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\begin{document}

\title{Cyclic and Torsional Fatigue Resistance of a New Rotary File on a Rotary
and Reciprocating Motion.}



\author[1]{Gabriel Barcelos Só}%
\author[1]{Giovana Siocheta}%
\author[2]{Pedro Calefi}%
\author[2]{Murilo Alcalde}%
\author[2]{Rodrigo Vivan}%
\author[2]{Marco Antonio Duarte}%
\author[1]{Marcus Vinícius Só}%
\author[1]{ricardo rosa}%
\affil[1]{Universidade Federal do Rio Grande do Sul Faculdade de Odontologia}%
\affil[2]{Universidade de Sao Paulo Faculdade de Odontologia de Bauru}%


\vspace{-1em}



  
  \date{June 18, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
\textbf{Introduction:} This study aimed to evaluate the cyclic and
torsional fatigue resistance of a new nickel-titanium (Flat File 25.04)
instrument on continuous and reciprocating motion. \textbf{Methods:}
Sixty instruments of the ProDesign Logic2 25.03 and 25.05 (Easy
Equipamentos Odontol\selectlanguage{ngerman}ógicos, Belo Horizonte, Brazil), and MK Flat File
25.04 (n=20) (MK Life, Porto Alegre, Brazil) were used. For the cyclic
fatigue test, an artificial stainless steel simulated canal with an
angle of 60° and a radius of curvature of 5mm located 5mm from its tip
was used. Torque and angle of rotation at failure of instruments on
torsional fatigue test was based on the ISO 3630-1 protocol, in which
the 3mm tip of each instrument was fixed and connected to an electric
motor and a load cell. The fractured surface of each fragment was
examined by scanning electron microscopy. Data were analyzed using 1-way
analysis of variance and Tukey's test with a significance level of 5\%.
\textbf{Results:} Flat File 25.04 had lower cyclic fatigue in both
kinematics than the Logic instruments (P \textless{} .05). Reciprocating
motion improved the cyclic fatigue of the tested instruments (P
\textless{} .05). Flat File 25.04 had similar torque to Logic2 25.05 (P
\textless{} .05), and both were superior to Logic2 25.03 (P \textless{}
.05). The angular deflection values were different for the three tested
instruments (P \textless{} .05), in the decreasing order: Logic2 25.03,
25.05, and Flat File 25.04. \textbf{Conclusion:} Flat File presented
acceptable resistance to cyclic and torsional fatigue resistance.
Reciprocating motion improved the cyclic fatigue resistance of the
instruments and can be considered when using programmable motors.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Cyclic and Torsional Fatigue Resistance of a New Rotary File on
a Rotary and Reciprocating Motion.}

Gabriel Barcelos S\selectlanguage{ngerman}ó\textsuperscript{1}, Giovana
Siocheta\textsuperscript{1}, Pedro Calefi\textsuperscript{2}, Murilo
Alcalde\textsuperscript{2}, Rodrigo Ricci Vivan\textsuperscript{2},
Marco Antônio H. Duarte\textsuperscript{2}, Marcus Vinicius Reis
Só\textsuperscript{1}, Ricardo Abreu da Rosa\textsuperscript{1}

\textsuperscript{1}Department of Conservative Dentistry, School of
Dentistry, Rio Grande do Sul Federal University (UFRGS), Porto Alegre,
RS, Brazil

\textsuperscript{2}Department of Operative Dentistry, Endodontics and
Dental Materials, Bauru School of Dentistry, University of São Paulo,
São Paulo, Brazil

Running Title: New rotary file on different kinematics

Acknowledgments: The authors deny any conflict of interest or financial
support/

\textbf{Corresponding author}

Ricardo Abreu da Rosa

Federal University of Rio Grande do Sul, Conservative Department 2492
Ramiro Barcelos Street Porto Alegre, RS, BR 90040-060

E-mail: rabreudarosa@yahoo.com.br

Phone: (+55) 55 9927-5625

\textbf{Keywords:} Endodontics. Cyclic fatigue. Torsional resistance.
NiTi instruments.

