An Evaluation of the Effect of Pulsed Ultrasound on the Cleaning Efficacy of Passive Ultrasonic Irrigation Lei-Meng Jiang, DMD,* Bram Verhaagen, MSc, †‡ Michel Versluis, PhD, †‡ Chiara Zangrillo, § Doris Cuckovic, § and Lucas W.M. van der Sluis, DDS, PhD* Abstract Introduction: Multiple activations of the irrigant by using pulsed ultrasound may enhance the removal of dentin debris because of repeated acceleration of the ir- rigant. The aim of this study was to evaluate the effect of pulsed ultrasound on passive ultrasonic irrigation (PUI) in its ability to remove artificially placed dentin debris from a simulated apical oval extension within standardi- zed root canals. Methods: Each of 20 in vitro root canal models with a standard groove in the apical portion of one canal wall filled with dentin debris received PUI repeatedly, either without pulsation (group1) or with pulsation (730 milliseconds on/100 milliseconds off in group 2, 400 milliseconds on/400 milliseconds off in group 3, and 100 milliseconds on/ 670 milliseconds off in group 4), corresponding to duty cycles of 100%, 88%, 50%, and 13%, respectively. After each irrigation procedure, the amount of dentin debris in the groove was evaluated by taking photo- graphs of the groove and scoring. The irrigation proce- dures were also visualized in vitro using high-speed imaging performed in glass root canal models. Results: The debris score was significantly lower only in group 3 (p = 0.023). The in vitro visualization showed increased streaming and cavitation during the start-up phase of each pulse. Conclusions: PUI with a pulsation pattern of 400 milliseconds on/400 milliseconds off and a duty cycle of 50% is more effective in removing dentin debris from a simulated apical oval extension in standardized root canals than continuous ultrasonic activation. Duty cycles of 13% and 88% showed no difference compared with continuous oscillation. (J En- dod 2010;36:1887–1891) Key Words Dentin debris, passive ultrasonic irrigation, pulsation, pulsed ultrasound A fter the completion of a standard root canal preparation, the debridement of the root canal is, however, by far complete, leaving large untouched areas that may harbor tissue or dentin debris, microbes, and their byproducts (1–7). The root canal system has better access for cleaning by an irrigant after finishing the instrumentation, and irrigation has a better possibility for cleaning the space beyond the prepared canal (8). Therefore, a final rinse after the completion of the preparation is an essential part of root canal debridement. It has been realized in recent years that irrigation dynamics play an important role in the cleaning process (9–11). The use of a file in conjunction with an (ultra)sonic device that activates the irrigant has been proposed for the final rinsing step to enhance the cleaning of the root canal through streaming and cavitation (12–15). Laser-activated irrigation has been shown to be more effective in removing dentine debris from the apical part of the root canal than passive ultrasonic irrigation (PUI) (16). This improvement in cleaning efficacy may be associated with the fact that the ir- rigant becomes accelerated at every laser pulse (16). Similarly, the acoustic streaming of the irrigant introduced by the ultrasonic activation may also be enhanced by repeated activations after introducing ultrasound pulsations into the system. Each activation causes an acceleration of the irrigant, and the governing fluid physics laws link accel- eration to force. In addition, pulsed ultrasound has a direct effect on acoustic cavitation in a liquid (17–19). Therefore, this study looks into the enhancement of the cleaning efficacy of PUI by pulsed ultrasound under the hypothesis that PUI with pulsation is more effective than without pulsation within 10 seconds. Materials and Methods Dentin Debris Removal Model Straight roots from 20 extracted human maxillary canines were decoronated to obtain uniform root sections of 15 mm. The roots were embedded in self-curing resin (GC Ostron 100; GC Europe, Leuven, Belgium) and then bisected longitudinally through the canal in mesiodistal direction with a saw microtome (Leica Microsystems SP1600, Wetzlar, Germany). The surfaces of both halves were ground successively with 240-, P400- and 600-grit sandpaper, resulting in smooth surfaces on which only little of the original root canal lumen was left. Four holes were drilled in the resin part, and the two halves were reassembled by four self-tapping bolts through the holes (9). All the models were checked for any leakage of liquid or gas apically or laterally before experiments; if there was any, rubber dam caulk was applied to ensure the root canal space of the model was a closed system. New root canals were prepared by K-files #15/.02 (Dentsply Maillefer, Ballaigues, Switzerland) and HERO 642 (MicroMega, Besanc ¸on, France) nickel-titanium rotary From the *Department of Cariology, Endodontology & Pedodontology, Academic Center for Dentistry, Amsterdam, The Netherlands; † Physics of Fluids group, Faculty of Science and Technology, University of Twente, Twente, The Netherlands; ‡ Research Institute for Biomedical Technology and Technical Medicine MIRA, University of Twente, Twente, The Netherlands; and § Clinica Odontoiatrica, Universita Degli Studi di Roma ‘La Sapienza’, Rome, Italy. Address requests for reprints to Dr Lei-Meng Jiang, Academic Center for Dentistry, Department of Cariology, Endodontology & Pedodontology, Gustav Mahlerlaan 3004, 1081LA Amsterdam, Noordholland, Netherlands. E-mail address: l.jiang@acta.nl. 0099-2399/$ - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.08.003 Basic Research—Technology JOE — Volume 36, Number 11, November 2010 Effect of Pulsed US on the Cleaning Efficacy of Passive US Irrigation 1887