Introduction
Endodontic retreatment aims to remove the filling material allowing cleaning and disinfection
of the root canal system.[1] However, the presence of root canals with curvature makes it difficult to remove
the filling material from the apical third in the root canal, contributing to the
failure of endodontic retreatment.[2]
[3]
Different endodontic sealers associated to gutta-percha are usually used for filling
root canals.[4] Sealers based on calcium silicate may be more difficult to remove during retreatment[5]
[6] in comparison to resin-based sealers. Furthermore, obturation techniques influence
the removal of the remaining filling material in curved root canals.[6] Thermoplastic obturation techniques provide a homogeneous filling,[7]
[8] making it difficult to remove the filling material.[6] Retreatment of curved root canals filled by the single-cone technique presented
similar removal of NeoMTA Plus (NuSmile, Houston, Texas, United States) or AH Plus
(Dentsply DeTrey GmbH, Konstanz, Germany).[9] However, no studies using continuous wave condensation technique with different
sealers evaluated the retreatment in curved root canals.
No retreatment technique using different instruments is able to completely remove
the remaining filling material,[10] especially in the apical third.[3] Thus, additional apical preparation using nickel–titanium (NiTi) instruments with
large diameter and small taper has been proposed to improve the removal of remaining
material in curved canals.[11]
[12] ProDesign Logic 50/0.01 (Easy Equipamentos Odontológicas, Belo Horizonte, Minas
Gerais, Brazil) has diameter of 50 and a small taper of 0.01. This instrument significantly
reduces the amount of filling material in the apical third of maxillary lateral incisors[11] and curved canals of mandibular molars.[12] However, no study evaluated this procedure in the retreatment using different sealers.
This study evaluated the percentage of remaining filling material in curved root canals
filled with NeoMTA Plus or AH Plus after retreatment with ProDesign R and the effectiveness
of the additional apical preparation using ProDesign Logic 50/0.01. The first null
hypothesis was that there would be no difference in removing filling material in root
canals filled with NeoMTA Plus or AH Plus. The second null hypothesis was that the
ProDesign Logic 50/0.01 instrument would not influence the percentage of remaining
filling material in curved canals.
Materials and Methods
Sample Size Calculation
G* Power 3.1.7 for Windows program (Heinrich-Heine-Universitat Dusseldorf, Dusseldorf,
Germany) was used for the sample size calculation. The t-test was used with an alpha-type error of 0.05 and beta power of 0.90. Previous study
was used to determine the effect size of 1.389.[9] A total of 12 specimens were indicated as being the ideal size required.
Specimen Selection
All procedures were approved by the University Ethics Committee (Protocol CAAE No.
64736116.4.0000.5416). Mandibular first and second molars stored in 0.1% thymol solution
at 5°C were used. The inclusion criteria were two independent mesial root canals,
type IV, according to configuration to the classification of Vertucci,[13] angle of curvature between 25 and 35 degrees by the method of Schneider,[14] and radius of curvature smaller than 10 mm,[15] besides complete apical formation, absence of root fractures, calcifications, or
internal resorptions. For this purpose, the specimens were selected by a digital radiography
system (Kodak RVG 6100 Digital Radiography System, Marne-la-Vallée, France) and micro–computed
tomography (micro-CT SkyScan 1176; Bruker-micro-CT, Kontich, Belgium). The first scanning
was performed at a low-resolution (isotropic voxel 35 µm) under the following settings:
copper and aluminum filter, exposure time of 87 ms, frame averaging 3, rotation angle
180 degrees, rotation step of 0.5, 80 kV X-ray tube voltages, and 300 µA anode current.
After the exclusion of all teeth that did not reach the inclusion criteria, 12 specimens
were selected. The specimens were embedded in condensation silicone (Oranwash, Zhermack
SpA, Badia Polesine, Italy) to simulate the periodontal ligament.
