Schematic diagrams depicting modus operandi of OCRS, when applied for the 1st premolar extraction case: (a) at rest position of OCRS, its total length is shorter by 8 mm than total span between molar hook and anterior archwire hook; (b) with activation, open coil gets sandwiched between two “helical stop;” (c) with deactivation of OCRS, space closure is accomplished.
