Spatial effect of passive ultrasonic irrigation on a bacterial biofilm

Abstract

AIM: To examine the spatial cleaning effect of ultrasonic irrigation on a bacterial biofilm in a simulated root canal model with an oblong cross section. METHODOLOGY: A 7-day E. faecalis biofilm was cultivated on a flat polystyrene sheet that was assembled in a box-shaped, simulated canal model. Passive ultrasonic irrigation with sterile saline was performed for 5 min. The model was then dissembled and the biofilm on this artificial canal wall examined under confocal laser scanning microscope (CLSM) after a bacterial viability stain. Fifty-eight images were acquired from the polystyrene surface at vertical sites along the length of the file, at regular horizontal distances away from the file (at the same vertical height), and beyond its tip. These digital images were analyzed in software for the percentage of live or dead bacteria. Paired t-test, one-way ANOVA and Tukey-Kramer Multiple Comparisons, or the non-parametric equivalents were performed where indicated. RESULTS: Dead bacteria were not found in all specimens. At the vicinity of the ultrasonic file, the amount of viable bacteria ranged from 13.1% (2.75 mm from the tip) to 40.5% (4.5 mm level). Small amounts of live bacteria were observed within 1 mm horizontal distance from the vibrating file, which amount increased for sites farther away. At 3 mm distance, the amount of bacteria (35.5–64.4%) was significantly greater than sites near the file (P < 0.01). Sites next to the anti-nodes of the file showed less bacteria than those near the nodes (P < 0.050). The amount of bacteria was increased significantly beyond the tip of the file (P < 0.05). CONCLUSIONS: Passive ultrasonic irrigation, without the use of disinfectant, was able to dislodge bacteria from a single-species biofilm that was situated in close vicinity to the endosonic file. However, the effect was neither uniform across the surface, nor along the length of the file. The ability of ultrasonic irrigation to remove bacteria beyond the file tip was limited.