Study on the Inﬂuence of Refreshment/Activation Cycles and Irrigants on Mechanical Cleaning Efﬁciency During Ultrasonic Activation of the Irrigant Lucas W.M. van der Sluis, PhD,* Maikel P.J.M. Vogels, DDS, † Bram Verhaagen, Msc, ‡ Ricardo Macedo, DDS,* and Paul R. Wesselink, PhD* Abstract Introduction: The aims of this study were to evaluate dentin debris removal from the root canal during ultrasonic activation of sodium hypochlorite (2% and 10%), carbonated water, and distilled water and to determine the inﬂuence of 3 ultrasonic refreshment/acti- vation cycles of the irrigant by using the intermittent ﬂush technique. Methods: Root canals with a standard- ized groove in 1 canal wall, which was ﬁlled with dentin debris, were irrigated ultrasonically. The irrigant was refreshed and ultrasonically activated 3 times for 20 seconds. The quantity of dentin debris after irrigation was determined after each refreshment/activation cycle. Results and Conclusions: Ultrasonic activation of the irrigant combined with the intermittent ﬂush method produces a cumulative effect over 3 refreshment/activa- tion cycles. Sodium hypochlorite as an irrigant is signif- icantly more effective than carbonated water, which is signiﬁcantly more effective than distilled water, in removing dentin debris from the root canal during ultrasonic activation. (J Endod 2010;36:737–740) Key Words Cavitation, irrigation, root canal, streaming, ultrasonic T he aim of irrigation of the root canal system is to remove pulp tissue and/or micro- organisms, smear layer, and dentin debris from the root canal system, neutralize endotoxins, and lubricate canal walls and instruments (1). Irrigation of the root canal system allows the irrigant to be chemically active (chemical aspect) and permits the ﬂushing of debris (mechanical aspect). Passive ultrasonic irrigation (PUI) is ultrasonic activation of an irrigant in the root canal via a small, ultrasonically oscillating instrument (#15 or #20) placed in the center of the root canal after the root canal has been shaped up to the master apical ﬁle (2). PUI can induce acoustic streaming and/or cavitation of an irrigant, thereby enhancing the ﬂushing effect (mechanical) (2, 3). Furthermore, PUI results in an increase in the temperature of the irrigant (4), which will enhance the tissue-dissolving capacity of NaOCl (chemical) (5, 6). These factors facilitate the removal of pulp tissue, bacteria, the smear layer, dentin debris, and Ca(OH) 2 from the root canal (2, 7, 8). However, whether this is due to the acoustic streaming, cavitation, or both is unknown. The mechanical effect of irrigation is not similar for all irrigants activated by ultra- sound. For example, distilled water is less effective than 2% NaOCl (8). However, whether a higher concentration of NaOCl or carbonated water (water with CO 2 bubbles) is more effective than distilled water or 2% NaOCl is unknown. In this study we have chosen for a 10% NaOCl solution to make the difference with the 2% more signiﬁcant. To refresh the irrigant during PUI, the intermittent ﬂush method (IntFM) can be used. During the IntFM, a syringe is used to deliver the irrigant into the root canal; then the irrigant is activated ultrasonically (4). Depending on the irrigation time, this method is equally or more effective than refreshment with a continuous ﬂow of irrigant in the pulp chamber (9). In previous studies, 3 refreshment/activation cycles were used (8), but it is not clear whether a cumulative effect occurs. In another study, however, that used the IntFM in removing bovine pulp tissue from lateral canals, a cumulative effect was reported with a plateau of efﬁciency after the third activation cycle (6). Therefore, the purposes of this study were (1) to measure the ﬂuidic properties of 2% and 10% NaOCl and carbonated and distilled water, (2) to evaluate the effect of these irrigants on the removal of dentin debris from the root canal during passive ultra- sonic irrigation, and (3) to evaluate the effect of 3 ultrasonic refreshment/activation cycles during the IntFM. Materials and Methods Fluidic Properties Measurements Density was measured on a balance (Sartorius LE324S, Elk Grove, IL). Surface tension was measured by using a tensiometer (Kru ¨ ss K11, Hamburg, Germany) by submerging a plate into the ﬂuid, slowly pulling it out, and measuring the resultant force. Viscosity was measured by using a rheometer (Haake RheoStress 600; Thermo Scientiﬁc) by measuring the stress during rotation at speeds of 10–200 s 1 . The exper- iments were done at room temperature (21  C). Dentin Debris Removal Twenty canines (maxillary and mandibular) were instrumented with the GT system (Dentsply Maillefer, Ballaigues, Switzerland) until size 30, taper 0.06 (master apical ﬁle From the *Department of Cariology, Endodontology & Pedodontology, Academic Center for Dentistry, Amsterdam, The Netherlands; † Department of Periodontology, Cariology, Endodontology & Pedodontology, Academic Center Dentistry and Oral Health, Groningen, The Netherlands; and ‡ Physics of Fluids Group, Faculty of Science and Technology, University of Twente, and Research Institute for Biomedical Technology & TM MIRA, University of Twente, Enschede, The Netherlands. Address requests for reprints to Dr Lucas van der Sluis, ACTA, CEP-Endodontology, Louwesweg 1, 1066 EA Amster- dam, The Netherlands. E-mail address: l.vd.sluis@acta.nl. 0099-2399/$0 - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2009.12.004 Basic Research—Technology JOE — Volume 36, Number 4, April 2010 Mechanical Cleaning Efﬁciency of the Irrigant 737