\textbf{Research Highlights:} Scanning eletron microscopy evaluation of
different endodontic rotary file and fatigue resistance tests.

\textbf{Graphical Abstract}

\textbf{Hosted file}

\verb`image1.emf`  available at \url{https://authorea.com/users/594553/articles/628954-cyclic-and-torsional-fatigue-resistance-of-a-new-rotary-file-on-a-rotary-and-reciprocating-motion}

ABSTRACT

\textbf{Introduction:} This study aimed to evaluate the cyclic and
torsional fatigue resistance of a new nickel-titanium (Flat File 25.04)
instrument on continuous and reciprocating motion.
\textbf{Methods:}Sixty instruments of the ProDesign Logic2 25.03 and
25.05 (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil), and MK
Flat File 25.04 (n=20) (MK Life, Porto Alegre, Brazil) were used. For
the cyclic fatigue test, an artificial stainless steel simulated canal
with an angle of 60° and a radius of curvature of 5mm located 5mm from
its tip was used. Torque and angle of rotation at failure of instruments
on torsional fatigue test was based on the ISO 3630-1 protocol, in which
the 3mm tip of each instrument was fixed and connected to an electric
motor and a load cell. The fractured surface of each fragment was
examined by scanning electron microscopy. Data were analyzed using 1-way
analysis of variance and Tukey's test with a significance level of
5\%.\textbf{Results:} Flat File 25.04 had lower cyclic fatigue in both
kinematics than the Logic instruments (P \textless{} .05). Reciprocating
motion improved the cyclic fatigue of the tested instruments (P
\textless{} .05). Flat File 25.04 had similar torque to Logic2 25.05 (P
\textless{} .05), and both were superior to Logic2 25.03 (P \textless{}
.05). The angular deflection values \selectlanguage{english}\selectlanguage{english}were different for the three
tested instruments (P \textless{} .05), in the decreasing order: Logic2
25.03, 25.05, and Flat File 25.04. \textbf{Conclusion:} Flat File
presented acceptable resistance to cyclic and torsional fatigue
resistance. Reciprocating motion improved the cyclic fatigue resistance
of the instruments and can be considered when using programmable motors.

Keywords: Endodontics. Cyclic fatigue. Torsional resistance. NiTi
instruments.

INTRODUCTION

Conventional nickel-titanium (NiTi) alloy instruments present super
elasticity and memory control characteristics, predominantly in the
austenite phase. However, when induced by temperature drops or
mechanical stress application, they change to martensite, acquiring more
flexibility {[}1,2{]}.

However, these instruments are subject to failure, for example,
torsional or cyclic fatigue {[}3{]}. Thus, technologies that prioritize
variations in kinematics, cross-sectional design, and surface treatments
have been proposed to improve their mechanical properties and,
consequently, their clinical performance and safety of use {[}4-8{]}.

Recently, a new NiTi instrument was created with the trade name of Flat
File (MK Life, Porto Alegre, Brazil). This instrument has a Gold heat
treatment and is available in a sequence of three instruments: 20.04,
25.04, and 35.04. It has an innovative design, with a flat side, without
cutting blades, to allow more space for the irrigating solution, escape
for debris, and less pushing effect of the instrument inside the root
canal.

NiTi endodontic instruments are constantly subjected to tension and
compression forces during root canal preparation, especially in
accentuated curvatures. In addition, due to the simplification of the
preparation technique, often, when only one instrument is used, there is
a possibility that the tip of these instruments is in close contact with
the root canal walls and, therefore, subject to torsional fractures
{[}6{]}.

Due to this, mechanical tests of cylic and torsional fatigue should be
performed, and the results compared with existing instruments before
their clinical use. Therefore, the objective of this study was to
compare a new NiTi instrument (Flat File) with another instrument with
similar dimensions (ProDesign Logic2) regarding its mechanical
properties of torsional and cyclic fatigue on the continuous and
reciprocating motion {[}7,8{]}.

