Keywords passive ultrasonic activation - hard-tissue debris - micro–computed tomography
Introduction
During root canal preparation, auxiliary chemical solutions act as disinfectants and
lubricants. They help eliminate pulp tissue, necrotic remnants, and debris produced
by the mechanical action of instruments.[1 ] However, accumulated hard-tissue debris (AHTD) may persist within the root canal
system (RCS). This is clinically relevant, as AHTD can harbor microorganisms, especially
in difficult-to-access areas, compromising disinfection protocols and interfering
with root canal filling procedures.[2 ]
[3 ]
[4 ]
Studies have shown that conventional syringe and needle irrigation may be ineffective
in removing AHTD, especially in anatomical irregularities and/or difficult-to-reach
areas.[5 ]
[6 ] To overcome this limitation, several strategies to optimize the irrigating solution
activity have been proposed, such as the use of different types of needle, sonic activation,
passive ultrasonic irrigation (PUI), and the use of a negative pressure irrigation
system.[7 ]
[8 ]
[9 ]
[10 ] PUI is the technique used to activate the root canal irrigant using ultrasonically
oscillating noncutting tips as a supplementary protocol after the completion of biomechanical
preparation. The acoustic streaming provided by the ultrasonic activation allows a
deeper penetration of irrigants into complex anatomic regions of the RCS.[11 ] The efficacy of PUI in AHTD removal has been studied extensively.[7 ]
[12 ]
[13 ]
[14 ]
[15 ]
[16 ]
[17 ]
[18 ] Although studies show an improvement in AHTD removal after PUI protocols, none of
them have shown that this technique was able to completely clean and disinfect the
entire root canal space.[17 ]
Irrisonic tip (Helse Dental Technology, São Paulo, Brazil) is an instrument introduced
to be used after root canal instrumentation, during PUI. Due to the inherent fragility
of its small core size (tip size #25, 0.01 taper), it is recommended to be activated
at a power of 10%.[19 ] Irrisonic Power tip (Helse Dental Technology) is a recently developed instrument
launched aiming to overcome the limited activation power of its predecessor. This
instrument presents some modifications in the insert length and bending angle, which
according to the manufacturer allows this device to be used at higher powers without
major risks of fracture. Since the activation power of an instrument is directly related
to its cleaning capacity,[8 ]
[20 ] the use of this new tip with higher activation power could lead to a greater AHTD
removal, improving the root canal cleaning during the final irrigation protocol.
Compared with other activation systems reported in the literature, such as EndoActivator,
EndoUltra, and XP-Endo Finisher, the Irrisonic Power tip presents notable structural
and functional differences. The EndoActivator operates at lower sonic frequencies,
generating limited cavitation and acoustic streaming effects.[8 ]
[20 ] The EndoUltra, although ultrasonic, is battery-powered and may present limitations
in continuous activation and tip flexibility.[7 ]
[17 ] The XP-Endo Finisher, although effective in mechanical agitation, relies on direct
contact with canal walls and shape-memory alloy expansion to clean irregular anatomies,
which may limit its efficacy in narrow or complex regions.[17 ]
[18 ] In contrast, the Irrisonic Power tip was developed with a reinforced core and modified
geometry, specifically in its insert length and bending angle, which allow safe use
at higher ultrasonic power settings without increasing the risk of tip deformation
or fracture.[19 ] These structural modifications enhance the stability and resistance of the insert,
enabling more intense and sustained acoustic streaming, which may improve irrigant
penetration and AHTD removal, especially in the apical third and anatomically complex
areas of the RCS.[8 ]
[17 ]
[18 ]
In this context, the aim of the present study was to evaluate the effectiveness of
the Irrisonic Power ultrasonic tip activated using 10 and 30% power settings on the
removal of AHTD from mandibular premolars using micro–computed tomography (micro-CT)
analysis. The null hypothesis tested was that there would be no difference in AHTD
removal when different powers are used to activate the Irrisonic Power insert.
Materials and Methods
Sample Size Calculation
Sample size was calculated from previous studies with similar methodologies.[13 ]
[17 ]
[21 ] The effect size for this study was 0.91 and added to a power β = 95% with a statistical
significance level set at α = 5% in an F test family for one-way analysis (G*Power
3.1.7 Software for MacBook, Heinrich Heine, Universität Düsseldorf). The ideal total
sample size required to observe significant differences was indicated to be 17 specimens.
A total of 20 specimens (n = 10) were used to compensate for possible sample loss.
