History and Development of the Frankel Appliance
- Developed by Rolf Fränkel in Germany in the 1950s
- Fränkel used the activator functional appliance with mixed results
- Believed in correcting functional deviations of muscles along with dentition for stable treatment outcomes
- Developed functional regulator appliances to train and reprogram the musculature around the mouth
- Published around 70 articles emphasizing the importance of his appliance in expanding dental arches

Fränkel's Philosophy and Principles
- Mirrored Melvin Moss's philosophy
- Functional performance of oral capsule muscles influences functional spaces
- Atmospheric pressure also influences functional spaces
- Perioral muscles have a restraining effect on dental arches
- Appliance insertion expands the capsule and allows new muscle adaptation

Types of Frankel Appliances
- Frankel Appliance I (FR 1): Used for Class 1 and Class 2 Division 1 malocclusion
- Frankel Appliance II (FR II): Primarily used for Class 2 Division 1 and 2 malocclusion
- Frankel Appliance III (FR III): Used for Class 3 malocclusion
- Frankel Appliance IV (FR IV): Used for open bite and bimaxillary protrusion cases
- Frankel Appliance V (FR V): Used with headgear in patients with high mandibular plane angle and vertical maxillary excess

Modifications of the Frankel Appliance
- Otton (1992): Capped Frankel Appliance
- Owen (1985): Modified functional regulator for Vertical Maxillary Excess
- Chate (1986): Changed angulation of Cross Wires
- Kingston: Modified buccal shields
- Haynes (1986): Modified appliance with continuous buccolabial shield palatal acrylic support

References and Research on the Frankel Appliance
- De Almeida, Marcio Rodrigues; Henriques, José Fernando Castanha; Ursi, Weber (2002-05-01). Comparative study of the Fränkel (FR-2) and bionator appliances in the treatment of Class II malocclusion.
- Bionator/Orthopedic Corrector - DynaFlex.
- Rudzki-Janson, I.; Noachtar, R. (1998-03-01). Functional appliance therapy with the Bionator.
- Perillo, Letizia; Cannavale, Rosangela; Ferro, Fabrizia; Franchi, Lorenzo; Masucci, Caterina; Chiodini, Paolo; Baccetti, Tiziano (2011-02-01). Meta-analysis of skeletal mandibular changes during Frankel appliance treatment.
- Rodrigues de Almeida, Marcio; Castanha Henriques, José Fernando; Rodrigues de Almeida, Renato; Ursi, Weber (2002-10-01). Treatment effects produced by Fränkel appliance in patients with class II, division 1 malocclusion.