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Despite it is not questionable that static tests give readers only a partial view of the performance of an endodontic instrument they are currently accepted as valid ones to evaluate and compare mechanical properties of endodontic instruments. Therefore, aim of the present study was to evaluate a new single-file reciprocating instrument (Direct RGold 25, Direct Endo, Paris, France) and compare by using the three above-mentioned tests them with the same features of other reciprocating instruments which have been commercialized since many years and consequently have been widely investigated: Wave One Gold Primary (Dentsply- Maillefer, Baillagues, Switzerland), Reciproc and the Reciproc Blue (VDW, Munchen, Germany). For each of the four tested instruments (in size 25) 60 instruments were selected and randomly divided into three groups (n=20). Each group was subjected to a different in vitro mechanical test. Prior to test, each instrument was carefully examinated under magnification. Instruments with visible defects and flute deformation were discarded. Stiffness, cyclic fatigue, torsional resistance tests were performed using methodologies validated in previous studies. For each test data were recorded, then the mean values and the standard deviations were statistically analyzed using a 1-way ANOVA test followed by the post hoc Tukey test with significance set to a 95% confidence level. Results showed that Direct R Gold was significantly more resistant in terms of torsional resistance when compared with all the other instruments. In terms of cyclic fatigue resistance no statistically relevant differences were found amongst the three thermally treated instruments (Direct R Gold, Reciproc Blue and WaveOne Gold) which were all significantly more resistant than Reciproc. Flexibility of Direct R Gold and Reciproc was significantly lower than the other tested instruments. Since the tip and taper dimensions are almost the same for every instrument tested, and since the Direct R gold has the same cross-sectional design as Reciproc and Reciproc Blue, the explanation of these results must be due to the proprietary thermal treatments of the instruments. Direct R-Gold heat treatment allowed a significant increase in both torsional and fatigue resistance, which is a clinically relevant advantage in a single-file technique where only one instrument is used and, as a consequence, it is subjected to all instrumentation stresses.
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1971-1441
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Massimo  Galli
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Annali di stomatologia
reciprocation
A comparative analysis of mechanical properties of different reciprocating Niti endodontic instruments
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Case Report
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Ann Stomatol (Roma)
Massimo  Galli
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University of Rome, La Sapienza
1971-1441
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reciprocation
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A comparative analysis of mechanical properties of different reciprocating Niti endodontic instruments
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                                                                                                    Case report


A comparative analysis of mechanical properties of
different reciprocating Niti endodontic instruments



Maya Feghali*                                             and WaveOne Gold) which were all significantly
Alaa Al Daeen Al Atta**                                   more resistant than Reciproc. Flexibility of Direct R
Massimo Galli***                                          Gold and Reciproc was significantly lower than the
                                                          other tested instruments.
*Private practictioner, Paris, France                     Since the tip and taper dimensions are almost the
**Private practictioner, Unit Arab Emirates               same for every instrument tested, and since the
***University of Rome, La Sapienza                        Direct R gold has the same cross-sectional design
                                                          as Reciproc and Reciproc Blue, the explanation of
Corresponding author: Massimo Galli massimo.              these results must be due to the proprietary ther-
galli@uniroma1.it                                         mal treatments of the instruments. Direct R-Gold
                                                          heat treatment allowed a significant increase in
Key words: Endodontic instrument, Nickel-titanium,        both torsional and fatigue resistance, which is a
reciprocation                                             clinically relevant advantage in a single-file tech-
                                                          nique where only one instrument is used and, as a
                                                          consequence, it is subjected to all instrumentation
Abstract                                                  stresses.