MATERIALS AND METHODS

Sample size determination was performed using G*Power 3.1 for Windows
(Heinrich Heine, University of Dusseldorf) and the Wilcoxon-Mann-Whitney
test from the ''t'' test group. An alpha-type error of 0.05, a beta-type
power of 0.95, and an N2/N1 ratio of 1 were also adopted {[}8{]}.

For the tests, a total of 60 NiTi instruments were selected: ProDesign
Logic2 25.03 (n=20) and 25.05 (n=20) (Easy Equipamentos Odontologicos,
Belo Horizonte, Brazil) and MK Flat File 25.04 (n=20) (MK Life, Porto
Alegre, Brazil). All instruments were inspected for possible defects or
deformations under a microscope (Alliance, Sao Paulo, Brazil) at 16x
magnification. Flat File instruments are sold in a sterile blister, with
no need for sterilization prior to testing. ProDesign Logic2 instruments
have been subjected to a sterilization process according to the
manufacturer's standards to simulate a precondition of clinical use.

\emph{Cyclic fatigue test}

All instruments used were analyzed, and resistance to cyclic fatigue
(ten for each group of instrument {[}n=5 for continuous mode and n=5 for
reciprocating mode{]}) was tested at controlled room temperature (37o +-
1oC) \textsuperscript{12,13}. The instruments were connected to a VDW
Silver engine (VDW GmbH, Munich, Germany), which was connected to the
cyclic fatigue device. The predefined programs were selected according
to the manufacturers for the continuous motion. ProDesign Logic2 25.03
and 25.05 instruments were used in continuous motion at 950 rpm with 2
N/cm and 4N/cm of torque, respectively. Flat File instruments were used
in continuous motion at 500 rpm with 2 N/cm of torque. When the
reciprocating motion was tested, the instruments were coupled to an
Eighteeth E-connect Pro motor (Eighteeth, Changzhou City, China)
connected to the cyclic fatigue device. The ProDesign Logic 25.03,
25.05, and Flat File 25.04 were used in reciprocating motion at 350rpm
with an angle of rotation of 150o forward and 30o reverse.

The instruments were positioned in a device simulating an artificial
canal made of stainless steel, with a curvature of 60o and a radius of
curvature of 5 mm located 5 mm from the instrument's tip. The device has
an outer arch with a 1 mm deep groove that served as a guide for the
instruments' path, keeping them in the curvature and allowing them to
rotate freely during the tests. This device allowed a precise and
reproducible position of the curvature that was established for all
instruments used.

A digital stopwatch recorded the time to fracture, and a digital camera
captured data to ensure fracture time accuracy in seconds.

\emph{Torsional fatigue test}

For the torsional tests, a specific machine (Analogica, Belo Horizonte,
Brazil) was used that measured the torque and controlled the rotation
angle through the connection to a computer, collecting all the data. The
tests performed was based on the ISO 3630-1 (1992)

Torque was measured through the force exerted on a small load cell
attached to a lever arm on the long axis of torsion. Ten instruments
from each system were used for this step. Before testing, the
instrument's handles were removed at the point where they were attached
to the torsion shaft. The 3 mm ends of the instruments were attached to
a chuck connected to an electric motor. The electric motor was operated
clockwise at a speed of 2 rpm.

\emph{Scanning Electron Microscopic Evaluation}

The fractured surfaces of 5 instruments of each file, randomly selected
after cyclic and torsional fatigue tests, were examined by scanning
electron microscopy JSM-6060 (Jeol Brasil Ltda, Mirandopolis, Sao Paulo)
to look for the topographic features of the fractured instruments.
Before scanning electron microscopic (SEM) evaluation, instruments were
ultrasonically cleaned to remove debris. The photomicrographs were taken
at 200X magnification. Furthermore, additional photomicrographs were
taken at 1000X magnification in the center of the fractured surface of
the instruments submitted to torsional testing.

RESULTS

The mean and standard deviation values \selectlanguage{english}\selectlanguage{english}of the cyclic (seconds) and
torsional (maximum torque), and angular deflection (rotation angle)
fatigue tests are shown in Table 1.

