Reciprocation of OTR motion improved significantly cyclic fatigue resistance of all instruments tested compared with continuous rotation. Mtwo and TF had significantly higher cyclic fatigue than the other instruments, in both continuous rotation and reciprocation of OTR motion.

Nickel-titanium (NiTi) rotary instruments are commonly used for endodontic practice today. These instruments offer many advantages, including flexibility over conventional stainless steel files. 1 Despite their undeniably favorable qualities, there is a potential risk of unexpected fracture. Many variables might contribute to file separation, but the two main causes are cyclic fatigue and torsional stress. 2 Recent attempts have used thermal treatments to modify the phase transition temperatures, and thereby enhance the mechanical properties of the files. 3 In addition to this, file manufacturers have tried to develop new designs, manufacturing processes, and kinematics to minimize fracture occurrence. 1 Moreover, the use of reciprocating motion was shown to extend the lifespan of NiTi instruments, and thus resistance to fatigue, compared with continuous rotation. 4 Reciproc R25 (Rec) (VDW, Munich, Germany) and WaveOne Primary (WO) Sirona Maillefer, Ballaigues, Switzerland) are two well-known reciprocating single-file instruments. 5 Rec and WO have the same nominal size (tip size of 25 with a 0.08 taper). The taper is constant in the apical 3 mm of the instruments, Abstract Aim: The aim of the present study was to evaluate the resistance to cyclic fatigue of heat-treated single files used in proper or in reciprocating optimum torque reverse motions. Methods: Ninety-six HyFlex electrical discharge machining (EDM), Reciproc R25 (Rec), WaveOne Primary (WO), and WaveOne Gold (WOG) Primary were used.Resistance to cyclic fatigue was determined by recording time to fracture in a stainless steel artificial canal. Differential scanning calorimetric analysis was performed.Data were analyzed by two-way analysis of variance and Bonferroni post-hoc tests at 0.05. Results:In both movements, HyFlex EDM showed higher time to fracture than other files (P < 0.0001). Rec showed higher time to fracture than WO (P < 0.0001), while WOG showed higher cyclic fatigue resistance than Rec and WO with both movements (P < 0.005). Conclusions:Reciprocating optimum torque reverse motion improved significantly cyclic fatigue resistance of gold and controlled memory wire single files. K E Y W O R D S differential scanning calorimetric analysis, fatigue resistance, nickel-titanium, optimum torque reverse, reciprocation 2 of 7 | PEDULLÀ Et aL. but it is reduced in the middle and coronal portion of the working part of the instrument. Rec instruments have a constant S-shaped cross-section with two cutting blades; WO instruments have a modified convex triangular cross-section at the tip and a convex triangular cross-section in the middle and coronal portion of the instrument. 5 Additionally, Rec and WO are manufactured using M-wire NiTi, which increases their flexibility and resistance to cyclic fatigue. 6 Recently, WO was upgraded to WaveOne Gold (WOG) (Sirona Maillefer, Switzerland). The kinematics of this system was unchanged, but the design of the files has been modified, and the heat treatment has been changed in the gold treatment, which allows...

Objective: Different single-file instruments and kinematics have been introduced on the market. It is important to know the cyclic fatigue performance of these instruments in these new kinematics such as reciprocation of Optimum Torque Reverse (OTR) motion. The aim of this study was to evaluate the resistance to cyclic fatigue of F6 SkyTaper and OneShape used in continuous rotation (proper rotation) or in reciprocating OTR motion. Methods: A total of forty-eight nickel-titanium files were tested. Twenty-four instruments of both brands were divided into two groups (n=12) on the basis of the motion tested: continuous rotation (group 1) or reciprocating OTR motion (group 2). Resistance to cyclic fatigue was determined by recording time to fracture (TtF) in a stainless steel artificial canal with a 60° angle of curvature and 5 mm radius of curvature. Data were analysed by two-way analysis of variance and post-hoc Bonferroni tests for multiple comparisons with P<0.05 as the level of significance. Results: F6 SkyTaper showed higher TtF compared with OneShape, both in continuous and in OTR motion (P<0.0001). The two tested instruments showed higher cyclic fatigue resistance in reciprocating OTR motion than continuous rotation (P<0.0001). Conclusions: OTR motion significantly improves cyclic fatigue resistance of the tested instruments. In addition, F6 SkyTaper showed higher cyclic fatigue resistance than OneShape in both motions.