Real-Time Imaging and Quantification of Bioluminescent Bacteria in Root Canals In Vitro

The effects of aperture position and length in side-vented needles on root canal irrigation: A computational fluid dynamics study

INTRODUCTION

Root canal irrigation is crucial for infection control during root canal treatment. Side-vented needles for positive pressure irrigation are commonly used in clinical practice. However, variations in needle design among manufacturers can impact the fluid dynamics of irrigation. This study aims to use computational fluid dynamics to explore the flow characteristics of different needle aperture lengths and positions, and their effects on the effectiveness and safety of irrigation, using a validated passive scalar transport numerical model.

METHODS

The validation of the CFD irrigant model was achieved by comparing it with an in vitro irrigation experiment model. The CFD model used scalar concentration, while the in vitro experiment model used red dye tracing. Using a standard 30G side-vented needle as a reference, virtual needle models featuring four aperture lengths and three positions were created. These virtual irrigation needles were then placed in two root canal geometries for CFD simulation to evaluate fluid exchange capabilities and related fluid dynamic parameters.

RESULTS

The results of the CFD simulation, using a scalar transport model, closely matched the in vitro tracer tests for irrigation experiments across seven root canal geometries. The CFD analysis indicated that positioning the aperture lower increased the irrigant exchange distance. Notably, decreasing the aperture length to 0.25x, and positioning it at the lower end of the needle significantly increased exchange distance and shear stress, while reducing apical pressure.

CONCLUSIONS

These results indicate that the position and length of the aperture affect the exchange distance of irrigant flow, wall shear stress, and apical pressure. The CFD validation model for scalar transport, based on a steady state, can function as a valuable tool for optimizing the side-vented needle in research. Further research on the design of side-vented needles will enhance the understanding of flow characteristics beneficial for irrigation efficiency in clinical practice.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Effect of Chemical Debridement and Irrigant Activation on Endodontic Treatment Outcomes: An Updated Overview

Chemical debridement is considered one of the most important steps during root canal treatment to target unreached areas and provide thorough disinfection of the canals. The efficiency of this step efficiency can be increased using different agitation and irrigation techniques/devices. This comprehensive review aimed to summarize the effect of various irrigant activation and agitation techniques/devices on endodontic treatment outcomes. Using mechanical active irrigation, which enables the activation or agitation of the irrigating solution, is beneficial in root canal treatment by increasing the efficiency of delivering the irrigant up to working length and ensuring isthmus cleanliness. However, considerable variation was noticed between the protocols used in each technique with a lack of well-designed randomized clinical trials to focus on the long-term outcome. Moreover, a low level of evidence was noticed regarding the effectiveness of certain activation techniques over others. Therefore, each study needs to be carefully weighed before using its results and embracing its conclusion. Future studies need to focus more on the antimicrobial effect of each technique and its effect on the healing of apical periodontitis. Also, recent advances, such as multisonic and laser activation, are promising tools that need more clinical investigations to show their efficiency.

CFD analysis on the effect of combining positive and negative pressure during the irrigation of artificial isthmuses

Fluid dynamics generated by irrigation needles have not been deeply analyzed in root canal irregularities such as apical ramifications or isthmus where the cleaning capacity of irrigants might be compromised and hence the treatment outcome. The goal of this study was to compare the key irrigation parameters (flow pattern, irrigant velocity, apical pressure, and shear stress) between two irrigation needles and the additional effect of aspiration cannulas through computational fluid dynamics. A 3D-model consisting of two canals linked by an isthmus was modeled. The abovementioned needles irrigated the primary canal, whereas an aspiration cannula was located inside the secondary canal. Both the geometry definition and spatial discretization were carried out with ANSYS 16.2, through which six different simulations were performed: lateral exit (LE) needle, frontal exit (FE) needle, LE and cannula in crown (LEC), FE and cannula in crown (FEC), LE and cannula in middle third (LEM), FE and cannula in middle third (FEM). FE and FEM showed that the irrigation flow only passes through the isthmus in the most apical section (maximum irrigant velocity / shear stress = 8.44 m/s / 1628.44 Pa and 8.63 m/s / 1185.69 Pa, respectively). However, the remaining simulations showed the irrigation flow passing through the isthmus twice, through the most apical section first and through the upper part of the isthmus later (maximum irrigant velocity / shear stress = 8.48 m/s / 1298.24 Pa (LE), 8.61 m/s / 1261.36 Pa (LEM), 8.61 m/s / 1355.24 Pa (LEC), 8.59 m/s / 1256.87 Pa (FEC)). Furthermore, the highest velocity values were detected when aspiration cannulas were added.

