Cyclic fatigue resistance tests of Nickel-Titanium rotary files using simulated canal and weight loading conditions

Abstract

ObjectivesThis study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions.Materials and MethodsProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods.ResultsSpearman's rank correlation coefficient (ρ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files.ConclusionsThe new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.

Cyclic Fatigue Resistance of Rotary NiTi Instruments after Simulated Clinical Use in Curved Root Canals

“…Other studies have proposed a new fatigue testing method for NiTi rotary instruments in which the number of fatigue cycles to failure is determined under controlled loading conditions (12,23). Unlike common fatigue tests that impose the flexure in artificial canal shapes (24), cyclic fatigue apparatus test allows a precise control over how a file is loaded during the test.…”

“…Unlike common fatigue tests that impose the flexure in artificial canal shapes (24), cyclic fatigue apparatus test allows a precise control over how a file is loaded during the test. This precise control can help standardizing fatigue performance testing, and predicting the fatigue lifetime of NiTi rotary instruments (23).…”

Buckling resistance, bending stiffness, and torsional resistance of various instruments for canal exploration and glide path preparation

“…However, conventional SS files are still used for the canal exploration and negotiation. While the mechanical properties of shaping instruments, particularly the NiTi rotary files, have been studied extensively, rare studies have investigated the small instruments used manually for canal exploration and negotiation 3,17,18,19,20…”

Elastic Limits in Torsion of Reciprocating Nickel-Titanium Instruments

“…Researchers and manufacturers have tried to increase the fracture resistance of the instruments as well as clinical efficiency in various ways (8)(9)(10)(11)(12). Geometric characteristics, heat treatments, and surface treatments have all been shown to have a considerable effect on the mechanical properties and clinical performances of NiTi instruments (11)(12)(13)(14)(15).…”