Measurement and visualization of file-to-wall contact during ultrasonically activated irrigation in simulated canals

Aim (i) To quantify in a simulated root canal model the file-to-wall contact during ultrasonic activation of an irrigant and to evaluate the effect of root canal size, file insertion depth, ultrasonic power, root canal level and previous training, (ii) To investigate the effect of file-to-wall contact on file oscillation. Methodology File-to-wall contact was measured during ultrasonic activation of the irrigant performed by 15 trained and 15 untrained participants in two metal root canal models. Results were analyzed by two 5-way mixed-design anovas. The level of significance was set at P < 0.05. Additionally, high-speed visualizations, laser-vibrometer measurements and numerical simulations of the file oscillation were conducted. Results File-to-wall contact occurred in all cases during 20% of the activation time. Contact time was significantly shorter at high power (P < 0.001), when the file was positioned away from working length (P < 0.001), in the larger root canal (P < 0.001) and from coronal towards apical third of the root canal (P < 0.002), in most of the cases studied. Previous training did not show a consistent significant effect. File oscillation was affected by contact during 94% of the activation time. During wall contact, the file bounced back and forth against the wall at audible frequencies (ca. 5 kHz), but still performed the original 30 kHz oscillations. Travelling waves were identified on the file. The file oscillation was not dampened completely due to the contact and hydrodynamic cavitation was detected. Conclusion Considerable file-to-wall contact occur-red during irrigant activation. Therefore, the term ‘Passive Ultrasonic Irrigation’ should be amended to ‘Ultrasonically Activated Irrigation’