Evaluation of needle movement effect on root canal irrigation using a computational fluid dynamics model

Background

Irrigation is considered to be a critical part of root canal treatment. However, little is known about the effect of needle movement on the irrigation process. Therefore, this study aimed to investigate the influence of the syringe and needle movement on root canal irrigation using a three-dimensional computational fluid dynamics (CFD) numerical model.

Methods

The CFD codes Flow-3D was adopted to simulate the root canal irrigation process with the syringe and needle moving up and down in motions at different amplitudes and frequencies. One stationary needle was adopted to allow comparison with the needles in up-and-down motions. Six cases where the needles were moving up and down with different amplitudes and frequencies were used to investigate the relationships between the motion of needle and irrigation efficacy.

Results

The stationary needle gained relatively higher flow velocity and apical pressure all through the irrigation process, while the needles in constant up-and-down motions exhibited lower mean flow velocity and apical pressure. The larger the amplitude, the less mean flow velocity and apical pressure were developed. In addition, the needles moving with different frequencies were similar in the terms of irrigant replacement and apical pressure.

Conclusions

To avoid periapical extrusion accidents while obtaining adequate irrigant replacement, the needle should be moving up and down with a moderate amplitude during manual root canal irrigation; and the motion frequency was not highly relevant in terms of the irrigation efficiency.

Electronic supplementary material

The online version of this article (10.1186/s12938-019-0679-5) contains supplementary material, which is available to authorized users.

Which Parameters Affect Biofilm Removal with Acoustic Cavitation? A Review

Bacterial biofilms are a cause of contamination in a wide range of medical and biological areas. Ultrasound is a mechanical energy that can remove these biofilms using cavitation and acoustic streaming, which generate shear forces to disrupt biofilm from a surface. The aim of this narrative review is to investigate the literature on the mechanical removal of biofilm using acoustic cavitation to identify the different operating parameters affecting its removal using this method. The properties of the liquid and the properties of the ultrasound have a large impact on the type of cavitation generated. These include gas content, temperature, surface tension, frequency of ultrasound and acoustic pressure. For many of these parameters, more research is required to understand their mechanisms in the area of ultrasonic biofilm removal, and further research will help to optimise this method for effective removal of biofilms from different surfaces.

Ultrasonic Irrigant Activation during Root Canal Treatment: A Systematic Review

INTRODUCTION

The aim of this study was to systematically review the evidence on the cleaning and disinfection of root canals and the healing of apical periodontitis when ultrasonic irrigant activation is applied during primary root canal treatment of mature permanent teeth compared with syringe irrigation.

METHODS

An electronic search was conducted of the Cochrane Library, Embase, LILACS, PubMed, SciELO, and Scopus databases using both free-text key words and controlled vocabulary. Additional studies were sought through hand searching of endodontic journals and textbooks. The retrieved studies were screened by 2 reviewers according to predefined criteria. The included studies were critically appraised, and the extracted data were arranged in tables.

