A removable arch adjustment appliance includes a removable shell having a plurality of cavities formed therein, wherein the plurality of cavities are shaped to receive at least one posterior tooth of a patient on each side of a patient's jaw. The shell can include an elastic transpalatal element that spans a palate of the patient and provides force to expand at least one of the spaces between the posterior teeth on each side of a patient's jaw or the palate of the patient. The transpalatal element can include a predetermined force characteristic, a number of force control elements to control the force provided by the transpalatal element, and/or a regulating structure to balance and direct the force provided by the transpalatal element, wherein the transpalatal element has a width specific to a stage of a treatment plan.