Introduction: This study aims to evaluate the cyclic and torsional fatigue resistance of seven rotary systems. Methods and Materials: A total of 140 instruments were tested, 20 of each system including Genius (GN) 25/0. 04, TruShape (TS) 25/0. 06, Logic (LOG) 25/0. 06 taper, Vortex Blue (VB) 25/0. 06, ProTaper Gold (PTG) 25/0. 08, Hyflex CM (HCM) 25/0. 06 and Hyflex EDM (EDM) 25/0. 08 taper. cyclic fatigue resistance testing was performed using an artificial stainless steel canal with a curvature (60° angle and 5-mm radius) located at 5 mm from the tip. The files (n=10) rotated until fracture, and time was recorded in seconds. The torsional test was evaluated according to ISO 3630-1. Data were analysed with one-way ANOVA and Tukey’ s tests (α =5%). The fractured surface of the instruments were assessed using scanning electron microscopy to confirm the type of fracture. Results: The cyclic fatigue resistance value of EDM was significantly higher than those of all tested instruments (P<0. 05). LOG showed a higher cyclic fatigue resistance than GN or TS (P<0. 05). There was no difference among the other groups (P>0. 05). The torsional test showed that PTG 25/0. 08 had the highest torsional strength value of all instruments tested followed by VB and EDM (P<0. 05). The LOG showed significant difference only with GN (P<0. 05). No difference was found among the other groups (P>0. 05). In relation to angular deflection, the GN; TS; HCM, and EDM showed significantly higher values until fracture than the other groups (P<0. 05). No difference was found among PTG, LOG, and VB (P>0. 05). Conclusion: Our in vitro study EDM group had the highest cyclic fatigue resistance among all the tested instruments. For the torsional test, the PTG showed highest torsional strength and lowest angular deflection values.

Introduction: This study compared the cyclic fatigue resistance (CFR) of new instruments manufactured by heat-treated nickel-titanium wire. Methods and Materials: Ninety-six new instruments from HyFlex CM (HF), Edge File (EF), Pro Design S (PDS/L) and Mtwo (MT) (20/0. 06 and 25/0. 06) (n=12) systems were evaluated. A stainless steel device was used and time and number of cycles to fracture (NCF) were observed. Fragments were measured and fracture surface was evaluated using scanning electron microscope (SEM). ANOVA and Tukey’ s tests were applied with the level of significance set at 0. 05. Results: PDS 20/0. 06 and PDL 25/0. 06 instruments presented the highest CFR. MT 20/0. 06 and MT 25/0. 06 showed the lowest CFR (P<0. 05). The length of fragments was similar for 25/0. 06 instruments and HF presented the highest one for 20/0. 06 instruments. SEM analyses showed morphology suggestive of ductile fracture. Conclusion: Heat treatment increased resistance to cyclic fatigue differently for each type of instrument. PDS 20/0. 06 and PDL 25/0. 06 present higher cyclic fatigue resistance.

In this research, the effect of cyclic loading values, stroke value and weft density on the mechanical properties of woven fabrics is investigated. Six different woven fabrics, plain, rib 2.2, twill 1.3, twill 1.7, satin 1.7 and herringbone twill, with three different weft densities, are produced from polyester filament warp and weft yarns. Samples are then subjected to the fatigue test in warp wise and weft wise directions, under two stroke levels and four loading cycle values. The results indicate that, the trend of mechanical properties changes due to cyclic loading is approximately same for all fabrics. Increasing of cyclic loading increases the value of second modulus of fabrics and decreases the value of tensile strain of the samples while the maximum load of samples does not change. Besides, the increasing of fabric weft density raises the measured mechanical properties of all samples. Increasing of stroke value causes the increase in the second modulus and decreasing the tensile strain of fabrics and has no significant effect on the maximum load.

Introduction: The objective of this in vitro study was to evaluate whether cervical preparation with Mtwo files in a crown-down technique influences instrumentation time and the cyclic fatigue resistance of these instruments. Methods and Materials: Two instrumentation techniques were evaluated (manufacturer and crown-down). Each group consisted of 10 kits containing four Mtwo instruments (10/0. 04, 15/0. 05, 20/0. 06, and 25/0. 06), which were used to prepare three standard simulated curved resin canals. The mean instrumentation time and the corresponding number of cycles for each instrumentation (NCI) were recorded. The instruments were rotated at a constant speed of 300 rpm in a stainless-steel canal (diameter of 1. 5 mm) at a 90° angle of curvature and 5-mm radius. The center of the curvature was 5 mm from the tip of the instrument. The cyclic fatigue resistance of the files was determined by counting the number of cycles to failure (NCF). Data were analyzed by the Mann-Whitney test. Results: The mean instrumentation time and NCI of files 10/0. 04 and 15/0. 05 were significantly lower (P<0. 05) when the crowndown technique was used compared to the manufacturer’ s method for the same tip size/taper file. There was no significant difference in the mean NCF between the two techniques. Conclusion: The crown-down technique did not interfere with resistance to cyclic fatigue. However, the shorter instrumentation time of files 10/0. 04 and 15/0. 05 could reduce the fracture risk in the case of reuse of these instruments.

INTRODUCTION: This study investigated the fatigue and fracture modes of RaCe and ProTaper rotary instruments.MATERIALS & METHODS: fatigue resistance was evaluated by rotating the files 30o or 60o and with 2 or 5mm radius of curvature. RaCe taper 06 size 25 and ProTaper F1 files (n=40) were used. The number of rotations to failure was analyzed by two-way ANOVA and independent sample t-test. Fracture surfaces were examined under a scanning electron microscope.RESULTS: Both files exhibited significantly more resistance to fracture when angle severity was reduced and increase in curvature radius (P=0.000). ProTaper demonstrated higher number of cycle of failure (P=0.0029) in one group (r=5mm, 60o). SEM observation revealed fatigue mark/features in 17 specimens, shear characteristics in 37 samples, and tensile overload in 26 samples.CONCLUSION: Radius of curvature was the main factor in torsional and fatigue failures.