 A myriad of other functional appliance have been invented including the standard activator, the medium opening activator (MOA), Bionator and Frankel.The MOA is a single piece functional appliance that allows for greater patient comfort with minimal acrylic than any of the other single-piece removable functional appliances but complaince with all of these can be limited due to these paradoxically limiting normal mandibular function during wear.All of these appliances allows selective eruption of the lower posterior teeth which is useful for reducing a deep overbite whilst correcting the Class II malocclusion.