The tongue plays an important role in the normal development of the upper and lower arch. When a tongue thrust and/or abnormal swallowing pattern is exhibited, the posterior segments of the arches can collapse lingually. Uprighting the posteriors in the mandible can be accomplished with this unique Lower Posterior Expansion Appliance. Its screw mechanism is designed to initiate expansion in the lower molar region without corresponding expansion in the anteriors. Since it operates on a fan principal, with the distal lingual flanges opening toward the buccal, activation will cause more expansion to occur in the molar region than in the premolar area.