Passive ultrasonic irrigation (PUI) involves the placing of a file into the root canal which is driven to oscillate freely in the presence of an irrigant. Such a technique uses the biophysical forces alone to clean the canal. The aim of this work was to determine the file oscillation modes which may occur if the PUI technique is employed clinically.
Methods:
The current study investigated, using laser vibrometry, the vibrations of files when immersed in a water bath, to better understand.
Results:
The results show that file mode shapes comprise a series of nodes / antinodes with thinner, longer files producing more antinodes. The maximum vibration of each file occurred at its free end and increasing generator power generally had no significant effect on this maximum amplitude (p>0.20). Antinodes occurring along the remaining file length were significantly larger at generator power 1 than at powers 2-5 (p<0.03). Analysis of the frequency spectra generated during scans reveals that at powers 2-5, frequency peaks were much broader, with multiple sub peaks, suggesting that energy being delivered to the file is dissipated as unwanted vibration, with file motion more of a rattle.
Conclusion:
Based on these observations, a method of constantly moving the file within the canal is required to maximise the interaction between the free end of the file and the irrigant. An improvement in the design of current instrumentation, with better transmission of ultrasound from the transducer to the working file is indicated.
Supported by EPSRC Grant No: EP/F020090