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Aim. The manual files are still widely used for initial canal negotiation prior the use of nickel-titanium shaping instruments, to determine working length and to verify patency. A mechanical glide path can be performed using manual files with handpieces, such as M4 Handpiece (SybronEndo, USA) that allows a 30°/30° reciprocating motion. The Pathfinders (SybronEndo, USA) are hand files designed to negotiate complex canals, made from stainless steel (SS) or carbon steel (CS) alloys. The aim of this in vitro study was to compare cyclic fatigue resistance of these two different types of manual Pathfinder instruments used in a M4 reciprocating handpiece in double curved artificial canals.
Materials and methods. Manual instruments designed for glide path (size #9 ISO .02 taper) made from different alloys were selected: Group SS - stainless steel Pathfinders (Sybron Endo) and Group CS - carbon steel Pathfinders size K2 (Sybron Endo). Ten instruments of each group were tested for resistance to cyclic fatigue with a reciprocating M4 handpiece inside an artificial S-shaped canal; the time to fracture was recorded for each file and data were statistically analyzed (ANOVA).
Results. Mean values (and SD) were 527 (± 89) seconds for the CS instruments and 548 (± 104) seconds for the SS files. No significant differences were observed between groups (p=0,062).
Conclusions. According to the results, both carbon and stainless steel instruments presented similar fatigue resistance when used with M4 reciprocating handpiece in double curved canals.
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Annali di stomatologia
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Mechanical resistance of carbon and stainless steel hand instruments used in a reciprocating handpiece
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Mechanical resistance of carbon and stainless steel hand instruments used in a reciprocating handpiece
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                                                                                                     Original article



    Mechanical resistance of carbon and stainless steel
    hand instruments used in a reciprocating handpiece




                                                                                                                       li
                                                                   na
    Lucila Piasecki, DDS, MSc1                               canal; the time to fracture was recorded for each
    Dina Al-Sudani, DDS, MSc2                                file and data were statistically analyzed (ANOVA).




                                                                 io
    Alessio Giansiracusa Rubini, DDS, MSc3                   Results. Mean values (and SD) were 527 (± 89) sec-
    Giampaolo Sannino, DDS3                                  onds for the CS instruments and 548 (± 104) sec-
    Maurizio Bossù, DDS3                                     onds for the SS files. No significant differences
    Luca Testarelli, DDS, MSc3                               were observed between groups (p=0,062).




                                                              az
    Roberto Di Giorgio, DDS3                                 Conclusions. According to the results, both carbon
    Ulisses Xavier da Silva-Neto, DDS, MSc, PhD1             and stainless steel instruments presented similar
    Christian Giampietro Brandão, DDS, MSc, PhD4             fatigue resistance when used with M4 reciprocating
    Gianluca Gambarini, MD, DDS, PhD3                        handpiece in double curved canals.




                                                           rn
                                                             Key words: cyclic fatigue, endodontic instruments,
    1 School of Health and Biosciences, PUCPR,               carbon steel, stainless steel, reciprocating hand-
      Curitiba, Brazil                                       piece.




                                                        te
    2 KSU, Riyadh, Saudi Arabia, Arabia
    3 Department of Oral and Maxillo-Facial Sciences,

      “Sapienza” University of Rome, Italy                   Introduction
                                                     In
    4 State University of West Paraná, Cascavel, Brazil

                                                             Despite nickel-titanium (NiTi) rotary or reciprocating in-
                                                             struments have gained popularity among practitioners
    Corresponding author:                                    and endodontic specialists, the stainless steel (SS)
    Lucila Piasecki                                          manual files are still widely used for initial canal negoti-
                                              ni
    School of Health and Biosciences, PUCPR                  ation, to establish an endodontic glide path, to deter-
    Rua Imaculada Conceicao, 1155                            mine working length either radiographically or with the
    80215-901 Curitiba, Brazil                               aid of electronic apex locators and to verify patency.
    E-mail:lucilapiasecki@hotmail.com                        Canal negotiation is easier due to the fact the manual
                               o

                                                             SS files usually have a cutting tip: however, this tip and
                                                             the inherent rigidity of the alloy are theoretically not ide-
                           izi


