Keywords oval-shaped canals - gutta-percha-filled area - sealer - voids - filling techniques
Introduction
Endodontic treatment aims to maintain or reestablish the health of periapical tissues
by cleaning and filling the root canals.[1 ]
[2 ] Biomechanical preparation and intracanal dressing (when used) are responsible for
disinfection; however, they are not able to completely eliminate the root canal system
content.[3 ]
[4 ] Therefore, an effective root canal filling must be performed to maintain cleanliness,
trap remaining microorganisms, interrupt the supply of nutrients needed for their
survival, and avoid contamination or recontamination.[5 ]
Obturation has most commonly been performed with gutta-percha and a sealer. Schilder[1 ] and Epley et al[6 ] suggested that root canal filling material should adapt adequately to the canal
walls as well as its irregularities. Furthermore, it is important that gutta-percha
be placed along the entire length of the canal, be densely compacted, and consist
of a homogeneous mass. For this reason, a widely used strategy to evaluate the quality
of obturations is to analyze the percentages of areas filled with gutta-percha, sealer
and voids (PGFA, PSFA, and PVFA, respectively).[7 ]
[8 ]
The cold lateral condensation technique (CLCT) is the most common approach used in
endodontic clinics. Its advantages include relative ease of use, low cost, predictability,
and controlled placement. However, this technique has been known to leave voids, use
an excessive amount of sealer, and be deficient in adapting gutta-percha adequately
to root canal walls.[5 ]
The warm vertical condensation technique enables gutta-percha to be provided in a
homogeneous and dimensionally stable mass; this makes it easier for the material to
penetrate root canal system ramifications. This technique has been simplified by certain
recently introduced devices such as System B (SybronEndo; Orange, California, United
States). This or similar equipment allows the heating of the filling material in a
single step. Moreover, this approach leads to the creation of the continuous wave
of condensation technique (CWCT). CWCT is not only a more costly technique, requiring
specific equipment, but it also promotes higher extrusion of filling materials.[5 ]
No obturation technique can completely fill the root canal.[5 ] This limitation is even more critical in teeth with oval canals, such as the mandibular
incisors.[9 ]
[10 ] For this reason, different materials,[11 ]
[12 ] techniques,[13 ]
[14 ] and modifications[15 ]
[16 ] have been proposed and studied using several methodologies.[17 ]
[18 ]
One of the preferred tools to assess the adhesive interface and the topographic features
of the root canal filling is confocal laser scanning microscopy (CLSM). It stands
out because it allows samples to be measured in depth despite a wet environment. A
fluorescent dye is used to mark root canal sealers so that they can be analyzed under
CLSM. Certain dyes are added to sealers to cause certain wavelengths to excite the
marked structure for the purpose of making the spectrum visible. CLSM is capable of
accurately determining the degree of adaptation and penetration of the root canal
filling materials.[18 ]
This in vitro study aimed at determining PGFA, PSFA, and PVFA in oval-shaped root
canals obturated with CLCT and CWCT and assessing two respective procedural modifications
using CLSM.
Materials and Methods
Tooth Selection
Sixty extracted human mandibular central incisors were selected for this study after
approval by the University Research Ethics Committee (no. 5690/11). The selection
was based on acquiring teeth with straight and single root canals ending in just one
main apical foramen, without radicular cracks, resorption process, or other anatomical
complexities, and with prior endodontic treatment. Buccal and proximal radiographs,
and a stereomicroscope under 20× magnification (Expert DN; Mueller-Optronic, Erfurt,
Germany) were used to confirm these features. The teeth were kept in a 0.1% thymol
solution at 4°C until use.
Root Canal Shaping and Filling
The roots of the teeth were standardized at 14 mm in length by sectioning tooth crowns
with a low-speed steel cutting disc (IsoMet, Buehler, Lake Bluff, Illinois, United
States). Root canal orifices were prepared with a 3082 tapered-tip bur (KG Sorensen,
São Paulo, Brazil) and a Largo No. 2 drill (Dentsply-Maillefer, Ballaigues, Switzerland),
whereas cervical and middle thirds were prepared using Gates-Glidden No. 3 and No.