Despite it is not questionable that static tests give
                                                          Introduction
readers only a partial view of the performance of an
endodontic instrument they are currently accepted         The goal of any endodontic therapy is to obtain a che-
as valid ones to evaluate and compare mechanical          mo-mechanical disinfection and debridement of the root
properties of endodontic instruments.                     canal, by proper shaping and cleaning procedures, and
Therefore, aim of the present study was to evaluate       to obtain a stable apical and coronal sealing, to avoid
a new single-file reciprocating instrument (Direct R-     the re-infection of the root canal system (1-2). These
Gold 25, Direct Endo, Paris, France) and compare          objectives were indicated many decades ago and are
by using the three above-mentioned tests them             still valid; on the contrary the way they are reached
with the same features of other reciprocating in-         drastically changed with the introduction of Nickel-Tita-
struments which have been commercialized since            nium (NiTi) rotary instruments, which completely revo-
many years and consequently have been widely              lutionized the root canal treatment (RCT). NiTi rotary
investigated: Wave One Gold Primary (Dentsply-            files increased the predictability, speediness, and effec-
Maillefer, Baillagues, Switzerland), Reciproc and         tiveness of the RCT, due to the improved properties of
the Reciproc Blue (VDW, Munchen, Germany).                the alloy (3). Moreover, in the last decade new thermal
For each of the four tested instruments (in size 25)      treatments have been developed to improve flexibility
60 instruments were selected and randomly divided         and fatigue resistance of the instruments, resulting in a
into three groups (n=20). Each group was subjected        differentiation between heat-treated (HT) and non heat-
to a different in vitro mechanical test. Prior to test,   treated (NHT) instruments, with the first type of instru-
each instrument was carefully examinated under            ments being pre-bendable and showing less bounce
magnification. Instruments with visible defects and       back (4). All these improvements currently allow a more
flute deformation were discarded. Stiffness, cyclic       efficient and safe instrumentation of curved canals.
fatigue, torsional resistance tests were performed        Another important improvement in the shaping proce-
using methodologies validated in previous studies.        dure has been the introduction of the reciprocating mo-
For each test data were recorded, then the mean           tion (RM). The idea was to simplify shaping by using a
values and the standard deviations were statisti-         single-file technique, while keeping safety, thanks to a
cally analyzed using a 1-way ANOVA test followed          motion which is less stressful than continuous rotation,
by the post hoc Tukey test with significance set to a     because the instruments is not continuously engaged,
95% confidence level.                                     but works by alternating engagement and disengage-
Results showed that Direct R Gold was significantly       ment of the blades (5).
more resistant in terms of torsional resistance when      RM has been defined as a repeated backward and for-
compared with all the other instruments. In terms         ward (CW/CCW) movement; this kind of cinematic can
of cyclic fatigue resistance no statistically relevant    be applied to every endodontic file. There are many
differences were found amongst the three thermally        kinds of RM:
treated instruments (Direct R Gold, Reciproc Blue         - complete reciprocation (oscillation),


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     A comparative analysis of mechanical properties of different reciprocating Niti endodontic instruments

