with E faecalis and C albicans. Subsequently, the roots were divided into 4 treatment groups: group 1 was treated with calcium powder hydroxide in distilled water, group 2 was treated with calcium hydroxide powder in 2% chlorhexidine, group 3 was treated with 2% chlorhexidine gel, and group 4 was treated with 0.9% sterile saline serving as negative control. Microbial samples were taken after 7, 15, and 30 days. After incubation, dentine chips were obtained form each root canal and examined microbiologically. The microbiological samples were plated to count colony-forming units in per milligram of dentin.

RESULTS

The results showed that the 2% chlorhexidine gel was significantly more effective than calcium hydroxide with 2% chlorhexidine, calcium hydroxide, and control saline solution (P < .05).

CONCLUSION

Under the conditions of this study, 2% chlorhexidine gel is effective in the elimination of E faecalis and C albicans from the root canal system. However, to support this in vitro observation, further in vivo studies are needed.

Enterococcus faecalis Adhesin, Ace, Mediates Attachment to Particulate Dentin

An enzyme linked immunosorbent assay was developed to assess E. faecalis adhesion to particulate dentin. E. faecalis, OG1RF, which expresses the collagen binding protein (Ace+), and a derivative of OG1RF, TX5256, deficient in the collagen binding protein (Ace-) were grown at 46 degrees C, necessary for in vitro expression of Ace, and at 37 degrees C. E. faecalis binding to dentin was measured at 0, 15, 30, 60, 120, and 360 minutes. Compared to TX5256 and OG1RF grown at 37 degrees C, OG1RF grown at 46 degrees C adhered significantly better at all time points except 15 minutes (p < 0.001) exhibiting maximum binding at 120 minutes (17.4% of a positive control). Type I collagen at 100 microg/ml inhibited dentin binding by OG1RF grown at 46 degrees C in both competition (p < 0.005) and displacement assays (p < 0.046). Immunoaffinity purified anti-Ace IgG at 200 microg of protein inhibited adhesion of OG1RF grown at 46 degrees C to dentin.

Phenotypic and genotypic identification of enterococci isolated from canals of root-filled teeth with periapical lesions

The objectives of the present study were to identify enterococcal species isolated from the canals of root-filled teeth with periapical lesions using biochemical and molecular techniques, and to investigate the genetic diversity of the isolates. Twenty-two Enterococcus strains, isolated from the canals of root-filled teeth with persisting periapical lesions, were identified to species level using rapid ID 32 STREP galleries and partial 16S rDNA sequencing. To subtype the strains, genomic DNA from the isolates was analyzed by pulsed field gel electrophoresis (PFGE) after digestion with SmaI. Intragenic regions of two genes, ace and salA, were sequenced for further differentiation of the isolates. All strains were identified as Enterococcus faecalis by both commercial kit and partial 16S rDNA sequencing. PFGE with SmaI of 22 isolates demonstrated 18 macrorestriction profiles, whereas 13 distinct genotypes were identified after analysis of the ace and salA composite sequences. Most of the isolates from distinct patients had different PFGE profiles. Moreover, in two cases, different E. faecalis strains were found in different root-filled teeth from the same mouth. E. faecalis was the only enterococcal species isolated from the canals of root-filled teeth with periapical lesions. Genetic heterogeneity was observed among the E. faecalis isolates following PFGE and sequence-based typing method. Furthermore, the genetic diversity within root canal strains was similar to previous reports regarding E. faecalis isolates from different clinical and geographic origins.

On the causes of persistent apical periodontitis: a review

Apical periodontitis is a chronic inflammatory disorder of periradicular tissues caused by aetiological agents of endodontic origin. Persistent apical periodontitis occurs when root canal treatment of apical periodontitis has not adequately eliminated intraradicular infection. Problems that lead to persistent apical periodontitis include: inadequate aseptic control, poor access cavity design, missed canals, inadequate instrumentation, debridement and leaking temporary or permanent restorations. Even when the most stringent procedures are followed, apical periodontitis may still persist as asymptomatic radiolucencies, because of the complexity of the root canal system formed by the main and accessory canals, their ramifications and anastomoses where residual infection can persist. Further, there are extraradicular factors -- located within the inflamed periapical tissue -- that can interfere with post-treatment healing of apical periodontitis. The causes of apical periodontitis persisting after root canal treatment have not been well characterized. During the 1990s, a series of investigations have shown that there are six biological factors that lead to asymptomatic radiolucencies persisting after root canal treatment. These are: (i) intraradicular infection persisting in the complex apical root canal system; (ii) extraradicular infection, generally in the form of periapical actinomycosis; (iii) extruded root canal filling or other exogenous materials that cause a foreign body reaction; (iv) accumulation of endogenous cholesterol crystals that irritate periapical tissues; (v) true cystic lesions, and (vi) scar tissue healing of the lesion. This article provides a comprehensive overview of the causative factors of non-resolving periapical lesions that are seen as asymptomatic radiolucencies post-treatment.

