10.59987/ads/2015.1.6-9
Aim. To compare the effect of brushing motion on torsional and cyclic fatigue resistance of TF Adaptive instruments after clinical use.
Methods. 20 packs of TFA small sequence (SybronEndo, Orange, CA, USA) were used for this study and divided into two groups. Each instrument prepared one resin tooth, consisting in 4 canals with a complex anatomy. In group A, no brushing motion was performed. In group B, after the green instrument reached the working length, brushing motion with circumferential filing was performed for 15 seconds in each canal (overall 1 minute). All the instruments were then subjected to cyclic fatigue test and mean values and standard deviation for time to fracture were evaluated. Data were subjected to one-way analysis of variance and Bonferroni t-test procedure with a significance set at P &lt; 0.05.
Results. No instruments were broken during preparation of root canals. Two TF Adaptive green and 5 yellow showed unwinding after intracanal clinical use. No statistically significant differences were found between green instruments of both groups (P &gt; 0.05), while a statistically significant difference was found between the yellow instruments (P &lt; 0.05), with group B showing an higher resistance to cyclic fatigue.
Conclusions. A prolonged passive brushing motion did not adversely affected mechanical resistance of the instrument used for this purpose. Resistance to both deformations and cyclic fatigue of the second instrument within the TFA small sequence was enhanced by the coronal flaring provided by the brushing action of the first instrument used.
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Annali di stomatologia
cyclic fatigue
Deformations and cyclic fatigue resistance of nickel-titanium instruments inside a sequence
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cyclic fatigue
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Deformations and cyclic fatigue resistance of nickel-titanium instruments inside a sequence
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                                                                                                     Original article



    Deformations and cyclic fatigue resistance
    of nickel-titanium instruments inside a sequence




                                                                                                       i
                                                                                                     al
                                                                                                  on
    Gianluca Gambarini, MD,DDS1                               ferences were found between green instruments
    Gianluca Plotino, DDS, PhD1                               of both groups (P > 0.05), while a statistically sig-
    Lucila Piasecki, DDS2                                     nificant difference was found between the yellow
    Dina Al-Sudani, DDS3                                      instruments (P < 0.05), with group B showing an
    Luca Testarelli, DDS, PhD1                                higher resistance to cyclic fatigue.




                                                                                        zi
    Gianpaolo Sannino, MD, DDS4                               Conclusions. A prolonged passive brushing mo-
                                                              tion did not adversely affected mechanical resis-
                                                              tance of the instrument used for this purpose. Re-




                                                                           na
    1 Endodontics Unit, Department of Oral and Maxillo-       sistance to both deformations and cyclic fatigue
      facial Sciences, “Sapienza” University of Rome, Italy   of the second instrument within the TFA small se-
    2 PUC University, Curitiba, Brasil                        quence was enhanced by the coronal flaring pro-
    3 Department of Restorative Dental Science, College of    vided by the brushing action of the first instru-
                                                              ment used.




                                                                er
      Dentistry, King Saud University, Riyadh, Saudi Arabia
    4 University of Rome II, Tor Vergata, Italy

                                                              Key words: nickel-titanium, brushing action, de-
                                                              formations, cyclic fatigue.
    There are no disclosures for the present study.


                                                         t
                                                      In      Introduction
    Corresponding author:
    Gianluca Gambarini                                        In the last decades the use of nickel-titanium (NiTi) ro-
    Department of Endodontics Unit                            tary instruments has become the most effective and
                                         ni
    Oral and Maxillo-facial Sciences                          popular method amongst endodontists for shaping
    “Sapienza” University of Rome                             root canals, due to their greater elasticity, strength
    Via Calabria, 25                                          and cutting efficiency (1). Despite these advantages,
                                io

    00187 Rome, Italy                                         fracture of NiTi rotary instruments caused by torsional
    E-mail: ggambarini@gmail.com                              stress and/or cyclic fatigue has remained a primary
                                                              concern in endodontics practice, because they tend to
                                                              break unexpectedly during intracanal use (2). Follow-
                        iz



