Irrigant flow in the root canal during ultrasonic activation: A numerical fluid-structure interaction model and its validation.

AIM: The aim of the study was (a) to develop a three-dimensional numerical model combining the oscillation of a tapered ultrasonic file and the induced irrigant flow along with their two-way interaction in the confinement of a root canal. (b) To validate this model through comparison with experiments and theoretical (analytical) solutions of the flow. METHODOLOGY: Two partial numerical models, one for the oscillation of the ultrasonic file and another one for the irrigant flow inside the root canal around the file, were created and coupled in order to take into account the two-way coupled fluid-structure interaction. Simulations were carried out for ultrasonic K-files and for smooth wires driven at four different amplitudes in air or inside an irrigant-filled straight root canal. The oscillation pattern of the K-files was determined experimentally by Scanning Laser Vibrometry, and the flow pattern inside an artificial root canal was analysed using high-speed imaging together with Particle Image Velocimetry. Analytical solutions were obtained from an earlier study. Numerical, experimental and analytical results were compared to assess the validity of the model. RESULTS: The comparison of the oscillation amplitude and node location of the ultrasonic files and of the irrigant flow field showed a close agreement between the simulations, experiments and theoretical solutions. CONCLUSIONS: The model is able to predict reliably the file oscillation and irrigant flow inside root canals during ultrasonic activation under similar conditions.

The Effect of the Ultrasonic Irrigant Activation Protocol on the Removal of a Dual-species Biofilm from Artificial Lateral Canals.

INTRODUCTION: Lateral canals are particularly challenging to clean and disinfect. The aim of this study was to compare the removal efficacy of a dual-species biofilm from a lateral canal model by different ultrasonic irrigant activation protocols in vitro. METHODS: Artificial root canal models with 270 simulated lateral canals were made of polydimethylsiloxane. A dual-species biofilm (Streptococcus oralis and Actinomyces naeslundi) was grown in vitro in the lateral canals using a constant depth film fermenter. Two percent NaOCl or demineralized water was delivered by a syringe and an open-ended needle for 30 seconds and subsequently activated by an ultrasonic file for a total activation time of 30, 60, or 90 seconds divided in 1 or 3 consecutive activation cycles. In the control groups, the irrigant was allowed to rest for 30, 60, or 90 seconds. The volume of the biofilm in the lateral canal was evaluated before and after the final irrigation protocol by optical coherence tomography. The results were analyzed by 3-way factorial analysis of variance (α = 0.05). RESULTS: Irrigation with NaOCl rather than demineralized water resulted in more effective biofilm removal from the lateral canal (P < .001). Three cycles of intermittent ultrasonic activation were significantly more effective than no activation (P = .029). The total irrigant contact time did not affect biofilm removal (P = .403). CONCLUSIONS: The type of the irrigant and the ultrasonic activation protocol affected biofilm removal from artificial lateral canals. None of the compared protocols was able to eradicate the biofilm.

Present status and future directions - irrigants and irrigation methods.

Irrigation is considered the primary means of cleaning and disinfection of the root canal system. The purpose of this review was to set the framework for the obstacles that irrigation needs to overcome, to critically appraise currently used irrigants and irrigation methods, to highlight knowledge gaps and methodological limitations in the available studies and to provide directions for future developments. Organization of bacteria in biofilms located in anatomic intricacies of the root canal system and the difficulty to eliminate them is the main challenge for irrigants. Sodium hypochlorite remains the primary irrigant of choice, but it needs to be supplemented by a chelator. Delivery of the irrigants using a syringe and needle and activation by an ultrasonic file are the most popular irrigation methods. There is no evidence that any adjunct irrigation method, including ultrasonic activation, can improve the long-term outcome of root canal treatment beyond what can be achieved by instrumentation and syringe irrigation. It is necessary to redefine the research priorities in this field and investigate in greater depth the penetration of the irrigants, their effect on the biofilm and the long-term treatment outcome. New studies must also focus on clinically relevant comparisons, avoid methodological flaws and have sufficiently large sample sizes to reach reliable conclusions. Future multidisciplinary efforts combining the knowledge from basic sciences such as Chemistry, Microbiology and Fluid Dynamics may lead to more effective antimicrobials and improved activation methods to bring them closer to the residual biofilm in the root canal system.

