The functional appliances include Activators, Frankels, Bionators, Orthopedic Correctors, Twin Block™ and Herbst® designs. The doctor can choose from various removable and fixed appliance designs. All functional appliance designs address Skeletal Class II problems by advancing the mandible forward to a corrected Class I position.

Dr. Willian Clark, and Orthodontist, developed an uncomplicated technique that incorporates the use of upper and lower bite blocks to reposition the mandible forward for skeletal Class II correction. The Twin Block technique is easy to use and very patient friendly. The design utilizes two separate appliances that fit the maxilla and mandible. The unique design allows for more patient comfort and increased patient cooperation. The Twin Block design also allows for independent development of the upper and lower arches with the addition of transverse and/or sagittal screws.