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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 (α = 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 ≤ 0.007) but only when preceded by irrigation at medium or high flow rate during phase 1. The effect of NaOCl concentration was not significant (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. [ABSTRACT FROM AUTHOR]

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., (© 2022 The Authors. International Endodontic Journal published by John Wiley & Sons Ltd on behalf of British Endodontic Society.)