    Summary                                                   ing the introduction of NiTi alloy in endodontics, man-
                                                              ufacturers have frequently changed the cross-section-
    Aim. To compare the effect of brushing motion on          al design and geometrical features of instruments to
          Ed




    torsional and cyclic fatigue resistance of TF             improve both torsional and cyclic fatigue resistance
    Adaptive instruments after clinical use.                  (3, 4). Since 2007, new alloys and new manufacturing
    Methods. 20 packs of TFA small sequence (Sybro-           processes were adopted to optimize the microstruc-
    nEndo, Orange, CA, USA) were used for this                ture of NiTi, basically through innovative thermome-
    study and divided into two groups. Each instru-           chanical processing (5). NiTI instruments produced
    ment prepared one resin tooth, consisting in 4            with these technologies (M-wire, CM wire or Twisted
IC




    canals with a complex anatomy. In group A, no             Files) showed better properties in terms of flexibility
    brushing motion was performed. In group B, after          and resistance to mechanical stress when compared
    the green instrument reached the working length,          to traditional NiTi alloy and processing (5-7).
    brushing motion with circumferential filing was           More recently, the use of single-file NiTi reciprocating
C




    performed for 15 seconds in each canal (overall 1         instruments have been advocated as a simple, safe
    minute). All the instruments were then subjected          alternative to rotary instrumentation techniques (8).
    to cyclic fatigue test and mean values and stan-          Current literature data show that reciprocating motion
    dard deviation for time to fracture were evaluated.       can extend both torsional and cyclic fatigue resis-
©




    Data were subjected to one-way analysis of vari-          tance of NiTi instruments when compared to continu-
    ance and Bonferroni t-test procedure with a sig-          ous rotation, by reducing instrumentation stress (9-
    nificance set at P < 0.05.                                12). Despite this improvement, the accumulation of all
    Results. No instruments were broken during                instrumentation stress on one single-file may still be
    preparation of root canals. Two TF Adaptive               high, and consequently new reciprocating movements
    green and 5 yellow showed unwinding after intra-          were developed to be used within a sequence, such
    canal clinical use. No statistically significant dif-     as TF Adaptive (TFA) (13, 14).

    6                                                                              Annali di Stomatologia 2015; VI (1): 6-9
    Deformations and fatigue resistance of endodontic instruments


    Other clinical factors, mainly related to individual            1 minute) to increase coronal flaring. Before any
    skill, sensitivity and operative choice, also affect            brushing motion, instruments were withdrawn 1 mm
    torsional and cyclic fatigue resistance of NiTi instru-         short of the working length, thus preventing any over
    ments: the applied pressure, the tendency to force              engagement with the canal walls. After shaping pro-
    the instrument apically, the use of torque control              cedures were completed all the 40 used NiTi instru-




                                                                                                            i
    motors, prolonged re-use, the creation of a glide               ments were inspected under magnification (3x) to




                                                                                                          al
    path (15) and so on. It has been shown that resis-              check any sign of plastic deformation or undwinding
    tance to fatigue is related to instrumentation time,            of flutes.
    being significantly reduced after multiple clinical             All the instruments were then subjected to cyclic fa-




                                                                                                       on
    use (16).                                                       tigue test using a testing device that was previously
    Traditionally, NiTi instruments are used as reamers,            described (21-27). Briefly, all instruments were tested
    while progressing to the working length, More re-               using the TFA motion powered by Elements motor
    cently, the use of a brushing motion in addition to             (SybronEndo, Orange, CA, USA). After positioning
    the traditional reaming action was proposed to im-              the instrument into a simulated root canal with a 60°




                                                                                              zi
    prove safety and efficiency of NiTi instrumentation             angle of curvature and 5-mm radius of curvature, as
    (17). The benefit of the brushing action is not only to         soon as rotation started timing was initiated and then
    enhance the amount of canal walls touched by the                stopped when instrument breakage was observed.




                                                                                 na
    file, but also to provide more coronal enlargement              For each instrument, the time to fracture in seconds
    for a safer progression of instruments within a se-             was recorded by the same operator with a chronome-
    quence (18, 19).                                                ter to an accuracy of 0.1 second. Since the motor au-
    Since the brushing motion increases instrumentation             tomatically selects the mode of use and the recipro-




                                                                      er
    time, the aim of this study was to compare its effect           cating angles depending on the canal anatomy,
    on torsional and cyclic fatigue resistance of TFA in-           speed and number of cycles to failure could not be
    struments after clinical use.                                   precisely calculated. Mean values and standard devi-
                                                                    ation (SD) for time to fracture were evaluated. To de-



