Biofilm removal from a simulated isthmus and lateral canal during syringe irrigation at various flow rates:a combined experimental and Computational Fluid Dynamics approach

Aim (i) To quantify biofilm removal from a simulated isthmus and a lateral canal in an artificial root canal system during syringe irrigation with NaOCl at different concentrations and delivered at various flow rates (ii) to examine whether biofilm removal is further improved by a final high-flow-rate rinse with an inert irrigant following irrigation with NaOCl. (iii) to simulate the irrigant flow in these areas using a computer model (iv) to examine whether the irrigant velocity calculated by the computer model is correlated to biofilm removal. Methodology Ninety-six artificial root canals with either a simulated isthmus or lateral canal were used. A dual-species in vitro biofilm was formed in these areas using a Constant Depth Film Fermenter. NaOCl at various concentrations (2, 5 and 10%) or adhesion buffer (control) was delivered for 30 s by a syringe and an open-ended needle at 0.033, 0.083, or 0.166 mL s(-1) or passively deposited in the main root canal (phase 1). All specimens were subsequently rinsed for 30 s with adhesion buffer at 0.166 mL s(-1) (phase 2). The biofilm was scanned by Optical Coherence Tomography to determine the percentage of the remaining biofilm. Results were analysed by two 3-way mixed-design ANOVAs (alpha = 0.05). A Computational Fluid Dynamics model was used to simulate the irrigant flow inside the artificial root canal system. Results The flow rate during phase 1 and additional irrigation during phase 2 had a significant effect on the percentage of the remaining biofilm in the isthmus (P = 0.004 and P <0.001). Additional irrigation during phase 2 also affected the remaining biofilm in the lateral canal significantly (P 0.05). Irrigant velocity in the isthmus and lateral canal increased with increasing flow rate and it was substantially correlated to biofilm removal from those areas. Conclusions The irrigant flow rate affected biofilm removal in vitro more than NaOCl concentration. Irrigant velocity predicted by the computer model corresponded with the pattern of biofilm removal from the simulated isthmus and lateral canal

Apical transportation associated with ProTaper® Universal F1, F2 and F3 instruments in curved canals prepared by undergraduate students

Objective: This study evaluated apical transportation associated with ProTaper® Universal F1, F2 and F3 rotary files in curved canals prepared by undergraduate students. Material and Methods: Twenty mesial roots of mandibular molars with curvatures ranging between 25° and 35° were selected. Mesiobuccal canals were instrumented by twenty students with the ProTaper® system (Dentsply-Maillefer, Ballaigues, Switzerland) according to the manufacturer’s instructions. Pre-flaring was performed with S1 and SX files. A #15 K-file was inserted into the root canal up to the working length (WL), and an initial digital radiograph was taken in a buccolingual direction (baseline). Afterwards, the S1, S2, F1, F2, and F3 files were employed up to the WL. Other radiographies were taken in the same orientation of the baseline after the use of the F1, F2, and F3 files, with each file inserted into the root canal. The radiographic images were overlapped, and the Image J software was used to measure the distance between the rotary files’ ends and the #15 K-file’s end, characterizing the apical transportation. Data were analyzed by Repeated Measure ANOVA and by the SNK post hoc test (P<0.05). Results: It was verified that file size affected apical transportation significantly (P<0.001). The F3 file showed higher apical transportation than F1 and F2, while between these last files there was no difference. Conclusion: The undergraduate students produced lower apical transportation in curved canals when they did not use the F3 rotary file

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

Observer variation in the assessment of root canal curvature

Aim: To evaluate the inter- and intra-observer agreement between training/trained endodontists regarding the ex vivo classification of root canal curvature into three categories and its measurement using three quantitative methods. Methodology: Periapical radiographs of seven extracted human posterior teeth with varying degrees of curvature were exposed ex vivo. Twenty training/trained endodontists were asked to classify the root canal curvature into three categories (30°), to measure the curvature using three quantitative methods (Schneider, Weine, Pruett) and to draw angles of 10° or 30°, as a control experiment. The procedure was repeated after six weeks. Inter- and intra-observer agreement was evaluated by the intraclass correlation coefficient and weighted kappa. Results: The inter-observer agreement on the visual classification of root canal curvature was substantial (ICC = 0.65, P  0.10), but the results of individual participants varied. When quantitative methods were used, the inter- and intra-observer agreement on the angle measurements was considerably better (ICC = 0.76–0.82, P  0.895). Conclusions: Visual estimation of root canal curvature was not reliable. The use of computer-based quantitative methods is recommended. The measurement of radius of curvature was more subjective than angle measurement. Endodontic Associations need to provide specific guidelines on how to estimate root canal curvature in case difficulty assessment forms