Dentin enhances the effectiveness of bioactive glass S53P4 against a strain of Enterococcus faecalis

OBJECTIVE

The aim of the current study was to test the impact of dentin powder on the antimicrobial efficacy of bioactive glass S53P4 (BAG).

STUDY DESIGN

BAG was suspended (preincubated) in saline at 37 degrees C for different time periods with or without human dentin powder, hydroxylapatite, or decalcified dentin. Subsequently, Enterococcus faecalis ATCC 29212 cells were added to these suspensions and bacterial recovery measured with and without the use of gentle sonication. Furthermore, survival of bacteria in test and control suspensions was assessed over time. Supernatants of suspensions were analyzed for their element contents using atomic absorption spectrophotometry. The effects of pH, silica, and osmolarity on E faecalis viability were assessed using specifically prepared solutions.

RESULTS

BAG preincubated with dentin powder caused a significant (P < .05) decrease in viability compared to pure BAG suspensions. This was not based on adherence of bacteria to solid particles or agglutination of the cells, because sonication did not increase bacterial yields. Hydroxylapatite and decalcified dentin did not increase BAG killing efficacy. The additive effect of BAG + dentin powder was dose dependent, occurred only with solids in suspension, and increased with suspension time. An augmented dissolution of glass components, especially silicon, was measured in BAG + dentin powder compared to pure BAG suspensions or counterparts containing hydroxylapatite or decalcified dentin. High osmolarity per se did not affect E faecalis viability, whereas high pH and silica levels did.

CONCLUSION

The observed phenomenon was related to an increased BAG dissolution triggered by dentin powder, causing elevated local pH and silica levels.

Effectiveness of a calcium hydroxide and chlorhexidine digluconate mixture as disinfectant during retreatment of failed endodontic cases

OBJECTIVE

The purpose of this in vivo investigation is to compare the effect of a slurry of Ca(OH)2 mixed in aqueous 2% chlorhexidine (CHX) versus aqueous Ca(OH)2 slurry alone on the disinfection of the pulp space of failed root-filled teeth during endodontic retreatment.

STUDY DESIGN

Forty single-rooted previously root-filled teeth with associated periradicular lesions were included. The teeth were nonsurgically retreated and medicated over 3 treatment visits with 7-10-day intervals with either Ca(OH)2 in water or Ca(OH)2 in 2% aqueous CHX. Root canal cultures were collected in fluid thioglycollate, and bacterial growth was assessed by turbidity daily for 1 week, then weekly for an additional 3 weeks. The presence of enterococci in the root canals at the initial treatment session was determined.

RESULTS

Of the total sample population, 12 of 40 (30%) were positive for bacteria before root filling. The control medication disinfected 12 of 20 (60%) teeth including 2 of 4 teeth originally diagnosed with enterococci. The experimental medication resulted in disinfected 16 of 20 (80%) teeth at the beginning of the third appointment. None of the teeth originally containing enterococci showed remaining growth. This difference between the overall positive cultures was not statistically significant (P > .05).

CONCLUSIONS

Canal dressing with a mixture of 2% CHX and Ca(OH)2 slurry is as efficacious as aqueous Ca(OH)2 on the disinfection of failed root-filled teeth.

Calcium hydroxide: a review

Calcium hydroxide is a multipurpose agent, and there have been an increasing number of indications for its use. Some of its indications include direct and indirect pulp capping, apexogenesis, apexification, treatment of; root resorption, iatrogenic root perforations, root fractures, replanted teeth and interappointment intracanal dressing. The purpose of this paper is to review the properties and various indications for the use of calcium hydroxide.

Short-term antibacterial activity of root canal sealers towards Enterococcus faecalis

AIM

To investigate the antimicrobial activity of root canal sealers on Enterococcus faecalis, either allowing or avoiding direct contact between sealers and bacteria.

