Non-destructive natural frequency tests of cyclic fatigue-loaded nickel–titanium rotary instruments

Abstract

Nickel-titanium (NiTi) instruments are extensively used in endodontic treatment because of their outstanding mechanical properties. However, unexpected fracture of NiTi rotary instruments occurs during endodontic procedures. Therefore, a reliable method to detect the structural status of a used NiTi instrument is needed. The aim of this study is to use natural frequency for monitoring structural changes of a NiTi instrument during and after the instrumentation process. In this study, laboratory modal testing experiments were performed on cyclic fatigue-loaded NiTi rotary instruments with a natural frequency detecting device. In addition, three-dimensional finite element (FE) models were established for assessing the structural changes that take place in repeatedly loaded NiTi instruments. Repeated rotational loading resulted in a significant decrease (p < 0.05) in natural frequency (with a decreasing ratio of 5.6%) when the tested instruments reached 77-85% of their total life limit. In FE analysis, a strong correlation between natural frequency and change in elastic modulus of the NiTi instrument was found. These findings indicated that natural frequency may represent an effective parameter for evaluating the micro-structural status of NiTi rotary instruments subjected to fatigue loadings.

Metallurgical Characterization of M-Wire Nickel-Titanium Shape Memory Alloy Used for Endodontic Rotary Instruments during Low-cycle Fatigue

“…Coercivity measurement was suggested as a useful quantitative and nondestructive method for characterizing work hardening of austenitic stainless steel in relation to the amount of its plastic deformation (dislocation density because of work hardening) (14). Repeated rotational loading resulted in a significant decrease in natural frequency when the tested ProFile instruments reached 77%-85% of their total life limit (15). As a new NiTi wire used for rotary files, M-Wire showed substantial growth of the martensite grains and martensite twins in the microstructure after 60% fatigue life.…”

Deflecting load of nickel titanium rotary instruments during cyclic fatigue

“…From the endodontic literature, to prevent intracanal instrument separation, inspection of the NiTi instrument before each use under high magnification is recommended which might reveal defects necessitating instrument disposal. In addition, change in the resonance frequency of vibration of the NiTi instrument was shown to be a useful parameter to predict the lifespan of NiTi instruments 41,42) . This study focused on one brand of one size and taper of NiTi instruments where differences in thermomechanical history and geometry of other instruments will show different DL measurements.…”

Structural Analysis of Cyclic-loaded Nickel-Titanium Rotary Instruments by Using Resonance Frequency as a Parameter

“…During preparation, ethylenediaminetetraacetic acid gel and distilled water were used for lubrication and irrigation. The simulated canal was enlarged to an apical size of 25, and the RF values of the rotary NiTi instruments were determined as described in our previous report (10). Then the simulated canal was replaced with a new one, and the above procedure was repeated.…”

“…RF analysis has been used for measuring the structural status of small threaded structures such as orthopedic fixation pins (7) and has become the standard for detecting dental implant stability (8,9). In 2010, Hsieh et al (10) found that RF effectively detected the microstructural status of conventional NiTi rotary instruments before they broke down. Their data demonstrated that when ProFile (PF) instruments (Dentsply Maillefer, Ballaigues, Switzerland) are close to the end of their life spans, RF values were 5% lower than their initial values.…”