RESULTS

The electronic and hand search retrieved 1966 titles. Three clinical studies and 45 in vitro studies were included in this review. Ultrasonic activation did not improve the healing rate of apical periodontitis compared with syringe irrigation after primary root canal treatment of teeth with a single root canal. Conflicting results were reported by the in vitro microbiological studies. Ultrasonic activation was more effective than syringe irrigation in the removal of pulp tissue remnants and hard tissue debris based on both clinical and in vitro studies. Ultrasonic activation groups were possibly favored in 13 studies, whereas syringe irrigation groups may have been favored in 3 studies.

CONCLUSIONS

The level of the available evidence was low, so no strong clinical recommendations could be formulated. Future studies should focus on the antimicrobial effect and healing of apical periodontitis in teeth with multiple root canals.

In-vivo monitoring of infectious diseases in living animals using bioluminescence imaging

Traditional methods of localizing and quantifying the presence of pathogenic microorganisms in living experimental animal models of infections have mostly relied on sacrificing the animals, dissociating the tissue and counting the number of colony forming units. However, the discovery of several varieties of the light producing enzyme, luciferase, and the genetic engineering of bacteria, fungi, parasites and mice to make them emit light, either after administration of the luciferase substrate, or in the case of the bacterial lux operon without any exogenous substrate, has provided a new alternative. Dedicated bioluminescence imaging (BLI) cameras can record the light emitted from living animals in real time allowing non-invasive, longitudinal monitoring of the anatomical location and growth of infectious microorganisms as measured by strength of the BLI signal. BLI technology has been used to follow bacterial infections in traumatic skin wounds and burns, osteomyelitis, infections in intestines, Mycobacterial infections, otitis media, lung infections, biofilm and endodontic infections and meningitis. Fungi that have been engineered to be bioluminescent have been used to study infections caused by yeasts (Candida) and by filamentous fungi. Parasitic infections caused by malaria, Leishmania, trypanosomes and toxoplasma have all been monitored by BLI. Viruses such as vaccinia, herpes simplex, hepatitis B and C and influenza, have been studied using BLI. This rapidly growing technology is expected to continue to provide much useful information, while drastically reducing the numbers of animals needed in experimental studies.

Apical negative pressure irrigation versus syringe irrigation: a systematic review of cleaning and disinfection of the root canal system

The aim of this study was to systematically review and critically analyse the published data on the treatment outcome (primary outcome) and on the cleaning and disinfection of root canals (secondary outcomes) achieved by negative pressure irrigation as compared to syringe irrigation. An electronic search was conducted in EMBASE, LILACS, PubMed, SciELO, Scopus and Web of Knowledge using both free-text keywords and controlled vocabulary. Additional studies were sought through hand searching of endodontic journals and of the relevant chapters of endodontic textbooks. No language restriction was imposed. The retrieved studies were screened by two reviewers according to predefined criteria. Included studies were critically appraised and the extracted data were arranged in tables. The electronic search and hand search retrieved 489 titles. One clinical study and 14 in vitro studies were finally included in the review; none of these studies assessed treatment outcome, four studies assessed the antimicrobial effect, seven studies evaluated the removal of pulp tissue remnants, and four studies investigated the removal of hard tissue debris or both hard tissue debris and pulp tissue remnants. Poor standardization and description of the protocols was evident. Inconclusive results were reported about the cleaning and disinfection accomplished by the two irrigation methods. Negative pressure irrigation was more effective under certain conditions when compared to suboptimal syringe irrigation; however, the variability of the protocols hindered quantitative synthesis. There is insufficient evidence to claim general superiority of any one of these methods. The level of the available evidence is low, and the conclusions should be interpreted with caution.

