Cyctic Fatigue Resistance of Four different Nickel-Titanium Rotary lnstruments in Continuous or Reciprocating Motion

INTRODUCTION Manufacturers have recentty introduced new atloys and/or reciprocating motion to improve fracture resistance of nickeltitanium (NiTi) rotary fites (r-l). Recently, two different reciprocating systems were introduced: Reciproc and Wave0ne (4). Manufacturers recommended the use of these fites with a specific motor and the unchangebte and appropriated setting (Reciproc fites with the "RECIPROC ALL" mode and Wave0ne with the "WAVEONE ALL" mode) (5). These two types of presetted reciprocating motion have different angles of rotation and velocity (6). 0BJECTTVE Aim of the study was to evaluate the resistance to flexuraI fatigue of Reciproc Rz5, Wave0ne Primary, Mtwo and Twisted Fite NiTifites used in continuous rotation or in two different reciprocating motion. MATERIALS & METHODS A total of r8o fites from four brands of NiTi fites marketed two for use in reciprocating motion (Reciproc Rz5 and WaveOne Primary) and two for use in continuous rotation (Mtwo and Twisted Fite both taper (.06/0.25 tip diameter) were tested. Fourty-five instruments for each brand were divided into three groups (n=r5) on the basis of the motion tested: continuous rotation (group 1- 30o rpm); reciprocaI motion (group z'"ReciprocALL" mode); reciprocatmotion (group 3 - "WaveOne ALL" mode). Resistance to cyclic fatigue was determined by counting the numbers of cycles to failure in a 6oo curve with a 5-mm radius. Data were anatyzed by two-way analyses of variance. RIESULTS Cyclic fatigue resistance of the two type of reciprocating motion "Reciproc ALL" (group z) and "WaveOne ALL" (group 3) was significant higherthan continuous rotation (group r) in every brand (P<o.oor). lnstead, no significant difference was found in cyclic fatigue between the two different reciprocaI motions tested (group 2 vs group 3) in every brand (P>0.05). When considering the appropriate clinical motion for every brand no significant difference was found in cyclic fatigue between Twisted File, Mtwo and Reciproc Rz5, white the cyctic fatigue resistance of WaveOne was [ess than otherthree brands (P<o.ol). DISCUSSION ReciprocaI motions tested both significantty increased cyclic fatigue resistance of alI brands tested than continuous rotation. Agree with this result, other recent papers reported a higher cyctic fatigue resistance of reciprocating motion than continuous rotation in instruments specifically designed to be used in reciprocalmotion as we[[as in those manufactured to a continuous rotation use (Z 8). The increased fatigue resistance has been postutated to be due to the retease of reaction stresses built up in the materiaI by reversing the rotationaI direction (q). No diflerences were found between the two reciprocating motions. Therefore a possibte exptanation of the diflerent results amongthe instruments tested in the present study can be retated to the different cross-sectionaldesign (5, ro). Moreover, when instruments was used with their appropriate clinical rotation cyclic fatigue resistance was not significant different with the exception of WaveOne Primary