Comparison of the High Cycle Fatigue Behavior of the Orthodontic NiTi Wires: An in Vitro Study

Abstract

Objective: To compare the high-cycle fatigue behavior of four commercially available NiTi orthodontic wires. Material and Methods: Twelve NiTi orthodontic wires, round, 0.016-in, three per brand, were selected and divided into four groups: G1 -Heat-activated NiTi, G2 -Superelastic NiTi, G3 -Therma-Ti, and G4 -CopperNiTi. The atomic absorption spectrometry method was used to determine the chemical composition of investigated NiTi wires. We also performed a fatigue test at three-point bending using a universal testing machine for 1000 cycles in a 35 °C water bath. For the first and thousandth cycle, the average plateau load and the plateau length were determined in the unloading area of the force versus displacement diagram. In addition, we calculated the difference between the average plateau load of the first and thousandth cycle (∆F), as well as the difference between the plateau length of both cases (∆L). Results: According to our results, there were no significant differences between the average plateau load of the first and thousandth cycles of each group (p>0.05) and in the plateau length of the first and thousandth cycles of the groups (p>0.05). Conclusion: There were no significant differences between the groups changing the superelasticity property after high-cycle fatigue.

Simulation of the surface and volume stress in the contact archwire/bracket for classical friction and critical contact angle

“…Referring to the various (fatigue induced by small deflection) simulation tests [5], it has been noticed that under a given normal load P, the application of cyclic stress generates a certain asymmetry of the facies characterizing the micro-sliding generated on both sides. Thus, if the load is high enough that macro-sliding does not occur, the area located on the side of the eccentric will be more stressed than that located on the embedded side [6,7]. Under these conditions, the alternating deformation will therefore be weaker if not zero on the side of the embedding, and consequently the micro-sliding can only occur on the side most stressed.…”