 Functional appliances are orthodontic appliances that are used to correct a malocclusion by utilising, eliminating or guiding muscle function forces, tooth eruption and growth.Although there are many different types (fixed and removable), the majority work by via forward mandibular posturing to promote mandibular growth in growing patients.They are mostly used to reduce the projection of the front teeth (increased overjet) in patients with class II malocclusion.