A quantitative method to measure biofilm removal efficiency from complex biomaterial surfaces using SEM and image analysis

Biofilm accumulation on biomaterial surfaces is a major health concern and significant research efforts are directed towards producing biofilm resistant surfaces and developing biofilm removal techniques. To accurately evaluate biofilm growth and disruption on surfaces, accurate methods which give quantitative information on biofilm area are needed, as current methods are indirect and inaccurate. We demonstrate the use of machine learning algorithms to segment biofilm from scanning electron microscopy images. A case study showing disruption of biofilm from rough dental implant surfaces using cavitation bubbles from an ultrasonic scaler is used to validate the imaging and analysis protocol developed. Streptococcus mutans biofilm was disrupted from sandblasted, acid etched (SLA) Ti discs and polished Ti discs. Significant biofilm removal occurred due to cavitation from ultrasonic scaling (p < 0.001). The mean sensitivity and specificity values for segmentation of the SLA surface images were 0.80 ± 0.18 and 0.62 ± 0.20 respectively and 0.74 ± 0.13 and 0.86 ± 0.09 respectively for polished surfaces. Cavitation has potential to be used as a novel way to clean dental implants. This imaging and analysis method will be of value to other researchers and manufacturers wishing to study biofilm growth and removal.

Reporter systems for in vivo tracking of lactic acid bacteria in animal model studies

Bioluminescence (BLI) and fluorescence imaging (FI) allow for non-invasive detection of viable microorganisms from within living tissue and are thus ideally suited for in vivo probiotic studies. Highly sensitive optical imaging techniques detect signals from the excitation of fluorescent proteins, or luciferase-catalyzed oxidation reactions. The excellent relation between microbial numbers and photon emission allow for quantification of tagged bacteria in vivo with extreme accuracy. More information is gained over a shorter period compared to traditional pre-clinical animal studies. The review summarizes the latest advances in in vivo bioluminescence and fluorescence imaging and points out the advantages and limitations of different techniques. The practical application of BLI and FI in the tracking of lactic acid bacteria in animal models is addressed.

Real-time evaluation of two light delivery systems for photodynamic disinfection of Candida albicans biofilm in curved root canals

Antimicrobial photodynamic therapy (APDT) combined with endodontic treatment has been recognized as an alternative approach to complement conventional root canal disinfection methods on bacterial biofilms. We developed an in  vitro model of bioluminescent Candida albicans biofilm inside curved dental root canals and investigated the microbial reduction produced when different light delivery methods are employed. Each light delivery method was evaluated in respect to the light distribution provided inside curved root canals. After conventional endodontic preparation, teeth were sterilized before canals were contaminated by a bioluminescent strain of C. albicans (CEC789). Methylene blue (90 μM) was introduced into the canals and then irradiated (λ = 660 nm, P = 100 mW, beam diameter = 2 mm) with laser tip either in contact with pulp chamber or within the canal using an optical diffuser fiber. Light distribution was evaluated by CCD camera, and microbial reduction was monitored through bioluminescence imaging. Our findings demonstrated that the bioluminescent C. albicans biofilm model had good reproducibility and uniformity. Light distribution in dental tissue was markedly dependent on the light delivery system, and this strategy was directly related to microbial destruction. Both light delivery systems performed significant fungal inactivation. However, when irradiation was performed with optical diffuser fiber, microbial burden reduction was nearly 100 times more effective. Bioluminescence is an interesting real-time analysis to endodontic C. albicans biofilm inactivation. APDT showed to be an effective way to inactivate C. albicans biofilms. Diffuser fibers provided optimized light distribution inside curved root canals and significantly increased APDT efficiency.

Irrigation of human prepared root canal--ex vivo based computational fluid dynamics analysis

AIM

To analyze the influence of the needle type, insertion depth, and irrigant flow rate on irrigant flow pattern, flow velocity, and apical pressure by ex-vivo based endodontic irrigation computational fluid dynamics (CFD) analysis.

METHODS

Human upper canine root canal was prepared using rotary files. Contrast fluid was introduced in the root canal and scanned by computed tomography (CT) providing a three-dimensional object that was exported to the computer-assisted design (CAD) software. Two probe points were established in the apical portion of the root canal model for flow velocity and pressure measurement. Three different CAD models of 27G irrigation needles (closed-end side-vented, notched open-end, and bevel open-end) were created and placed at 25, 50, 75, and 95% of the working length (WL). Flow rates of 0.05, 0.1, 0.2, 0.3, and 0.4 mL/s were simulated. A total of 60 irrigation simulations were performed by CFD fluid flow solver.