2 drills (Dentsply-Maillefer). The working lengths (WLs) were established at 1 mm
short of the point where a 15-K file (Dentsply-Maillefer) was visible at the apical
foramen.
Instrumentation of root canals used the crown-down technique and rotary ProTaper instruments
(Dentsply-Maillefer) up to size F3 at the WL. At each change of file, the canals were
irrigated with 2.5 mL of 2.5% NaOCl (Fórmula & Ação, São Paulo, Brazil) prepared immediately
before, together with a flush of 3 mL of 17% ethylenediaminetetraacetic acid (EDTA)
(Fórmula & Ação) for 3 minutes. The final rinse consisted of 5 mL of sterile water.
The root canals were dried with sterile absorbent paper points (Tanari, São Paulo,
Brazil). A 10-μL aliquot of AH Plus (Dentsply DeTrey, Konstanz, Germany), labeled
with 0.1% Rhodamine B dye (Sigma-Aldrich, St. Louis, Missouri, United States), was
placed into the root canal using a size 20 Lentulo spiral in a counterclockwise rotation.
The filling procedure was performed by dividing the teeth into four groups (n = 15) according to the respective technique ([Table 1 ]). The teeth were then stored in 100% humidity at 37°C for 2 weeks.
Table 1
Groups and protocols for root canal fillings
Group
Protocol
Abbreviations: CLCT, cold lateral condensation technique; CWCT, continuous wave of
condensation technique; ISO, International Organization for Standardization; MCLCT,
modified cold lateral condensation technique; MCWCT, modified continuous wave of condensation
technique; WL, working length.
G1 (CLCT)
Cold lateral condensation technique was performed with an ISO-sized 30 gutta-percha
master cone (Tanari). A size 25 NiTi finger spreader calibrated up to 1 mm from the
WL was introduced up to the allowed depth. R7 accessory cones (Tanari) were used for
lateral condensation. As many accessory cones as possible were placed in the canal.
G2 (CWCT)
Continuous wave of condensation technique was performed using an F3 master cone (Dentsply-Maillefer)
with a sectioned tip locked at 1 mm short of the WL. The heat carrier of System B
(SybronEndo) was used up to 5 mm from the WL.
G3 (MCLCT)
The same protocol described for G1 but using an F3 master cone.
G4 (MCWCT)
The same protocol described for G2 but using an ISO-sized 30 gutta-percha cone.
Confocal Laser Scanning Microscopy
The filled specimens were embedded in crystal resin to obtain 1.5-mm-thick cross-sections
3 and 6 mm from the apex using a diamond cutting disc (∅ 127 vmm × 0.4 vmm × 12.7
vmm, Buehler, Ltd. Lake Bluff, IL, United States) coupled to an automatic precision
cutter (IsoMet 4000, Buehler Ltd.) at a speed of 5 mm/minute at 400 rpm rotational
speed and under abundant water cooling, resulting in a total of 120 slices. The coronally
facing surface of each slice was polished with a standard procedure to produce a surface
of high reflection.
Images were then taken by CLSM (Leica, Jena, Germany) for analysis of the PGFA, PSFA,
and PVFA using two Ne-He laser beams excited with a 568-nm wavelength. The teeth were
scanned axially and laterally using the fluorescence mode with a resolution of 220
and 330 nm, respectively. Root third images were obtained by Leica Microsystems LAS
AF TCS MP5 software (Leica, Jena, Germany). The images were analyzed using a noncompressed
format (.TIFF) ([Fig. 1 ]), and the measurements were performed using Adobe Photoshop Cs3 (Adobe, San Jose,
California, United States) by a single operator. Each section was measured three times,
and the means were calculated. Areas of gutta-percha, sealer, and void were converted
into percentages (PGFA, PSFA, and PVFA, respectively) of the total canal area.