A critical analysis of research methods and experimental models to study irrigants and irrigation systems.

Irrigation plays an essential role in root canal treatment. The purpose of this narrative review was to critically appraise the experimental methods and models used to study irrigants and irrigation systems and to provide directions for future research. Studies on the antimicrobial effect of irrigants should use mature multispecies biofilms grown on dentine or inside root canals and should combine at least two complementary evaluation methods. Dissolution of pulp tissue remnants should be examined in the presence of dentine and, preferably, inside human root canals. Micro-computed tomography is currently the method of choice for the assessment of accumulated dentine debris and their removal. A combination of experiments in transparent root canals and numerical modeling is needed to address irrigant penetration. Finally, models to evaluate irrigant extrusion through the apical foramen should simulate the periapical tissues and provide quantitative data on the amount of extruded irrigant. Mimicking the in vivo conditions as close as possible and standardization of the specimens and experimental protocols are universal requirements irrespective of the surrogate endpoint studied. Obsolete and unrealistic models must be abandoned in favour of more appropriate and valid ones that have more direct application and translation to clinical Endodontics.

Methodological quality assessment criteria for the evaluation of laboratory-based studies included in systematic reviews within the specialty of Endodontology: A development protocol.

High-quality systematic reviews in the field of Dentistry provide the most definitive overarching evidence for clinicians, guideline developers and healthcare policy makers to judge the foreseeable risks, anticipated benefits, and potential harms of dental treatment. In the process of carrying out a systematic review, it is essential that authors appraise the methodological quality of the primary studies they include, because studies which follow poor methodology will have a potentially serious negative impact on the overall strength of the evidence and the recommendations that can be drawn. In Endodontology, systematic reviews of laboratory studies have used quality assessment criteria developed subjectively by the individual authors as there are no comprehensive, well-structured, and universally accepted criteria that can be applied objectively and universally to individual studies included in reviews. Unfortunately, these subjective criteria are likely to be inaccurately defined, unreliably applied, inadequately analysed, unreasonably biased, defective, and non-repeatable. The aim of the present paper is to outline the process to be followed in the development of comprehensive methodological quality assessment criteria to be used when evaluating laboratory studies, that is research not conducted in vivo on humans or animals, included in systematic reviews within Endodontology. The development of new methodological quality assessment criteria for appraising the laboratory-based studies included in systematic reviews within Endodontology will follow a three-stage process. First, a steering committee will be formed by the project leaders to develop a preliminary list of assessment criteria by modifying and adapting those already available, but with the addition of several new items relevant for Endodontology. The initial draft assessment criteria will be reviewed and refined by a Delphi Group (n = 40) for their relevance and inclusion using a nine-point Likert scale. Second, the agreed items will then be discussed in an online or face-to-face meeting by a group of experts (n = 10) to further refine the assessment criteria. Third, based on the feedback received from the online/face-to-face meeting, the steering committee will revise the quality assessment criteria and subsequently a group of authors will be selected to pilot the new system. Based on the feedback collected, the criteria may be revised further before being approved by the steering committee. The assessment criteria will be published in relevant journals, presented at national and international congresses/meetings, and will be freely available on a dedicated website. The steering committee will update the assessment criteria periodically based on feedback received from end-users.

Syringe Irrigation in Minimally Shaped Root Canals Using 3 Endodontic Needles: A Computational Fluid Dynamics Study.

