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Ex vivo evaluation of four final irrigation protocols
on the removal of hard-tissue debris from the
mesial root canal system of mandibular first
molars
G. B. Leoni
1
, M. A. Versiani
1
, Y. T. Silva-Sousa
2
, J. F. B. Bruniera
2
,J.D.P
ecora
1
&
M. D. Sousa-Neto
1
1
Department of Restorative Dentistry, Dental School of Ribeir~
ao Preto, University of S~
ao Paulo, Ribeir~
ao Preto, SP; and
2
Department of Endodontics, Faculty of Dentistry, University of Ribeir~
ao Preto, Ribeir~
ao Preto, SP, Brazil
Abstract
Leoni GB, Versiani MA, Silva-Sousa YT, Bruniera
JFB, P
ecora JD, Sousa-Neto MD. Ex vivo evaluation of
four final irrigation protocols on the removal of hard-tissue
debris from the mesial root canal system of mandibular first
molars. International Endodontic Journal.
Aim To evaluate the efficacy of four final irrigation
protocols on the reduction of hard-tissue debris accu-
mulated within the mesial root canal system of
mandibular first molars using micro-CT analysis.
Methodology Forty mesial roots of mandibular
molars with a single and continuous isthmus con-
necting the mesiobuccal and mesiolingual canals
(Vertucci’s Type I configuration) were selected and
scanned at a resolution of 8.6 lm. Canals were
enlarged sequentially using WaveOne Small and Pri-
mary instruments activated in reciprocating motion
without intracanal irrigation to allow debris to accu-
mulate within the mesial root canal system. Then,
specimens were anatomically matched and distributed
into four groups (n=10), according to the final irri-
gation protocol: apical positive pressure (APP), passive
ultrasonic irrigation (PUI), Self-adjusting File (SAF)
and XP-endo Finisher (XPF). The final irrigation pro-
cedures were performed over 2 min using a total of
5.5 mL of 2.5% NaOCl per canal. Reconstructed data
sets were coregistered, and the mean percentage
reduction of accumulated hard-tissue debris after the
final irrigation procedures was compared statistically
between groups using the ANOVA post hoc Tukey test
with a significance level set at 5%.
Results Reduction of accumulated hard-tissue debris
was observed in all groups after the final irrigation
protocol. Overall, PUI and XPF groups had higher
mean percentage reductions of accumulated hard-tis-
sue debris (94.1% and 89.7%, respectively) than APP
and SAF groups (45.7% and 41.3%, respectively)
(P<0.05). No significant differences were found
when comparing the results of PUI and XPF groups
(P>0.05) or APP and SAF groups (P>0.05).
Conclusions The PUI technique and XP-endo Fin-
isher instrument were associated with significantly
lower levels of AHTD compared with conventional
irrigation and the modified SAF system protocol in
mesial root canals of mandibular molars.
Keywords: apical positive pressure, hard-tissue
debris, isthmus, mandibular molar, microcomputed
tomography, root canal irrigation.
Received 22 January 2016; accepted 15 March 2016
Introduction
During biomechanical preparation of the root canal
system, the irrigating solution acts as a disinfectant,
lubricant and cleaning agent, helping to eliminate
Correspondence: Manoel D. Sousa Neto, Rua C
elia de Oli-
veira Meirelles n 350, Ribeir~
ao Preto, S~
ao Paulo, CEP
14024-070, Brazil (e-mail: sousanet@forp.usp).
International Endodontic Journal©2016 International Endodontic Journal. Published by John Wiley & Sons Ltd
doi:10.1111/iej.12630
1
tissue debris created by the cutting action of instru-
ments on dentine, and neutralizing microbes and
their by-products (Siqueira et al. 2013). Standard irri-
gation uses a needle adapted to a syringe associated
with apical positive pressure. In this approach, the tip
of the needle must be positioned 1–2 mm from the
working length, and irrigation performed with large
volumes and frequent exchange of irrigants to
improve disinfection (Gu et al. 2009). Although it
allows good irrigant control, conventional syringe irri-
gation has been reported to be ineffective in flushing
out tissue remnants and cleaning the most apical por-
tions of the root canal system (Thomas et al. 2014).
