Keywords
endodontic - X-ray Micro-CT - root canal filling - root canal preparation
Introduction
The success of endodontic treatment is based on obtaining adequate antisepsis and
root canal filling, followed by dentistry rehabilitation and functional recovery of
the involved tooth.[1]
[2] Infection control is obtained by chemical strategies using endodontic irrigation
systems as solutions with antimicrobial activity and solvent of organic matter in
association with mechanical endodontic instruments.[3]
However, the chemical-mechanical preparation of the root canals can be impaired by
local anatomic complexity since in isthmus area the endodontic instruments do not
act effectively, as well as the action of irrigation solutions, such as sodium hypochlorite,
is drastically minimized.[4]
[5] Also, stainless steel instruments showed restriction of use, as reduced flexibility
and low torsional strength, providing inadequate cleaning of the pulp cavity, especially
in root canals of mandibular molars.[3]
[4]
[5]
Through the introduction of the endodontic nickel-titanium (NiTi) alloy, new endodontic
instruments have been designed and manufactured, allowing its use in mechanically
automated systems, with different types of kinematics, such as continuous or reciprocating
rotation motion, in root channels with different anatomical characteristics.[2]
[6]
[7] This technology allowed to optimize the chemical-mechanical preparation phase.[8]
[9]
[10]
Because of the good acceptance and clinical performance of this metal alloy, endodontic
instruments and/or clinical strategies have been refined leading to several mechanized
instrumentation systems, such as the twisted file (TWF), Reciproc R25 (RCP), and self-adjusting
file (SAF).[3]
[11] Different of traditional continuous mechanized rotation systems using NiTi instruments,
the TWF consists of rotatory instruments subjected to torsion and a specific heat
treatment, which provide satisfactory flexural strength and separation during root
canal instrumentation.[1]
[7]
[8]
On the other side, the minimally invasive concept with greater preservation of the
dental structure has gained attraction. Therewith, it has arisen the alternate rotatory
instrumentation systems (Reciproc), with the use of an instrument that is virtually
unique in the extension of instrumentation.[3]
[10]
[11]
[12] However, preparation of the root canal, mainly those of oval section and/or in areas
of root isthmus can be insecure, due to the kinematics proposed for its use.[12]
[13]
The SAF system has been proposed to minimize this deficiency, since it consists of
a single instrument associated with expandable devices, that friction with the dentin
surface of the root canal, under continuous irrigation.[3]
[12]
[14] However, there is still a lack of studies evaluating its effectiveness and productivity
during endodontic treatment.
Though we have observed a great technological advance in relation to instruments and
techniques of endodontic instrumentation, proper modeling of the pulp cavity is crucial
for endodontic filling in a more practical, reliable, and compact manner.[15]
[16] The modified continuous wave compaction (MCWC) technique of endodontic obturation
provides a vigorous cervical-apical condensation of the gutta-percha and endodontic
cement, promoting the filling of voids spaces in the root canal.[16]
[17]
[18] However, the quality of root canal modeling offered by instrumentation systems may
have effects on the final result expected to be obtained by endodontic filling.[16]
The interaction among the type of final preparation provided by the instrumentation
systems described previously and the final result proportionated by CWC can be evaluated
through the incidence of voids in the root canal, after endodontic obturation, by
means of micro-computed tomography (micro-CT) analysis, since it is a three-dimensional
and noninvasive evaluation technique.[13]
[14]
Therefore, the aim of this study was to evaluate the influence of mesiobuccal root
canal preparation of mandibular molars with the RCP, the SAF, and the TWF, on the
incidence of voids in endodontic obturation by the MCWC technique, by analysis of
images produced by micro-CT, in the cervical–middle and apical thirds or in the entire
extension of the root canal. The inexistence of differences in the incidence of voids
in each third or in all extension of the root canal was considered as the null hypothesis
(H0).