    Summary                                                  al for instrumentation of curved canals (1,2). Therefore,
                                                             the tendency nowadays is to use SS instruments only
    Aim. The manual files are still widely used for ini-     in small sizes (generally smaller than ISO #20) and pre-
    tial canal negotiation prior the use of nickel-titani-   curve the instrument when canal curvatures are ob-
            Ed




    um shaping instruments, to determine working             served.
    length and to verify patency. A mechanical glide         Motion and methods of use are also very important in
    path can be performed using manual files with            making negotiation easier while preventing iatrogenic
    handpieces, such as M4 Handpiece (SybronEndo,            errors. It has been shown (3) that when a filing or ream-
    USA) that allows a 30°/30° reciprocating motion.         ing motion are applied to an instrument inside a curved
    The Pathfinders (SybronEndo, USA) are hand files         canal, the greatest amount of cutting occurs at the in-
    C




    designed to negotiate complex canals, made from          ner curve and apex because of the action of a lever
    stainless steel (SS) or carbon steel (CS) alloys.        arm and fulcrum (4). Intending to overcome the curva-
CI




    The aim of this in vitro study was to compare            ture influence, the balanced force technique was pro-
    cyclic fatigue resistance of these two different         posed, resulting in better cleaning and less apical
    types of manual Pathfinder instruments used in a         transportation compared to hand filing motion (5-7).
    M4 reciprocating handpiece in double curved arti-        The concept of balanced-forced technique was intro-
    ficial canals.                                           duced for manual hand filing, but it can be also be
    Materials and methods. Manual instruments de-            mechanized. The M4 Safety Handpiece (Sybron Endo,
©




    signed for glide path (size #9 ISO .02 taper) made       Glendora, CA, USA), was developed for mechanical
    from different alloys were selected: Group SS -          preparation of root canals, using manual endodontic in-
    stainless steel Pathfinders (Sybron Endo) and            struments in a 30°/30° reciprocating motion, that can be
    Group CS - carbon steel Pathfinders size K2              considered the mechanical expression of the balanced
    (Sybron Endo). Ten instruments of each group were        force motion. This M4 handpiece, which can be used
    tested for resistance to cyclic fatigue with a recip-    with electric endodontic motors or be directly connected
    rocating M4 handpiece inside an artificial S-shaped      to the dental unit, features a 4:1 gear reduction, and os-

    Annali di Stomatologia 2013; IV (3-4): 259-262                                                                    259
    L. Piasecki et al.


    cillates 30 degrees in both clockwise/counterclockwise       so can be made by using a stiffer alloy, carbon steel
    directions. It can be used with most of commercially         (an alloy that cannot be autoclaved) to allow better ne-
    available SS or nickel-titanium (NiTi) manual files, not     gotiation in complex canals since they can be consider
    only for preparation but also for enhancing final irriga-    single use instruments that easily deform and need to
    tion or for gutta-percha removal (8).                        be discarded after one use.




                                                                                                                            li
    Notwithstanding these interesting properties, a very few     Therefore, the aim of this in vitro study was to compare
    number of studies had been published in the last




                                                                     na
                                                                 two different types of Pathfinder handfiles (size #9 ta-
    decades about the M4 handpiece (9,10). On the other          per .02) made by stainless steel or carbon steel, used
    hand, many studies demonstrated that SS K-files              in a M4 reciprocating handpiece for the negotiation of
    mounted in a Giromatic (MicroMega, Besancon, France)         S-shaped artificial canals, to evaluate if different alloys
    90°-90° reciprocating handpiece, were able to negotiate      could be more or less beneficial in terms of resistance




                                                                   io
    narrow canals and maintain the original path, when           to cyclic fatigue.
    used up to a size 25 (11-13). The M4 Handpiece pre-
    sents smaller reciprocation angles than Giromatic (re-
    spectively 30°/30° vs 90°/90°), which theoretically




                                                                az
                                                                 Materials and methods
    should result in a safer movement, because torsional
    stress and bending stress are lower when angles are
                                                                 Two different types of size #9 .02 taper manual instru-
    smaller. Such a constant and predictable 1/12 turn mo-
                                                                 ments were selected:
    tion can be consider an improved hand filing, being




                                                             rn
                                                                 Group SS - stainless steel handfiles, Pathfinders;
    more precise and reproducible than what can be manu-
                                                                 Group CS - carbon steel handfiles, Pathfinders CS,
    ally achieved (usually 1/4 or 1/8 turn). Therefore, the M4
                                                                 size K2.
    handpiece could be used as an alternative for both initial
                                                                 All the instruments (Fig. 1) were produced by the same




