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

T. C. Pereira,R. J. B. Dijkstra,M. V. R. So,X. Petridis,W. J. van de Meer,M. Versluis,F. B. de Andrade,P. K. Sharma,C. Boutsioukis,L. W. M. van der Sluis

doi:10.1111/iej.13420

Abstract

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.MethodologyNinety‐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.ResultsThe 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.ConclusionsThe 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.

Highlights

Root canal irrigation is one of the most important steps during root canal treatment (Gulabivala et al 2005, Zehnder 2006)
Biofilms located in remote areas such as isthmuses, fins, oval extensions and lateral canals and in some parts of the main root canal are beyond the reach of instruments (Peters 2004, Gulabivala et al 2005, Ricucci et al 2013), so irrigants are expected to disrupt and remove them by a combination of chemical and mechanical effects
Sodium hypochlorite penetration and exchange in the main root canal and the developed wall shear stress are strongly affected by the irrigant flow rate (Boutsioukis et al 2009, Verhaagen et al 2012, van der Sluis et al 2015) but there is very little information about the effect of the flow rate on irrigant penetration in areas beyond the main root canal, such as isthmuses and lateral canals, and on biofilm removal

Summary

Introduction

Root canal irrigation is one of the most important steps during root canal treatment (Gulabivala et al 2005, Zehnder 2006). Biofilms located in remote areas such as isthmuses, fins, oval extensions and lateral canals and in some parts of the main root canal are beyond the reach of instruments (Peters 2004, Gulabivala et al 2005, Ricucci et al 2013), so irrigants are expected to disrupt and remove them by a combination of chemical and mechanical effects (van der Sluis et al 2015). Sodium hypochlorite penetration and exchange in the main root canal and the developed wall shear stress are strongly affected by the irrigant flow rate (Boutsioukis et al 2009, Verhaagen et al 2012, van der Sluis et al 2015) but there is very little information about the effect of the flow rate on irrigant penetration in areas beyond the main root canal, such as isthmuses and lateral canals, and on biofilm removal

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