Restor Dent Endod.  2013 Feb;38(1):31-35. 10.5395/rde.2013.38.1.31.

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

• Cho OI
• Versluis A
• Cheung GS
• Ha JH
• Hur B
• Kim HC

• KMID: 1995474
• DOI: http://doi.org/10.5395/rde.2013.38.1.31

Abstract

OBJECTIVES
This 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 METHODS
ProFile 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.
RESULTS
Spearman's rank correlation coefficient (rho = -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.
CONCLUSIONS
The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.

Keyword

Constant angle; Constant load; Cyclic fatigue fracture; Nickel-titanium rotary file; Simulated canal

MeSH Terms

Androsterone
Fatigue
Androsterone

Figure

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  Figure 1 (a) Customized cyclic fatigue test device for applying a controlled constant load condition for the L-test; (b) An artificial curved root canal with constant curvature in the C-test.

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  Figure 2 Mean number of cycles to failure (NCF) values under the constant load (L-test) and fixed-curvature condition (C-test). Groups with different superscript letters, for each test method, were significantly different from each other (p < 0.05). Note that the higher bar in L-test means the lower fatigue resistance whilst the higher bar means higher resistance in C-test. The numbers with the bar means the mean NCF and error bar indicates standard error. PF, ProFile; K, K3.

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  Figure 3 Scanning electron micrographs of the fracture surface of specimens after the fatigue test (a to d, ProFile; e to h, K3): L-test (Left column) and C-test (Right column). Both experimental methods showed similar fractographic features of cyclic fatigue failure for all instruments.

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