Sample Selection
This study was approved by the Local Ethics Committee (#2.975.186). A total of 55
human lower premolars were selected and stored in 0.1% thymol solution at 5°C. Digital
radiographs were taken for each specimen in the mesiodistal and buccolingual direction
to verify the internal anatomy of the root canals. Digital periapical radiographs
were taken using an X-ray unit (Gnatus Timex 70E, Ribeirão Preto, SP, Brazil) operating
at 70 kVp, 8 mA, and an exposure time of 0.2 seconds. A digital CMOS sensor (RVG 5200,
Carestream Dental, Atlanta, GA, USA) was used for image acquisition. The X-ray tube
was positioned at a 30-cm distance from the sensor, and all images were captured with
a paralleling technique to ensure standardization. These radiographs were used to
confirm the presence of a single canal, and the absence of previous root canal treatment,
calcifications, root resorptions, or fractures. Initially, 55 extracted human mandibular
premolars were scanned using micro-CT. From this pool, 20 teeth were selected based
on morphological similarity in terms of length, canal volume, and three-dimensional
anatomy, to ensure group homogeneity.
The teeth were scanned on a microtomograph (SkyScan 1174, Bruker, Kontich, Belgium)
with the following acquisition parameters: 800 mA and 50 kV, 27 µm isotropic resolution,
0.5 mm thick aluminum filter, 5,200 millisecond exposure time, rotation step of 0.5,
and 180 degrees about the vertical axis. All images were reconstructed using NRecon
software (v1.6.1.0; Bruker, Kontich, Belgium) with the same parameters: ring artifact
reduction,[8 ] beam hardening correction (35%), and smoothing[4 ] for all images. To ensure sample homogeneity, the surface area (mm2 ) and volume (mm3 ) of root canals were calculated by the CTAn program (Bruker Micro-CT, Kontich, Belgium)
and the three-dimensional image was obtained with CTVol (Bruker Micro-CT, Kontich,
Belgium). Subsequently, the selected teeth were randomly distributed into two experimental
groups (n = 10). Normal distribution of the data (ρ > 0.05; Shapiro-Wilk) and group homogeneity were evaluated for morphological dimensions
(length, volume, and three-dimensional anatomy), confirming the anatomical similarity
between experimental groups (ρ > 0.05; Student's t-test and Mann-Whitney test).
Root Canal Preparation
After access cavity preparation, a glide path was created by scouting a stainless-steel
size #15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) up to the working length
(WL), which was established as being 1 mm short of the apical foramen. The apices
of the teeth were sealed with hot glue to create a close-end system. Then root canals
were prepared using Reciproc R25 (25/.08v) instrument (VDW, Munich, Germany) in a
reciprocating motion (RECIPROC ALL) powered by an electric motor (VDW Silver; VDW).
The instrument was moved apically using a sequence of three in-and-out reciprocating
motions, with approximately 3 mm of amplitude and slight apical pressure. Throughout
instrumentation and after preparing each third (cervical, middle, and apical), the
root canals were irrigated using with 5 mL of 2.5% NaOCl using a 30-G NaviTip needle
(Ultradent Products Inc, South Jordan, USA) using a total of 15 mL to each specimen.
The foraminal patency was maintained using the #15 K-file during the entire procedure.
The specimens were submitted to new micro-CT procedures, applying the above-mentioned
parameters, to calculate the root canal space volume and AHTD after preparation.
Supplementary Irrigation Protocol
One tooth from each pair-matched teeth was randomly assigned to one of the two experimental
groups (n = 10), according to the final irrigation protocol:
Irrisonic Power 10%: Root canals were irrigated with 3 mL 2.5% NaOCl using a NaviTip
needle, held within the root canal for 30 s, and then agitated for 30 s using the
Irrissonic Power tip 1 mm short of the WL mounted on a piezoelectric ultrasonic device
(P5 Newton XS; Acteon Satelec, Norwich, UK), with the power setting at 10% (2/20).
Next, the root canals were irrigated with 3 mL of 17% EDTA, held within the root canal
for 30 s, and then activated for 30 s using the same technique as described above.
This protocol was repeated twice, and a final rinse with 3 mL of saline solution was
performed ([Fig. 1 ]).
Irrisonic Power 30%: Root canals were irrigated with 3 mL 2.5% NaOCl using a NaviTip
needle, held within the root canal for 30 s, and then agitated for 30 s using the
Irrissonic Power tip 1 mm short of the WL mounted on a piezoelectric ultrasonic device
(P5 Newton XS; Acteon Satelec, Norwich, UK), with the power setting at 30% (6/20).
Next, the root canals were irrigated with 3 mL of 17% EDTA, held within the root canal
for 30 s, and then activated for 30 s using the same technique as described above.
