Geometric Analysis of Root Canals Prepared by Four Rotary NiTi Shaping Systems

Abstract

A great number of nickel-titanium (NiTi) rotary systems with noncutting tips, different cross-sections, superior resistance to torsional fracture, varying tapers, and manufacturing method have been introduced to the market. The purpose of this study was to evaluate and compare the effect of 4 rotary NiTi preparation systems, Revo-S (RS; Micro-Mega, Besancon Cedex, France), Twisted file (TF; SybronEndo, Amersfoort, The Netherlands), ProFile GT Series X (GTX; Dentsply, Tulsa Dental Specialties, Tulsa, OK), and ProTaper (PT; Dentsply Maillefer, Ballaigues, Switzerland), on volumetric changes and transportation of curved root canals.
Forty mesiobuccal canals of mandibular molars with an angle of curvature ranging from 25° to 40° were divided according to the instrument used in canal preparation into 4 groups of 10 samples each: group RS, group TF, group GTX, and group PT. Canals were scanned using an i-CAT CBCT scanner (Imaging Science International, Hatfield, PA) before and after preparation to evaluate the volumetric changes. Root canal transportation and centering ratio were evaluated at 1.3, 2.6, 5.2, and 7.8 mm from the apex. The significance level was set at P ≤ .05.
The PT system removed a significantly higher amount of dentin than the other systems (P = .025). At the 1.3-mm level, there was no significant difference in canal transportation and centering ratio among the groups. However, at the other levels, TF maintained the original canal curvature recording significantly the least degree of canal transportation as well as the highest mean centering ratio.
The TF system showed superior shaping ability in curved canals. Revo-S and GTX were better than ProTaper regarding both canal transportation and centering ability.

Full text

Geometric Analysis of Root Canals Prepared by Four Rotary
NiTi Shaping Systems
Ahmed Abdel Rahman Hashem, BDS, MSc, PhD,*Angie Galal Ghoneim, BDS, MSc, PhD,
†
Reem Ahmed Lutfy, BDS, MSc, PhD,
†
Manar Yehia Foda, BDS, MSc, PhD,
†
and Gihan Abdel Fatah Omar, BDS, MSc, PhD
‡
Abstract
Introduction: A great number of nickel-titanium (NiTi)
rotary systems with noncutting tips, different cross-
sections, superior resistance to torsional fracture,
varying tapers, and manufacturing method have been
introduced to the market. The purpose of this study
was to evaluate and compare the effect of 4 rotary
NiTi preparation systems, Revo-S (RS; Micro-Mega,
Besancon Cedex, France), Twisted file (TF; SybronEndo,
Amersfoort, The Netherlands), ProFile GT Series X (GTX;
Dentsply, Tulsa Dental Specialties, Tulsa, OK), and Pro-
Taper (PT; Dentsply Maillefer, Ballaigues, Switzerland),
on volumetric changes and transportation of curved
root canals. Methods: Forty mesiobuccal canals of
mandibular molars with an angle of curvature ranging
from 25to 40were divided according to the instru-
ment used in canal preparation into 4 groups of 10
samples each: group RS, group TF, group GTX, and
group PT. Canals were scanned using an i-CAT CBCT
scanner (Imaging Science International, Hatfield, PA)
before and after preparation to evaluate the volumetric
changes. Root canal transportation and centering ratio
were evaluated at 1.3, 2.6, 5.2, and 7.8 mm from the
apex. The significance level was set at P#.05. Results:
The PT system removed a significantly higher amount of
dentin than the other systems (P= .025). At the 1.3-mm
level, there was no significant difference in canal trans-
portation and centering ratio among the groups.
However, at the other levels, TF maintained the original
canal curvature recording significantly the least degree
of canal transportation as well as the highest mean
centering ratio. Conclusions: The TF system showed
superior shaping ability in curved canals. Revo-S and
GTX were better than ProTaper regarding both
canal transportation and centering ability.
