Misconceptions

Niti wires can’t be permanently deformed.
Many of us are under the impression that niti archwires cannot be permanently deformed with pliers or that they will never take a permanent set after being in a patient's mouth for a period of time. These are misconceptions. All types of Niti wires can be easily and permanently bent beyond the yield point. This simply means that if a bend in the wire is sharp enough, the wire will not be able to recover and will take a permanent set. This happens sometimes when we force the wire into a bracket or when we ligate the wire into adjacent brackets where one of the brackets is substantially out of the plane. Light (.012" - .014") niti archwires will sometimes take a permanent set in certain orthodontic cases. These are light force wires that don't have the strength of larger diameter archwires.

Niti wires are unbreakable.
NiTi wires can break after certain amount of cold work or when a nick is placed in the wire while inserting into patient’s mouth. Extraction cases present a situation where the archwire is now exposed with no support as it spans the extraction area. As the patient chews their food, the wire will cold work (caused by repetitive bending) and eventually break. This is a common concern. Some clinicians slide a piece of bumper tubing over this exposed section of the wire. This will usually stop the wire from cold working enough to break.

It is very important when handling NiTi wires that the surface of the pliers is smooth and free of nicks or scratches. Due to the microstructure of niti wire, any small nick in the wire will cause it to fracture. A Bird Beak plier may also be used, but care must be taken when gripping the wire with the pliers. It is always better that we never hold a NiTi wire with very tight grip.