Fig. 1 Illustrative confocal laser scanning microscopy image used for analysis.
Statistical Analysis
The data were analyzed statistically using analysis of variance and Games–Howell’s
tests, with a significance level set at p = 0.05.
Results
No significant differences in PGFA, PSFA, and PVFA were observed in the apical thirds
among the groups (p > 0.05). The higher PGFA and PVFA values were obtained in G3 and G1, respectively
(p < 0.05). Both G1 and G3 promoted lower PSFA than G2 and G4 (p < 0.05) ([Table 2 ]).
Table 2
PGFA, PSFA, and PVFA in each third
Group (n =15)
Apical third
Middle third
PGFA, mean ± SD
PSFA, mean ± SD
PVFA, mean ± SD
PGFA, mean ± SD
PGSA, mean ± SD
PVFA, mean ± SD
Abbreviations: PGFA, percentage of areas filled with gutta-percha; PSFA, percentage
of areas filled with sealer; PVFA, percentage of areas filled with voids.
Note: Different superscript letters indicate statistically significant differences
(p < 0.05).
G1
67.30 ± 11.76a
29.84 ± 11.33a
1.62 ± 1.47a
62.85 ± 10.44b
28.81 ± 7.18b,c
4.53 ± 2.19b
G2
62.77 ± 6.54a
36.59 ± 6.71a
0.40 ± 0.28a
61.93 ± 11.76b
36.50 ± 10.86b
1.22 ± 1.22c
G3
65.79 ± 12.20a
32.50 ± 11.89a
1.05 ± 0.86a
77.15 ± 11.05c
19.39 ± 10.45c
2.00 ± 1.78c
G4
56.60 ± 8.91a
42.22 ± 11.22a
0.76 ± 0.68a
54.10 ± 16.82b
43.88 ± 16.30b
1.59 ± 1.58c
Discussion
Obturation of a shaped and cleaned root canal is most effective when a maximum amount
of gutta-percha is packed into the canal, and sealer amounts are kept to a minimum
because most sealers shrink on setting and dissolve over time, unlike gutta-percha,
which is dimensionally stable.[5 ] For this reason, PGFA, PSFA, and PVFA were used in the investigation to assess obturation
quality based on the procedure used in previous studies.[7 ]
[8 ]
The main disadvantages of CLCT and CWCT are the excessive quantity of sealer and voids
and the extrusion of filling materials, respectively.[5 ] For these reasons, we proposed two respective procedural modifications to offset
these adverse features, namely, the use of matched tapered master cones for performing
CLCT (G3–MCLCT) and standardized cones for performing CWCT (G4–MCWCT).