To overcome the limitations of conventional irriga-
tion, several techniques have been proposed. Amongst
them, activation of irrigants via sonic, ultrasonic or
laser devices has been associated with improvement
in the cleaning and disinfection of the root canal sys-
tem (Gu et al. 2009, Haapasalo et al. 2014, Nusstein
2015). Passive ultrasonic irrigation (PUI) is the acti-
vation of an irrigant in the root canal using ultrasoni-
cally oscillating small files (Weller et al. 1980) or
smooth noncutting wires (van der Sluis et al. 2005a)
following the completion of canal preparation. Effec-
tiveness of PUI to remove tissues and debris has been
studied extensively (Nusstein 2015). Overall, PUI has
been reported to be more effective than conventional
needle-delivered irrigation (Paqu
eet al. 2011, Haa-
pasalo et al. 2014). A new approach for root canal
shaping and cleaning has emerged with the develop-
ment of a hollow, cylinder-like, nickel–titanium
motor-driven Self-adjusting File system (SAF; ReDent-
Nova, Ra’anana, Israel). Its unique design allows
simultaneous and continuous irrigation throughout
the mechanical preparation of the canal (Metzger
et al. 2010), and SAF has been shown to be efficient
as a potential irrigation adjunct for debris removal
after root canal preparation (Dietrich et al. 2012,
Paqu
eet al. 2012a).
Recently, a size 25 universal nontapered nickel–ti-
tanium-based instrument (XP-endo Finisher; FKG, La
Chaux-de-Fonds, Switzerland) was launched. XP-endo
Finisher is made of a proprietary alloy (Martensite-
Austenite Electropolish-FleX) that reacts at different
temperature levels. When it is cooled, the instrument
is straight (M-phase), but when exposed to the body
temperature, it changes its shape to the A-phase,
which allows the instrument to expand its reach to
6 mm in diameter or 100-fold of an equivalent sized
file when in rotation motion (Trope & Debelian
2015). According to the manufacturer, this inherent
feature gives the instrument high flexibility that
would help to remove packed debris from the com-
plexities of the root canal system, while limiting the
impact on dentine (FKG 2015).
Traditionally, debridement of root canals has been
evaluated by means of histology, scanning electron
microscopy and sectioning methods (Haapasalo et al.
2014). Hard-tissue debris accumulated after different
biomechanical protocols has also been quantified
using microcomputed tomography (micro-CT) (Paqu
e
et al. 2009, 2011, 2012a,b, Robinson et al. 2012,
2013, De-Deus et al. 2014, 2015, Freire et al. 2015).
Even though there is accumulating evidence on the
efficacy of several irrigating techniques using conven-
tional methodologies, a comprehensive knowledge
regarding the activation of irrigants in different final
irrigation protocols, aiming to remove hard-tissue
debris from the isthmus area by means of micro-CT
technology is still lacking. Thus, the purpose of this
ex vivo study was to evaluate the percentage reduc-
tion of accumulated hard-tissue debris (AHTD) in isth-
mus-containing mesial root canals of mandibular
molars using different final irrigation protocols. The
null hypothesis was that there is no difference in the
reduction of AHTD amongst the four irrigation proto-
cols tested.
Material and methods
Sample size estimation
Sample size was calculated after the effect size estima-
tion of the percentage volume of AHTD as reported
by Paqu
eet al. (2012a). In that study, the percentage
volume of AHTD after SAF preparation was 1.7%. An
a priori ANOVA (fixed effects, omnibus, one-way) was
selected from the F-tests family in G*Power 3.1.7 soft-
ware for Macintosh (Heinrich Heine, Universit€
at
D€
usseldorf, Dusseldorf, Germany). Nine samples per
group were indicated as the ideal size required for
observing the same effect of instruments over dentine
with an alpha-type error <0.05 and power beta of
99%.
Tooth selection
After ethics committee approval (protocol
0072.0.138.000-09), forty mandibular first molars
that had a mesial root with a fully formed apex, mild
curvature (15°–20°) in both mesiodistal and buccolin-
gual directions (Schneider 1971), and two mesial
Hard tissue debris removal by irrigation Leoni et al.
©2016 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal
2
canals connected by a single and continuous isthmus
that joined together in the apical third to exit in a
single foramen (Vertucci’s Type I configuration) were
selected. To prevent the introduction of confounding
variables, teeth were decoronated ~3 mm above the
cemento-enamel junction. Then, mesial roots were
mounted on a custom attachment and imaged sepa-
rately at an isotropic resolution of 8.6 lm using a
micro-CT device (SkyScan 1176; Bruker-microCT,
Kontich, Belgium). The scanner parameters were set
at 90 kV, 278 lA, 180°rotation around the vertical
axis, and rotation step of 0.4°, using a 0.1-mm-thick
copper filter.
