A novel experimental approach to investigate the effect of different agitation methods using sodium hypochlorite as an irrigant on the rate of bacterial biofilm removal from the wall of a simulated root canal model

Objective. Root canal irrigation is an important adjunct to control microbial infection. This study aimed primarily to develop a transparent root canal model to study in situ Enterococcus faecalis biofilm removal rate and remaining attached biofilm using passive or active irrigation solution for 90s. The change in available chlorine and pH of the outflow irrigant were assessed. Methods. A total of forty root canal models (n =10 per group) were manufactured using 3D printing. Each model consisted of two longitudinal halves of an 18 mm length simulated root canal with size 30 and taper 0.06. E. faecalis biofilms were grown on the apical 3 mm of the models for 10 days in Brain Heart Infusion broth. Biofilms were stained using crystal violet for visualization. The model halves were reassembled, attached to an apparatus and observed under a fluorescence microscope. Following 60s of 9 mL of 2.5% NaOCl irrigation using syringe and needle, the irrigant was either left stagnant in the canal or activated using gutta-percha, sonic and ultrasonic methods for 30s. Images were then captured every second using an external camera. The residual biofilm percentages were measured using image analysis software. The data were analyzed using Kruskal-Wallis test and generalized linear mixed model. Results. The highest level of biofilm removal was with ultrasonic agitation (90.13%) followed by sonic (88.72%), gutta-percha (80.59%), and passive irrigation group (control) (43.67%) respectively. All agitation groups reduced the available chlorine and pH of NaOCl more than that in the passive irrigation group. Significance. The 3D printing method provided a novel model to create a root canal simulation for studying and understanding a real-time biofilm removal under microscopy. Ultrasonic agitation of NaOCl left the least amount of residual biofilm in comparison to sonic and gutta-percha agitation methods. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.