RESULTS

Closed-end side-vented needle required insertion depth closer to WL, regarding efficient irrigant replacement, compared to open-end irrigation needle types, which besides increased velocity produced increased irrigant apical pressure. For all irrigation needle types and needle insertion depths, the increase of flow rate was followed by an increased irrigant apical pressure.

CONCLUSIONS

The human root canal shape obtained by CT is applicable in the CFD analysis of endodontic irrigation. All the analyzed values -irrigant flow pattern, velocity, and pressure - were influenced by irrigation needle type, as well as needle insertion depth and irrigant flow rate.

Silicon photomultiplier (SPM) detection of low-level bioluminescence for the development of deployable whole-cell biosensors: possibilities and limitations

Whole-cell bacterial bioreporters await miniaturized photon counting modules with high sensitivity and robust compatible hardware to fulfill their promise of versatile, on-site biosensor functionality. In this study, we explore the photon counting readout properties of the silicon photomultiplier (SPM) with a thermoelectric cooler and the possibilities of detecting low-level bioluminescent signals. Detection performance was evaluated through a simulated LED light source and the bioluminescence produced by the genetically engineered Pseudomonas fluorescens bacterial bioreporter 5RL. Compared with the conventional photomultiplier tube (PMT), the results revealed that the cooled SPM exhibits a wider linear response to inducible substrate concentrations (salicylate) ranging from 250 to 5000 ppb. Although cooling of the SPM lowered dark count rates and improved the minimum detectable signal, and the application of a digital filter enhanced the signal-to-noise ratio, the detection of very low light signals is still limited and remains a challenge in the design of compact photon counting systems.

Pseudomonas fluorescens HK44: lessons learned from a model whole-cell bioreporter with a broad application history

Initially described in 1990, Pseudomonas fluorescens HK44 served as the first whole-cell bioreporter genetically endowed with a bioluminescent (luxCDABE) phenotype directly linked to a catabolic (naphthalene degradative) pathway. HK44 was the first genetically engineered microorganism to be released in the field to monitor bioremediation potential. Subsequent to that release, strain HK44 had been introduced into other solids (soils, sands), liquid (water, wastewater), and volatile environments. In these matrices, it has functioned as one of the best characterized chemically-responsive environmental bioreporters and as a model organism for understanding bacterial colonization and transport, cell immobilization strategies, and the kinetics of cellular bioluminescent emission. This review summarizes the characteristics of P. fluorescens HK44 and the extensive range of its applications with special focus on the monitoring of bioremediation processes and biosensing of environmental pollution.

Noninvasive biophotonic imaging for studies of infectious disease

According to World Health Organization estimates, infectious organisms are responsible for approximately one in four deaths worldwide. Animal models play an essential role in the development of vaccines and therapeutic agents but large numbers of animals are required to obtain quantitative microbiological data by tissue sampling. Biophotonic imaging (BPI) is a highly sensitive, nontoxic technique based on the detection of visible light, produced by luciferase-catalysed reactions (bioluminescence) or by excitation of fluorescent molecules, using sensitive photon detectors. The development of bioluminescent/fluorescent microorganisms therefore allows the real-time noninvasive detection of microorganisms within intact living animals. Multiple imaging of the same animal throughout an experiment allows disease progression to be followed with extreme accuracy, reducing the number of animals required to yield statistically meaningful data. In the study of infectious disease, the use of BPI is becoming widespread due to the novel insights it can provide into established models, as well as the impact of the technique on two of the guiding principles of using animals in research, namely reduction and refinement. Here, we review the technology of BPI, from the instrumentation through to the generation of a photonic signal, and illustrate how the technique is shedding light on infection dynamics in vivo.