Root canal preparation
Mesial canals were accessed and canal patency con-
firmed with a size 10 K-file (Dentsply Maillefer, Bal-
laigues, Switzerland). When the tip of the instrument
was visible through the main foramen, 0.5 mm was
subtracted to determine working length (WL). Then,
the apical foramen of each root was sealed with fast
set epoxy resin to create a closed-end system. Coronal
flaring was performed using Gates-Glidden drills 2
and 3 (Dentsply Maillefer), and glide path was
achieved to WL using ProGlider instrument
(0.16 mm tip diameter; Dentsply Maillefer). Canals
were sequentially enlarged using WaveOne Small (size
21, .06 taper over the first 3 mm from apical tip) and
Primary (size 25, .08 taper over the first 3 mm from
apical tip) instruments (Dentsply Maillefer) activated
in reciprocating motion (VDW Silver motor; VDW
GmbH, Munich, Germany) until they reached the WL.
To allow debris to accumulate into the isthmus area,
irrigation and aspiration throughout the preparation
procedures were carried out only at the orifice level
with a total of 5 mL of distilled water per canal using
a 30-gauge NaviTip needle (Ultradent, South Jordan,
UT, USA) adapted to a disposable plastic syringe.
Then, each canal was slightly dried with one absor-
bent paper point (WaveOne Small; Dentsply Maillefer)
and the roots submitted to a new scan, applying the
parameter settings previously mentioned.
The acquired projection images were reconstructed
into cross-section slices with NRecon v.1.6.9 software
(Bruker-microCT) with a beam hardening correction
of 15%, smoothing of five, ring artefact correction of
seven and an attenuation coefficient ranging from
0.00007 to 0.025, resulting in the acquisition of
1800–1900 transverse cross-sections per root. The
volume of interest was selected extending from the
furcation level to the apex of the mesial root, set by
integration of all cross-sections. For the purpose of
this study, the region of interest in each slice com-
prised the area of the mesial canals and the isthmus.
Pre- and postoperative 3D models of the mesial canals
were rendered (CTVol v.2.2.1; Bruker-microCT) and
coregistered with their respective preoperative data
sets, using the rigid registration module of the 3D Sli-
cer 4.3.1 software (available from http://www.slicer.-
org). Then, matched images were examined to
calculate volume (in mm
3
) and surface area (in mm
2
)
of the mesial root canal system, before and after
preparation using CTAn v.1.14.4 software (Bruker
micro-CT).
For the quantitative analysis of AHTD, the label
masks of the registered data sets of each tooth were
imported into the Fiji software (Fiji v.1.47n; Madi-
son, WI, USA) and normalized. The sequence of
images resulting from this operation was further
used to identify the AHTD by means of morphologic
operations. Quantification of AHTD was performed
by the difference between nonprepared and prepared
root canal space using post-processing procedures.
The presence of a material with density similar to
dentine in regions previously occupied by air in the
nonprepared root canal space was considered debris
and quantified by intersection between images before
and after canal instrumentation (Paqu
eet al. 2009,
Robinson et al. 2012, De-Deus et al. 2014). The
total volume of AHTD was calculated in cubic mil-
limetre (mm
3
) and expressed as the percentage of
the total canal system volume after preparation (vol
%).
Final irrigation protocols
Aiming to enhance the internal validity of the experi-
ment, the mesial root canals were matched to create
10 groups of four based on the morphological aspects
of the root canal system (configuration, length, vol-
ume and surface area) and in the vol% of AHTD after
preparation. Then, one root from each group was
randomly assigned to one of the four experimental
groups (n=10), according to the final irrigation pro-
tocol, which was completed within 2 min using a
total of 5.5 mL of 2.5% NaOCl per canal by an experi-
enced and previously trained operator:
•Apical positive pressure (APP group): A total of
0.5 mL of 2.5% NaOCl was flushed into the canal
using conventional needle/syringe technique and
left stand for 1 min. Then, irrigation was performed
Leoni et al. Hard tissue debris removal by irrigation
International Endodontic Journal©2016 International Endodontic Journal. Published by John Wiley & Sons Ltd 3
with 5 mL of 2.5% NaOCl delivered during a 1-min
interval using a 30-gauge NaviTip needle (Ultra-
dent, South Jordan, UT, USA) adapted to a dispos-
able plastic syringe placed up to 2 mm short of the
WL, with a gentle in-and-out movement.