Regarding the cyclic fatigue in continuous motion, Flat File 25.04
instruments showed the lowest cyclic fatigue resistance than the Logic
25.03 and 25.05 instruments (P \textless{} .05). In addition, Logic
25.03 presented the highest cyclic fatigue resistance (P \textless{}
.05). In reciprocating motion, all instruments had higher cyclic fatigue
resistance than when activated in continuous motion (P\textless{} .05).
The Flat File 25.04 showed the lowest values of cyclic fatigue
resistance when compared to Logic 25.03 and Logic 25.05 (P\textless{}
.05). Logic 25.03 presented higher cyclic fatigue resistance values than
Logic 25.05 (P\textless{} .05)

The torsional test showed that the Flat 25.04 instruments presented
similar torque to the Logic 25.05 instrument (P \textgreater{} .05). The
Logic 25.03 instrument presented the lowest torque values \selectlanguage{english}\selectlanguage{english}(P
\textless{} .05). Regarding the angular deflection, all the instruments
had significantly different values, according to the following
decreasing order: Logic 25.03, 25.05, and Flat File 25.04
(P\textless{}.05)

\emph{SEM evaluation}

Scanning electron microscopy of the fracture surface showed similar and
typical torsional and cyclic fatigue features for all instruments
tested. After the torsional test, the instruments showed concentric
abrasion marks and tear-shaped marks at the center of rotation (Fig.
1A--C and a--c). In the cyclic fatigue test, all the files presented
fractured surfaces with microcracks, with morphologic characteristics of
a ductile fracture (Fig. 2A--C and a-c).

DISCUSSION

Several factors may have been responsible for the results obtained in
this study. The instruments performance in mechanical tests are also
influenced by the type of NiTi alloy used and the heat treatment used.
Flat File files are featured with gold heat treatment that has an
austenite finish temperature approximately at 50oC {[}9{]} , while Logic
files are featured with a controlled memory alloy (CM wire) that has an
austenite finish temperature around 55oC {[}10,11{]}. So, when the
cyclic fatigue test is performed with a controlled temperature (37oC)
simulating a body temperature {[}12,13{]} ,CM Wire instruments present
more martensite phase during the test than gold heat treatment. This
austenitic finishing temperatures influence properties during root canal
preparation at body temperature {[}14{]}. So far, with a crystalline
structure predominantly martensite that allows the control of the shape
memory of the instrument, being extremely flexible and more resistant to
cyclic fatigue, for example, when compared to ''Gold'' instruments
{[}2{]} .These aspects justify the higher fatigue cyclic values
presented by Logic instruments compared with Flat File.

Core mass and cross-sectional design also can influence the results of
mechanical tests. A smaller metal volume is associated with more
excellent cyclic fatigue resistance {[}15{]}. This fact could be
explained when calculating the bending section modulus, the ratio of
moment of inertia, and the distance from the neutral axis in the
instrument center to the instrument surface and geometrical shape
{[}14{]}. In short, flat cross-section designs such as S-Shape are
associated with an increased cyclic fatigue resistance {[}15, 16{]}.
Also, bigger cross-sections are associated with a stiffer instrument,
with great flexural strength and torsional resistance {[}17{]}. Logic
instruments have a double helix cross-section, while Flat File
instruments have a modified S-section. However, the reduction of the
metallic mass of Flat File instruments to generate only one side with
active spirals can negatively influence the cyclic fatigue values
compared to Logic instruments. Besides, the manufacturing process
(surface treatment) of Flat File instruments to provide a flat surface
may also influence their structural characteristics, generating
irregularities in this portion {[}18{]}. Possible microcracks can lead
to instrument fractures under clinical or laboratory stress, especially
in curvatures when the alloy is subjected to tension and compression
{[}19{]}.