INTRODUCTION: The aim of this study was to compare the irrigant flow in curved root canals prepared to various apical sizes by constant-taper or variable-taper instruments during syringe irrigation with 3 endodontic needles at 2 different flow rates. METHODS: Two matched curved mesial root canals of human mandibular molars were imaged by micro-computed tomographic imaging after preparation to apical size 20, 25, and 30/.06 taper either by constant-taper or variable-taper instruments. A Computational Fluid Dynamics model was used to simulate the irrigant flow in the 2 root canals prepared to each apical size during syringe irrigation with a 30-G open-ended needle and 30-G and 31-G closed-ended needles at 0.05 and 0.15 mL/s. RESULTS: The irrigant could not penetrate up to the working length in root canals prepared to apical size 20 or 25/.06 taper. The 30-G open-ended needle combined with the low flow rate allowed the irrigant to reach the working length in size 30/.06 taper root canals while maintaining a relatively low apical pressure, but the wall shear stress was very low. The 31-G closed-ended needle combined with the high flow rate also delivered the irrigant to the working length in size 30 root canals and developed higher wall shear stress, but the apical pressure was also higher. CONCLUSIONS: Syringe irrigation using 30-G and 31-G needles was compromised in minimally shaped root canals.

PRILE 2021 guidelines for reporting laboratory studies in Endodontology: A consensus-based development.

Reproducible, skilfully conducted and unbiased laboratory studies provide new knowledge, which can inform clinical research and eventually translate into better patient care. To help researchers improve the quality and reproducibility of their research prior to a publication peer-review, this paper describes the process that was followed during the development of the Preferred Reporting Items for Laboratory studies in Endodontology (PRILE) 2021 guidelines and which used a well-documented consensus-based methodology. A steering committee was created with eight individuals (PM, RO, OP, IR, JS, EP, JJ and SP), plus the project leaders (PD, VN). The steering committee prepared an initial checklist by combining and adapting items from the modified Consolidated Statement of Reporting Trials checklist for reporting in vitro studies of dental materials and the Clinical and Laboratory Images in Publications principles as well as adding several new items. The steering committee then formed a PRILE Delphi Group (PDG) and PRILE Online Meeting Group (POMG) to provide expert advice and feedback on the initial draft checklist and flowchart. The members of the PDG participated in an online Delphi process to achieve consensus on the items within the PRILE 2021 checklist and the accompanying flowchart for clarity and suitability. The PRILE checklist and flowchart developed by the online Delphi process were discussed further by the POMG. This online meeting was conducted on 12 February 2021 via the Zoom platform. Following this meeting, the steering committee developed a final version of the PRILE 2021 guidelines and flowchart, which was piloted by several authors when writing up a laboratory study for publication. Authors are encouraged to use the PRILE 2021 guidelines and flowchart to improve the clarity, completeness and quality of reports describing laboratory studies in Endodontology. The PRILE 2021 checklist and flowchart are freely available and downloadable from the Preferred Reporting Items for study Designs in Endodontology website (http://pride-endodonticguidelines.org/prile/).

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.

Uncontrolled Removal of Dentin during In Vitro Ultrasonic Irrigant Activation in Curved Root Canals.

INTRODUCTION: The aim of this study was to examine the effect of file type and activation time on the uncontrolled removal of dentin during in vitro ultrasonic irrigant activation in prepared curved root canals. METHODS: Seventy-two curved mesial root canals of human mandibular molars were prepared to size 35/.04 taper. The specimens were randomly allocated to 4 groups (n = 18). Two milliliters of 2% sodium hypochlorite were delivered 3 times to each root canal, and the irrigant was ultrasonically activated every time for 10 seconds at 35% power either by a ultrasonic K-file (group A), an Irrisafe file (Acteon Satelec, Merignac, France) (group B), or a smooth wire (group C). The same specimens also received further activation continuously for another 30 seconds. No activation took place in group D. Specimens were scanned by micro-computed tomographic imaging before and after preparation and after the first and second activation period. Scans were coregistered and segmented, and the amount of dentin removed during activation was quantified by morphological operations. Results were analyzed by nonparametric statistical tests (α = 0.05). RESULTS: Defects with a maximum depth of 0.18 mm were identified. Both the type of file and activation time affected the removal of dentin (P ≤ .002 and P ≤ .031, respectively). K-files removed more dentin than Irrisafe files and smooth wires in the coronal and middle third. All files removed comparable amounts in the apical third. CONCLUSIONS: All 3 types of files may result in uncontrolled removal of dentin. A longer activation time may increase this effect.