Recognition of root canal orifices in video sequences as a future support system during endodontic treatment

INTRODUCTION

The objective of this study was to show the practical application of computer-aided techniques for detecting root canal orifices through the access cavity using a video camera mounted on a microscope.

METHODS

A minimum distance classification image recognition algorithm was tested in an in vitro study to assess the possibilities of computer-aided recognition of root canal orifices. A Motic DM143 digital stereo microscope (Motic Germany GmbH, Wetzlar, Germany) was used because it includes a video camera that can be connected via USB1.1 to any computer.

RESULTS

The newly developed software is capable of communicating with a video camera and can automatically detect the root canal orifices in all teeth used in this study. A total of 165 extracted human teeth (molars and premolars) were used as test data to collect 8,250 images via screenshots for the evaluation of the detection quality. The software provided a detection sensitivity of 90.1%, with only 11.9% of the images as false-positive detections.

CONCLUSION

The study shows that computer-aided recognition of root canal orifices with video cameras is possible.

Irrigant flow within a prepared root canal using various flow rates: a Computational Fluid Dynamics study

AIM

To study using computer simulation the effect of irrigant flow rate on the flow pattern within a prepared root canal, during final irrigation with a syringe and needle.

METHODOLOGY

Geometrical characteristics of a side-vented endodontic needle and clinically realistic flow rate values were obtained from previous and preliminary studies. A Computational Fluid Dynamics (CFD) model was created using FLUENT 6.2 software. Calculations were carried out for five selected flow rates (0.02-0.79 mL sec(-1)) and velocity and turbulence quantities along the domain were evaluated.

RESULTS

Irrigant replacement was limited to 1-1.5 mm apical to the needle tip for all flow rates tested. Low-Reynolds number turbulent flow was detected near the needle outlet. Irrigant flow rate affected significantly the flow pattern within the root canal.

CONCLUSIONS

Irrigation needles should be placed to within 1 mm from working length to ensure fluid exchange. Turbulent flow of irrigant leads to more efficient irrigant replacement. CFD represents a powerful tool for the study of irrigation.

Antimicrobial photodynamic therapy combined with conventional endodontic treatment to eliminate root canal biofilm infection

BACKGROUND AND OBJECTIVE

To compare the effectiveness of antimicrobial photodynamic therapy (PDT), standard endodontic treatment and the combined treatment to eliminate bacterial biofilms present in infected root canals.

STUDY DESIGN/MATERIALS AND METHODS

Ten single-rooted freshly extracted human teeth were inoculated with stable bioluminescent Gram-negative bacteria, Proteus mirabilis and Pseudomonas aeruginosa to form 3-day biofilms in prepared root canals. Bioluminescence imaging was used to serially quantify bacterial burdens. PDT employed a conjugate between polyethylenimine and chlorin(e6) as the photosensitizer (PS) and 660-nm diode laser light delivered into the root canal via a 200-micro fiber, and this was compared and combined with standard endodontic treatment using mechanical debridement and antiseptic irrigation.

RESULTS

Endodontic therapy alone reduced bacterial bioluminescence by 90% while PDT alone reduced bioluminescence by 95%. The combination reduced bioluminescence by >98%, and importantly the bacterial regrowth observed 24 hours after treatment was much less for the combination (P<0.0005) than for either single treatment.

CONCLUSIONS

Bioluminescence imaging is an efficient way to monitor endodontic therapy. Antimicrobial PDT may have a role to play in optimized endodontic therapy.

The antimicrobial effects of root canal irrigation and medication

The role of microorganisms in the development and maintenance of pulpal and periapical inflammation have been well documented. The success of root canal treatment largely depends on the elimination of microbial contamination from the root canal system. Although mechanical instrumentation of root canals can reduce bacterial population, effective elimination of bacteria cannot be achieved without the use of antimicrobial root canal irrigation and medication. This review will discuss the antimicrobial effects of the known root canal irrigants and medicaments and explore future developments in the field.