                                                          te
    negotiation and creation of an endodontic glide path.
                                                                 manufacturer (Sybron Endo,Glendora,Ca,USA), pre-
    Initial negotiation is the most delicate part of manual
                                                                 senting the same features, to eliminate all variables re-
    hand filing especially in thin, narrow, calcified and
                                                                 lated to design or manufacturing process; they were vi-
    curved canals. Clinicians often start by using very small
                                                       In
    instruments (ISO sizes #6 to #8) that are meant to find
    the path towards the apex in complex and challenging
                                                                 sually examined under a stereomicroscope to discard
                                                                 any defective instruments. The device used to test the
    situations. Therefore, these instruments need a lot of       instrument resistance to cyclic fatigue in double shaped
    different mechanical properties, which often contradict      artificial canal have been previously used and de-
    among themselves: excellent cutting ability, and a cut-      scribed in a peer-reviewed scientific article (14).
                                                                 The device (Fig. 2) consists of a mainframe to which a
                                          ni
    ting tip to progress easily through dentin, but only to a
    certain amount, due to the risk of apical blockage; flexi-   mobile plastic support for the electric handpiece is con-
    bility to follow canal anatomy and prevent transporta-       nected, and a stainless steel block containing the artifi-
    tion, but some inherent rigidity is needed to make pos-      cial canals. The electric handpiece was mounted on a
                             o

    sible to progress a small instrument through the canal,      mobile device to allow the precise and reproducible
    especially when calcified or constricted. Intending to       placement of each instrument inside the artificial canal.
                         izi


    provide these requirements, special instruments have         This placement ensured three-dimensional alignment
    been manufactured and commercialized for the cre-            and the positioning of the instruments to the same
    ation of glide path, such as the Pathfinders (Sybron En-     depth. The artificial canal was manufactured by repro-
    do, Glendora, CA, USA).                                      ducing an instrument’s size and taper, thus providing
           Ed




    The manual Pathfinder instruments present a different        the instrument with a suitable trajectory. A simulated
    design from traditional K-files or Reamers, and they al-     root canal with a double curvature was constructed: the

                                                                                      Figure 1. The two types of tested in-
                                                                                      struments: a. Stainless steel Pathfin-
                                                                                      der; b. Carbon steel Pathfinder CS
    C




                                                                                      K2.
CI
©




    260                                                                          Annali di Stomatologia 2013; IV (3-4): 259-262
    Mechanical resistance of carbon and stainless steel hand instruments used in a reciprocating handpiece


                                                                   files. No significant differences were noted between
                                                                   groups (p=0,062).


                                                                   Discussion




                                                                                                                           li
                                                                   Many dentists fear that manual instruments could easily




                                                                       na
                                                                   break when used in an M4 handpiece, especially when
                                                                   working in thin, narrow, constricted or calcified canals.
                                                                   They have read or heard that SS instruments present a
                                                                   high risk of intracanal separation when rotated inside a




                                                                     io
                                                                   curved canal (15). This statement is correct, but in clini-
                                                                   cal practice we need to fully understand how different
                                                                   motions influence performance and safety of endodon-
                                                                   tic instruments. A recent study from Gambarini et al.




                                                                  az
                                                                   (16) showed that SS ISO instruments used in a M4 rec-
                                                                   iprocating handpiece were significantly more resistant
                                                                   that .02 tapered NiTi rotary instruments designed for
                                                                   glide path. These results can be easily explained due to




                                                               rn
                                                                   the fact that M4 handpiece allows only an oscillating
                                                                   movement inside a canal, not a full rotation: conse-
                                                                   quently, reciprocating SS instruments are very resistant




                                                            te
                                                                   to cyclic fatigue, significantly more than NiTi rotary in-
                                                                   struments. In fact, even if the NiTi alloy presents a su-
                                                                   perior resistance to fatigue, rotation creates much more
                                                                   instrumentation stresses compared to reciprocation and
                                                         In        as a consequence failure may occur earlier (17).
                                                                   Many studies have been published recently showing
    Figure 2. The testing apparatus for cyclic fatigue with dou-
    ble curvature (S-shaped artificial canal).                     that reciprocating motions reduce both torsional stress
                                                                   and cyclic fatigue of NiTi, regardless of the different
                                                                   manufacturing process (18-22). Interestingly, no stud-
                                              ni
    first coronal curve has 60o angle of curvature with a ra-      ies have evaluated the differences between a recipro-
    dius of 5 mm, located 8mm from the tip of the instru-          cating movement and the M4 one.
    ment, and the second is apical, with 70o angle and a ra-       Moreover, in the past many studies have demonstrated
    dius of curvature of 2 mm, whose center was placed at          that resistance to fracture is dependent on the size, de-
                               o

