## 1 Introduction  
Skeletal Class II is a frequent malocclusion in orthodontic practice, and it shows the highest prevalence among Caucasians, both in permanent dentition (23%) and mixed dentition (26%) [1]. Decreased mandibular growth is the most consistent diagnostic finding in Skeletal Class II [2]. It has been reported that the Class II disharmony does not tend to self-correct with growth and an intervention to correct the underlying skeletal discrepancy is therefore necessary [3]. A conservative approach is more indicated for patients in the developmental age, involving a modification of the growth, redirecting the bone bases [4]. Functional appliances are often the preferred modality of treatment in patients with growth potential [5]. Several removable and fixed appliances were proposed to promote mandibular repositioning during growth in the sagittal and vertical direction, resulting in orthodontic and/or orthopedic changes [5]. Functional appliances reduce excessive overjet in Class II malocclusion through dentalveolar effects, modification of the soft tissue and mandibular advancement, relying on the patient's growth peak [6]. According to a recent review by [PERSON] et al., the skeletal correction of the Class II malocclusion obtained with functional appliances seems to be stable in a long-term observation [7].  
The function regulator appliance of Frankel (FR-2) is a functional orthopedic appliance used to correct Class II malocclusion by advancing the mandible with muscular training [8].  
The appliance prevents incorrect muscle function and corrects poor postural behavior of the orofacial musculature during the pubertal phase, characterized by an intense hormonal activity [8]. In a study conducted by [PERSON] et al. [9], in which no specific appraisals of skeletal maturation were taken into account, less dramatic changes were described in mandibular length between subjects starting FR-2 treatment during the early to mid-mixed dentition (average chronological age, 8.8 years) and those starting during the late mixed to early permanent dentitions (average age, 11.6 years). [PERSON] et al. [10] demonstrated long-term stability for both skeletal and dentoalveolar changes for subjects treated with FR-2 appliance.  
Many studies underline the importance of the muscles in stabilizing the cervical spine and the existence of various connections between muscles in the oral and neck regions. Impaired mandibular growth can affect head posture: most of the studies reported a significant correlation between distal jaw position, sagittal mandibular length, and increased cervical lordosis. [PERSON] and [PERSON] [11] demonstrated that subjects with Class II malocclusion exhibit an anteriorly displaced posture, whereas subjects with Class III malocclusion exhibit a posteriorly displaced posture. Therefore a greater extension of the head on the spine is related to a more lordotic curve of the spine and to a Skeletal Class II [12]. According to [PERSON] et al. [13], functional therapy for Skeletal Class II with a forward jaw repositioning of the mandible seems to cause an increase of the cervical lordosis angle.  
The existing relationship between dental occlusion and body posture is a controversial topic in the literature. In 2011, [PERSON] et al. published an overview stating that the prevention or treatment of postural disorders cannot justify an occlusal and/or orthodontic treatment [14]. In 2021, [PERSON] et al. introduced the use of posturostabilometric platforms as an aid for the mandibular repositioning treatment in gnathological patients [15].  
To our knowledge, this is the first study aiming to investigate the implications of an orthodontic treatment performed in growing subjects on the overall body posture.  
The aim of the current study was to evaluate changes in body posture in children with Skeletal Class II pre- and post-Frankel II treatment, by testing the null hypothesis that no postural changes during orthodontic treatment occurs.