# An In Vitro Investigation of the Impact of Ultrasound Induced‐Streaming Motions on the Flow Inside Lateral Features of the Root Canal

## TL;DR

This study examines how ultrasound affects fluid flow in root canal lateral canals, showing that file position and canal angle influence cleaning effectiveness.

## Contribution

The paper experimentally characterizes flow dynamics in lateral canals during ultrasonic irrigation, revealing the impact of file positioning and canal inclination.

## Key findings

- The position of the endodontic file significantly affects flow patterns in lateral canals.
- A 90° canal angle allows for maximum velocity and effective jet alignment, while a 60° angle results in lower velocities and backflow.
- Recirculation zones form near the canal inlet, with transverse velocities comparable to axial ones.

## Abstract

The study aims to experimentally characterize the flow inside lateral canals during ultrasonic irrigation. The effect of the canal angle as well as the relative position of the endodontic file with the inlet of the channel was quantified.

An idealized endodontic geometry was 3D printed and used as a mould to fabricate a channel made of PEG‐modified hydrophilic PDMS. The mould comprises a 20 mm tapered (6%) root canal with a 0.4 mm apical diameter and a 5 mm long lateral canal with a 200 μm square cross section, forming an angle of either 90° or 60° with the axis of the root canal and placed 6 mm from the apex. The channel was filled with a NaI‐water solution and seeded with 1 μm particles. An ultrasonic instrument with a 15# K‐file was employed for the irrigation. The flow field was characterized by Particle Image Velocimetry.

The flow inside the lateral canals is notably affected by the position of the endodontic file. There is a competition between the impingement of the ultrasound‐induced jets on the walls of the root canal and the recirculation flows around the file, leading to either flow into the lateral canal or suction phenomena that generate backflow towards the root canal. Aligning the jet with the axis of the lateral canal maximizes the magnitude of the velocities that can be achieved therein. This alignment can only be achieved in the 90° channel. Inclining the lateral canal to 60° leads to lower velocities and a domination of the backflows towards the root canal. In both cases, a recirculation zone forms near the inlet of the channel where transverse velocities are comparable with the axial ones. The recirculation zone length is affected by the inclination of the channel. Further inside the canal, the flow becomes uniaxial.

The flow during ultrasonic irrigation inside lateral features of the root canal is complex and considerably affected by the position of the endodontic file and the inclination of the channel. An optimum location of the file tip leads to maximization of the induced velocity inside the lateral canal, suggesting more effective cleaning.