     - partial reciprocation (rotational effect),                    three groups (n=20). Each group was subjected to a dif-
     - hybrid reciprocation (combined movements).                    ferent in vitro mechanical test, according to the current
     According to the review of the literature of Grande &Plo-       dental literature. Prior to test, each instrument was care-
     tino (6-7) it can be stated the reciprocating motion en-        fully examinated under magnification. Instruments with
     hance the metallurgical in vitro performances of the NiTi       visible defects and flute deformation were discarded.
     files without significantly affecting in any way the cutting
     efficiency of the same files.
     These undoubtfully advantages has brought the manu-             Bending Resistance (Stiffeness) Test
     facturer to produce new endodontic motors and a lot of
                                                                     Twenty instruments for each brand underwent the bend-
     different instruments thought to be used in counterclock-
                                                                     ing resistance test (Fig. 1a). The stiffness tests were per-
     wise reciprocating motion. Whenever a new NiTi instru-
                                                                     formed using a device already validated in a previously
     ment is released on the market, it is important to evalu-
                                                                     published study (10). The device consists of a load cell,
     ate the file characteristics and compare to similar files
                                                                     an electronic display, and a mobile holder to allow re-
     already present on the market. Indeed, it is well known
                                                                     peatable positioning of the instruments on the load cell.
     the influence of each characteristic on a particular per-
                                                                     The stiffness tests were performed by bending each file
     formance of the NiTi rotary file (6-7). To be more precise,
                                                                     at a 45° angle at 3 mm from its tip and recording the ap-
     the cyclic fatigue is influenced by two main characteris-
                                                                     plied force (g). The higher the value, stiffer (less flexible)
     tics: the metal mass at the point of maximum stress and
                                                                     the instrument. The measurements indicated by the elec-
     the percentage of martensite. Lower the mass, higher
                                                                     tronic display connected to the load cell were recorded,
     the cyclic fatigue resistance and higher the martens-
                                                                     and then the mean values and the standard deviations
     ite percentage, higher the cyclic fatigue resistance as
                                                                     of the bending force were statistically analyzed using a
     well. Similarly, the bending properties on the file are
                                                                     1-way ANOVA test followed by the post hoc Tukey test
     influenced in the same way as the cyclic fatigue resis-
                                                                     with significance set to a 95% confidence level.
     tance. The torsional resistance is instead influenced
     mainly by the cross-sectional design and specifically by
     the distribution of the mass around the rotation cen-           Cyclic Fatigue Test
     ter of the file. The greater the mass gathered far from
     the rotation center, the greater is the torque to fracture.     Twenty instruments for each brand were rotated accord-
     On the other hand, several studies demonstrate that             ing to the manufacturers’ recommendation in a stainless-
     the martensite percentage, does not or negatively af-           steel artificial canal of 16 mm characterized by a 90°
     fect the torsional resistance (8). Finally, the cutting ef-     angle of curvature and a 2-mm radius of curvature using
     ficiency has been demonstrated depending mainly on              glycerin as a lubricant to avoid any friction between the
     the cross-sectional, tip and flute design. The s shaped         files and the artificial canal (Fig. 1b). Resulting speed
     cross section is the most cutting efficient, as demon-          was always same (300 rpm). Each test was performed
     strated by Plotino et al (7).                                   by the same expert operator to avoid error due to differ-
     Therefore, the influence of each single characteristic          ent operators’ skill. Each instrument reciprocated inside
     of a file is well-known from the literature, despite that       the canal until a visible and/or audible sign of fracture
     the performance of a file is influenced by the interaction      was detected (11-12). The time to fracture (TtF) was
     between all these different factors and this result is still    measured using a digital chronometer with a sensitivity
     impossible to predict.                                          of 0.01 seconds. The higher the value the more resistant
     Despite it is not questionable that static tests give readers   the instrument.
     only a partial view of the performance of a new instru-         The length of the fragments (FL) was measured with a
     ment (8), it is likewise not questionable that the scientific   digital caliber and statistically analyzed to evaluate the
     method is based on repeatable and comparable studies,           correct positioning of the instruments inside the artificial
     and nowadays these kinds of parameters can only by ob-          canal (13) and to verify the comparability of the results of
     tained using the static test used. Therefore, it is possible    the cyclic fatigue test.
     only using the cyclic fatigue, bending and torsional resis-     The mean values and the standard deviations of both
     tance tests. This comparison could help the general den-        TtF and FL were statistically analyzed using a 1-way
     tist as well as the endodontists, who undoubtfully already      ANOVA test followed by the post hoc Tukey test with sig-
     knows the other instruments tested, to preliminary evalu-       nificance set to a 95% confidence level.
     ate the potential performances of the newly released one.
     Therefore, aim of the present study was to evaluate             Torsional Resistance Test
     the stiffness, the cyclic fatigue and torsional resistance
     of a new (9) single-file reciprocating instrument (Di-          Twenty instruments for each brand underwent the tor-
     rect R-Gold, Direct Endo, Paris, France) and compare            sional resistance test ((Fig. 1c). The torsional resistance
     them with the same features of other reciprocating in-          test was performed with a custom-made torsiometer-like
     struments which have been commercialized since many             device previously validated in a published study at 300
     years and consequently have been widely investigated :          rpm in counterclockwise reciprocating motion because it
     Wave One Gold Primary (Dentsply-Maillefer, Baillagues,          has been demonstrated that rotational speed does not
     Switzerland), Reciproc and the Reciproc Blue (VDW,              affect the results (8,14). The device was used to avoid
     Munchen, Germany).                                              the bending of the coronal part of the instrument and to
                                                                     have a straight angle of insertion because it has been
                                                                     demonstrated in recently published studies that it can
     Materials and Methods
                                                                     deeply influence the result of the torsional test. Precisely,
     For each of the four tested instruments (in size 25 ) sixty     the test was performed blocking the tip of the instrument
     instruments were selected and randomly divided into             with a vise at 3 mm from the tip and rotating it at 300



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M. Feghali et al.




Figure 1. The three tests : A. Stiffness. B Fatigue resistance C Torsional resistance


rpm in the counterclockwise direction with a dedicated              cantly more resistant than Reciproc. Flexibility of Direct
electronic motor (Kavo, Biberach, Germany) allowing                 R Gold and Reciproc was significantly lower than the
a real-time (0.1 seconds) recording of the torque with              other tested instruments.
a sensitivity of 0.05 Ncm. The torque at fracture results
were collected on a spreadsheet. The higher the value               Discussion
the more resistant the instrument.
The length of the fragments (FL) was measured with a                In the current study, a three methods approach was
digital caliber and statistically analyzed to evaluate the          performed to compare Direct R-Gold, a new HT recip-
correct positioning of the instruments’ tip inside the tor-         rocating NiTi file recently introduced on the market and
                                                                    designed to be used in a single-file technique with the
siometer and to verify the comparability of the results of
                                                                    most commonly used and tested single-file reciprocat-
the torsional test. The mean values and the standard
                                                                    ing instruments commercially available. The instruments
deviations of both FL and the torque at fracture were
                                                                    tested in this study share some characteristics such as
statistically analyzed using 1-way ANOVA followed by
                                                                    the taper and the tip dimensions, 0.25mm for all of them
the post hoc Tukey test with significance set to a 95%
                                                                    and the shaping technique. Indeed, each of the tested
confidence level.
                                                                    file is thought to be used in a CCW reciprocating single-
                                                                    file technique. Moreover, the Direct R Gold presents
Results                                                             a s-shaped cross-sectional design, which is the same
Results are shown in Table 1. Direct R showed the best              design as the Reciproc and Reciproc Blue instruments
mechanical performance in terms of torsional resistance             (5). According to the manufacturer (9), the Direct R Gold
with statistically significant difference with all the other        instruments undergo a proprietary treatment, but at the
instruments. In terms of cyclic fatigue resistance no sta-          moment no published study on this kind of treatment is
tistically relevant differences were found amongst the              present in literature, while many studies are available for
three thermally treated instruments (Direct R Gold, Re-             the other two HT instruments . It must be underlined that
ciproc Blue and WaveOne Gold) which were all signifi-               HT are not disclosed by manufacturers and it has been