METHODOLOGY

Filter paper discs were immersed in standardized E. faecalis suspensions and exposed to freshly mixed sealers (MCS, AH Plus, Grossman's sealer, Sealapex, Apexit) in teflon wells for 30 min, with or without a filter membrane placed between filter paper discs and sealers (membrane-restricted contact test and direct contact test, respectively). After exposure, the filter paper discs were transferred to vials containing phosphate-buffered saline (PBS) and glass beads, and vigorously vortexed. PBS with resuspended bacterial cells was serially diluted and 25 microL droplets were seeded on TSA plates. The plates were incubated in air at 37 degrees C for 24 h and colony-forming units were counted. Using alpha = 0.05 as level for statistical significance, the data obtained were analysed using Student's t-test.

RESULTS

In the direct contact test, MCS and AH Plus killed the bacteria to a level below the detection limit. They were followed in decreasing order of efficacy by Grossman's sealer, Sealapex and Apexit. In the membrane-restricted contact test, the sealers ranked: MCS, AH Plus, Grossman's sealer, Apexit and Sealapex, in descending order of antibacterial potency. MCS, AH Plus and Grossman's sealer significantly reduced the number of viable bacteria in both tests. Sealapex and Apexit were not statistically different from control.

CONCLUSIONS

MCS, AH Plus and Grossman's sealer were effective in reducing the number of cultivable cells of E. faecalis. Calcium hydroxide-based sealers, Sealapex and Apexit were ineffective in this short-term experiment.

Effect of endodontic procedures on enterococci, enteric bacteria and yeasts in primary endodontic infections

AIM

To detect enterococci, enteric bacteria and yeast species from the canals of teeth with primary endodontic infections before and after canal preparation and to test the antibiotic susceptibility of enterococcal strains isolated from infected root canals.

METHODOLOGY

Twenty-five single-rooted teeth with pulp necrosis, intact pulp chambers and periradicular lesions were selected for study. Samples were collected from canals before and after instrumentation. Amongst isolated microorganisms from infected root canals only enterococci, enteric bacteria and yeasts were identified by biochemical tests. The in vitro antimicrobial susceptibility of isolated enterococci strains was evaluated by the Etest system.

RESULTS

Microorganisms were isolated from 92% of the samples following intracoronal access, 22% were enterococci, enteric bacteria or yeast species. After biomechanical preparation, these species were no longer detected. After 7 days without intracanal dressing, 100% of the canals contained microorganisms, 52% of which were target species. However, after using paramonochlorophenol [PRP (2.0 g), Rinosoro and polyethylene glycol (400 equal parts up to 100 mL)] as an intracanal dressing for 7 days, enteric bacteria and yeasts were not detected; only enterococci were still present. All strains of enterococci were susceptible to ampicillin, but exhibited variable susceptibility to rifampin and ciprofloxacin.

CONCLUSIONS

Enterococci, enteric bacteria and yeasts were present in primary endodontic infections. Enterococci, particularly Enterococcus faecalis and E. faecium were resistant to removal by root canal preparation followed by intracanal dressing.

Growth at high pH increases Enterococcus faecalis adhesion to collagen

AIM

To evaluate the effect of growth at pH levels from 7.1 to 9.5 on the adherence of Enterococcus faecalis to bovine serum albumin (BSA) and collagen type I.

METHODOLOGY

Enterococcus faecalis strain A197A was grown in broth of adjusted pHs varying between 7.1 and 9.5. Aliquots of bacterial suspensions were added to wells coated either with BSA or with collagen type I. Bacteria adhering to the surfaces were stained with crystal violet. Spectrophotometric measurements of the dissolved stain were used to assess the number of bacteria adhering to the surfaces. The data obtained were analysed using the Kolmogorov-Smirnov test, Levene's test and Student's t-test, with alpha = 0.05 as the level for statistical significance.

RESULTS

The adhesion of E. faecalis to BSA-coated surfaces decreased inversely with alkalinity of the growth medium. The pH 7.1-grown bacteria bound to BSA significantly more than the other BSA groups. On the contrary, the adhesion to collagen type I-coated surfaces of bacteria grown at pH 8.0 and 8.5 was significantly greater than for those grown at pH 7.1.

CONCLUSIONS

A minor increase in pH up to 8.5, which may be a consequence of insufficient treatment with alkaline medicaments such as calcium hydroxide, increases the collagen-binding ability of E. faecalis, in vitro. This can be a critical mechanism by which E. faecalis predominates in persistent endodontic infections.