•Passive ultrasonic irrigation (PUI group): A total of
0.5 mL of 2.5% NaOCl was flushed into the canal
and ultrasonically agitated with an E1 Irrisonic tip
(0.20 mm in diameter; Helse Dental Technology,
S~
ao Paulo, Brazil) mounted on a piezoelectric
ultrasonic unit (Piezon 150, Electron Medical Sys-
tems, Nyon, Switzerland), with the power setting
at 10% (30 Hz). The tip was placed 2 mm coronal
to the WL, and an up-and-down motion without
touching the walls was applied for 20 s with inter-
mittent flux. The canals were then flushed with
1.67 mL of 2.5% NaOCl and activated for another
20 s. This latter procedure was repeated, and a
final irrigation was performed with 1.67 mL of
2.5% NaOCl. A total of 5 mL of 2.5% NaOCl was
used per canal during a 1-min activation time
(three cycles of 20 s). Replenishment of the irrig-
ant was performed using conventional syringe/
needle irrigation, as in the APP group.
•Self-adjusting File (SAF group): A total of 0.5 mL of
2.5% NaOCl was flushed into the canal using a
conventional needle/syringe technique and left to
stand for 1 min. Then, a 1.5-mm diameter SAF
instrument (ReDent-Nova) was inserted into the
root canal and operated to WL with an in-and-out
motion using a vibrating handpiece (GentlePower
Lux 20LP; KaVo, Biberach, Germany) combined
with a RDT3 head (ReDent-Nova). In this group, a
modified protocol was used with continuous irriga-
tion of 2.5% NaOCl (5 mL) applied for 1 min in
each canal using a special irrigation apparatus
(VATEA, ReDent-Nova).
•XP-endo Finisher (XPF group): an XP-endo Finisher
instrument was placed in a contra-angle hand-
piece (VDW GmbH), cooled down (Endo-Frost;
Roeko, Langenau, Germany) and removed from
the plastic tube in rotation mode by applying a lat-
eral movement. Each canal was filled with 0.5 mL
of 2.5% NaOCl, and the XP-endo Finisher was
inserted into it without rotation. Then, rotation
was turned on (800 rpm; torque of 1 N.cm) and
the instrument was activated for 1 min using slow
and gentle 7–8 mm lengthwise movements to the
full length of each canal. After that, the XP-endo
Finisher instrument was removed from the canal
and the final irrigation protocol performed with
5 mL of 2.5% NaOCl using syringe/needle irriga-
tion, as in the APP group.
After completion of the final irrigation procedures,
the solution was aspirated at the level of coronal ori-
fice and each root canal was slightly dried with one
absorbent paper point (WaveOne Small; Dentsply
Maillefer). A final micro-CT scanning was performed,
data sets were registered with their respective post-
preparation counterparts, and the vol% of AHTD in
each canal was calculated. Then, percentage reduc-
tion (red%) of the AHTD was calculated according to
the formula: 100[(V
AF
9100)/V
BF
], where V
BF
and
V
AF
are the volume of AHTD before and after the irri-
gation protocol, respectively. An examiner blinded to
the final irrigation protocol used in each specimen
performed all the measurements.
Matched colour-coded root canal models (green and
red colours indicating pre- and postoperative canal
surfaces, respectively) and debris (in black colour)
enabled qualitative comparison of the distribution of
the AHTD in each portion of the root canals, before
and after the experimental procedures.
Statistical analysis
Data were normally distributed (Shapiro–Wilk test)
and homoscedastic (Levene test). Therefore, results
were expressed as means and standard deviations and
compared between groups using one-way ANOVA post
hoc Tukey test, with a significance level set at 5%
(SPSS v17.0; SPSS Inc., Chicago, IL, USA).
Results
Mean volume, surface area and AHTD evaluated
before and after root canal preparation and irrigation
are detailed in Table 1. Pre- and postoperatively, the
degree of homogeneity (baseline) of the groups was
confirmed regarding length, volume and surface area
of the root canals, as well as, the vol% of AHTD after
preparation (P>0.05).