This protocol was repeated twice, and a final rinse with 3 mL of saline solution was
performed ([Fig. 1 ]).
Fig. 1 Flowchart of experimental procedures. PUI, passive ultrasonic irrigation.
The same final volume of irrigating solution (15 mL) was used in each group, being
6 mL 2.5% NaOCl, 6 mL 17% EDTA, and 3 mL saline solution. Finally, the specimens were
dried with absorbent paper points (Dentsply Maillefer). A single experienced operator
conducted all experimental procedures. At the end of this stage, the specimens were
submitted to new micro-CT procedures, applying the above-mentioned parameters.
Micro-CT Scanning and Three-Dimensional Analysis
After supplementary irrigation protocols, the tooth image slices were recorded with
their respective postoperative images from the 3D Slicer 4.4.0 software (available
at http://www.slicer.org ), overlapping the images at an accuracy greater than 1 voxel.[17 ] Root canal volume, before and after instrumentation, was calculated by the ImageJ
program (v.1.49, Fiji, Madison, WI).[21 ] Material with dentin-like density located in the region of the instrumented root
canal was considered AHTD,[13 ] which was quantified, as previously described, by the intersection between images
before and after irrigation activation protocols[21 ] and expressed as the percentage of the total volume of root canals after instrumentation
of each sample.
For the quantification of dentinal debris, the reconstructed axial images were exported
in TIFF format and analyzed using ImageJ. All images were converted to 8-bit grayscale
and binarized using the Otsu automatic thresholding method, with a fixed threshold
range set between 35 and 255 gray values. This range was selected based on preliminary
evaluations to distinguish high-density debris from the surrounding canal space. Following
binarization, images were converted to binary, with debris appearing as high-intensity
(white) structures. Small particles and background noise were excluded using the “Analyze
Particles” tool with a minimum size threshold of 50 pixels. For each cross-sectional
image, the area occupied by debris was measured and expressed as a percentage relative
to the total area of the root canal lumen. This procedure was applied uniformly to
all samples and groups to ensure consistency and comparability of measurements. Then
the images obtained after the quantification of dentinal debris were transformed into
three-dimensional images using the CTVol program (v. 2.2.1, Bruker microCT).
Statistical Analysis
The volume (mm3 ) and accumulation of dentinal debris (%) of supplemental irrigation protocols were
used as reference parameters to verify if specimens within groups had similar conditions.
Volume demonstrated a normal distribution of data (Shapiro-Wilk test—ρ > 0.05) and therefore the Student's t -test was used to compare volume between groups. For the evaluation of debris (%),
the sample did not present normal distribution, and therefore the nonparametric Mann-Whitney
test was performed (α = 0.05).
Results
The baseline homogeneity of the experimental groups was confirmed with respect to
root canal length, volume, surface area, and initial AHTD volume after root canal
preparation (ρ > 0.05). [Table 1 ] presents the pre- and post-irrigation AHTD volumes and their respective percentages
for both groups. Both the supplemental cleaning protocols significantly reduced AHTD
compared with the baseline (paired t -test, ρ < 0.05). However, the Irrisonic Power 30% group achieved a significantly greater
reduction in AHTD (mean final value: 0.16%) than the Irrisonic Power 10% group (mean
final value: 0.90%) (Mann-Whitney test, ρ < 0.05).
Table 1
Mean and standard deviation of the volume of the root canal space and accumulated
debris after instrumentation and supplementary irrigation protocols
Parameters
Irrisonic Power 10%
Irrisonic Power 30%
(mean ± standard deviation)
Root canal space volume
Post-instrumentation (mm3 )
9.08 ± 2.91
9.70 ± 2.40
Post-activation (mm3 )
9.55 ± 2.97
10.66 ± 2.48
Debris
volume
Post-activation (mm3 )
0.08 ± 0.09
0.01 ± 0.01
Post-activation (%)
0.90 ± 1.16
0.16 ± 0.13
[Fig. 2 ] shows a three-dimensional representation of mandibular premolars before and after
the supplementary irrigation protocol using the Irrisonic Power insert at 10 and 30%
power setting.
Fig. 2 Representation of three-dimensional models of flattened lower premolar canals. Irrisonic
Power 10% group: (A ) Post-instrumentation volume (yellow), (B ) volume before (yellow) and post-activation (red), and (C ) remnant debris accumulation (gray). Irrisonic Power 30% group: (D ) Post-instrumentation volume (yellow), (E ) volume before (yellow) and post-activation (red), and (F ) remnant debris accumulation (gray).