The Susceptibility of Starved, Stationary Phase, and Growing Cells of Enterococcus faecalis to Endodontic Medicaments

The purpose of this investigation was to compare the susceptibility of cells of Enterococcus faecalis during exponential growth, stationary phase and starvation phase to three endodontic medicaments. E. faecalis strains VP3-80 and A197A in different growth phases were exposed to saturated calcium hydroxide solution, 0.05% chlorhexidine digluconate and 0.0001% sodium hypochlorite. Cells in the exponential growth phase were the most sensitive to all three medicaments and were killed between 3 s and 10 min. Cells in stationary phase were more resistant and living cells could be recovered at 10 min. However, cells in starvation phase were the most resistant and were not totally eliminated by the medicaments during the 10-min test period. Number of surviving cells of E. faecalis cells to the tested medicaments increased 1000- to 10,000-folds in aging cultures.

Chairside sensor for rapid monitoring of Enterococcus faecalis activity

In this study, optical spectroscopy was used to monitor a chromogenic, enzyme-substrate reaction for the rapid identification of Enterococcus faecalis. The detection system, comprising a miniature spectrophotometer and an accompanying data acquisition system, was placed in an incubator. During testing, a 3-ml test sample was placed in a cuvette within the spectrophotometer. This permitted online, real-time, and remote analysis of spectral signature needed to monitor the bacteria. It was observed that the absorption peak intensity increased conspicuously 3.5 h after inoculation and through the entire period of testing. A linear-regression analysis demonstrated a significant correlation between the increase in absorption peak intensity at 610 nm (r = 0.9389) and 653 nm (r = 0.9387) with the formation of colony-forming units. Optical spectroscopy-based sensing systems can pave the way for rapid, nonlaboratory-based approaches to monitor microbial status quantitatively and qualitatively from clinical samples.

Antimicrobial Efficacy of Chlorhexidine and Two Calcium Hydroxide Formulations Against Enterococcus faecalis

The purpose of this study was to investigate the efficacy of chlorhexidine (CHX) and calcium hydroxide (Ca(OH2) against Enterococcus faecalis in vitro. Extracted single-rooted human teeth were instrumented up to size 40. After removal of the smear layer, an inoculum of E. faecalis was inserted into the root canals. After incubation, the inoculum was removed and the root canals were filled with one of three different disinfectants: Ca(OH2 paste, CHX 2%, and a mixture of CHX and Ca(OH2 paste (n = 10 in each group). Control teeth were filled with water of standardized hardness (n = 10). The teeth were then incubated for 3 days. After incubation, each root canal was instrumented, and the removed dentin was examined microbiologically. CHX was significantly more effective against E. faecalis than was Ca(OH2 paste or a mixture of CHX with Ca(OH2 paste (p < 0.05). There was no increase in the efficiency of Ca(OH2 paste when CHX was added (p > 0.05). The results suggest that CHX is effective in the elimination of E. faecalis from dentinal tubules under the conditions of this study.

Dentinal Tubule Disinfection Using Three Calcium Hydroxide Formulations

The objective of this study was to determine the antibacterial efficacy of three calcium hydroxide (CH) formulations using an in vitro model of Enterococcus faecalis dentinal tubule infection. CH mixed with water (CH), CH mixed with iodine-potassium iodide (CH+IKI), and CH mixed with iodoform and silicone oil (Metapex) were tested. Human cylindrical dentin specimens infected with E. faecalis were filled with disinfectants and incubated for 1 week. Dentin powder samples collected with ISO 018 burs showed a statistically significant reduction in E. faecalis for all three experimental groups in comparison with untreated control specimens. Statistically significant differences were also found between the three experimental groups. Metapex was the most effective dentinal tubule disinfectant, followed by CH+IKI and then CH. Similar results were observed at greater dentin tubule depths (ISO 021 burs) with the exception that intracanal treatment with CH resulted in significantly higher numbers of E. faecalis in comparison with untreated control specimens.