    2 mm, from the tip.                                            sign and manufacturing differences of the SS instru-
    Ten instruments of each group were activated inside            ments (24,25). More recently, Gambarini et al. con-
                           izi


    the double curved artificial canal with a M4 handpiece         firmed these data (article in press), showing that file de-
    (4:1 reduction, 30°/30° reciprocation), mounted in an          sign and manufacturing processes play a significant
    endodontic motor (ASEPTICO, Woodinville, WA), until            role in determining resistance to fatigue of SS instru-
    fracture occurred.                                             ments also when used with a reciprocating handpiece.
            Ed




    For each instrument, the time to fracture in seconds (s)       The K-files and Reamers with flutes created by a twist-
    was recorded by the same operator with a chronometer           ing process showed greater fatigue resistance, while
    to an accuracy of 0.1s. After positioning the instrument       Hedström files manufactured by a grinding process,
    into the artificial canal, as soon as the reciprocation        were weaker. It has been demonstrated also for NiTi
    started, timing was initiated and it was stopped when          that grinding process is likely to create defects and mi-
    instrument breakage occurred. Since the instruments            crocracks on the external surface of the instruments,
    C




    are not fully rotated inside the canal, the actual speed       thus reducing resistance to metal fatigue (24).
    cannot be properly measured. Therefore, time to failure        On the contrary, the present study demonstrated that in
CI




    was selected as the most precise way to describe resis-        vitro resistance to fracture of manual instruments used
    tance to breakage.                                             in a M4 Handpiece produced with different alloys (car-
    Mean values and standard deviation (SD) were then              bon vs stainless steel) was not significantly dependent
    calculated for each group. Cyclic fatigue data were an-        on the different characteristics of alloys. Data showed
    alyzed by one-way ANOVA test to determine any statis-          no statistically significant difference between the two
    tical difference between groups; the significance was          tested instruments.
©




    determined at the 95% confidence level.

                                                                   Conclusion
    Results
                                                                   Carbon steel is a slightly harder and more rigid alloy
    Mean time to fracture was 527 (± 89) seconds for the           than SS, and it is being used for Pathfinder instruments
    CS instruments and 548 (± 104) seconds for the SS              because improved cutting efficiency and a slightly high-

    Annali di Stomatologia 2013; IV (3-4): 259-262                                                                        261
    L. Piasecki et al.


    er stiffness can be beneficial properties for a small in-               11. Weine FS, Kelly RF, Bray KE. Effect of preparation with en-
    strument, which is meant to negotiate and pre-enlarge                       dodontic handpieces on original canal shape. J Endod
    thin, narrow and curved canals. However, in cases of                        1976;2:298-303.
                                                                            12. Klayman SM, Brilliant JD. A comparison of the efficacy of se-
    complex anatomy such as double curvature canals,
                                                                                rial preparation versus Giromatic preparation. J Endod
    flexibility and resistance to fracture are more important




                                                                                                                                              li
                                                                                1975;1:334-7.
    parameters, reducing the risk of iatrogenic errors and                  13. Hülsmann M, Stryga F. Comparison of root canal prepara-
    intracanal separation.




                                                                               na
                                                                                tion using different automated devices and hand instru-
    Hence we may conclude that tested different alloys did-                     mentation. J Endod 1993;19(3):141-5.
    n’t play a significant role in determining fatigue resis-               14. Al-Sudani D, Grande NM, Plotino G, Pompa G, Di Carlo S,
    tance of the tested instruments. These results support                      Testarelli L, et al. Cyclic fatigue of nickel-titanium rotary in-
    the clinical use of both SS and CS Pathfinder instru-                       struments in a double (S-shaped) simulated curvature. J En-




                                                                             io
    ments with the reciprocating M4 Handpiece for the cre-                      dod 2012;38:987-9.
                                                                            15. Lopes HP, Elias CN, Siqueira JF, Soares RG, Souza LC,
    ation of an endodontic glide path in the most complex
                                                                                Oliveira JCM, et al. Mechanical behavior of pathfinding en-
    curvatures, when safety is a concern.
                                                                                dodontic instruments. J Endod 2012;38:1417-21.




                                                                          az
                                                                            16. Gambarini G, Plotino G, Sannino G, Grande NM, Giansira-
                                                                                cusa A, Piasecki L, et al. Cyclic Fatigue of Instruments for
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    C
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©




    262                                                                                        Annali di Stomatologia 2013; IV (3-4): 259-262
