Fig. 2

Design models for determining the center of resistance: (A) Boundary condition and force loading of retraction units; (B) The approximate force level axis; (C), Comparison of the maximum initial displacements (blue to red reflects lower to higher displacement) of the teeth (level 0–7); (D) Comparison of the maximum initial displacements of the teeth (level 4.0–5.0); (E), Comparison of the maximum initial displacements of the teeth (level 4.80–4.95)