Fluid Dynamics and Biofilm Removal Generated by Syringe-delivered and 2 Ultrasonic-assisted Irrigation Methods: A Novel Experimental Approach

INTRODUCTION: Thorough understanding of fluid dynamics in root canal irrigation and corresponding antibiofilm capacity will support improved disinfection strategies. This study aimed to develop a standardized, simulated root canal model that allows real-time analysis of fluid/irrigation dynamics and its correlation with biofilm elimination. METHODS: A maxillary incisor with an instrumented root canal was imaged with micro-computed tomography. The canal volume was reconstructed in 3 dimensions and replicated in soft lithography-based models microfabricated from polyethylene glycol-modified polydimethylsiloxane. Canals were irrigated by using a syringe (SI) and 2 ultrasonic-assisted methods, intermittent (IUAI) and continuous (CUAI). Real-time fluid movement within the apical 3 mm of canals was imaged by using microparticle image velocimetry. In similar models, canals were inoculated with Enterococcus faecalis to grow 3-week-old biofilms. Biofilm reduction by irrigation with SI, CUAI, and IUAI was assessed by using a crystal violet assay and compared with an untreated control. RESULTS: SI generated higher velocity and shear stress in the apical 1-2 mm than 0-1 and 2-3 mm. IUAI generated consistently low shear stress in the apical 3 mm. CUAI generated consistently high levels of velocity and shear stress; it was the highest of the groups in the apical 0-1 and 2-3 mm. Biofilm was significantly reduced compared with the control only by CUAI (two-sample permutation test, P = .005). CONCLUSIONS: CUAI exhibited the highest mechanical effects of fluid flow in the apical 3 mm, which correlated with significant biofilm reduction. The soft lithography-based models provided a novel model/method for study of correlations between fluid dynamics and the antibiofilm capacity of root canal irrigation methods.