Materials and Methods
This research study was submitted to the Ethics Committee on Human Research of Estácio
de Sá University, registered and approved by this committee under protocol number
CAAE 0182.0.308.000–08.
Preparation of Samples
Fifteen human mandibular molars were extracted for orthodontic or periodontal purposes,
containing fully formed roots with similar internal and external root morphology,
and similar crown-apical dimension. The teeth were preserved in a 10% formalin solution
until the moment of use.
Coronary access has been performed with diamond burs (FG 1012; KG Sorensen, Cotia,
São Paulo, Brazil), at high rotation and under continuous irrigation. Thereafter,
both independent mesial canals were explored with files #10K (Maillefer Dentsply,
Pirassununga, SP, BR) and after observing the two independent foramen openings, the
Glyde path was performed with the file #15K (Maillefer Dentsply, Pirassununga, SP,
BR), under irrigation with 5 mL of 2.5% sodium hypochlorite solution (Rioquímica,
São José do Rio Preto, SP, BR).
The teeth were buccolingual sectioned using a diamond disk (Vortex, Sao Paulo, SP,
BR) in the area of the pulpal chamber, under constant refrigeration. Fifteen mesial
roots with two independent root canals were obtained and verified by radiographs in
the mesiodistal direction. Subsequently, the total root length was determined from
the mesiovestibular cusps until visualization of #15K file penetration guide, in the
foraminal opening. The working length (CT) was determined at 1 mm below to the total
root length.
Preparation of Experimental Groups
Fifteen mesial roots contained 30 root canals that were randomly divided into three
groups (n = 10 root canals, in 5 roots/group) and distributed according to the root canal instrumentation
protocols:
RCP (VDW, Munich, Germany): After obtaining the glide path described previously, the
root canal was prepared with the RCP instrument (VDW, Munich, Germany) adapted to
a specific counter-angle, activated by an electric motor (VDW, Munich, Germany) in
alternative rotatory motion. The instrumentation progression was performed with discrete
movements with amplitude of approximately 3 mm in the cervicoapical and apicocervical
directions.
After each progression in the apical direction, the root canal was irrigated with
5 mL of 2.5% sodium hypochlorite solution (Rioquímica, São José do Rio Preto, SP,
BR) using 30-gauge irrigation cannula (Navitip; Ultradent, Southern Jordan, Utah,
United States) and apical patency properly verified with file #15K in exploratory
endodontic movement. The instrumentation procedure was performed again until the working
length was reached. The instrument was discarded after each use, and a new instrument
was used in each root.
SAF (Redent-Nova; Raánana, IL): The root canal was submitted to a previous modeling
until the working length, with the instrument #25/.04 (Bio RaCe BR2; FKG Dentaire;
Le Crêt-du-Locle, CH) adapted to a specific low speed hand piece and an electric motor
(VDW, Munich, Germany) in continuous rotation, at 600 rpm and torque of 1.5N.
Thereafter, the root canal was irrigated with 5 mL of 2.5% sodium hypochlorite solution
and submitted to apical patency with #15K file. A SAF instrument of 1.5 mm diameter
and 25 mm length was adapted to a RDT3 contra angle (Redent-Nova Inc; Ra'anana, IL),
correctly adapted to a specific handpiece (GENTLEpower; Kavo, Biberach Riss; GE).
The instrument was introduced into the root canal, the motor was started with a constant
vibratory motion (5.000 vibrations/minute) and an amplitude of 0.4mm to reach the
working length, with discrete movements in the cervicoapical and apicocervical directions.
During preparation of the root canal, the SAF system was connected of a silicone tube
to the VATEA (Redent-Nova Inc; Ráanana, IL) system irrigation that provided continuous
irrigation with 2.5% sodium hypochlorite solution.
