01 November 2021

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Evaluation of biofilm removal from isthmus and collateral canals by different irrigation modalities

Lara Figini

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Root canal irrigation is one of the most important steps in root canal treatment and its main purpose is to eliminate microorganisms, which often adhere to the root canal wall forming a biofilm, from the infected root canal system. However, the biofilm located in remote areas such as isthmuses, oval canals and lateral canals, as well as in some parts of the main root canal, is out of reach of the instruments and its removal can only be entrusted to irrigants through the combination of a chemical action. and a mechanical action.

Materials and methods
In an in vitro study, published in the International Endodontic Journal of March 2021, the authors quantified the removal of biofilm from a simulated sample, characterized by an isthmus and a lateral canal of an artificial root endodontic system, obtained by:

- syringe irrigation of NaOCl at different concentrations and with delivery at various flow rates

- with the addition of a high-flow final rinse with an inert irrigant after washing with NaOCl.

Different irrigation rates calculated by the computer model were considered and the amount of biofilm removal related to the various irrigation rates was evaluated. Ninety-six artificial root canals were artificially contaminated with predetermined biofilm, sprayed with NaOCl at various concentrations (2, 5 and 10%) or with an inert irrigant (control group) delivered for 30 seconds at the following irrigation rates: 0.033, 0.083 or 0.166 mL s -1 or passively deposited in the main root canal (step 1). All samples were subsequently rinsed for 30 s with an inert irrigant at 0.166 mL s 1 (step 2). The biofilm was scanned with optical tomography to determine the percentage of biofilm remaining. The results were analyzed by 3-way ANOVA (a = 0.05). The Computational Fluid Dynamics model was used to simulate the flow of irrigant within the artificial root canal system.

Results
The speed of irrigation during phase 1 and additional irrigation during phase 2 showed a significant effect on the percentage of biofilm remaining in the isthmus. Additional irrigation during phase 2 also affected the remaining biofilm in the side channel significantly (P ≤ 0.007) but only when preceded by medium or high velocity flow irrigation during phase 1. The effect of different NaOCl concentrations resulted in no significant differences (P> 0.05) on the amount of biofilm removal. The irrigation rate in the isthmus and lateral canal was found to be increased with increasing flow rate and was substantially related to the amount of biofilm removed from those areas.

Conclusions
From the data from this in vitro study, which need to be confirmed by other similar in vitro study results, it can be concluded that the flow rate of the irrigant influences biofilm removal in vitro more than the concentration of NaOCl used.

Clinical implications
The endodontist must be aware that the flow rate and speed of irrigation affect the amount of biofilm removed from the root canal system.

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