Photonic real-time monitoring of bacterial reduction in root canals by genetically engineered bacteria after chemomechanical endodontic therapy

Microbial infection plays an important role in the development of pulp necrosis and formation of periapical lesions. In vitro and in vivo research in this field, traditionally microbiological culture methods using paper point sampling and quantitative culture, faces difficulties in completely removing bacteria from the root canal system and analyzing sequential procedures. This study employed genetically engineered bioluminescent bacteria and a light-sensitive imaging system to allow real-time visualization of the infection. Ten extracted teeth incubated with P. aeruginosa were treated by mechanical instrumentation with K-files (#30 K-file, #35 K-file and #40 K-file) and chemical irrigation with sodium hypochlorite and hydrogen peroxide. Irrigation alone reduced the contamination in 18%; the first chemomechanical sequence (instrumentation with a #30 K-file + irrigation) provided 41% of reduction; the second sequence (#35 K-file + irrigation) achieved 62%; and the complete therapy (#30 K-file + #35 K-file + #40 K-file + irrigation) achieved 93% of bacterial reduction. These results suggest that the endodontic treatment is dependent on the association of a chemical and mechanical approaches and that root canal enlargement improves bacterial reduction probably because the irrigation has more access to the apical third.

The Influence of Canal Curvature on the Mechanical Efficacy of Root Canal Irrigation In Vitro Using Real-Time Imaging of Bioluminescent Bacteria

There are no quantitative data on the mechanical efficacy of irrigation in the removal of bacteria from curved canals. This study quantitatively analyzed the effects of root canal curvature and preparation size on the mechanical efficacy of irrigation using 33 mandibular single-rooted bicuspids allocated to groups according to root canal curvatures, group 1 (straight) 4 to 8 degrees, group 2 (intermediate curvature) 15 to 19 degrees, and group 3 (greatest curvature) 24 to 28 degrees. Teeth were sequentially instrumented to sizes 27/.04, 36/.04, and 46/.04 using a crown-down technique. Suspensions of the bioluminescent reporter strain Pseudomonas fluorescens 5RL (1.5 x 10(6) cells) were inoculated into canals of sterilized teeth after each sequential instrumentation. Canals were irrigated with 6 ml of irrigant delivered 1 mm from working length using a 30-gauge needle. Remaining bacteria were quantified using real-time bioluminescent imaging. Irrigation was significantly less effective in 24 to 28 degrees curvature canals prepared to size 27/.04 compared to 46/.04 (p < 0.007, repeated-measures ANOVA).

Survival of Enterococcus faecalis in root canals ex vivo

AIM

The hypotheses tested in this study were that: (i) Enterococcus faecalis can survive long-term entombment in root filled teeth without additional nutrients, (ii) initial cell density influences the survival of E. faecalis in instrumented root canals and (iii) gelatinase-production capacity influences the survival of E. faecalis in root canals.

METHODOLOGY

The root canals of 150 extracted single canal teeth were instrumented to apical size 60 and divided into six groups of 25. Within each group 10 canals were inoculated with either gelatinase-producing E. faecalis OG1-S and the other 10 with its gelatinase-defective mutant E. faecalis OG1-X. Five canals per group were kept as uninoculated controls. The root canals in groups 1 and 2 were inoculated with 10(6) bacteria, incubated for 48 h at 37 degrees C then filled with gutta-percha and zinc-oxide eugenol sealer. Root canals were inoculated with 10(6), 10(5), 10(4) and 10(3) bacteria in groups 3-6, respectively, and left unfilled. All teeth were sealed coronally with glass-ionomer cement. After 6- (groups 1, 3-6) and 12-month (group 2) incubation at 37 degrees C in 100% humidity, root fragments were analysed for presence of E. faecalis, using culture, polymerase chain reaction and histological methods.

