The appliance is based around a prefabricated modular spring, built into a maxillary occlusal splint. Two integral vertical springs make contact with a fi xed lingual arch.

The appliance partly acts as a training device, harnessing the patient’s own muscle forces. The vertical springs create an avoidance refl ex and a new postural position for the mandible.

The mandible is brought forward in a stepwise manner as the growth of the patient responds, approximately 2 mm every 6-8 weeks. This stimulates the maximum rate of growth of the condyle and the fossa and leads to a new skeletal position of the mandible.