Reduction of AHTD was observed in all groups after
the final irrigation protocol. Overall, PUI and XPF
groups were associated with greater mean percentage
reductions of AHTD (94.1% and 89.7%, respectively)
than APP and SAF groups (45.7% and 41.3%, respec-
tively) (P<0.05). No significant differences were
found when comparing the results of PUI and XPF
groups (P>0.05) or APP and SAF groups
(P>0.05). Therefore, the null hypothesis was
rejected.
Hard tissue debris removal by irrigation Leoni et al.
©2016 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal
4
Three-dimensional models of representative mesial
root canals show the distribution of the AHTD after
preparation and irrigation protocols (Fig. 1). In gen-
eral, residual debris after final irrigation protocols in
the PUI and XPF groups was located at the apical
and coronal thirds, respectively, while in the APP and
SAF groups debris was commonly observed in both
middle and apical thirds.
Discussion
An isthmus has been defined as a narrow, ribbon-
shaped communication between two root canals that
contains pulp or pulpally derived tissue. In a review
of 15 studies, the presence of isthmus communica-
tions in the mesial roots of 1615 mandibular first
molars averaged 54.8% (de Pablo et al. 2010). In
clinical practice, this anatomical variation has been
considered one of the most difficult challenges for
proper cleaning and disinfection because mechanical
instrumentation of this area is unfeasible (Siqueira
et al. 2013). Thus, isthmus-containing mesial roots of
mandibular molars were selected for this study and
specimens were properly matched to reduce the
potentially significant anatomical biases that could
interfere with the results (Peters et al. 2001, Versiani
et al. 2013).
Although nondestructive micro-CT imaging analy-
sis cannot directly evaluate remaining soft tissue or
biofilm in the canal, it allows for a three-dimensional
quantitative and qualitative analysis of AHTD that is
not removed but rather transported into recesses dur-
ing root canal preparation (Paqu
eet al. 2009). In
infected canals, AHTD may contain bacteria and serve
as a nidus for root canal reinfection (Versiani et al.
2015). Besides, it has been claimed that AHTD in the
isthmus area may potentially interfere with disinfec-
tion by preventing irrigant flow and neutralizing the
antibacterial effects of the irrigating solution (Paqu
e
et al. 2012a). Therefore, improving irrigation is con-
ceivable the best way to prevent the formation or
remove accumulated debris (Gu et al. 2009, Haa-
pasalo et al. 2014).
The delivery of the irrigant solution has been tradi-
tionally achieved using syringe and needle irrigation,
and most publications that aimed to evaluate new
irrigation techniques use this approach as a control
(Gu et al. 2009, Haapasalo et al. 2014). Even though
some authors have recommended relatively high flow
rates (~0.25 mL s
1
) in positive irrigation protocols
(Boutsioukis et al. 2007, Khan et al. 2013), in a
Table 1 Pre- and postoperative parameters evaluated in the root canal system of 40 mesial roots of mandibular molars after different final irrigation protocols
Parameters
Preparation/
Irrigation
Final Irrigation Protocols
Apical Positive Pressure
(APP group; n=10)
Passive Ultrasonic Irrigation
(PUI group; n=10)
Self-adjusting File (SAF
Group; n=10)
XP-endo Finisher (XPF
group; n=10)
Mean SD Range Mean SD Range Mean SD Range Mean SD Range
Root Canal Volume (mm
3
) Before Prep. 6.62 2.03 3.9–10.8 6.77 2.59 4.1–10.6 6.88 1.81 4.0–9.4 6.73 2.27 3.7–12.2
After Prep. 10.05 2.01 7.3–14.0 10.03 3.06 6.4–15.5 10.78 1.17 8.9–12.8 9.88 2.62 6.9–16.3
Surface Area (mm
2
) Before Prep. 60.43 13.48 38.7–86.3 60.67 12.31 48.1–82.1 65.20 15.16 34.1–86.6 61.77 15.84 41.0–97.2
After Prep. 66.14 11.97 44.5–90.6 68.75 12.37 54.7–88.7 73.92 14.85 43.0–91.9 66.46 12.36 49.0–89.2
AHDT Volume (mm
3
) After Prep. 0.67 0.25 0.3–1.1 0.81 0.12 0.6–1.0 0.79 0.29 0.3–1.2 0.72 0.24 0.3–1.1
After Irrig. 0.36 0.12
a
0.1–0.5 0.05 0.05
b
0.0–0.2 0.47 0.22
a
0.2–0.8 0.08 0.09
b
0.0–0.3
Vol% After Irrig. 3.7 1.5
a
0.7–5.8 0.6 0.7
b
0.0–2.5 4.3 1.8
a
2.0–7.1 0.8 1.0
b
0.0–3.3
Red% 45.7 15.0
a
24.4–74.2 94.1 6.8
b
75.9–100.0 41.3 9.4
a
29.4–56.3 89.7 10.4
b
63.0–99.8
AHTD, accumulated hard-tissue debris; SD, standard deviation; Vol%, percentage volume of AHTD in relation to the canal volume after preparation; Red%, percentage reduction of
AHTD after irrigation protocols.
