The Lower Jackson active expansion appliance is well suited for the mixed dentition stage of growth where lateral development of the lower arch is indicated. The “pumping” action makes it particularly effective and produces rapid results. Since the upper arch develops faster than the lower, it is not uncommon for a doctor to prescribe an Upper Schwarz and a Lower Jackson to keep pace with the upper. Typical activation involves adding a uniform 3mm to 4mm lateral adjustment to the body wire -- but the unique design of this appliance makes it possible to differentially expand the arch in both the anterior and posterior regions. Note: Some patients find this appliance uncomfortable if care is not taken to relieve the acrylic from the lingual-inferior undercut.