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The aim of this study was to analyze in vitro the fatigue resistance of nickel–titanium (NiTi) and CuNiTi orthodontic wires when subjected to forces and fluids which are present intraorally. The wires were subjected to dynamic mechanical analysis (DMA) while they were immersed into different fluids with mechanical loading parameters similar to those that are subjected in the mouth. The characteristic temperatures of transitions and a rough surface structure on the perimeter of the wires were determined by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively, before and after the DMA experiments. Stainless steel wires were used for comparison. In general, NiTi wires fractured earlier than the stainless steel specimens. Survival times were lower for the NiTi wires when immersed in fluids (water, citric acid, NaCl solution, artificial saliva, and fluoridated artificial saliva) than in air. SEM surface analysis showed that the NiTi and CuNiTi wires had a rougher surface than steel wires. The fracture occurred within a short number of loading cycles. Until fracture occurred, the mechanical properties remained mostly constant. [Copyright &y& Elsevier]

Nickel–titanium shape memory alloys (NiTi-SMA) have outstanding mechanical properties (superelasticity, shape memory effect) that make them very interesting for clinical applications. Due to the high nickel content of the material, there are concerns about possible immunological reactions of the surrounding tissue. The proliferation of osteoblast-like cells (MG-63) and the cytokine release (interleukin (IL)-6, IL-8, tumor necrosis factor (TNF)-α) from polymorphonuclear neutrophil (PMN) leukocytes as well as peripheral blood mononuclear cells (PBMC) in response to different NiTi specimen was studied:In the first two cases, the aim was to improve the biocompatibility while retaining the mechanical properties. In the third case, the effect of mechanical treatment (damage of the passivating TiO2 surface layer) was investigated. In comparison to non-coated samples the OCP/HAP-coated SMA led to an increase in the release of cytokines, in contrast, the HAP-coated samples led to a decrease in cytokine release from PBMC. The attachment, viability, and the proliferation of MG-63-cells in the near vicinity of microdrilled structures was not different from non-strained surface areas. These results show that cell-biological in vitro techniques are suitable for the prediction of tissue reactions towards implant coatings or mechanically altered NiTi-surfaces. The surface morphology (platelets versus globular particles) appear to play a significant role that supersedes that of the chemical composition of the surface. [Copyright &y& Elsevier]