Different superscript bold letters in the same line mean statistical significant difference between groups (one-way ANOVA post hoc Tukey test; P<0.05).
Leoni et al. Hard tissue debris removal by irrigation
International Endodontic Journal©2016 International Endodontic Journal. Published by John Wiley & Sons Ltd 5
recent ex vivo study, a flow rate of 4 mL min
1
(or
0.066 mL s
1
) using a small-gauge needle positioned
3 mm from the working length, achieved the maxi-
mum effectiveness in the irrigant replenishment (Park
et al. 2013). In the present study, conventional syr-
inge irrigation was applied with an open-ended needle
placed 2 mm short of working length at a flow rate of
0.083 mL s
1
and was able to reduce the percentage
volume of AHTD by 45.7%. This result is corrobo-
rated by previous studies in which syringe irrigation
was unable to remove AHTD or soft tissue remnants
from the isthmus area of the mesial root canal system
of mandibular molars (Adcock et al. 2011, Endal et al.
2011, Paqu
eet al. 2011).
Few studies have attempted to use micro-CT tech-
nology to investigate the reduction of AHTD in isth-
mus-containing mesial roots of mandibular molars
(Paqu
eet al. 2011, 2012a,b, Freire et al. 2015, Ver-
siani et al. 2015). Overall, supplementary irrigation
procedures after root canal preparation with chelating
Figure 1 Distal views of representative 3D reconstructions of the mesial root canal systems of four representative mandibular
molars before (in green) and after (in red) preparation with reciprocating instruments and after a final irrigation protocol with
conventional irrigation, passive ultrasonic irrigation, Self-Adjusting File and XP-endo Finisher instrument. Accumulated hard-
tissue debris (AHTD) is depicted in black.
Hard tissue debris removal by irrigation Leoni et al.
©2016 International Endodontic Journal. Published by John Wiley & Sons LtdInternational Endodontic Journal
6
agents (Paqu
eet al. 2011, 2012a,b), ultrasonic agita-
tion (Paqu
eet al. 2011, Freire et al. 2015) and the
EndoVac system (Freire et al. 2015, Versiani et al.
2015) have resulted in less AHTD. Clinically, these
results can be translated into improved cleanliness in
areas within the root canal system generally
untouched by instruments during preparation proce-
dures (Nusstein 2015).
In the present study, the highest mean percentage
reduction of AHTD was observed after supplementary
protocols with PUI (94.1%; range: 75.9–100%) and
the novel XP-endo Finisher instrument (89.7%; range:
63.0–99.8%), compared to SAF (41.3%; range: 29.4–
56.3%) and conventional irrigation (45.7%; range:
24.4–74.2%) protocols. Previous studies have
reported a significant reduction in debris following
the use of PUI when compared to needle irrigation
(Lee et al. 2004a,b, van der Sluis et al. 2005a,b,
2006, 2007), which is in accordance with the present
results. The efficiency of PUI-activated irrigation has
been explained because of the production of acoustic
microwaves, cavitation and heat generation, favour-
ing the removal of tissue remnants and dentinal deb-
ris (Nusstein 2015). However, only two studies using
micro-CT technology evaluated the impact of PUI on
cleaning noninstrumented recesses of the root canal
system. In these studies, Paqu
eet al. (2011) reported
an overall debris reduction after EDTA irrigation and
PUI of 50.8 18.7%, while Freire et al. (2015)
reported that the use of PUI for irrigant activation led
to a 55.55% decrease in the percentage of debris vol-
ume. Therefore, half of the debris accumulated during
instrumentation could not be removed by the subse-
quent irrigating steps with PUI, which is disagree-
ment with the present results (94.1%). This higher
percentage value compared to those previously
reported (Paqu
eet al. 2011, Freire et al. 2015) might
be explained as the consequence of differences in the
methodological design including the type of root canal
configuration, preparation protocol (apical size and
taper), irrigant solution (concentration, volume and
flow rate), ultrasonic approach (tip type, activation
time and power setting) and the %vol of AHTD after
root canal preparation. Additionally, unlike these
studies, no chelating agent or intracanal aspiration of
irrigant solution was used to avoid the introduction
of confounding factors.