Discussion
The AHTD produced during mechanical preparation are considered a clinically relevant
issue, since it may be packed into anatomical complexities harboring bacterial contents
away from the disinfection procedures.[14 ]
[16 ]
[22 ] The amount of hard-tissue debris accumulated after biomechanical preparation has
been extensively demonstrated and discussed, pointing out the need of a final irrigation
protocol after root canal preparation.[1 ]
[2 ]
[3 ]
[4 ]
The present study evaluated the efficacy of different ultrasonic powers in the use
of PUI supplemental cleaning protocols in the removal of AHTD from uniradicular mandibular
premolars by micro-CT. This three-dimensional nondestructive technique allows the
quantitative and qualitative evaluation of AHTD accumulation in RCS irregularities
and has been used successfully as a gold standard technique to evaluate this.[13 ]
[22 ]
[23 ]
Due to the heterogeneity found in the morphology of root canals and to avoid anatomic
biases that may interfere with the study outcomes, specimens were pre-screened using
micro-CT. The micro-CT screening of the length, area, and volume, and three-dimensional
configuration was performed to provide an overall anatomical mapping of the root canals.[13 ]
[21 ] Based on these data and on root canal configuration and morphology, 10 pair-matched
mandibular premolars were grouped and further allocated into one of the two experimental
groups. Statistical analysis confirmed the effective balance among the groups with
respect to the baseline parameters, thus enhancing the internal validity of this study.
The results of the present study showed that supplementary root canal cleaning using
passive ultrasonic agitation improves the efficiency of removal of AHTD. These results
are in line with previous studies that also showed similar AHTD removal using PUI.[6 ]
[16 ]
[24 ] However, in the present study Irrisonic Power 30% group had higher root canal cleaning
capacity when compared with the Irrisonic Power 10% group (ρ < 0.05). Therefore, the null hypothesis tested was rejected. In the present study,
supplemental irrigation protocols were identical, differing only in the power setting
of the equipment. Consequently, the results can be explained by a more precise activation
of the irrigating solution and an increased acoustic flow[24 ] provided by the high power employed (30%) through the ultrasonic device. Possibly,
these mechanical improvements in the instrument design allowed this newly developed
tip to be used at 30% power level with better results than the same tip used at 10%
power level. However, to the best of the authors' knowledge, this is the first study
evaluating the removal of AHTD with Irrisonic Power tips.
Although both the final irrigation protocols showed a significant decrease in the
accumulation of hard-tissue debris (ρ < 0.05), none of them was able to completely remove the AHTD. This finding is in agreement
with several previous studies,[6 ]
[13 ]
[16 ]
[17 ]
[18 ]
[24 ]
[25 ] and highlights the fact that the biomechanical preparation of RCS invariably creates
accumulation of AHTD in areas of anatomical irregularities that cannot be completely
removed with the currently available techniques.
This study presents some limitations that should be acknowledged. First, only uniradicular
mandibular premolars were included, which typically present relatively simple and
straight canal anatomies. As such, the results may not be fully generalizable to molars
or other teeth with more complex canal systems, such as those containing curvatures,
isthmuses, or accessory canals. Second, the absence of additional control groups using
other activation systems or a no-activation protocol limits the ability to make broader
comparative conclusions. Future studies should include a wider variety of tooth anatomies
and additional control groups to validate and expand upon the present findings.
Although both the power settings resulted in a significant reduction of AHTD, the
30% power group demonstrated a substantially lower final debris percentage. This difference,
although numerically modest, may be clinically relevant, especially in anatomical
conditions such as isthmuses, apical deltas, or oval-shaped canals, where debris tends
to persist even after thorough instrumentation and irrigation.[6 ]
[15 ]
[17 ] The ability to activate irrigants more intensely, while maintaining structural safety,
could enhance cleaning and disinfection in these challenging areas. Previous studies
have shown that improved irrigant activation can significantly increase debris removal
from complex root canal regions.[7 ]
[16 ]
[18 ] These findings support the consideration of higher ultrasonic activation powers
in clinical protocols and suggest that future investigations should evaluate the performance
of the Irrisonic Power tip in multi-rooted teeth or anatomically irregular canals
to validate its effectiveness across different clinical scenarios.
Within the conditions of the present study, it can be concluded that both the supplementary
irrigation protocols were effective in removing AHTD. However, Irrisonic Power at
30% power level has been shown to be more efficient at removing debris from root canals.
Conclusion
Both supplementary irrigation protocols using the Irrisonic Power tip significantly
reduced the volume of accumulated hard-tissue debris in mandibular premolars. However,
activation at 30% power proved to be significantly more effective than the 10% power
setting.