(J Endod
2012;38:996–1000)
Key Words
Computed tomography, canal transportation, root canal volume, twisted file, Revo-S,
GTX, ProTaper, nickel-titanium instruments
Canal shaping remains to be one of the critical aspects of endodontic treatment
because a number of mishaps such as ledges, zips, perforations, and root canal
transportation can occur, particularly when preparing curved canals (1). The introduc-
tion of nickel-titanium (NiTi) rotary instruments has represented a major breakthrough
in root canal preparation by permitting easier and faster instrumentation while main-
taining the original canal shape with considerably less iatrogenic errors (2–4).
However, it has been shown that the design features and method of manufacturing
might significantly affect the clinical performance of NiTi rotary instruments (5–7).
Hence, a constant search for better performance in terms of the quantity of material
removed from the root wall concurrent with faithful adherence to the original shape
of the root canal is progressing through introducing new methods of manufacturing
NiTi rotary instruments (2, 5).
Recently, new generations of NiTi rotary instruments with higher flexibility and
greater cutting efficiency have been introduced (2). The Twisted File (TF; Sybro-
nEndo, Amersfoort, The Netherlands) represents one of the most advanced
endodontic NiTi rotary files in the market. It has 3 unique design features: the R-phase
heat treatment, twisting of the metal, and special surface conditioning. These features
significantly increase the instrument’s resistance to fracture (8, 9) and provide greater
flexibility (10).
The ProFile GT Series X (GTX; Dentsply, Tulsa Dental Specialties, Tulsa, OK), the
new generation of ProFile GT, is characterized by innovative M-wire NiTi technology,
more open blade angles, variable-width lands, and a 1-mm maximum shank diameter
(11). The variable-width lands are claimed to minimize taper lock in the canal and
produce larger chip space between the cutting flutes, accordingly increasing the cutting
efficiency without transportation.
Revo-S (RS; Micro-Mega, Besancon Cedex, France), another NiTi rotary system,
was developed with a distinctive asymmetric cross-section intended to decrease the
stress on the instrument (12). The manufacturer claims that this particular instrument
geometry facilitates canal penetration and the upward removal of debris. To date, the
effect of these new NiTi rotary systems on root canal geometry has not been compared.
Therefore, the aim of the present study was to evaluate and compare the effect of using
different NiTi rotary systems (ie, Revo-S, TF, GTX, and ProTaper [PT; Dentsply Maillefer,
Ballaigues, Switzerland]) on the volume of removed dentin, canal transportation, and
canal centering ability in extracted human teeth using cone-beam computed tomog-
raphy (CBCT) scanning.
From the Departments of *Endodontics and
‡
Oral Radiology, Future University, Cairo, Egypt; and
†
Department of Endodontics, Cairo University, Cairo, Egypt.
Address requests for reprints to Dr Ahmed Abdel Rahman Hashem, Department of Endodontics, Faculty of Oral and Dental Medicine, Future University, Fifth District,
Cairo, Egypt. E-mail address: endohashem@gmail.com
0099-2399/$ - see front matter
Copyright ª2012 American Association of Endodontists.
doi:10.1016/j.joen.2012.03.018
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996 Hashem et al. JOE —Volume 38, Number 7, July 2012

Materials and Methods
Selection and Specimen Preparation
Forty extracted human mandibular first molars with an average
length of 20 to 21 mm, curved mesial roots, 2 separate mesial canals,
and apical foramina were selected. Teeth were accessed using an Endo-
Access bur (Dentsply Maillefer), and the meisobuccal canals were
localized and explored with a size 10 K-file (Dentsply Maillefer). Mesio-
buccal canal curvatures were assessed according to Schneider’s tech-
nique (13). Only canals with curvature (25-40) were included in
the study. Distal roots with the respective part of the crown were
sectioned at the furcation level and discarded. The determination of
the working length was performed at magnification 8 using a surgical
microscope (Opmi-Pico; Karl Zeiss, Jena, Germany) by inserting a #10
K-file to the root canal terminus and subtracting 1 mm from this
measurement. Specimens were coded and randomly divided into 4
equal experimental groups (n= 10) according to the rotary NiTi
file system used in canal instrumentation: the RS group, the TF group,
the GTX group, and the PT group.
