Frankel I Appliance: Corrects overcrowding in Class I cases and reduces the overbite and overjet in Class II, Division 1 cases. External muscle pressure is eliminated by the vestibular shields. Promotes transverse arch development dentally and skeletally.
Frankel II Appliance: Promotes transverse and vertical development of maxillary and mandibular arches. Corrects Class II, Division 2 cases and opens bite. Used after the maxillary incisors have been slightly proclinated by an upper removable appliance.
Frankel III Appliance: Corrects Class III malocclusions.
Frankel IV Appliance: Used for open bites and bimaxillary protrusions.