When a primary cuspid is lost prematurely during the mixed dentition stage, the anteriors can shift off of the midline. This creates a loss in arch length in that quadrant and blocks the eruption of the adult cuspid. It is not uncommon to see this type of arch length loss associated with a deficiency in arch width...and it is possible to correct both problems with one appliance. To correct a narrow arch and a midline shift with a removable appliance, simply add a midline correction spring to a standard Schwarz appliance. As shown, the midline correcting lap spring attaches to the right side of the appliance, runs along the lingual of the anteriors and finally wraps around the distal of the left lateral incisor. As the appliance is expanded laterally, this spring will pull the anteriors back to the midline. Once the midlines are aligned, the end of the spring that wraps around the lateral should be straightened out or cut off.