## 1 Introduction  
A skeletal class II malocclusion is often characterized by a retrognathic mandible and a hyperdivergent pattern of growth, which makes it challenging to treat [1]. [PERSON], in a 1964 article, was the first to suggest the term facial divergence to indicate a vertical variation with two extremes: hyperdivergence and hypodivergence [1,2]. Hyperdivergence, also denoted as skeletal open bite, refers to the excessive vertical development of the bone bases due to genetic and environmental factors. This pattern is characterized by increased lower face heights, steeper mandibular planes, and larger gonal angles [3]. Skeletal open bite has to be distinguished from dental open bite, characterized by the absence of contact between the upper and lower incisors in the vertical plane while the posterior elements occlude. It is often determined by bad habits such as atypical swallowing, prolonged sucking of the finger or thumb, and oral breathing [4].  
Orthodontic treatment is necessary both for aesthetical and functional reasons. Generally, the profile of these patients is convex and presents an augmented facial lower third (from the lower lip to the menton cephalometric point). Different authors evaluated the preferences on facial profiles, concluding that a straight profile, or class I profile, is the most appreciated [5,6]. In a 2012 article, [PERSON] et al. reported that significant chin height is considered unattractive by clinicians, patients, and laypeople with minor criticism [7]. Functionally speaking, [PERSON] et al., evaluating occlusal force during maximum effort, swallowing, and simulated chewing, found that this is lower in long-faced adults than in normal vertical facial ones [8]. In a second study conducted among 6- to 11-year-old children with normal and long faces, these differences were not noticed, and their occlusal forces were similar to a long-faced adult. It also emerged that children with the long-faced pattern do not develop proper muscular strength, especially in the mandibular elevator muscles, during growth. Consequently, it is essential to control the lower facial third growth tendency using interceptive orthodontics devices. Clinicians should guide these patients toward the most appreciated facial characteristics and better muscular functionality [9,10].  
The early treatment aimed to control and contain maxilla vertical growth in the posterior region, prevent downward and backward mandibular rotation, and promote its development in forwarding rotation [11,12]. In this way, the need for surgery in adulthood can be reduced [13,14,15,16].  
Several devices are used to control the excessive vertical size in growing patients, such as functional appliances, fixed appliances with extractions, high-pull headgears, bite blocks, or any combinations of the above [17,18,19]. In particular, headgear and functional appliances are two common nonsurgical therapy options for class II skeletal malocclusions. Some authors stated that the combined use of a removable functional appliance and high-pull headgear was more effective than using a single method [20,21].  
There was no adequate literature about long-term stability. However, a relapse seemed to occur in those cases with atypical tongue function or an incompetent oral seal [19,22,23].  
This study aims to assess the treatment of growing patients with class II malocclusion and hyperdivergent tendencies with AMCOP elastodontic bio-activators, and to evaluate the upper airway patency improvement after therapy.  
Elastodontic therapy with AMCOP(_Armonizzatori Multifunizionali Cranio-Occlusion-Posturali_/Cranio-Occlusion-Posturali Multifunctional Harmonizers) represents a new approach of interceptive orthodontics that uses light and biological forces of an elastic type for orthopedic and functional action [24,25,26,27].