American Board of Orthodontics (ABO) Practice Exam

The transformation temperature of NiTi (Nickel-Titanium) wires is influenced by the composition of the alloy. When copper is added to NiTi, it tends to increase the transformation temperature. To bring this transformation temperature back down to 27 degrees Celsius, one would typically introduce chromium into the alloy.

Chromium serves as an element that modifies the properties of NiTi through solid solution strengthening and alters the phase transformation characteristics of the alloy. The incorporation of chromium can lower the transformation temperature, allowing the modified alloy to return to the desired state for applications at lower temperatures.

Other elements such as nickel or aluminum might not have the same effect on reducing the transformation temperature, and iron is generally not a favorable choice for enhancing the desirable properties of NiTi alloys. Therefore, introducing chromium is the appropriate solution to achieve the desired transformation temperature after adding copper.