Root canal instrumentation was performed by a single operator
in strict accordance with the manufacturers’ recommendations for
each system. All files were operated by a 1:16 gear reduction hand-
piece powered by an electric torque control motor (Dentaport; J
Morita, Tokyo, Japan). Each canal was prepared to the working
length in a crown-down sequence, and the final apical preparation
was set to size 30 in each group. Between each file size, copious irri-
gation with 2 mL 5.25% NaOCl was performed using a 27-G needle
(Stropko NiTi Needle, SybronEndo), and patency was maintained
using a size #10 K-file. Each instrument was discarded after use in
5 canals.
Image Analysis
The roots were positioned in a custom-made specimen holder in
which they were aligned perpendicularly to the beam and scanned
before and after instrumentation using the i-CAT CBCT scanner
(Imaging Science International, Hatfield, PA). Exposure parameters
were 120 kV and 3 to 7 mA. The field of view had an 8-cm diameter
and was 8 cm high. Slices were 640 640 pixels, and the pixel size
was 0.13 mm. The acquired data were viewed, and measurements
were performed by the software SimPlant View 12.03 for Intel X86 Plat-
form V 12.0.3.14, operating system windows XP SP3 (1992-2008 Mate-
rialise Dental n.v., Technologielann 15, 3001 Leuven, Belgium). The
mesiobuccal canal was traced, and the total volume was measured
(Fig. 1Aand B). Four cross-section planes at levels 1.3, 2.6, 5.2, and
7.8 mm from the apical end of the root were viewed through the
explorer mode. The shortest distance from the canal wall to the external
root surface was measured in the mesial and distal directions for the
mesiobuccal root canal. The distance was measured on the recon-
structed 2-dimensional image without reduction by using the measure
length tool (Fig. 1Cand D). Measurements were recorded before and
after instrumentation to calculate the following: (1) the volume of
removed dentin determined in mm
3
for each root canal by subtracting
the uninstrumented canal volume from the instrumented canal volume,
(2) the degree of canal transportation at each level according to the
following formula (14):(x
1
-x
2
)(y
1
-y
2
), and (3) the canal centering
ratio at each level according to the following ratio (14):(x
1
-x
2
)/(y
1
-y
2
)
or (y
1
-y
2
)/(x
1
-x
2
), where x
1
is the shortest distance from the mesial
edge of the root to the mesial edge of the uninstrumented canal, x
2
is
the shortest distance from the mesial edge of the root to the mesial
edge of the instrumented canal, y
1
is the shortest distance from the distal
Figure 1. Volumetric changes measurements (A) before instrumentation and (B) after instrumentation. Canal transportation measurements (C) before instru-
mentation and (D) after instrumentation.
Basic Research—Technology
JOE —Volume 38, Number 7, July 2012 Shaping 4 NiTi Systems 997

edge of the root to the distal edge of the uninstrumented canal, and y
2
is
the shortest distance from the distal edge of the root to the distal edge of
the instrumented canal.
Statistical Analysis
Data were presented as means and standard deviation values. One-
way analysis of variance was used for comparisons of the centering ratio
and canal transportation in the studied groups. The Tukey post hoc test
was used for pair-wise comparisons between the groups when the anal-
ysis of variance test was significant. The Kruskal-Wallis test was used for
comparison between volume changes in the studied groups. The Mann-
Whitney Utest was used for pair-wise comparison between the groups
when the Kruskal-Wallis test was significant. The significance level was
set at P#.05.
Results
The mean and standard deviation values for the volume of the
removed dentin, the canal transportation, and the centering ratio at
the studied levels for the experimental groups are presented in
Tables 1 and 2.
Volume of Removed Dentin
The PT group recorded the significantly highest mean volume of
removed dentin (4.67 1.96 mm
3
). On the other hand, the RS, TF,
and GTX groups yielded the significantly lowest mean volume changes
(2.06 0.73, 2.1 1.48, and 3.03 1.93 mm
3
, respectively) with
no significant difference among them.
Canal Transportation
At the 1.3-mm level, there was no statistically significant difference
in canal transportation among the groups (P> .05). However, at the
2.6-mm level, the TF group recorded the least transportation among
all groups (0.059 0.02 mm). The RS group then followed with
a significantly higher transportation mean of 0.114 0.025 mm. Mean-
while, the GTX and PT groups yielded the significantly highest mean
transportation values (0.141 0.035 mm and 0.162 0.019 mm,
respectively) with no significance between them. At the 5.2-mm level,
the GTX and TF groups showed the significantly lowest mean transpor-
tation values (0.051 0.015 mm and 0.69 0.02 mm). At the 7.8-mm
level, the TF, GTX, and RS groups recorded the significantly lowest mean
transportation values (0.137 0.044 mm, 0.159 0.04 mm, and
0.162 0.032 mm, respectively) with no significance among them.
