Comparison of two methodologies for testing cyclic fatigue resistance of nickel-titanium rotary files
Yang, Eugenia You Yea
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Nickel titanium (NiTi) rotary files have become an important adjunct to endodontic treatment of the root canal system. However, despite the many advantages, Ni-Ti rotary files have a risk of unexpected fracture without any visible signs of previous permanent deformation. A wide range of methodologies have been developed over the years to test cyclic fatigue; yet to date, there is no specification or international standard for cyclic fatigue testing. The aim of this study was to compare the effect of the stainless steel and the glass tube method on the cyclic fatigue resistance of K3[R], K3xF[R], Vortex[R], Vortex Blue[R], and PROTAPER NEXT[R] NiTi rotary files. Material and Methods: A total of 450 new NiTi rotary fies were tested in this study. These files were divided equally into two groups: one group was subjected to a stainless steel (SS) artificial grooved canal model, and the other group employed the glass tube (GT) model (n=225). Three file sizes, 20.06, 25.06 and 30.06, were selected for the K3[R], K3xF[R], Vortex[R], and Vortex Blue[R] systems; and X1, X2 and X3 was selected from the PROTAPER NEXT[R] system. The files were subjected to an angle of curvature of 60 degrees with a 5mm radius of curvature at 300 rpm for both devices. The number of cycles to failure (NCF) and length of fracture file piece were recorded and statistically analyzed. Results: Significant differences were found between the stainless steel and glass tube testing methodologies; NCF ranged from 325 - 1147 for SS and 412 - 1901 for GT. Both methodologies showed a similar pattern of relationship between file comparisons with the GT method showing greater significant differences among file types. Vortex Blue[R] was the most resistant to cyclic fatigue, and K3[R] system was the least resistant to cyclic fatigue regardless of the testing methodology. The Vortex Blue[R] 20.06 file had the highest cyclic fatigue resistance with a mean NCF of l 147 [plus or minus] 184.3 for SS and 1530.3 [plus or minus] 258 for GT. ProtaperNext[R] X2 (325 [plus or minus] 48.3) and K3[R] 30.06 (412 [plus or minus] 93.4) files had the lowest cyclic fatigue life in the SS and GT method respectively. With the exception of Protaper Next[R], within the same file systems, there is an inverse relationship in regards to tip sizes and number of cycles to failure. Conclusion: The glass tube method is a more accurate measure of cyclic fatigue resistance than the stainless steel method for cyclic fatigue. Vortex Blue[R] and smaller tip sized files performed best in this study.
Thesis (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2015 (Department of Endodontics).Includes bibliography: leaves 69-74.
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