The Effect of the Ultrasonic Irrigant Activation Protocol on the Removal of a Dual-species Biofilm from Artificial Lateral Canals

Introduction: Lateral canals are particularly challenging to clean and disinfect. The aim of this study was to compare the removal efficacy of a dual-species biofilm from a lateral canal model by different ultrasonic irrigant activation protocols in vitro. Methods: Artificial root canal models with 270 simulated lateral canals were made of polydimethylsiloxane. A dual-species biofilm (Streptococcus oralis and Actinomyces naeslundi) was grown in vitro in the lateral canals using a constant depth film fermenter. Two percent NaOCl or demineralized water was delivered by a syringe and an open-ended needle for 30 seconds and subsequently activated by an ultrasonic file for a total activation time of 30, 60, or 90 seconds divided in 1 or 3 consecutive activation cycles. In the control groups, the irrigant was allowed to rest for 30, 60, or 90 seconds. The volume of the biofilm in the lateral canal was evaluated before and after the final irrigation protocol by optical coherence tomography. The results were analyzed by 3-way factorial analysis of variance (α = 0.05). Results: Irrigation with NaOCl rather than demineralized water resulted in more effective biofilm removal from the lateral canal (P < .001). Three cycles of intermittent ultrasonic activation were significantly more effective than no activation (P = .029). The total irrigant contact time did not affect biofilm removal (P = .403). Conclusions: The type of the irrigant and the ultrasonic activation protocol affected biofilm removal from artificial lateral canals. None of the compared protocols was able to eradicate the biofilm.