On the other hand, the PT group yielded the significantly highest
mean transportation value (0.25 0.035 mm).
Centering Ratio
At the 1.3-mm level, there was no statistically significant difference
in the canal centering ratio among the groups (P> .05). However, at the
2.6-mm level, the TF group recorded the significantly highest mean
centering ratio (0.91 0.15), whereas the PT group yielded the signif-
icantly lowest mean centering ratio (0.55 0.15). At the 5.2-mm level,
the TF group showed the significantly highest centering ratio (0.82 
0.13), whereas the RS group recorded the significantly lowest centering
ratio (0.52 0.12). At the 7.8-mm level, the TF and RS groups re-
corded the significantly highest mean centering ratio (0.76 0.11
and 0.70 0.17, respectively) with no significant difference between
them, whereas the PT group yielded the significantly lowest mean
centering ratio (0.50 0.10).
Discussion
The advantages of NiTi instruments in root canal preparation are
well documented; however, their cutting ability is a complex interrela-
tionship of different parameters such as the cross-sectional design,
chip-removal capacity, helical and rake angles, metallurgical proper-
ties, and surface treatment of the instrument (5, 15). The Revo-S, TF,
GTX, and ProTaper are recently introduced file systems that are
distinctly different in their geometric design and manufacturing method.
Hence, the purpose of this study was to compare the effect of these new
NiTi rotary instruments on canal transportation, the centering ratio,
and the volume of removed dentin using CBCT scanning. Noninvasive
CBCT scanning was used because it provides an accurate, reproducible,
3-dimensional evaluation of changes in both dentin thickness and root
canal volume before and after preparation without the destruction of
specimens (14, 16, 17).
An extracted teeth model was used because testing file systems
under realistic circumstances in natural dentin is considered more
beneficial than in standardized artificial canals (18). Crowns were
maintained to simulate clinical conditions in which the interference
of cervical dentin projections would create tensions on the files during
canal instrumentation (19). Four levels (ie, 1.3, 2.6, 5.2, and 7.8 mm
from the root apex) were chosen representing the apical and middle
thirds of root canal in which curvatures, highly susceptible to iatrogenic
mishaps, usually exist.
In the present study, ProTaper recorded the significantly highest
mean volume of removed dentin compared with the other tested rotary
TABLE 1. Statistical Analysis of the Mean Values for the Volume of Removed
Dentin (mm
3
) for the Tested Groups
Group Mean SD Pvalue
RS 2.06
b
0.73 .025*
TF 2.10
b
1.48
GTX 3.03
b
1.93
PT 4.67
a
1.96
Means with different letters are statistically significantly different according to the Mann-Whitney
Utest.
*Significant at P#.05.
TABLE 2. Statistical Analysis of Mean Transportation (mm) and the Centering Ratio Values for Tested Groups
Level Assessment RS TF GTX PT Pvalue
1.3 mm Transportation .044 .015 .025 .010 .046 .019 .033 .009 .387
Centering ratio .65 .15 .75 .07 .72 .15 .68 .13 .339
2.6 mm Transportation .114
b
.025 .059
c
.020 .141
a
.035 .162
a
.019 <.001*
Centering ratio .71
b
.09 .91
a
.15 .74
b
.14 .55
c
.15 <.001*
5.2 mm Transportation .104
b
.030 .069
c
.020 .051
c
.015 .164
a
.033 <.001*
Centering ratio .52
c
.12 .82
a
.13 .66
b
.11 .64
b
.15 .002*
7.8 mm Transportation .162
b
.032 .137
b
.044 .159
b
.040 .250
a
.035 <.001*
Centering ratio .70
a
.17 .76
a
.11 .61
b
.09 .50
c
.10 .001*
Means with different letters are statistically significantly different according to the Tukey test.
*Significant at P#.05.
