The term "functional appliance" refers to a variety of appliances designed to alter the arrangement of various muscle groups that influence the function and position of the mandible in order to transmit forces to the dentition and the basal bone. Typically, these muscular forces are generated by altering the mandibular position sagittaly and vertically, resulting in orthodontic and orthopedic changes. A number of functional appliances have been developed, since the time of the "activator" developed by Andresen which offers definite advantages in growth modification to correct skeletal...