The FR I appliance, which aims the sagittal, vertical and transversal development of intraoral cavity by keeping away the perioral muscles is used widely in crowded Angle Class I and Class II Division 1 cases. The most active period for Frankel I treatment is the time upper and lower incisors finish their eruption and the posterior decidious teeth are in their places only for retention. In the II year old patient tréated with FR I appliance for 6 months, the ANB angle decreased by 3.5° and an anterior development of mandible was established. Also a transversal development in lower and upper jaws and sagittal development in the lower jaw were seen.

Keywords: Class I crowding, Class II Division 1, Frankel I appliance, intraoral cavity