Antimicrobial potential of medicaments used in healing process in dogs' teeth with apical periodontitis

The objective of this study was to evaluate the influence of irrigants on the antimicrobial potential of calcium hydroxide paste in dogs' teeth with apical periodontitis. Forty-eight premolar teeth of adult mongrel dogs had their root canals opened to the oral environment for 6 months. The root canals were prepared and treated with different irrigating solutions and intracanal medicaments, according to the following groups: 1) 2.5% sodium hypochlorite (NaOCl) + calcium hydroxide paste (CHP); 2) 2% chlorhexidine (CHX) + CHP; 3) vinegar + CHP; 4) vinegar + vinegar. In group 4, both the irrigating solution and intracanal medicament were vinegar, which was renewed every 7 days. Each sample was collected by using two paper points maintained in position for 1 min, and individually transported and immersed in 7 mL of Letheen broth (LB), followed by incubation at 37ºC for 48 h. Microbial growth was analyzed by two methods: turbidity of the culture medium and subculture on a specific nutrient broth (brain heart infusion). After 21 days, all experimental groups had microbial growth, however, in different percentages: group 1 - 30%; group 2 - 30%; group 3 - 40%; group 4 - 60%. All materials tested had antimicrobial potential; however, the influence of calcium hydroxide paste on the control of microorganisms must be remembered.

Alkali-resistant bacteria in root canal systems

The aim of this study was to isolate and identify alkali-resistant bacteria from the dentin of infected root canals. Bacteria from homogenized dentin powder made up from infected root canal walls from human teeth were cultured on buffer-enriched Brain Heart Infusion agar supplemented with 4% sheep blood (BHI-blood agar), adjusted to pH 7.0, 9.0 or 10.0. Incubation took place for 7 days at 37 degrees C in an anaerobic glove box. Bacterial strains selected according to colony and morphology were subcultured in buffer-enriched BHI broth adjusted to pH 9.0, 10.0 or 11.0 to confirm their growth as alkali-resistant bacteria. Polymerase chain reaction amplification using specific primer sets and 16S rDNA sequence analysis was performed for identification of alkali-resistant isolates. In the present study, 37 teeth extracted from 37 patients were used for preparation of the dentin powder samples. Bacteria were detected in 25 samples when standard BHI-blood agars (pH 7.0) were used. Of these, 29 strains from 15 samples were alkali resistant, 25 strains growing at pH 9.0 and 4 at pH 10.0. The alkali-resistant strains included Enterococcus faecium (10 strains) and Enterococcus faecalis (2 strains), Enterobacter cancerogenus (1 strains), Fusobacterium nucleatum (1 strains), Klebsiella ornithinolytica (2 strains), Lactobacillus rhamnosus (2 strains), Streptococcus anginosus (2 strains), Streptococcus constellatus (3 strains), and Streptococcus mitis (2 strains). Three strains were also identified as bacteria of genus Firmicutes or Staphylococcus at the genus level. The present study showed that many bacterial species in infected root canal dentin were alkali-resistant at pH 9.0 and/or pH 10.0, and belonged mainly to the genus Enterococcus.

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.

Effects of Sonicated Enterococcus faecalis Extracts on Interleukin-2 and Interleukin-4 Production by Human T Cells

In the present authors' previous study, sonicated Enterococcus faecalis extracts were shown to suppress the cell cycle progression of human lymphocytes. To study the effect of this microorganism on the function of lymphocytes, the authors investigated the levels of interleukin-2 (IL-2) and interleukin-4 (IL-4) production by T lymphocytes before and after the addition of sonicated E. faecalis extracts. In this study, levels of IL-2 and IL-4 produced from T cells were evaluated by using the quantitative sandwich enzyme immunoassay technique. In response to phytohemagglutinin (PHA) stimulation, T cells produced increased levels of IL-2 and IL-4. However, the expressions of both cytokines were significantly inhibited when PHA-activated T cells were preexposed to 12.5 microg/ml and 25 microg/ml of sonicated E. faecalis extracts (p < 0.05). This effect was concentration-dependent, because the levels of IL-2 and IL-4 expressions were not affected by the addition of a low concentration (5 microg/ml) of sonicated extract. These findings suggest that Th1 and Th2 immunosuppression mediated by E. faecalis could be a part of the pathogenic mechanism of the endodontic failure associated with this microorganism.

An in-vitro investigation of the antibacterial effect of nisin in root canals and canal wall radicular dentine

AIM

To determine whether nisin, a bacteriocin, would be effective at killing Enterococcus faecalis and Streptococcus gordonii cells in solution and within the root canal system.

