Final answer:
Nickel-titanium arch wires are used in the initial stages of orthodontic treatment due to their flexibility and shape memory characteristics.
Step-by-step explanation:
Arch wires are a component used in the field of orthodontics, typically for dental braces to correct teeth alignment. In the early stages of treatment, arch wires made of Nickel-titanium are used because of their flexibility and the ability to return to their original shape after being bent.
This characteristic of Nickel-titanium, also known as Nitinol, is very useful in applying gentle forces to move teeth, making it the ideal material for initial stages of orthodontic treatment.