The Basic Activator is a mono-block appliance (solid block of acrylic) designed to be loose fitting in the patient’s mouth. This causes the muscles of mastication to become active in order to hold the appliance in place. It is thought to redirect the pressures of these muscles onto the teeth and jaws producing a favorable effect on a Class II malocclusion and redirecting the growth of the mandible. The maxillary arch has full acrylic coverage and the mandibular arch can be fully covered or the posteriors can be left uncovered to allow for eruption in the case of a deep bite. These appliances are usually used in conjunction with headgear. Headgear tubes are placed in the acrylic in the vicinity of the first molars (depending on the orthodontist’s preferences) to allow for the attachment of this device. The headgear is used to restrict the forward and downward growth of the maxilla while the Activator encourages desirable growth of the mandible. This allows the underdeveloped mandible to catch up to the maxilla for an improved jaw relationship.