METHODOLOGY

Bacterial isolates of E. faecalis and S. gordonii were grown from glycerol stocks in closed tubes containing BHY broth at 37 degrees C. The minimum bactericidal concentration (MBC) of nisin for both bacterial species was determined by a microdilution method. Extracted human teeth were decoronated to produce roots of equal length with a single canal and divided into six groups of 10 roots. The canals were prepared to a master apical size 30 file using 0.04 taper Ni-Ti rotary instruments. Bacterial samples of each species were inoculated into three groups of prepared roots and incubated in closed tubes at 37 degrees C for 21 days. The root canals in each group were then medicated with water (control), calcium hydroxide powder mixed with sterile water [Ca(OH)2], or nisin and incubated for a further 7 days. Rotary Ni-Ti files were used to take radicular dentine samples from the walls of each canal which were then incubated in BHY broth for 24 h. Optical density (OD600) readings were taken as a measure of bacterial growth.

RESULTS

The MBC of nisin for E. faecalis and S. gordonii was 70 and 20 mg mL(-1) respectively. Calcium hydroxide and nisin medication eradicated infection within the root canal while cells remained viable in the control group. Mean optical density (OD600) readings from canal wall dentine shavings infected with E. faecalis were 1.32 +/- 0.98, 0.73 +/- 0.27 and 0.69 +/- 0.38 for the control, Ca(OH)2 and nisin samples respectively. Corresponding mean readings for S. gordonii were 1.19 +/- 0.18, 0.73 +/- 0.15 and 0.60 +/- 0.29. The Ca(OH)2 and nisin group readings were significantly (P < 0.01) lower than the control for each species as tested by Student's t-test and Mann-Whitney U statistical analysis. Values for Ca(OH)2 and nisin were not significantly (P > 0.01) different.

CONCLUSION

Nisin was effective at eradicating E. faecalis and S. gordonii cells in pure culture and was comparable with Ca(OH)2 in the elimination of these species from within the root canal system.

Virulence factors of Enterococcus faecalis: relationship to endodontic disease

Enterococcus faecalis is a micro-organism that can survive extreme challenges. Its pathogenicity ranges from life-threatening diseases in compromised individuals to less severe conditions, such as infection of obturated root canals with chronic apical periodontitis. In the latter situation, the infecting organisms are partly shielded from the defense mechanisms of the body. In this article, we review the virulence factors of E. faecalis that may be related to endodontic infection and the periradicular inflammatory response. The most-cited virulence factors are aggregation substance, surface adhesins, sex pheromones, lipoteichoic acid, extracellular superoxide production, the lytic enzymes gelatinase and hyaluronidase, and the toxin cytolysin. Each of them may be associated with various stages of an endodontic infection as well as with periapical inflammation. While some products of the bacterium may be directly linked to damage of the periradicular tissues, a large part of the tissue damage is probably mediated by the host response to the bacterium and its products.

Cultivable microbial flora associated with persistent periapical disease and coronal leakage after root canal treatment: a preliminary study

AIM

To identify the cultivable bacterial flora in root filled teeth with persistent periapical lesions and to locate their distribution within the root canal system using an in vitro sampling protocol.

METHODOLOGY

Eight freshly extracted root filled teeth were collected from the Oral and Maxillo-facial Surgery Department, Eastman Dental Hospital. Seven teeth were associated with persistent apical periodontitis and also showed evidence of coronal leakage. Teeth were transferred to an anaerobic chamber immediately after careful extraction and sectioned transversely to give a crown (in all but one case) and two root segments (coronal and apical). Two samples were obtained from each segment, one from dentine and the other from the restoration or gutta-percha (GP) root filling (46 sites in total). The samples were dispersed, serially diluted and cultured on blood agar and fastidious anaerobic agar (with 5% defibrinated horse blood). The primary growth was subcultured to obtain pure isolates, which were identified by routine microbiological techniques and commercial enzyme tests.

RESULTS

A total of 252 strains were isolated from all the teeth. Of all the isolates, the most prevalent bacteria were Gram-positive facultative anaerobes 189/252 (75%) with staphylococci (48/252, 19%), streptococci (44/252, 17%), enterococci (20/252, 8%) and Actinomyces species (20/252, 8%) being found in most of the teeth (6/8, 6/8, 5/8, 5/8 and 7/8, respectively). Of the obligate anaerobes (17%), peptostreptococci (7%) were also present in most teeth (7/8). A statistical association between bacterial flora and site (crown/coronal/apical) or surface (dental/GP/restoration) could not be shown.

CONCLUSIONS

The predominant group of bacteria in root filled teeth with persistent apical periodontitis and coronal leakage was Gram-positive facultative anaerobes of which staphylococci followed by streptococci and enterococci were the most prevalent.