Efficacy of sonic and ultrasonic irrigation devices in the removal of debris from canal irregularities in artificial root canals

Abstract Objective To evaluate the efficacy of different sonic and ultrasonic devices in the elimination of debris from canal irregularities in artificial root canals. Materials and Methods A resin model of a transparent radicular canal filled with dentin debris was used. Five groups were tested, namely: Group 1 – ultrasonic insert 15.02; Group 2 – ultrasonic insert 25/25 IRRI K; Group 3 – ultrasonic insert 25/25 IRRI S; Group 4 – sonic insert 20/28 Eddy on a vibrating sonic air-scaler handpiece; Group 5 – 20.02 K-file inserted on a Safety M4 handpiece. Two different irrigants (5% sodium hypochlorite and 17% EDTA) and 3 different times of activation (20, 40, and 60 seconds) were tested. Means and standard deviations were calculated and statistically analyzed with the Kruskal-Wallis and Wilcoxon tests (p<0.05). Results No statistically significant differences were found between the two irrigants used. Group 4 removed more debris than the other groups (p<0.05). Groups 1, 2, and 3 removed more debris than group 5 (p<0.05). A statistically significant difference (p<0.05) was found for the time of activation in all groups and at all canal levels, except between 40 and 60 seconds in group 4 at coronal and middle third level (p>0.05). Conclusions No significant differences were found between 5% sodium hypochlorite and 17% EDTA. When the time of activation rises, the dentin debris removal increases in all groups. Both sonic and ultrasonic activation demonstrate high capacity for dentin debris removal.


Introduction
Biomechanical preparation is known for being one of the key steps in root canal treatment. 1 As the etiologic role of intracanal microorganisms is wellestablished in the development and advancement of periradicular and pulpal diseases, the fundamental goal of endodontic treatment is to eliminate all the pulp tissue and to disinfect the canal. 2,3 Biofilms formed by bacteria are recognized to be present in unreachable areas of the root canal system, 4 namely fins, accessory canals, and isthmuses. According to several studies, the mechanical instrumentation does not touch all the walls of the root canal 5,6 and remaining biofilms and infected debris can be a possible source of persistent infection and treatment failure. 7 For this reason, an adequate instrumentation and irrigation must be combined to decrease the microbial load within the root canal system and to complete the cleaning process. 8 Different irrigating solutions have been used throughout the years and, among them, sodium hypochlorite has been the most used solution. 9 Some concerns have been raised over sodium hypochlorite concentration and about the diffusion of the solution in some areas of the root canal, as complete root canal debridement has not been achieved. 10,11 To improve the action of disinfection and debridement, different irrigation delivery devices are available, namely the use of sonic, ultrasonic and negative pressure devices. 12 Agitation of sodium hypochlorite increases tissue dissolution 13 and its continuous renewal affords an uninterrupted source of nascent chlorine for organic tissue dissolution. 14 Most of the literature advises that ultrasonic devices are more powerful than sonic ones. 15 Ultrasonic irrigation exhibits better canal debridement efficacy over the use of needle irrigation alone. 16 Several in vitro and in vivo investigations studied the debridement efficacy of ultrasonic irrigation in the apical from 1 to 3 mm. 10,11,13,17,18  Recently, a new sonic system has been introduced into the market, the Eddy system (VDW GmbH, Munich, Germany), which is driven at a frequency of 6000 Hz by an air-driven handpiece (SONICflex 2003 Airscaler, Kavo, Genova, Italy). The manufacturer claims that the high-frequency vibration produced is transferred to the polyamide tip, which is moved in an oscillating movement at high amplitude thanks to the original qualities of the material. This threedimensional movement generates "cavitation" and to obtain a compound similar to wet sand, drying it for 5 seconds with an absorbent paper.

Experimental groups
The same simulator of the root canal was employed for all the groups tested and the test was repeated 10 times for each experimental group. Each time, the same irrigation procedure was adopted, using inserts The first image was taken to confirm that all lateral extensions were filled with dentine debris, and to calculate the total area of the lateral extensions filled with dentine debris and consisting in the sum of the six  Table 1 shows the percentage of debris removal for each experimental group.

Results
No statistically significant differences have been found between the two different irrigants used, at all levels and intervals of activation (p>0.05).
Concerning the total amount of debris removed, group 4 has statistically removed more debris than the other groups (p<0.05). Moreover, group 1, 2, and 3 statistically removed more debris than group 5 (p<0.05), whereas there were no differences among   Table 1-Percentage of debris removal for each experimental group ± standard deviation (SD). Considering the total section, same superscript letters ("a," "b," or "c") on the same line indicate no statistically significant differences. Considering the total section, same superscript letters ("x," "y," "w," or "z") on the same column indicate no statistically significant differences. Same superscript letter "d" means no statistical difference among thirds in the same time of activation in the same group. Same superscript letter "e" means no statistical difference among time of activation in the same group. The groups that do not have any letter do not have significant differences with the other groups 2019;27:e20180045 5/6 group 4 (p>0.05). No differences were found between the middle and apical levels in all groups (p>0.05).

Discussion
The aim of this study was to evaluate the efficacy of different sonic and ultrasonic devices in the elimination of debris from canal irregularities in artificial root canals filled with sodium hypochlorite or EDTA. The results showed no statistically significant differences between NaOCl and EDTA, therefore, it seems that the mechanical movement of the liquid is more important than the chemical action for removal of debris.
The predominant irrigation method among endodontists seems to be passive ultrasonic irrigation (PUI). 26 To the date, most studies showed favorable results for PUI compared to sonic irrigation. 15 PUI has some advantages, namely the acoustic streaming effect that increases wall shear stress and enhances the rupturing of intra-radicular biofilm. 27 However, PUI has also some drawbacks. First of all, the contact of the file with the root canal walls dampens the energy of the oscillating instrument and constrains the file movement. 9 This is an important limitation in curved root canals because the file stops and cannot oscillate freely. Moreover, ultrasonic files, although having a non-cutting tip, are made of steel, and steel is harder than dentin, so ultrasonic tips could deform the root canal and are only recommended as a final irrigation. 28 The results of this study revealed no significant differences among the different ultrasonic inserts used, despite their differences in dimensions and type of the tips.
Marketed sonic devices until present showed lower results than ultrasonic devices, mainly due to their lower power. Typically, a sonic device operates at 1-8 kHz and ultrasonic at 25-40 kHz. 9 In this study, 3 activation times of 20 seconds each were used, according to the clinical protocol suggested previously. 16  Further clinical and laboratory studies are needed to evaluate the Eddy system efficacy.

Conclusions
No statistically significant differences were found between 5% sodium hypochlorite and 17% EDTA activation and among the ultrasonic inserts used.