"Comparision of Cyclic FatigueResistance of Waveone and WaveOne Gold Small, Primary and LargeInstruments Dept. of endodontics Faculty of the Dental Medicine University of Lisbon By Guidance By,• For the past 2 decades niti instruments have been used to shape root canals because of their high flexibility and cutting efficiency (AriasA et al 2012, Perez- HiguerasJJetal2013) • Niti rotary files have unfavourable results due to fracture especially in curved and narrow canals. • File separation occurs as a result of cyclic fatigue or torsional failure (Knowleset al2006,Parashos etal2006) • Cyclic fatigue occurs because of tension-compression stress cycles at the point of maximum flexure, especially when preparing canals exhibiting curvature, finally leading to fracture. (BouskaJ2012,KimHC2012,SetzerFC2013) • Torsional fracture occurs when part of instrument is locked to the dentin and shank maintains to rotate (KimHC2012) • New concepts and designs in niti alloys including thermomechanical improvements have improved the cyclic fatigue resistance (Gambarini 2012,Uygun2016)WaveOne (WO; Dentsply Maillefer, Ballaigues, Switzerland) reciprocating instruments manufactured from heat-treated NiTi M-Wire technology. WO is a single instrument system that uses 2 different working patterns a counter clockwise motion (cutting direction) and a clockwise motion (release of the instrument) to prepare root canals. When engaging the dentin and advancing in the canal, the instrument uses a large angle of rotation in the cutting direction(counterclockwise). in contrast, in the opposite direction(clockwise), it uses a small angle of rotation for safe progression through the canal and to reduce the risk of fractures and so called screw in tendency. (Elsakase 2015)• Wave one gold introduced using same reciprocation motion as WO. • WOG have a modified cross section, size and geometry with those WO files. • WO files have a convex triangular cross sectional design (WycoffRC2012). • In contrast, WOG have an off-center paralellogram design, which provides an WaveOne 85degree active cutting edge with alternate 1 point contact. • WO and WOG have modified tapers. • WOG files are also smaller than those of WO files. • WOG manufactured with advanced metallurgy and using heat treatment technology. (Topcuoglu 2016, Ozyurek 2016) their unique gold color comes from thermal cycling procedure (heated and cooled slowly many times). The manufacture claims that gold technology design improves the flexibility of the files. • The aim of the study was to compare the cyclic fatigue resistance of WO and WOG.• One hundred twenty instruments were tested in this study. • The WO and WOG files were evaluated in 2 curved artificial canals, with different angles and radii of curvatures. • WO instrument systems with small (21/.06), primary (25/.08), and large (40/.08) files and WOG instrument systems with small (20/.07), primary (25/.07), and large (45/.05) files were selected for the cyclic fatigue resistance test (n = 10 in each test). • Each instrument was inspected under a dental operating microscope to detect defects or deformities before the experiment. • Whole defective instruments were discarded and changed with new ones.• Two simulated canals, one with a radius of 5 mm and a 90 degree angle of curvature and one with a radius of 3mm and a 60 degree angle of curvature, were prepared in a metal block as described previously by Larsen et al. • The working length was adjusted to 19 mm. • Synthetic oil (WD-40 Company, Milton Keynes, UK) was used for lubrication, and the stainless steel block was covered with a glass plate to prevent the instruments from slipping out and to observe the files during the experimental procedure. • The instruments were allowed to rotate according to the man ufa cture r s’ instructions. • The instruments were run using the motor (Silver Reciproc; VDW) in the ‘ ‘W A VEONE AL L ’ ’ mode. • For all instruments, the time until occurrence of fracture was recorded in seconds. • The length of the fractured tip of the instruments was also recorded using a digital caliper (Digimatic; Mitutoyo Co, Kawasaki, Japan)• The collected data were analyzed with SPSS version 18.0 (SPSS Inc, Chicago, IL). • The normal distribution of the variables was tested using the Kolmogorov-Smirnov test. • An independent St ud ent’t test was used to compare the means between the 2 groups. • One-way analysis of variance and T ukey ’ post hoc tests were used for multiple comparisons. • Data are given as the mean standard deviation. • A P value less than .05 was considered statistically significant (Fig. 2).• There were statistically significant differences among the groups (P < .001). • In both artificial canals, the WOG small, primary, and large files resulted in significantly higher cyclic fatigue resistance when compared with that of the corresponding WO small, primary, and large files (P < .001). • The WOG small files and WOG primary files had the highest time to failure in the simulated canal with a 3-mm radius and a 60 degree angle of curvature. • The WO large files had the lowest time to failure in the simulated canal with a 5-mm radius and a 90 degree angle of curvature. • In addition, the cyclic fatigue resistance of the instruments working in the canal with the 3-mm radius and the 60 degree angle of curvature was significantly higher than that of the instruments working in the canal with the 5-mm radius and the 90 degree angle of curvature (P < .05). • The WOG instruments were approximately twice as resistant to failure as the WO instruments were at the 60 degree angle of curvature, whereas the WOG instruments were 3 times more resistant at the 90 degree angle of curvature. • The length of the fractured part of the instruments was similar among all groups (P > .05)."