Higher cyclic fatigue values on both kinematics (continuous and
reciprocating) for the Logic 25.03 compared to the Logic 25.05 can be
justified by the taper of the instruments. Instruments with the same
heat treatment and structural characteristics but high taper will
present lower resistance to cyclic fatigue than those instruments with
low taper {[}20{]}. The static cyclic fatigue test was performed as
described in previous studies {[}8,21{]}. In this model, the instruments
are mounted in a stabilized handpiece that provides a free rotation in
an artificial canal under specific conditions until the instruments
fracture {[}22{]}. This condition leads the NiTi instruments to the
maximum stress, mainly because they remain in a static position inside
the simulated canal, generating areas of stress concentration (tension
and compression) of the alloy in a specific region of the instrument.
This method reduces some biases and induces less localized mechanical
stress, increasing the time and number of cycles to fatigue {[}17,23{]}.

Cyclic fatigue occurs through the formation of microcracks in surface
irregularities that extend through the instrument during cycles until
the fracture occurs {[}24{]}. Studies showed that reciprocating motion
increases resistance to cyclic fatigue compared to continuous motion
{[}25-27{]}. During reciprocating motion, the instrument disengages from
the canal walls at the moment of higher tension, delaying the formation
of microcracks on the surface of the endodontic instrument {[}28{]}. The
use of rotary instruments in conventional reciprocating motion (150o
reverse, 30o forward) had not been encouraged because their spirals were
designed to cut in a clockwise direction. However, with the development
of programable motors that allow modifications of the angle and
direction of rotation, reciprocating kinematics also can be employed for
rotary instruments (150o forward, 30o reverse) {[}29{]}. These
programmable endodontic motors allow reciprocating motion to both sides
(i.g. clockwise or counterclockwise){[}29{]}.

After the torsional resistance test, the Flat File 24.04 and Logic 25.05
showed higher values than the Logic 25.03 instrument (P \textless{}
.05). This finding could be explained because it may be associated with
its greater taper than the 0.3 instruments, which results in more
torsional resistance than instruments with smaller tapers {[}14,17{]}.
Higher values of torsional resistance are associated with instruments
with greater mass, either as a function of their cross-section, tip
diameter, or taper {[}30{]}. Also, torsional stiffness could be
increased by files with reduced pitch and increased cross-sectional
areas. For example, rectangular cross-sections had superior torsional
stiffness compared to triangular cross-sections {[}31{]}. Specific
cross-sectional configurations are more prone to failure by torsional
overload than others by the principle of mechanics when an instrument
with a small core diameter is more susceptible to failure by torsional
overload {[}4{]}. The investigation of this property is essential to
estimate the torque value necessary for the instrument to fracture
inside the simulated canal contributing to the possibility of working
with these instruments at a torque value lower than that necessary to
cause a fracture.

Scanning electron microscopic analysis showed a typical fractographic
appearance of cyclic fatigue and torsional fracture, presenting similar
images among the three analyzed instruments. The fragments showed crack
initiation areas on the cyclic fatigue test image, with numerous dimples
on the fractured surface. After the torsional test, the instruments
demonstrated the typical features of shear failure, including concentric
tear marks and fibrous microscopic dimples at the center of rotation
{[}21,32,33{]}.

Finally, angular deflection makes it possible to identify how much the
instrument can deform when attached to the root canal prior to its
fracture by torsion. The angular deflection values obtained in this
study differed for all instruments (P \textless{} .05). Flat File showed
the lowest angular deflection values. This result can be attributed to
its gold heat treatment since the CM treatment present in Logic files,
provides greater flexibility and ductility {[}2,5{]}. In addition, Flat
File instruments have a modified S section that is more irregular than
the double helix section of Logic instruments. Asymmetrical
cross-sections such as Flat File instruments generate worse stress
distribution when used, making instruments of this type more susceptible
to fracture {[}30{]}.

CONCLUSIONS

Geometric characteristics, Ni-Ti alloy, heat treatment and manufacturing
process influence the mechanical properties of the Ni-Ti instruments.
Flat File 25.04 instrument presented a good resistance to cyclic
fatigue, torsional loads, and angular deflection. Reciprocating motion
improved the cyclic fatigue resistance of Flat File instrument and can
be considered when using programmable endodontic motors.

