An underdeveloped maxilla is usually the causative factor when it comes to a crowded narrow mandible. Arch expansion with a lower Schwarz appliance is the easiest way to correct the crowding and upright the lingually tipped posterior segments. Taking the time to properly design the appliance in accordance with specific patient need is critical to success. For example, the labial arch wire usually passes over the occlusion -- either distal to the cuspid or distal to the first bicuspid. Selecting the best position depends upon available occlusal clearance. As the appliance is activated, the adjustment loops of the labial wire should be opened, permitting development in the anterior area. Once sufficient space is available, the lap springs can be activated to complete the alignment of the anteriors along the esthetically-formed labial arch. The labial loops can then be tightened to hold the aligned teeth in place. Note: Maxillary and mandibular development are usually done at the same time. Care must be taken not to over expand the maxillary arch, as it responds about twice as fast as the mandibular arch.