The influence of the ultrasonic intensity on the cleaning efficacy of passive ultrasonic irrigation

Introduction: It is not clear whether increasing the
ultrasonic intensity would enhance the cleaning efficacy
of passive ultrasonic irrigation (PUI) inside a root canal.
The aim of this study was to evaluate the effect of the
ultrasonic intensity on PUI to remove dentin debris
and whether there is any lateral effect beyond the ultrasonic
tip. Methods: Each of 15 in vitro root canal
models with four standard depressions in the apical
part of one canal wall were filled with dentin debris
and received PUI repeatedly. The most apical depression
was localized apically from the ultrasonic tip. The highest
intensity was applied in group 1, the lowest intensity
was applied in group 3, and syringe irrigation was
performed in group 4 as a control. Before and after irrigation,
images of the canal wall with depressions were
taken and compared. The removal of dentin debris in
the depressions was categorized as clean or not clean.
The data were analyzed by means of the chi-square
test. The oscillation amplitude of the ultrasonic file at
each intensity was recorded in vitro using timeresolved
high-speed imaging. Results: Group 1 (highest
intensity) exhibited significantly better cleaning than all
the other groups (P < .05); no significant difference was
found between the four levels of the depressions within
any of the four groups. High-speed imaging showed that
the amplitude of the oscillating file increased as the
intensity went up, which leads to a higher velocity of
the irrigant around the file. Conclusions: Higher ultrasonic
intensity resulted in a higher amplitude of the
oscillating file and, consequently, enhanced the cleaning
efficacy of PUI.