Functional appliances are usually fitted to reduce the prominence of upper incisors and to improve the way the teeth bite together. They usually consist of two removable blocks ('Twin Blocks'), one fits over the top teeth and one over the bottom teeth. By holding the lower jaw forward a force is generated which moves the upper teeth backwards and the lower teeth forwards.
Sometimes they may be some favourable growth of the jaws. Functional appliances should be worn on a full-time basis, day and night, for about 6 months. They must be removed for clean, swimming and contact sports/ Further orthodontic treatment with fixed braces is usually needed after functional appliance treatment.