Uncontrolled Removal of Dentin during In Vitro Ultrasonic Irrigant Activation.

INTRODUCTION: The aim of this study was to evaluate uncontrolled removal of dentin during in vitro ultrasonic irrigant activation in prepared root canals using 2 different files. METHODS: Fifty-four human single-rooted teeth with straight root canals were prepared to size 35/.06 taper. The specimens were randomly allocated to 3 groups (n = 18). Two milliliters of 2% sodium hypochlorite was delivered 3 times to each root canal by a syringe and an open-ended needle. After each delivery, the irrigant was ultrasonically activated for 10 seconds at 35% power either by a size 15 ultrasonic K-file (group A) or a size 20 Irrisafe file (Acteon Satelec, Merignac, France) (group B) placed at 2 mm short of the working length. The irrigant in the control specimens (group C) was not activated. Specimens were scanned by micro-computed tomographic imaging at 10-µm voxel size before preparation, after preparation, and after the final irrigation/activation sequence. Scans were coregistered and segmented, and the amount of dentin removed during the final step was quantified by morphologic operations. Results were analyzed by nonparametric statistical tests. The level of significance was set to P < .05. RESULTS: Defects with a maximum depth of 0.09 mm and 0.07 mm were identified in groups A and B, respectively. Both ultrasonic files removed significantly more dentin than irrigant delivery in the control group (P ≤ .005). K-files removed significantly more dentin than Irrisafe files in the apical third (P = .001). CONCLUSIONS: Ultrasonic irrigant activation may result in uncontrolled removal of dentin in straight root canals and at manufacturer-recommended power settings.

Porosity distribution in root canals filled with gutta percha and calcium silicate cement.

OBJECTIVE: Gutta percha is commonly used in conjunction with a sealer to produce a fluid-tight seal within the root canal fillings. One of the most commonly used filling methods is lateral compaction of gutta percha coupled with a sealer such as calcium silicate cement. However, this technique may result in voids and worse, the filling procedures may damage the root. METHODS: We compared the volume of the voids associated with two root canal filling methods, namely lateral compaction and single cone. Micro-computed tomography was used to assess the porosity associated with each method in vitro. An automated, observer-independent analysis protocol was used to quantify the unfilled regions and the porosity located in the sealer surrounding the gutta percha. RESULTS: Significantly less porosity was observed in root canals filled with the single cone technique (0.445% versus 3.095%, p<0.001). Porosity near the crown of the tooth was reduced 6 fold, whereas in the mid root region porosity was reduced to less than 10% of values found in the lateral compaction filled teeth. SIGNIFICANCE: Our findings suggest that changing the method used to place the endodontic biomaterials improves the quality and homogeneity of root canal fillings.

Effect of needle insertion depth and root canal curvature on irrigant extrusion ex vivo.

INTRODUCTION: The aim of this study was to evaluate the effect of needle type and insertion depth, apical preparation size, and root canal curvature on irrigant extrusion by using a recently introduced method. METHODS: Sixteen human teeth with a straight root canal (group A) and 16 with a moderately curved root canal (group B) were sequentially prepared to sizes 25 or 35, .06 taper and mounted on a plastic vial filled with distilled water to simulate a periapical lesion. The vial was either closed or open to the environment. A point-conductivity probe was used to determine the volume of extruded irrigant into the vial. NaOCl was delivered by an open-ended or a closed-ended needle at 1, 3, or 5 mm short of working length. Results were analyzed by two 4-way mixed-design analyses of variance. The level of significance was set to P < .05. RESULTS: The open-ended needle extruded significantly more irrigant than the closed-ended. Irrigant extrusion decreased as needles moved away from working length or when the apical size was increased. Needle wedging increased extrusion, especially when an open-ended needle was used. Root canal curvature did not have a statistically significant effect on irrigant extrusion. CONCLUSIONS: Needle type, needle insertion depth, and apical preparation size had a significant effect on irrigant extrusion.

The effect of needle-insertion depth on the irrigant flow in the root canal: evaluation using an unsteady computational fluid dynamics model.

