 The aim of this prospective, multicentric, randomized, open-label study is to assess the efficacy of the removable Twicare as mandibular propulsive appliance in children aged from 7 to 12 years old in the course of their orthodontic treatment, showing its noninferiority with the removable Herbst. One untreated group will be included to control the internal validity of the study as recommend in noninferiority trials. Patients will have a follow-up every two months during 6 to 12 months as planned in routine care. 