Root Canal Preparation
Conventional access cavities were performed, and the root canals were explored by
using a size no. 10 K-file (Dentsply Sirona, Ballaigues, Switzerland). The working
length (WL) was established 1-mm short from the apical foramen. All root canals were
prepared with ProDesign R (PDR; Easy Equipamentos Odontológicos, Belo Horizonte, Minas
Gerais, Brazil) 25/0.06, operated by electric motor VDW SILVER (VDW GmbH, Munich,
Germany) in “RECIPROC ALL” mode with in-and-out movements up to the WL. Root canals
were irrigated with 5 mL of 2.5% sodium hypochlorite (NaOCl; Ciclo Farma, Serrana,
São Paulo, Brazil) using a 5-mL syringe (Ultradent Products Inc., Salt Lake City,
Utah, United States) and a Navitip 30-G needle (Ultradent Products Inc.) at 2-mm short
of the WL. Final irrigation was performed using 5 mL of 2.5% NaOCL, 2.5 mL of 17%
EDTA (Biodinâmica, Ibiporã, Paraná, Brazil) under agitation for 3 minutes with a gutta-percha
cone size 25/0.06, followed by irrigation with 5 mL of distilled water.
Root Canal Filling
After preparation, the root canals were divided into two experimental groups (n = 12), using stratified random sampling, considering the volume of prepared canals.
The root canals were filled with NeoMTA Plus or AH Plus ([Table 1]) by the continuous wave of condensation technique—Thermo Pack II (Easy Equipamentos
Odontológicos, Belo Horizonte, Minas Gerais, Brazil).
Table 1
Materials, their manufacturer, composition, and proportions used
|
Materials
|
Manufacturer
|
Composition
|
Proportion
|
|
NeoMTA Plus
|
NuSmile, Houston, Texas, United States
|
Powder: tricalcium silicate, dicalcium silicate, tantalum oxide, tricalcium aluminate,
and calcium sulfate. Liquid/gel: water-based gel with thickening agent and water-soluble
polymers
|
0.33 g powder:150 μL liquid/gel
|
|
AH Plus
|
Dentsply DeTrey GmbH, Konstanz, Germany
|
Bisphenol-A epoxy resin, bisphenol-F epoxy resin, calcium tungstate, zirconium oxide,
silica, iron oxide pigments dibenzyl-diamine, aminoadamantane, silicone oil
|
1 g:1 g (paste/paste)
|
Gutta-percha cones 25/0.06 (Tanariman, Manacapuru, Amazonas, Brazil) were selected
according to the tip size and taper measured in the profilometer (Profile Projector
Nikon Model 6C-2; Nikon, Tokyo, Japan). After the radiographic evaluation of the gutta-percha
cone selected, the sealer was placed into root canal using a Lentulo 25 instrument
(Dentsply Sirona) and manual K-file 25 pre-curved (Dentsply Sirona). After this, the
gutta-percha cone covered by one of the endodontic sealers was placed in the root
canal. The thermoplastic plugger from Termo Pack II System was used to plasticize
and cut the gutta-percha. The compaction of the gutta-percha was performed using NiTi
condensers (Easy Dental Equipamentos, Belo Horizonte, Minas Gerais, Brazil) within
the apical root canal up to 3 mm of the working length. After this, the thermal gutta-percha
injector was used to inject the warmed gutta-percha. Compaction was performed with
NiTi condensers (Easy Dental Equipamentos, Belo Horizonte, Minas Gerais, Brazil).
A radiograph was taken in the buccal-lingual and mesiodistal to verify the quality
of the obturation.
After filling the root canals, each sample was sealed with provisional Coltosol (Vigodent,
Rio de Janeiro, Rio de Janeiro, Brazil) restorative material and kept in an oven at
37°C, in 95% humidity, for 7 days to allow the sealers to set completely.
Root Canal Retreatment
After removing the temporary restorations, all root canals were retreated with ProDesign
Logic RT (PDL RT; Easy Equipamentos Odontológicos, Belo Horizonte, Minas Gerais, Brazil)
and PDR systems, operated on an electric motor VDW SILVER. PDL RT 25/0.08 instrument
was operated in rotary motion at 600 rpm and torque 3 ncm, with in-and-out movements
to remove the cervical and middle third filling. PDR 25/0.06 instruments were activated
in “RECIPROC ALL” mode, with in-and-out movements, up to WL to remove apical third
filling. The root canals were enlarged with PDR 35/0.05 as described above. Each root
canal was irrigated with 6 mL of 2.5% NaOCl (2 mL for each instrument). Final irrigation
was performed, as described in the preparation step.