In regard to PGFA, PSFA, and PVFA, no significant differences in the apical third
(3 mm from the apex) were observed among the groups (p > 0.05), corroborating the results found in previous studies.[8 ]
[19 ]
[20 ] Leoni et al[21 ] used microcomputed tomography (CT) to study the anatomy of 100 mandibular central
and lateral incisors. At 3 mm from the apex, mandibular central and lateral incisors
showed areas of 0.16 ± 0.12 and 0.14 ± 0.08 mm2 and roundness of 0.43 ± 0.22 and 0.46 ± 0.21, respectively. This study performed
instrumentation up to the F3 file at the WL established at 1 mm short of the apical
foramen. The canals were then instrumented up to approximately 0.48 mm2 at 3 mm from this region. This shaping process was responsible for regularizing the
canals in terms of circularity, mainly in the apical third, thus increasing obturation
quality, regardless of the technique.[22 ]
[23 ]
In the middle third (6 mm from the apex), G1 presented higher PVFA than the other
groups (p < 0.05). Several studies have shown limitations of the CLCT for filling oval-shaped
canals in the cervical and middle thirds.[10 ]
[24 ] Schäfer et al[25 ] evaluated PGFA, PSFA, and PVFA after shaping and filling 60 extracted mandibular
incisors with the following systems: (A) FlexMaster (VDW Antaeos; Munich, Germany),
(B) Mtwo (VDW; Munich, Germany), (C) ProTaper (Dentsply; Weybridge, Surrey, United
Kingdom), (D) Reciproc (VDW; Munich, Germany), (E) WaveOne (Dentsply Maillefer; Ballaigues,
Switzerland), and (F) manual instrumentation. In groups A–E and F, they used matching
single-cone gutta-percha and CLCT, respectively, to perform the fillings. Curiously,
group F produced similar PVFA results at the 6-mm level compared with group C. These
results contrast with our findings, in which G1 presented higher PVFA than the other
groups. However, it is noteworthy to mention an important point about the methodology
used in the study performed by Schäfer et al[25 ]: there were four cases of teeth with an oval canal or a canal with isthmuses when
the teeth were sectioned; in this case, they were replaced by a new one. The authors
did not report from which groups these teeth were removed and replaced. This is an
important bias of the study, which even may have influenced the results, considering
that the performance of CLCT may be improved in teeth with circular canals.[22 ]
[23 ]
Still, in regard to the middle third, higher PGFA values were obtained in G3 compared
with the other groups (p < 0.05). The accessory cone sizes and tapers chosen were smaller than the finger
spreader so that GP could be placed in the entire extension of the space created.[26 ] However, in G3 specimens, finger spreader penetration was limited to the initial
millimeters of the root canal because an F3 cone was used. In G1 specimens, the finger
spreader reached the final millimeters of the root canal, mainly at the beginning
of lateral condensation. The G1 specimens commonly showed large unfilled round-shaped
voids (spreader tracks).[24 ] The reason the spreader tracks remained unfilled could be that there was a size
variation in the accessory cones of the same brand[27 ] and that there was no standardization between spreader size and accessory cones.[28 ] The arguments mentioned above explain the higher PGFA and PVFA of both G3 and G1
compared with the other groups.
All thermoplasticized gutta-percha techniques have a common feature, which is the
heating of gutta-percha to an extremely high temperature such as 200°C to 400°C to
ensure that the gutta-percha mass melts homogeneously.[29 ] However, high-temperature settings risk degradation of gutta-percha and the formation
of new compounds of low molecular mass such as peroxides and volatile products.[30 ] The loss of material stability and reduction in molar mass may explain both the
higher PGFA of G3, compared with the other groups, and the lower PSFA of G3, compared
with G2 and G4. According to Capurro et al,[31 ] 2 minutes after obturation using the warm vertical condensation technique, the gutta-percha
underwent significant shrinkage. Moreover, there were large areas of no adaptation
that increased even more after 5 minutes and 30 minutes.
This study used CLSM because it has advantages that are unavailable with scanning
electron microscopy and histological methods. These include providing detailed information
on gutta-percha, sealer, and void distribution in the total circumference of the root
canal at a magnification as low as 50× to 100× using just one image.[32 ]
[33 ] Furthermore, CLSM allows different analyses to be made under environmental conditions,
with no special specimen processing, resulting in lower production of technique artifacts.[34 ] The drawback is that CLSM does not give volume information, unlike micro-CT data,
and uses a technique that can be considered as destructive. Therefore, it is important
that future studies be conducted using micro-CT to elucidate the impact of each filling
technique on the complex root canal anatomy.[19 ]
Conclusion
Notwithstanding the limitations of this in vitro study, PGFA, PSFA, and PVFA ranged
significantly only in the middle third (6 mm from the apex), as observed by the different
filling techniques. Higher PGFA and PVFA values were obtained for G3 and G1, respectively.
Both cold techniques (G1 and G3) promoted lower PSFA than both warm techniques (G2
and G4).