ACKNOWLEDGMENTS

The authors deny any financial support and conflicts of interested
related to this study.

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  Journal of Endodontics 2012; 38, 684--687.
\item
  Silva EJNL, Hecksher F, Antunes HDS, De-Deus G, Elias CN, Vieira VTL.
  Torsional Fatigue Resistance of Blue-treated Reciprocating
  Instruments. J Endod. 2018;44:1038-1041.
\item
  De-Deus G, Moreira EJ, Lopes HP, Elias CN. Extended cyclic fatigue
  life of F2 ProTaper instruments used in reciprocating movement. Int
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\item
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  bending properties for six models of nickel-titanium root canal
  instruments with different cross-sections. J Endod 2006; 32: 372--5.
\item
  Baek SH, Lee CJ, Versluis A, Kim BM, Lee W, Kim HC. Comparison of
  torsional stiffness of nickel-titanium rotary files with different
  geometric characteristics. J Endod. 2011;37:1283-6
\item
  Kim HC, Kwak SW, Cheung GS, et al. Cyclic fatigue and torsional
  resistance of two new nickel-titanium instruments used in
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\end{enumerate}

TABLES\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Cyclic Fatigue(seconds) Rotary\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Cyclic Fatigue (seconds) Reciprocating\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Torque(Ncm)\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Angle(\selectlanguage{ngerman}º)\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Instruments\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Mean \selectlanguage{ngerman}± SD\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Mean \selectlanguage{ngerman}± SD\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Mean \selectlanguage{ngerman}± SD\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Mean \selectlanguage{ngerman}± SD\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Flat 25.04\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
194.89 \selectlanguage{ngerman}± 5.81 Cb\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
337.76 \selectlanguage{ngerman}± 15.12 Ca\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.15 \selectlanguage{ngerman}± 0.11 A\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
407.59 \selectlanguage{ngerman}± 6.18 C\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Logic 25.03\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
298.60 \selectlanguage{ngerman}± 27.07 Ab\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
654.13 \selectlanguage{ngerman}± 47.75 Aa\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.43 \selectlanguage{ngerman}± 0.06 B\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
862.43 \selectlanguage{ngerman}± 103.45 A\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
Logic 25.05\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
237.30 \selectlanguage{ngerman}± 42.99 Bb\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
575.42 \selectlanguage{ngerman}± 64.07 Ba\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.11 \selectlanguage{ngerman}± 0.08 A\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
672.30 \selectlanguage{ngerman}± 129.93 B\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{ngerman}

Table 1 -- Mean Cyclic Fatigue (Time in seconds), Torque (Ncm), and
Angle of Rotation (º) of the Instruments tested.

Different upper letters on columns indicate statiscal differences among
groups after ANOVA one-way and post-hoc of Tukey (P \textless{} 0,05).

FIGURES

Figure 1 - Scanning electron microscopy images of the fractured surfaces
of separate fragments after torsional testing (first row: A, a = Flat
File 25.04; second row: B, b = ProDesign Logic2 25.03; bottom row: C, c
= Prodesign Logic2 25.05). The left column shows images with the
circular boxes indicating concentric abrasion marks at × 200
magnification; the right column shows concentric abrasion marks at ×
1000 magnification; and the skewed dimples near the center of rotation
are typical features of torsional failure.

Figure 2 - Scanning electron microscopy images of the fractured surfaces
of separated fragments of cyclic fatigue testing (first row: A, a = Flat
File 25.04; second row: B, b = ProDesign Logic2 25.03; bottom row: C, c
= Prodesign Logic2 25.05). The crack origins are identified by circular
boxes. The images show numerous dimples spread on the fractured
surfaces, which constitute a typical feature of ductile fracture.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-1/Figure-1}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-2/Figure-2}

\end{center}
\end{figure}

\selectlanguage{english}
\FloatBarrier
\end{document}