Additional Apical Preparation
Following the retreatment procedures, an apical enlargement was performed with ProDesign
Logic (PDL) 50/0.01. The instrument was operated on an electric motor VDW SILVER,
in rotary motion, at a speed of 350 rpm and torque 1 ncm, with in-and-out movements
up to the WL. The root canals were irrigated with 2 mL of 2.5% NaOCl. Final irrigation
was performed as previously described.
Micro–Computed Tomography Scanning and Analysis
The roots were scanned using SkyScan 1176 micro-CT before and after retreatment procedures.
The roots were positioned in a standardization device, allowing the specimens to remain
in the same position during scanning procedures. The scanning parameters were copper
and aluminum filter, 90 kV X-ray tube voltages, 278 µA anode current, exposure time
of 125 ms, rotation angle of 180 degrees, rotation step of 0.5, frame averaging 4,
and isotropic voxel of 8.74 µm. The images obtained were reconstructed using the NRecon
software (v.1.6.3; Bruker-micro-CT) and were superimposed using geometric alignment
in the Data Viewer software (v.1.5.1; Bruker-micro-CT). Volumetric analysis was performed
in all root canals using CTAn software (v.1.14.4; Bruker-micro-CT) with specific task
lists. Root canal volume and remaining filling material were quantified after retreatment
steps. The grayscale range required to recognize each object under study was determined
in a density histogram using the adaptive threshold method. The following formula
was used to obtain the percentage remaining filling material: percentage remaining
filling material = (filling material after retreatment × 100 / filling material before
retreatment). The evaluation was performed in the apical third and cervical/middle
thirds of the root canals. The value of approximately 9 mm was determined for the
total length analysis and approximately 3 mm for the apical third and 6 mm for cervical/middle
thirds. Representative images were performed using CTVox software (v.3.2; Bruker-micro-CT).
Statistical Analysis
The data were submitted to the Shapiro–Wilk normality test. The no-paired t-test was used to compare groups. The paired t-test was used to compare the root canals retreatment before and after additional
apical preparation with PDL 50/0.01. The level of significance was 5% for all the
analyses.
Results
The percentage of remaining filling material was similar between the root canals filled
with AH Plus or NeoMTA Plus sealer after the retreatment procedure with PDR 35/0.05
and after additional apical preparation with PDL 50/0.01 (p > 0.05; [Table 2]). PDL 50/0.01 significantly decreased the percentage of remaining filling material
in the apical third after the additional apical preparation (p < 0.05; [Table 2]; [Fig. 1]).
Table 2
Means and standard deviations of the percentage of remaining filling material before
and after additional apical preparation with ProDesign Logic 50/0.01 in curved root
canals filled by continuous wave of condensation with NeoMTA Plus or AH Plus sealers
|
|
Before PDL 50/0.01
|
After PDL 50/0.01
|
Reduction in residual filling material (%)
|
|
NeoMTA Plus
|
Cervical/middle
|
15.98 ± 4.76[a]
|
14.05 ± 5.98[a]
|
8.43 ± 1.87
|
|
Apical
|
13.04 ± 8.06[a]
|
7.24 ± 5.50[b]
|
48.76 ± 7.31
|
|
AH Plus
|
Cervical/middle
|
14.56 ± 5.28[a]
|
13.76 ± 4.27[a]
|
8.04 ± 2.34
|
|
Apical
|
19.83 ± 9.34[a]
|
8.63 ± 3.38[b]
|
54.87 ± 8.21
|
Note: The percentage of reduction in residual filling material was also described.
There was no statistical difference between the groups (p > 0.05).
a,b Values represent significant differences intragroup (p < 0.05).
Fig. 1 Three-dimensional reconstructions and cross-sectional images of mesial root canals
of mandibular molars after the steps of retreatment and additional apical preparation
with ProDesign Logic (PDL) 50/0.01. Remaining filling material is showed in red.
