Why does treatment start with thin NiTi wires and finish with thick steel wires? Thin NiTi is superelastic — it engages badly misaligned brackets and delivers gentle continuous force over a long range, ideal for initial alignment. Thick stainless steel is stiff — it holds the arch form rigidly and transmits precise torque and bends for finishing details. Students learn the wire sequence as a material story: flexible for alignment, stiff for precision.