In recent years, the number of orthodontic patients in middle-aged and elderly age groups has been increasing. These patients have reduced surface area of the periodontal ligament supported by the alveolar bone, and their periodontal tissues are less responsive to orthodontic forces. Superelastic NiTi wire which had been developed 30 years ago possess only 1/3 the stiffness of stainless steel wires. Its superelasticity allows light continuous orthodontic forces, which may be suitable for the treatment of multi-bracket systems in elderly patients. While round NiTi wires are excellent for leveling, rectangular NiTi wires are superior for space closing and finishing stages. This is due to the fact that superelastic NiTi alloy wires have shape memory, excellent springback properties, as well as shock absorption and vibration damping capacity. And in order to effectively use these superelastic NiTi alloys, bending by an electric current heat-treatment machine is necessary.

But do we understand the orthodontic forces expressed in the oral cavity of NiTi wires? Does superelasticity not convert into excessive orthodontic forces? Is excellent springback property not harmful? What kind of orthodontic force does a wire with high stress hysteresis produce? Will a wire that has been subjected to electric current heat treatment become stiff? Can we answer these questions?

In this presentation, I will discuss the basic characteristics of NiTi alloy wires, changes in orthodontic force with intraoral temperature alteration, changes in wire characteristics due to electric heat treatment machines, and the force system using NiTi alloy wires in my practice. Understanding the properties of NiTi alloy in the intraoral environment and how to properly modify the wire will enable us to provide appropriate treatment.