Discussion
The percentage of remaining filling material in the cervical/middle and apical thirds
was similar between the root canals filled with NeoMTA Plus and AH Plus. Thus, the
first null hypothesis was accepted. A previous study showed similar result when comparing
the retreatment between NeoMTA Plus and AH Plus.[9] These results can be attributed to the mechanical and physical properties of the
evaluated sealers. NeoMTA Plus presents small particles[16] and ability to penetrate into dentinal tubules.[17] In addition, the higher bond strength of NeoMTA Plus when compared with Biodentine
(Septodont, Saint-Maur-des-Fosses, France) and White ProRoot MTA (Dentsply Tulsa Dental,
Oklahoma, United States) and the higher resistance to dislodgment of AH Plus than
MTA Fillapex (Angelus, Londrina, Paraná, Brazil) and EndoSequence BC Sealer (Brasseler,
Savannah, Georgia, United States)[16]
[18] may favor their interaction with the dentin surface for both sealers.
Several mechanized systems with different kinematics have been proposed for endodontic
retreatments.[10] Rotary motion increases the gutta-percha removal to the cervical direction, reducing
the compaction of filling material in the apical third.[19] On the other hand, the reciprocating motion improves the torsional and cyclic fatigue
resistance of the instruments,[20] allowing safer apical preparation of curved root canals, and filling removal similar
to the rotary kinematics.[10] Therefore, the aforementioned statements justify the use of a PDL RT 25/0.08 in
the cervical and middle thirds, and PDR 25/0.06 in the apical third for the retreatment's
procedures in the present study. Subsequently PDR 35/0.05 reciprocating file was used,
since apical enlargement larger than the initial root canal preparation is indicated
to improve filling material removal[9]
[10] and does not influence in the postoperative pain.[21]
[22] However, a considerable amount of remaining filling material could be observed in
all root canals since rotary and reciprocation instruments cannot completely remove
the filling material.[10]
The apical third is considered a critical zone due to the difficulty of cleaning and
disinfection.[23] Therefore, the apical enlargement allows greater contact of the instrument and dentin
walls reducing debris, providing better effect of the irrigating solution[24] and root canal filling.[25] In addition, the decrease of residual filling material was observed after apical
enlargement from size 25 to 40,[26] with a success rate of 90.4% after 2 years.[27] Although our study showed a percentage of remaining material less than 20% in the
apical third after apical enlargement, the complete removal of filling material was
not possible.
Additional apical preparation using in the retreatment are encouraged since previous
studies observed better filling removal after retreatment in curved canals.[9]
[12] In our study, PDL 50/0.01 decreased the percentage of remaining filling material
in the apical third for both sealers. Thus, the second hypothesis was partially rejected.
Similar result was observed when PDL 50/0.01 was used in curved root canals filled
with AH Plus.[12] In addition, the small and constant taper 0.01 avoided unnecessary dentin removal
in the cervical/middle thirds, preventing root weakening[26] and favoring less material extrusion.[28] In agreement, previous investigation showed the safety of this file during retreatments
of curved canals since PDL 50/0.01 has high flexural strength and provides apical
enlargement with no root canal transportation.[12]
Curved root canals may favor the occurrence of apical transportation, zipping or crack
formation during preparation, and retreatment procedures, with impair the treatment
outcome.[2]
[29] Mesial root canals of mandibular molars with a curvature of 25 and 35 degrees were
used in the present study representing moderate root curvatures.[30] Scanning in micro-CT using lower resolution (35 µm) has been performed to the initial
selection of samples.[8] It is important to highlight that the sample distribution was performed by simple
stratified randomization considering the preparation volume of the root canals. A
systematic review reported that few studies performed adequate randomization of samples.[31]
ProDesign Logic 50/0.01 appeared to be effective in removing the remaining material
filling in the apical third in curved root canals. The use of strategies, such as
additional apical preparation, can influence the success of endodontic treatment.
Conclusion
Within the limitations of the present study, it can be concluded that NeoMTA Plus
or AH Plus did not influence the retreatment of curved root canals. ProDesign Logic
50/0.01 promoted greater remaining filling material removal in the apical third.
