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Advances in Materials Science and Engineering
Volume 2015, Article ID 189703, 6 pages
http://dx.doi.org/10.1155/2015/189703
Research Article

Survival Analysis of Factors Influencing Cyclic Fatigue of Nickel-Titanium Endodontic Instruments

1Department of Mathematical Analysis and Applications of Mathematics, Faculty of Science, Palacký University in Olomouc, 17 Listopadu 12, 771 46 Olomouc, Czech Republic
2Department of Mathematics, Faculty of Applied Informatics, Tomas Bata University in Zlín, Nám. T.G. Masaryka 5555, 760 05 Zlín, Czech Republic
3Institute of Clinical and Experimental Dental Medicine, First Faculty of Medicine, Charles University General Teaching Hospital, Prague, Czech Republic
4Onedent, Příkop 8, 602 00 Brno, Czech Republic
5Communication and Information Systems Agency, Czech Army, Tychonova 1, 160 01 Prague, Czech Republic

Received 27 May 2015; Accepted 9 September 2015

Academic Editor: Luigi Nicolais

Copyright © 2015 Eva Fišerová et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective. The aim of this study was to validate a survival analysis assessing the effect of type of rotary system, canal curvature, and instrument size on cyclic resistance. Materials and Methods. Cyclic fatigue testing was carried out in stainless steel artificial canals with radii of curvature of 3 or 5 mm and the angle of curvature of 60 degrees. All the instruments were new and 25 mm in working length, and ISO colour coding indicated the instrument size (yellow for size 20; red for size 25). Wizard Navigator instruments, Mtwo instruments, ProTaper instruments, and Revo-S instruments were passively rotated at 250 rotations per minute, and the time fracture was being recorded. Subsequently, fractographic analysis of broken tips was performed by scanning electron microscope. The data were then analysed by the Kaplan-Meier estimator of the survival function, the Cox proportional hazards model, the Wald test for regression covariates, and the Wald test for significance of regression model. Conclusion. The lifespan registered for the tested instruments was Mtwo > Wizard Navigator > Revo-S > ProTaper; 5 mm radius > 3 mm radius; and yellow > red in ISO colour coding system.