Electrochemical and cytocompatibility assessment of NiTiNOL memory shape alloy for orthodontic use

Orthodontic arcs and wires are mostly realised from alloys and constitute the motor of dental shifting. Ti-base alloys rapidly replaced the formerly used stainless steel wires due to their excellent corrosion resistance, their high mechanical characteristics and their increased biocompatibility. NiTiNOL shape memory alloys add to these advantages their ability of deforming force. NiTiNOL, highly pure Nickel (hp-Ni) and commercially pure titanium (cp-Ti) were tested by electrochemical assays in artificial saliva and in vitro biological tests with L132 cells and HEPM cells. All tests gave concordant results: the electrochemical assays, the proliferation test, the colony forming method, and the inflammatory test clearly show, that nickel is a corrosive and a cytotoxic material. Ti and NiTiNOL are cytocompatible and in particular corrosion resistant. No significant differences are observed for both materials on the electrochemical and the biological level as well. The NiTiNOL shape memory alloy is a master trump for dental practitioners to repair occlusal defects by shifting teeth under optimal biological conditions. In spite of its high Ni-content, it is biocompatible. It considerably reduces the tune of therapeutic treatment, facilitate the occlusal concept and leads to a result of high clinical quality.