                                                          t         termine any statistical difference between the groups,
    Material and methods
                                                       In           the data were subjected to a one-way analysis of
                                                                    variance. When the overall F test indicated a signifi-
    Twenty packs of TFA small sequence (SybronEndo,                 cant difference, the multiple-comparison Bonferroni t-
    Orange, CA, USA) were used for this study and ran-              test procedure was performed to identify differences
    domly divided into two groups of ten each. To avoid             among groups. Significance was set at the 95% confi-
                                               ni
    any changes related to anatomy, twenty plastic first            dence level.
    maxillary molar 3D teeth with the same morphology
    (Real-T Endo, Aca Dental, Inc., Overland Park, KS,
                                     io

    USA) were used for this study as previously done                Results
    (20). Each instrument prepared one tooth, consisting
    in 4 canals with a complex anatomy. Following the               No instruments were broken during preparation of
    manufactures’ guidelines for the TF Adaptive small              root canals. Two TF Adaptive green, tip size 20 and
                           iz



    sequence, a manual glide path up to a ISO size 15               .04 taper (one in each group A and B), and 5 TF
    was performed using the stainless-steel (SS) K-file             Adaptive yellow, tip size 25 and .06 taper (4 from
    instrument available in the package. Following the              Group A and 1 from Group B) showed unwinding af-
           Ed




    traffic light concept given by the manufacturer                 ter intracanal clinical use.
    (http://axis.sybronendo.com/tfadaptive_confidence#ta            Results of cyclic fatigue test are reported in Table 1.
    b6), the instrumentation was stopped at yellow, using           No statistically significant differences were found be-
    only the first two instruments of the sequence: the             tween green instruments of both groups (P > 0.05),
    green TFA instrument (tip size 20, .04 taper) followed          showing that one additional minute of brushing mo-
    by the red TFA instrument (tip size 25, .06 taper). All         tion did not decreased fatigue resistance. A statisti-
IC




    instruments were used with the patented TFA motion              cally significant difference was found between the
    in a specific endodontic motor (Elements Motor,                 yellow instruments (P < 0.05), with group B showing
    SybronEndo, Orange, CA, USA), which automatically               an higher resistance to cyclic fatigue. These differ-
    selected the kinematics (continuous rotation or recip-          ences are attributed to coronal flaring provided by the
C




    rocation) according to intracanal stress applied on the         green instrument used with a brushing motion, which
    instrument during instrumentation. All instruments              reduced instrumentation stress for the next (yellow)
    reached the working length by incremental steps (1              instrument.
    mm) without being forced apically and the flutes were
©




    always cleaned after each 1 mm apical progression.
                                                                    Table 1. Mean time to fracture in seconds (Standard Devi-
    Irrigation was performed with alchool every each in-            ation) of the different instruments tested.
    strument.
    In group A, no brushing motion was performed. In                Instrument Size          Green (20/.04) Yellow (25/.06)
    group B, after the green instrument reached the work-
    ing length, brushing motion with circumferential filing         Group A (No Brushing) 142 (20)           73 (6)
    was performed for 15 seconds in each canal (overall             Group B (Brushing)    137 (15)           97 (7)


    Annali di Stomatologia 2015; VI (1): 6-9                                                                               7
    G. Gambarini et al.


    Discussion                                                  a) the coronal flaring provided by the brushing action
                                                                   of the first green instrument of the TFA small se-
    Clinical performance of NiTi instruments can be relat-         quence reduced the instrumentation stress exert-
    ed to the operative techniques. It has been suggested          ed on the second instrument within the same se-
    that any NiTi instrument may be used both as a ream-           quence. Resistance to both torsional stress




                                                                                                              i
    er cutting in advancement and with a brushing action           (which may cause undwinding of the flutes) and




                                                                                                            al
    as a hedstroem file, to improve coronal and/or circum-         flexural stress (which may affect resistance to
    ferential flaring (19), but safety and efficiency of the       cyclic fatigue of used instruments) was enhanced;
    proposed technique needed further assessments.              b) a prolonged passive brushing motion as per-




                                                                                                         on
    The present study demonstrates that a brushing ac-             formed in the present study (60 seconds) did not
    tion can be performed up to 60 seconds with minimal            adversely affected mechanical resistance of the
    or no risk of increasing instrument fatigue. The green         instruments used for this purpose. Resistance to
    TFA instrument (tip size 20, .04 taper) which per-             both torsional and flexural fatigue was not de-
    formed a brushing action for 15 seconds in each of             creased.




                                                                                               zi
    the four canals did not showed a significant decrease
    of resistance to cyclic fatigue. These findings are
    consistent with previously published results (17, 19).      References




                                                                               na
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IC




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©




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                                                                      t          2009;35:133-6.
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    Annali di Stomatologia 2015; VI (1): 6-9                                                                                                    9