TWF (SybronEndo, Orange, CA, EUA): The root canal was instrumented, into a gradual
crown down technique, by inserting files #25/.08TF, #25/.06TF and #25/.04TF adapted
to the specific low speed hand piece and an electric motor (VDW, Munich, Germany),
at 500 rpm and 1 N/cm2 of torque, until the working length under continuous irrigation. After the use of
each instrument, the root canal was irrigated with 5 mL of sodium hypochlorite at
2.5% and the apical patency was conferred with to the hand file #15K. The final shaping
of the root canal was performed again with instrument #25/.06 at working length.
All root canals were submitted to final irrigation with 5 mL of 2.5% sodium hypochlorite,
aspirated, filled with 17% EDTA (Biodinâmica, Ibiporã, PR, BR) and kept for 1 minute.
Then, the root canals were irrigated again with 2.5% sodium hypochlorite, followed
by suction and drying with absorbent paper points (MKLife, Porto Alegre, RS, BR).
Root Canal Filling
First, it was selected the master gutta-percha cone. In RCP, the cone system was used
and for the others systems the MF cone was adapted at the working length. The root
canal was filled with zinc oxide and eugenol sealer based endodontic cement (Pulp
Canal Sealer; SybronEndo, Orange, CA, EUA) inserted with a Lentulo spiral (Dentsply
Maillefer, Pirassununga, SP, BR).
Afterward, the master gutta-percha cone was sliced at approximately 3 mm of the working
length extension with the cutting device obturation (E & Q Plus; MetaBiomed, Chungbuk,
KOR). Thereafter, it was performed a vertical compaction with a gutta-percha condenser.
The obturation of cervical and middle thirds of the root canal was made with thermoplasticized
gutta-percha by using a thermoinjection device (E & Q Plus; MetaBiomed, Chungbuk,
KOR). A new cold vertical condensation was performed after inserting 3 mm of heated
gutta-percha into the root canal, as described by Buchanan[15] and Girelli et al.[16]
Incidence of Voids
The images of the specimens were obtained individually by micro-CT analysis (Skyscan
1176; Skyscan, Kontich, BE) as described by Versiani[3] to evaluate the incidence of spaces voids in the total volume and in the cervical-medial
and apical thirds of the root canal obturation. The images were obtained with an isotropic
voxel of 19.96 mm. The pictures were individually reconstructed using NRecon v.1.6.6.0
software (SkyScan, Konitich, BE).
Images were processed and analyzed with CTAn v.1.11.8 assistance program. Initially,
it was obtained the total volume of the root canal area to be evaluated, and thereafter,
the total volume of endodontic filling material present. The difference between root
canal volume, and/or the third analyzed, and the volume filled by the endodontic obturation
was obtained (in mm3). The value obtained for this difference was converted into a percentage of voids
space, in relation to the total volume or third under review of the root canal. Thus,
the volumetric percentage of voids was obtained.
Statistical Analysis
The data were evaluated using the Kruskal–Wallis and Dunn test, with a 5% significance
level. The nonparametric distribution of the results allowed the application of the
Kruskal–Wallis variance analysis test. Dunn method was used for the comparison between
two groups (p < 0.05).
Results
Total Volume Evaluation of Root Canal
The hierarchical sequence from lowest to highest incidence of spaces voids was TWF,
RCP, and SAF. However, there was only a significant difference in the incidence of
spaces voids between TWF and SAF (p < 0.05). No differences were observed in the incidence of voids between TWF and RCP
or RCP and SAF (p > 0.05).
[Table 1] shows the medians, maximum, and minimum values of the first and third quartile of
voids incidence (in percentage) in endodontic obturation and in relation to the total
volume of the root canal, after root canal preparation with different instrumentation
protocols.
Table 1
Median, maximum, and minimum value of the first and third quartile of the incidence
of voids spaces (in percentage) in endodontic obturation, in relation to the total
volume of the root canal
|
Third
|
|
RCP
|
SAF
|
TWF
|
|
Total
|
Median
|
7.31[ab]
|
9.86[b]
|
5.93[a]
|
|
Vmax–Vmin
|
11.97–2.82
|
15.02–5.76
|
7.97–4.48
|
|
1° e 3 ° Q
|
5.99–10.89
|
8.59–10.39
|
5.24–6.73
|
Abbreviations: Q, quartile; RCP, Reciproc; SAF, self-adjusting file; TWF, twisted
file; Vmax, maximum value; Vmin, minimum value.
a,b Different letters on the same median line indicate significant differences in the
incidence of voids spaces (p < 0.05).