RESULTS

Viable E. faecalis was recovered from all root filled teeth and from 95-100% of unfilled inoculated teeth. Initial cell density and gelatinase production did not influence the recovery of viable E. faecalis (P > 0.05; chi-square test). Enterococcus faecalis 16S rRNA gene products were present in all inoculated teeth and absent in all noninoculated controls. Dentinal tubule infection was evident under light microscopy in sections from inoculated teeth after 48-h, 6- and 12-month incubation.

CONCLUSIONS

Enterococcus faecalis inoculated into root canals maintained viability for 12-months ex vivo. The clinical implications are that viable E. faecalis entombed at the time of root filling could provide a long-term nidus for subsequent infection.

The Influence of Preparation Size on the Mechanical Efficacy of Root Canal Irrigation In Vitro

This study tested the hypothesis that the mechanical efficacy of irrigation in reducing intracanal bacteria is dependent on canal preparation size. Root canals of 30 extracted permanent cuspids were prepared consecutively to sizes 36, 60, and 77 at working length (WL) using ProFile 0.04 taper Series-29 files. Smear layer was removed and teeth autoclaved following completion of each instrumentation sequence. Root canals were inoculated with a 15-mul suspension (1x10 cells) of Pseudomonas fluorescens 5RL, a salicylate-inducible bioluminescent reporter strain. Bioluminescence was measured before inoculation (background), after inoculation and after irrigation with 6 ml of irrigant delivered 1 mm from WL using a 28G safety-ended needle. The percentage of bacteria remaining following irrigation was 26.95+/-9.71%, 10.46+/-5.87%, and 10.64+/-6.01% for sizes 36, 60, and 77, respectively (p<0.001; repeated-measures ANOVA), with no difference between sizes 60 and 77 (p>0.05; Tukeys). Irrigation 1 mm from WL was significantly less effective in canals prepared to size 36.

Influence of irrigant needle depth in removing bioluminescent bacteria inoculated into instrumented root canals using real-time imaging in vitro

AIM

To test the hypothesis that the mechanical efficacy of irrigation in reducing bacteria in the root canal is dependent on depth of placement of the irrigation needle.

METHODOLOGY

The root canals of 30 permanent cuspids were instrumented to apical size 60 using a crown-down technique. A suspension of the bioluminescent reporter strain Pseudomonas fluorescens 5RL was inoculated into each canal of sterilized teeth. Emission of bioluminescence (photons s(-1)) from each tooth was quantified on four sequential occasions using luminometry and bioluminescence imaging: (i) background, (ii) after inoculation, (iii) after irrigating the inoculated teeth with 3 mL of a nonantimicrobial irrigant delivered either 1 mm (group 1, n = 15) or 5 mm (group 2, n = 15) from working length (WL) using a 28G safety-ended irrigating needle, (iv) after an additional 3 mL irrigation (total 6 mL). Intragroup and intergroup comparisons were made using Wilcoxon matched pairs and Mann-Whitney tests, respectively.

RESULTS

In group 1, there was a mean log10 decrease in bacteria of 0.68 +/- 0.26 after 3 mL of irrigant compared with 1.19 +/- 0.48 after 6 mL (P < 0.001); in group 2 the mean log10 decrease was 0.58 +/- 0.28 after 3 mL of irrigant compared with 0.69 +/- 0.35 after 6 mL (P < 0.02) (Wilcoxon matched pairs). Using 3 mL of irrigant, needle depth did not have a significant effect on reduction of intracanal bacteria (P = 0.407), but the effect became significant when 6 mL of irrigant was used (P < 0.002) (Mann-Whitney tests).

CONCLUSIONS

The mechanical efficacy of 6 mL of irrigant in reducing intracanal bacteria was significantly greater when delivered 1 mm compared with 5 mm from WL.