INTRODUCTION: The aim of this study was to evaluate the effect of needle-insertion depth on the irrigant flow inside a prepared root canal during final irrigation with a syringe and two different needle types using a Computational Fluid Dynamics (CFD) model. METHODS: A validated CFD model was used to simulate irrigant flow from either a side-vented or an open-ended flat 30-G needle positioned inside a prepared root canal (45 .06) at 1, 2, 3, 4, or 5 mm short of the working length (WL). Velocity, pressure, and shear stress in the root canal were evaluated. RESULTS: The flow pattern in the apical part of the root canal was similar among different needle positions. Major differences were observed between the two needle types. The side-vented needle achieved irrigant replacement to the WL only at the 1-mm position, whereas the open-ended flat needle was able to achieve complete replacement even when positioned at 2 mm short of the WL. The maximum shear stress decreased as needles moved away from the WL. The flat needle led to higher mean pressure at the apical foramen. Both needles showed a similar gradual decrease in apical pressure as the distance from the WL increased. CONCLUSIONS: Needle-insertion depth was found to affect the extent of irrigant replacement, the shear stress on the canal wall, and the pressure at the apical foramen for both needle types.

Evaluation of irrigant flow in the root canal using different needle types by an unsteady computational fluid dynamics model.

INTRODUCTION: The aim of this study was to evaluate the effect of needle tip design on the irrigant flow inside a prepared root canal during final irrigation with a syringe using a validated Computational Fluid Dynamics (CFD) model. METHODS: A CFD model was created to simulate the irrigant flow inside a prepared root canal. Six different types of 30-G needles, three open-ended needles and three close-ended needles, were tested. Using this CFD model, the irrigant flow in the apical root canal was calculated and visualized. As a result, the streaming velocity, the apical pressure, and the shear stress on the root canal wall were evaluated. RESULTS: The open-ended needles created a jet toward the apex and maximum irrigant replacement. Within this group, the notched needle appeared less efficient in terms of irrigant replacement than the other two types. Within the close-ended group, the side-vented and double side-vented needle created a series of vortices and a less efficient irrigant replacement; the side-vented needle was slightly more efficient. The multi-vented needle created almost no flow apically to its tip, and wall shear stress was concentrated on a limited area, but the apical pressure was significantly lower than the other types. CONCLUSIONS: The flow pattern of the open-ended needles was different from the close-ended needles, resulting in more irrigant replacement in front of the open-ended needles but also higher apical pressure.

Ex vivo study of the efficiency of two techniques for the removal of mineral trioxide aggregate used as a root canal filling material.

The purpose of this study was to evaluate the removal efficiency of mineral trioxide aggregate (MTA) used as a root filling material. Ninety-three human teeth prepared with a step-back technique were randomly assigned to 2 groups and filled with vertically compacted MTA (group A) or MTA and a gutta-percha cone (group B). Fillings were removed by using ultrasonics and/or rotary nickel-titanium instruments. Roots were split into halves, and a 1 to 4 scoring system was used to assess the amount of residue. Data were analyzed with Kruskal-Wallis and Mann-Whitney tests. Remnants were found in all specimens. Rotary instruments were unable to penetrate canals in group A. The combination of rotary instruments and ultrasonics was superior in group B. Dark discoloration of most MTA fillings was evident. The results suggest that MTA cannot be completely removed from the root canal system by any of the methods examined.

Peripheral osteoma of the maxilla: report of an unusual case.

Peripheral osteomas of the maxilla are relatively rare. A case of a solitary peripheral osteoma of the anterior right maxilla in a 16-year-old girl is presented. The tumor was asymptomatic and was removed via an intraoral approach without any complications. Both hamartomatous and neoplastic factors have been advocated concerning the pathogenesis of such lesions, but no definite conclusion has been reported. Certain features of the case, such as obstruction of the eruption of the permanent canine, displacement of an adjacent tooth, intraoperatively noted infiltration of the interdental bone, and clearly abnormal histological bone structure might support the neoplastic nature of this lesion.