[Fig. 1] demonstrates a micro-CT image of the endodontic obturation and spaces voids within
the root canal, after MCWC technique, according to the chemical–mechanical protocol
used.
Fig. 1 Representative micro-computed tomography image of the specimens demonstrating endodontic
obturation using the continuous wave compaction technique, as a function of root canal
instrumentation protocols. (A) Reciproc protocol, (B), self-adjusting file protocol, and (C) twisted file protocol.
Evaluation of the Cervical, Middle, and Apical Third
Regarding the apical segment, RCP provided a lower incidence of voids compared with
SAF (p < 0.05). There was no difference between TWF and RCP or RCP and SAF (p > 0.05). Regarding the cervical–middle third, TWF provided a lower incidence of spaces
voids in the endodontic obturation compared with SAF (p < 0.05), but there were no differences between TWF and RCP or RCP and SAF (p > 0.05).
[Table 2] shows the medians, maximum and minimum values, and the first and third quartile
of the incidence of spaces voids (in percent), in the apical and cervical–middle root
thirds, after root canal preparation with different instrumentation protocols.
Table 2
Median, maximum, and minimum value of the first and third quartile of the incidence
of voids spaces (in percentage) in the apical and mid-cervical segments of the radicular
|
Third
|
|
RCP
|
SAF
|
TWF
|
|
Apical
|
Median
|
9.70[a]
|
16.57[b]
|
11.17[ab]
|
|
Vmax–Vmin
|
24.77–4.22
|
36.66–4.11
|
14.93–5.23
|
|
1° e 3 ° Q
|
7.22–11.19
|
14.20–19.13
|
9.27-12.59
|
|
Cervical
Medium
|
Median
|
8.36[ab]
|
9.07[b]
|
5.86[a]
|
|
Vmax–Vmin
|
12.09-2.92
|
13.41–6.93
|
8.10–3.44
|
|
1° e 3 ° Q
|
6.36–9.87
|
7.40–9.17
|
4.97–6.95
|
Abbreviations: Q, quartile; RCP, Reciproc; SAF, self-adjusting file; TWF, twisted
file; Vmax, maximum value; Vmin, minimum value.
a,b Different letters on the same median line indicate significant differences in the
incidence of voids spaces (p < 0.05).
Discussion
This study analyzed the incidence of voids in endodontic obturation performed by the
MCWC technique according to different mechanized instrumentation protocols of the
root canal. Based on the results obtained, the null hypothesis was rejected, as there
were significant differences in the incidence of voids in endodontic obturation, after
different mechanized instrumentation protocols for root canals.
The adequate chemical–mechanical preparation of the root canals is crucial for performing
endodontic obturation, to provide local antisepsis and shaping of the pulp cavity.[17] With these well-executed procedures, there will be a optimization of operative procedures,
preventing the formation of voids that can compromise the success of endodontic treatment.[18]
In this study, we used the mesial root canal of human extracted mandibular molars
containing two independent root canals with anatomical similarity, to perform an evaluation
as close as possible to the clinical situations.[8]
[19]
[20] With this methodology, it was possible to verify the direct interaction of different
instrumentation protocols with the dentin substrate on the final performance of MCWC
technique, through the incidence of the voids, preventing external interferences,
such as experiments performed on resin blocks and/or similar.[7]
[13]
[21]
The images obtained in micro-CT allowed a quantitative analysis, without destruction
of the sample, of the incidence of voids in obturation performed by the modified continuous
wave condensation technique after shaping of the root canal by different instrumentation
protocols, whereas parameters adopted for the study were obtained by a pilot study.[11]
[22]
[23]
[24]
[25]
[26]
The incidence of voids in endodontic obturation performed by CWC was lower after root
canal instrumentation with the TWF protocol, when evaluated in the total volume or
in the cervical–middle third of the root canal, compared with that provided by the
SAF protocol. Interestingly, RCP protocol provided a smaller incidence of voids only
in apical third in comparison to the SAF.
