The Functional Arch Form. The functional arch form must have the proper shape for optimal overcorrection. From a functional occlusion standpoint, the arch form should accommodate joint-dictated movement patterns. This means that both Tru-Arch forms are more broad and flat across the incisors. Additionally, the Straight-Wire® Appliance makes it possible to eliminate in/out archwire bends because the bracket thickness is engineered for the different tooth types. The customized bracket thickness also enables the bracket slots to accept the Tru-Arch shape without wire bends. Therefore, the Tru-Arch shape is the optimum shape for ideal occlusion with the Straight-Wire system.