GENERAL DESCRIPTION: Nickel Titanium, sometimes called Nitinol, or Niti, offers us flexibility and resiliency not found in any other orthodontic alloy. Niti archwires consist of about 55% nickel and 45% titanium. The use of Niti archwires, as well as stainless steel archwires and brackets, is not recommended when treating a nickel sensitive patient.

MANUFACTURING: Niti archwires require a more involved and intricate manufacturing process than does stainless steel. Nickel titanium is difficult to melt and draw into finished wire, because of the inherent properties of the material. Archwire characteristics (thermally activated, superelastic, multi-modulus, etc.) can be altered by changing the raw material formula, adjusting the manufacturing process, or a calculated combination of both.

MISCONCEPTIONS: Many of us are under the impression that niti archwires can not 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. Most 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.

It is very important when bending niti that the surface of the pliers are 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.

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.

TECHNICAL TIPS: To make a niti wire permanently soft for cinching etc., anneal the section of the wire that you would like soft with a lighter until red hot. The wire is now dead soft in the selected area and will not return to its original shape when bent. Please note that the annealed section of the archwire will bend very easily.

You can put desirable torque into various sections of rectangular wire by using a Rose Torquing Plier Set. You will have to over bend considerably to account for spring back in the niti wire. Always heat the wire gently (do not get red hot) with a lighter after torquing to ensure that the wire will not move once placed in the mouth.

Utility arches, loops, or most any other bends can easily be formed and maintained in your niti archwires. After bending into the desired shape a lighter must be waved under the bends to ensure that they will not move once in the mouth. Repeat this process until the desired bends are achieved. All nickel titanium fractures easily if nicked, so care must be taken to use the correct (smooth corners) pliers to avoid fracturing.

Martensitic wires can be manipulated slightly in the mouth by either placing an ice cube in the mouth to ease some discomfort or by introducing warm rinses to increase the force a little to possibly speed up tooth movement.

Wire breakage can be a common problem with nitinol, but is easily avoided when using any type of instrument on nitinol archwires. Always avoid nicking the wire. Even a blunt object can sometimes nick the wire and cause fracturing.