The incidence of condensation failure in endodontic obturation, interpreted as voids,
is relatively frequent on account of the anatomical complexity of the pulp cavity.[25] The mechanical preparation phase aims to shape the root canal, eliminating and/or
minimizing interferences that hinder access to the foraminal opening, therefore facilitating
the compaction of the sealing material.[27]
[28]
[29]
[30]
Thus, some items may have contributed to the results of this study: 1. final shaping
characteristic provided by the instrumentation protocols; 2. adaptation of gutta-percha
cone in the entire root canal thirds; 3. type and interaction of the obturation technique
of the cervical–middle third with the dilatation provided by the protocols and instrumentation.[3]
[27]
[28]
[29]
[30]
The incidence of voids in the endodontic obturation after preparation with the SAF
protocol can be attributed to the smaller dilatation of the root canal, since the
first preparation was made with the instrument #25/.04 and the final magnification
provided only by abrasion of the SAF instrument on the root dentin that is relatively
minimal.[29]
[30] Therewith, there was a greater difficulty in vertical condensation due to the lack
of adaptation of the manual condensers in relation to the root canal diameter.
Conversely, the TWF protocol was finished with instrument #25/.06 and consequently
in the cervical–middle third the enlargement and straightening of the root canal was
greater factor that optimized the filling material condensation.[3]
[18]
[19] However, in this protocol, instruments #25/.08 and #25/.04 were also used, which
may have caused similar root canal enlargement, compared with that provided by preparation
with the #25/.08 alternating-rotation instrument of the RCP system, parameter that
justifies the similarity of results also in the cervical–middle third.[8]
[9] Interestingly, also in this third, the RCP and SAF protocols provided a similar
incidence of void in endodontic filling, possibly due to the lower magnification provided,
but not significant compared with TWF, which was close to that of the SAF protocol.
The apical third, the RCP protocol provided the lowest incidence of voids due to the
main gutta-percha cone being that of the system itself. Although Metzger et al.[29]
[30] observed a better adaptation of gutta-percha to the pulp cavity after instrumentation
with SAF, but using the active lateral condensation technique.
The final shaping of the root canal provided by the instruments is another factor
that may also have contributed to the results obtained, since the instruments were
specific to each system itself. The SAF has peculiar geometrical and dynamics characteristics
of operation, working mainly by an abrasive action on dentin, maintaining the original
morphological characteristics of canal.[28] Contrarily, the RCP and TWF protocols have instrument taper defined, which allowed
a constant and standardized enlargement along the entire length of the root canal,
resulting in more uniform dilatation than the SAF system, independently of the root
canal third.[24]
[28]
[30]
The previous expansion of the cervical–middle third of the root canal may have had
an effect on the incidence of voids in the endodontic obturation, since when using
the SAF protocol alone there is a more uniform dilatation of this third, which will
lead to greater homogeneity of endodontic obturation.[5] In this study, the previous preparation with #25/.04 BioRace BR2 was performed,
resulting in a larger volume to be filled by the CWC.
Despite proving doubts and opening avenues for a good clinical understanding between
mechanized instrumentation protocols and CWC provided by this study, some limitations
should be highlighted, such as the need for further study with a larger sample size,
evaluation with other cementation and/or root canal filling strategies and with new
continuous wave compaction equipment.
Conclusion
Root canal preparation of the mesial root of mandibular molars using the TWF system
instrumentation protocol provides a smaller incidence of voids in endodontic obturation
performed by the MCWC technique.
