Which type of activation, sonic or ultrasonic, is more effective for irrigants?
Studies have shown that ultrasonic activation is more effective in removing dentin debris than sonic activation. This is due to the higher driving frequency of ultrasonics (29 kHz) compared to sonic devices (160-190 Hz), resulting in a higher flow velocity1,2. Moreover, the oscillation amplitude of the ultrasonic tip also increases with the flow velocity for a specific frequency. However, the diameter of the apical root
canal is smaller than 0.5 mm, while the oscillation amplitude of the sonically activated tip in water is approximately 1 mm. This extensive wall contact between the tip and the root canal wall reduces the efficient streaming of the irrigant, inhibiting free oscillation of the sonic tip and consequently reducing the activation of the irrigant. Furthermore, cavitation was shown to occur in ultrasonic activation at clinically relevant ultrasonic power settings in both straight and curved canals but not around sonically oscillating tips3.
1. Sabins R A et al. A comparison of the cleaning efﬁcacy of short-term sonic and ultrasonic passive irrigation after hand instrumentation in molar root canals. J Endod 2003;29:674–8.
2. Ahmad M et al. Ultrasonic debridement of root canals: acoustic cavitation and its relevance. J Endod 1988;14:486–93.
3. Macedo R et al. Cavitation measurement during sonic and ultrasonic activated irrigation. Journal of endodontics. 2014 Apr 1;40(4):580-3.
Can a curved canal obstruct ultrasonic activation of the fluid?
Cleaning the apical root canal can be challenging due to its complex anatomy. The canal's small dimensions and intricate structure can obstruct the flow of irrigants, making it challenging to clean1. Additionally, root canals often have curvatures that can reduce various irrigation techniques' effectiveness2, 3.
In syringe irrigation, severe root canal curvatures mainly affect the cleaning effectiveness4. On the other hand, in ultrasonically activated irrigation, the penetration of the irrigant is influenced by the intensity of the ultrasonic waves5 and the distance between the file tip apex and the curved root canal. Interestingly, the curvature does not affect the flow depth, indicating that microstreaming occurs on a much smaller scale than the curvature itself. This suggests that the extent of cleaning in curved canals is comparable to that in straight canals.
According to research studies, an ultrasonically oscillating tip effectively removes dentin debris from the root canal wall up to 3 mm in front of the file tip. The flow is observed to be correlated with this finding. Additionally, irrigant flow is unaffected by the root canal's curvature6.
1. Boutsioukis C et al. The effect of apical preparation size on the irrigant ﬂow in root canals evaluated using an unsteady Computational Fluid Dynamics model. IEJ 2010;43:874–81.
2. Amato M et al. Curved versus straight root canals: the beneﬁt of activated irrigation techniques on dentin debris removal. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2011;111:529–34.
3. Reodig T et al. Effectiveness of different irrigant agitation techniques on debris and smear layer removal in curved canals: a scanning electron microscopy study. JOE 2010;36:1983–7.
4. Nguy D. The inﬂuence of canal curvature on the mechanical efﬁcacy of root canal irrigation in vitro using real-time imaging of bioluminescent bacteria. JOE 2006;32:1077–80.
5. Peeters H H. Efﬁcacy of laser-driven irrigation versus ultrasonic in removing an airlock from the apical third of a narrow root canal. Aust Endod J 2013. http://dx.doi.org/10.1111/aej.12016.
6. Jiang L M et al. The inﬂuence of the ultrasonic intensity on the cleaning efﬁcacy of passive ultrasonic irrigation. JOE 2011; 37:688–92
Has ultrasonic power influenced the cleaning capacity?
The apical third of the root canal system is challenging to clean because of the complexity of the root canal morphology, making irrigant delivery and activation less effective1. The intensity of ultrasonic activation, adjusted by the power setting on the ultrasonic device, inﬂuences the energy transmission from the oscillating tip to the irrigant. It has been suggested that the velocity of the acoustic streaming occurring around oscillating tips is directly influenced by factors such as the intensity of the generator and its location on the tip2. A study showed that the cleaning efﬁcacy was enhanced when the ultrasonic intensity rose, especially at the highest intensity3.
1. Foschi F et al. SEM evaluation of canal wall dentine following use of Mtwo and ProTaper NiTi rotary instruments. IEJ 2004; 37:832–9.
2. Jiang L M et al. Inﬂuence of the oscillation direction of an ultrasonic ﬁle on the cleaning efﬁcacy of passive ultrasonic irrigation. JOE 2010;36:1372–6.
3. Jiang L M et al. The inﬂuence of the ultrasonic intensity on the cleaning efﬁcacy of passive ultrasonic irrigation. JOE 2011;37:688–92.