Basic Research—Technology
998 Hashem et al. JOE —Volume 38, Number 7, July 2012

instruments. This is in agreement with previous studies on extracted
teeth (20–22). This might be attributed to the sharp cutting edges of
the convex triangular cross-sectional design of ProTaper instruments
coupled with the flute design with its progressive tapers sequence along
the shaft compared with the constant taper embraced by the other tested
instruments. ProTaper recorded significantly more tooth structure
removal than TF as previously reported (23). On the other hand,
GTX showed more dentin removal than TF and Revo-S but with no statis-
tical significance. The current results could not be compared with other
reports because, to our knowledge, no previous published data are
available comparing these 3 systems.
In this study, all tested rotary systems resulted in canal transporta-
tion at all examined levels, a finding that is consistent with other studies
(18, 19, 24). At 1.3 mm, the 4 groups showed no statistically significant
difference among them in both canal transportation and the centering
ratio. This might be because of the noncutting tip design they all
possess, which functions only as a guide to allow easy penetration
with minimal apical pressure (25), and the standardized master apical
file size (23). At the other studied levels, TF recorded the significantly
lowest mean canal transportation as well as the highest mean centering
ratio among the tested groups. This result is consistent with another
study (26) and might be attributed to the new manufacturing method
(ie, R-phase heat treatment, twisting of the metal, and the surface de-
oxidation [8–10]) resulting in increased phase transformation temper-
atures and increased flexibility of TF files compared with the other NiTi
instruments manufactured by grinding (27).
Revo-S recorded significantly less transportation than ProTaper at
all of the studied canal levels. It was not even significant from TF at 7.8
mm regarding canal transportation and the centering ratio. This could
be related to the asymmetric cross-sectional geometry of the SC1 and SU
instruments intended to facilitate canal penetration by a snake-like
movement and upward removal of debris, hence leading to uniform
removal of dentin and less stress on the instrument as claimed by the
manufacturer.
GTX, a modified version of the Profile system, recorded a signifi-
cantly higher centering ratio than Revo-S at 5.2 mm. The centering
ability of the Profile system has been previously reported (25) and
has been suggested to be caused by the radial lands on the cutting edges
of the file that attenuated the effect of the instrument on the outside of the
root canal curve, thus keeping the file concentric within the natural
canal. Although GTX recorded significantly higher mean canal transpor-
tation than Revo-S and TF at 2.6 mm, it was not significant from TF at 5.2
mm and 7.8 mm and even recorded significantly less transportation
than Revo-S at 5.2 mm. This might be attributed to the innovative M-
wire NiTi technology (11). Furthermore, the unique feature of
variable-width lands was reported to minimize the taper lock in the
canal and to produce larger chip space between cutting flutes allowing
for rapid cutting without transportation (11). McSpaddan (28) has
speculated that radial lands help to distribute the pressure of the blades
evenly around the curvature, thus allowing more circumferentially
uniform cutting to occur compared with the actively cutting files without
lands. However, Peters et al (29) concluded that variations in canal
anatomy before preparation had more influence on the postoperative
canal geometry than the rotary system itself.
The ProTaper system recorded a significantly less centering ratio
and higher canal transportation than the other groups at 2.6, 5.2, and
7.8 mm. Similar results were reported and were attributed to the sharp
cutting edges and the multiple tapers along the cutting surface of the files
(26), especially the large increase in taper size from 0.04 to 0.07 (S2 to
F1) (30). In addition, the apical enlargement performed until F3 for
standardization might have an impact on the results because NiTi files
with tapers greater than 0.04 were previously suggested not be used for
apical enlargement of curved canals or else transportation would result
(25, 31).
Conclusion
Within the parameters of this study, it could be concluded that all
tested rotary systems produced canal transportation at the apical and
midregions of the canal. The innovated method of manufacturing the
TF system resulted in superior shaping ability in curved canals, with
the instruments remaining more centered and producing less canal
transportation than the other systems. On the other hand, Revo-S and
GTX exhibited superior performance than ProTaper in both canal trans-
portation and centering.
Acknowledgments
The authors thank Dr Khaled Kerra for his help in statistical
analysis.
The authors deny any conflicts of interest related to this study.
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