To date, only one study attempted to quantify
AHTD after using the SAF system in isthmus-contain-
ing mesial roots of mandibular molars (Paqu
eet al.
2012a). They reported that only 1.7% of the total
canal volume was filled with hard-tissue debris after
preparation with SAF. This value is lower than in this
study (4.3%) and might be explained by differences in
the methodological approach. Paqu
eet al. (2012a)
used the recommended protocol for SAF system to
prepare Type II mesial canals with a continuous flow
of 3% NaOCl delivered at 4 mL min
1
for 4 min,
while herein a modified protocol was used (5 mL of
2.5% NaOCl for 1 min) in previously prepared Type I
mesial canals. It is worth mentioning that the SAF’s
protocol was changed to reflect the clinical conditions
under which postoperative procedures are performed,
as recommended by the XP-endo Finisher and PUI
techniques. It explains the lower performance of the
SAF system in comparison with the other agitation
protocols, and further studies using its full irrigation
protocol with this methodological approach are
needed. In the XPF group, the percentage reduction
of AHTD (89.7%) was statistically similar to the PUI
(94.1%). This may be explained because of the highly
flexible proprietary alloy combined with the small
core size and zero taper of the XP-endo Finisher
instrument, which allowed it to expand its reach
when in rotation (FKG 2015, Trope & Debelian
2015). It is plausible to infer that this unique prop-
erty promoted the agitation of the irrigant solution
allowing the disruption of the hard tissue accumu-
lated within the isthmus area and its removal by the
final flushing action of the syringe/needle irrigation,
similarly to PUI. However, qualitative analysis demon-
strated that the XP-endo Finisher instrument was the
most effective technique on the removal of AHTD in
the apical third.
Although final irrigation protocols with PUI and
XP-endo Finisher instruments resulted in significantly
less mean percentage volume of AHTD (0.6% and
0.8%, respectively) compared to conventional irriga-
tion and SAF system (3.7% and 4.3%, respectively),
this result must be interpreted with caution because
this is only one indicator for the assessment of the
quality of root canal debridement. Besides, the clinical
relevance of AHTD remains unclear and further stud-
ies are necessary to evaluate its impact on the success
rate of the root canal treatment in isthmus-containing
canal system. Considering that none of the irrigation
protocols tested so far was able to render root canals
free of AHTD (Paqu
eet al. 2011, 2012a,b, Freire
et al. 2015, Versiani et al. 2015) and the high success
rate of the root canal treatment (Su et al. 2011), it
may be hypothesized that there is a threshold of
AHTD within the root canal system below which a
Leoni et al. Hard tissue debris removal by irrigation
International Endodontic Journal©2016 International Endodontic Journal. Published by John Wiley & Sons Ltd 7
favourable host response is expected. Then, maybe
the differences amongst the irrigant protocols tested
herein regarding AHDT reduction are unlikely to be
of clinical significance. Obviously, further studies are
necessary to evaluate the reduction of AHTD using
complex canal anatomies with different delivery sys-
tems, volume, flow and type of irrigation agents, as
well as, depth of insertion of different irrigation nee-
dles, ultrasonic tips and suction cannulas. Even
though it is difficult to draw reliable conclusions from
the literature because of the differences in method-
ological designs, a general agreement exists about the
benefits of using irrigant activation at the end of the
canal preparation (Nusstein 2015).
Conclusions
PUI and XP-endo Finisher instruments succeeded in
rendering the mesial root canal system with signifi-
cantly lower levels of AHTD compared with conven-
tional irrigation and the modified SAF system
protocol.
Conflict of interest statement
The authors have stated explicitly that there are no
conflict of interests in connection with this article.
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