Final answer:
In the final stages of orthodontic treatment, a rectangular arch wire is used to accurately position teeth by applying torque and controlled forces to align both crown and root.
Step-by-step explanation:
During the final stages of treatment, a rectangular arch wire is used to position the crown and root in the correct maxillary and mandibular relationship. The rectangular wire allows for the application of controlled forces in specific directions, which is crucial for the precise positioning of teeth in orthodontic treatment. Unlike round or other shapes of wires, the rectangular arch wire can exert torques to correct the rotation of the tooth and the tilting of the root, ensuring that both the crown and root are properly oriented within the jawline.