Table 1. Mean values and SD of Stiffness, Cyclic Fatigue and Torsional Resistance tests of the four instruments tested
(significant difference *)

                                        Direct R Gold            Reciproc           Reciproc Blue         Wave One Gold

                                       Mean         SD         Mean       SD        Mean        SD        Mean         SD

           Stiffness (g)               146.3        11.0       157.2      8.3       82.2*       3.2       88.5*       12.01
        Cyclic fatigue (s)              12.8        0.5        9.27*      1.18      13.31       1.26      11.98       1.20
  Torsional resistance (Ncm)            1.54*       0.12       0.66       0.08          0.52    0.07       0.46       0.09



10.59987/ads/2023.4.9-13                                                                                                          11
     A comparative analysis of mechanical properties of different reciprocating Niti endodontic instruments

     demonstrated that they are different from each manu-          the absence of dynamic investigations, such as cutting
     facturer, and consequently these differences may result       efficiency (16), shaping ability, centering ability.
     in different mechanical in vitro properties and clinical      Hence we may conclude that, despite the clinical rele-
     performance (8).                                              vance of in vitro studies can be doubtful, the importance
     Therefore, despite similarities in design and method of       of understanding the in vitro performances of new in-
     use, comparative tests are needed when new instru-            struments introduced on the market is undoubtedly (8).
     ments with new HTs are commercialized to compare              The evaluation of different in vitro characteristics, such
     their performances with the mostly known competitor           as flexibility, cyclic fatigue and torsional resistance and
     instruments (15).                                             comparison with widespread file could give provide im-
     Reciproc and Reciproc Blue are instruments from VDW           portant preliminar data on the quality positioning of new
     designed for be used in CCW reciprocating single-file         products and possible advantages in clinical practice
     technique (4,5). The two instruments shares every
     design characteristic (tip 0.25 and taper 0.08 variable
     and present an S-shaped cross-sectional design) but           References
     differ from for the heat treatment of the alloy; Recip-       1.  Valenti-Obino F, Di Nardo D, Quero L, Miccoli G, Gam-
     roc presents M-Wire heat treatment, containing the                barini G, Testarelli L, Galli M. Symmetry of root and root
     austenite phase with small amounts of martensite and              canal morphology of mandibular incisors: A cone-beam
     R-phase at body temperature, and the Reciproc Blue                computed tomography study in vivo. J Clin Exp Dent. 2019
                                                                       Jun 1;11(6):e527-e533. doi: 10.4317/jced.55629. PMID:
     alloy is the Blue Wire, which is characterized by lower
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     more ductile NiTi files. As previously mentioned, the dif-        dodontic sealer. Aust Endod J. 2006 Apr;32(1):31-4. doi:
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                                                                       L, Gaimari G, Di Nardo D, Testarelli L. Fatigue Resistance of
     two instruments. In fact, according to the results of the
                                                                       New and Used Nickel-Titanium Rotary Instruments: a Com-
     present study, Reciproc showed lower flexibility and              parative Study. Clin Ter. 2018 May-Jun;169(3):e96-e101.
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     the latter showed lower torsional resistance than the         4. Plotino G, Grande NM, Testarelli L, Gambarini G, Castagno-
     former. Wave One Gold is a thermally treated (single              la R, Rossetti A, Özyürek T, Cordaro M, Fortunato L. Cyclic
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                                                                       Reciprocating Files at Different Environmental Temperatu-
     Dentsply Maillefer. The primary file, tested in the cur-
                                                                       res. J Endod. 2018 Oct;44(10):1549-1552. doi: 10.1016/j.
     rent study, is 25.08 with a rectangular cross-sectional           joen.2018.06.006. Epub 2018 Aug 23. PMID: 30
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                                                                   6. Grande NM, Ahmed HMA, Cohen S, Bukiet F, Plotino G.
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                                                                       Current Assessment of Reciprocation in Endodontic Prepa-
     ones. Despite being heat-treated Direct R Gold pres-              ration: A Comprehensive Review-Part I: Historic Perspecti-
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M. Feghali et al.

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