## 1 Introduction  
Class II malocclusion affects about a third of the population [1], representing one of the most common problems in orthodontics. Among the numerous dental and skeletal factors that can lead to Class II malocclusion, mandibular skeletal retrusion is the main cause [2,3]. Data in the literature have shown that the characteristics of this type of malocclusion stabilize from early childhood and, in the absence of treatment or modification of the etiological factors, it never undergoes spontaneous self-correction [4]. Therefore, treatment is necessary.  
As Class II malocclusion is more frequently characterized by mandibular retrusion, a therapy capable of improving mandibular growth and position is recommended in these patients [2]. This type of dental and skeletal disharmony, in fact, can be corrected by the use of functional devices that stimulate mandibular growth with anterior repositioning of the mandible.  
[PERSON] et al. [5] divided the main etiological factors of malocclusions into three categories: specific causes, such as alterations during the embryonic, fetal, and neonatal periods, hereditary factors, and environmental factors. The latter are represented by the forces and pressures that the muscles exert physiologically on the skeletal and dental structures during development. The pressure generated by the muscles of mastication during chewing is a factor potentially significant in the development of malocclusion. As stated by [PERSON] [2], mandibular retrusion has an embryological origin. Furthermore, the position of the dental elements in the arch is dictated by the balance between centripetal and centrifugal muscular forces that cancel each other out. The alteration of the pressure balance generated by the early onset of a bad habit, such as finger sucking, can generate the onset of Class II malocclusion. Factors leading to mandibular retrusion, such as transverse discrepancy due to superior transverse minus [6], are considered \"Class II interferences\" and may cause the onset of a functional Class II malocclusion. If those interferences are not intercepted and removed, over time the malocclusion can turn into an anatomical alteration.  
The Paolone-Kaitsas appliance (PK appliance) [7] is a removable functional appliance that was described for the first time in 2017. It consists of two acrylic plates, one upper and one lower, joined by two lateral three-loop springs. The plates are characterized by the presence of occlusal bite planes with complete occlusal coverage to control the occlusal plane. Lateral springs enable the progressive activation of the device in order to control the posterior facial height/anterior facial height (PFH/AFH) Index due to the larger activation in the posterior than in the anterior area. Moreover, it is possible to incorporate an expansion screw in the upper plate to correct possible maxillary contraction, which is frequently associated with Class II malocclusion. No studies evaluating the skeletal and dentoalveolar effects of the device have been published so far.  
The aim of this study was to analyze the skeletal and dentoalveolar effects induced by the PK appliance in the treatment of growing patients with Class II malocclusion. This evaluation was based on the analysis of pre- and post-treatment lateral cephalospor compared with the cephalometric data of a control group of growing patients with untreated Class II malocclusion.