Archwires are a mainstay of your practice. Whether it’s nickel titanium, stainless steel, or beta titanium, your archwire choice allows you to give your patients their best smiles. Each wire type possesses different mechanical properties making each suitable for different stages in treatment, meaning nickel titanium archwires are ideal for the initial phase of treatment and beta titanium and stainless steel are more suitable in the finishing phase. But have you ever wondered what goes into making these wires do what they do?
First, it comes down to the raw materials, or wire alloys, according to Brandon Bernacchi, vice president of operations at G&H Orthodontics, a company that has been forming archwires for 40 years. And the most popular alloy in orthodontics is nickel titanium, otherwise known as nitinol. This alloy comes in a number of different “flavors,” if you will, from a combination of nickel and titanium to nickel and titanium doped with either copper or iron; and whatever flavor you use is going to have an effect on the mechanical properties of the wire during treatment. In the case of nickel titanium, the alloy allows it to accept a high amount of strain without permanently deforming or bending. And more importantly for orthodontic treatment, this alloy has the much desired shape memory effect clinicians seek.
As for stainless steel and beta titanium wires, those alloys don’t have the shape memory properties of nickel titanium, meaning they will accept a third-order bend or any torque the user wants to apply and hold it.
Now when it comes to the manufacturing process, nickel titanium is a bit of a special case. As Bernacchi puts it, “Not all nickel titanium is created equal.” What he means is “the outcome or the performance of the nickel titanium in the patient’s mouth is very sensitive to the processes when the wire is made.” For good quality and effective nickel titanium wires that produce consistent outcomes, it is important that the manufacturing processes are highly controlled. Now each manufacturer will have their own proprietary manufacturing process, but there are two factors within that process that will determine the performance of the wire: chemistry and temperature.
“You have to match the chemistry composition with the manufacturing process to yield a clinically effective product,” says Bernacchi, who has a background in engineering and has been at G&H for 16 years.
“Nickel titanium is very sensitive. For example, there are certain elements in chemicals during the forming/manufacturing process, that if they’re present, they can lead to breakage. It takes having a lot of good manufacturing process controls in place so you eliminate those chemical elements [introduced] during [manufacturing], and so you don’t have breakage or permanent deformation in the case of nickel titanium.”
From there, the alloy is shaped through a process of heating and cooling (or quenching). Time and temperature are the key factors during this shape setting phase, and, given the high sensitivity of nickel titanium to the manufacturing processes, these must be in sync to create a wire that produces the desired outcome and predictable and consistent tooth moving forces. More specifically, as the process sets the shape, it, in effect, programs the thermal transformation temperatures at which the wire goes from “soft to active,” which affects the force delivered in that specific shape during treatment. According to Bernacchi, G&H Orthodontics alone has over 160 different shapes for both upper and lower and for all orthodontic prescriptions.
As for stainless steel and beta titanium wires, the process is not as intricate, says Bernacchi. “There is less variability when forming stainless steel. It’s a cold-forming process. There’s no heat introduced. So you don’t have to worry about time and temperature. As long as you start with a base material that is acceptable and it has the mechanical properties that are within specifications of what the clinician wants, then it’s relatively straightforward.”
From there, the wire is mechanically polished. Here again, the raw materials used at the start of the process are extremely important, says Bernacchi. “Starting with the highest quality raw materials, we feel we already start with a very good surface finish, with little to no surface inclusions. But we take an extra step and mechanically polish the wire so that it has the smoothest surface finish to help with the sliding mechanics during treatment.”
After all that, G&H Orthodontics puts its wires through 14 separate quality tests and a 28-point final inspection, which includes testing the wire at body temperature. “Nitinol is heat sensitive. Therefore, we test it at body temperature to determine the forces that would be delivered during treatment. Through our testing, we want to be sure that each and every time a doctor uses our wire the forces applied by our archwires are the same every time.”
And that type of quality control, and overall commitment to using the best raw materials, is important to keep in mind when sourcing archwires for your practice.
“It’s very difficult for an orthodontist to just feel what’s going to happen when you’re talking about nickel titanium wires, for example,” says Bernacchi. While stainless steel archwires are more of a what-you-see-is-what-you-get type product, as they are not temperature sensitive, when a clinician buys from an unknown distributor, there’s no guarantee of the materials or performance of a nickel titanium archwire. OP