## 2 Materials and Methods  
At the beginning of this retrospective study, it was planned to include 38 participants in the peak puberty growth phase or shortly after (CVS3 and CVS4 stages) who were receiving treatment with a Twin Block appliance during the period from 2023 to 2024. Two participants declined to participate in the study, a further three were non-cooperative (discontinued treatment), and the remaining 33 finished the treatment. Unfortunately, it was established that a further 15 participants had either missed one of the facial scans, or they were not suitable for the analysis, even after inspection upon scanning. Therefore, the final sample consisted of 18 participants (Figure 1).  
All parents/guardians of the patients signed an informed consent form for the therapy, thereby giving their consent for the use of medical documentation for research purposes.  
Finally, this study included 18 participants (7 girls and 11 boys) who had all the necessary documentation before and after the treatment. Participants were receiving treatment with functional appliances at the clinical unit for orthodontics, which is part of the Department of Dental Medicine at the Clinical Hospital Center Rijeka. The median age of the participants at the start of therapy was 12.4 years, and at the end of therapy it was 13.6 years. The therapy lasted an average of 14.1 months. The Twin Block appliance consists of upper and lower plates with occlusal ramps and hooks that retain the appliance on the dental arch. The registration of the constructional bite is the most important step in the design and final fabrication of the functional appliance. It determines the new sagittal, vertical, and horizontal relationships of the lower jaw to the upper jaw. The activation of the lower jaw must sufficiently stretch the masticatory muscles and allow a positive proprioceptive response, while also staying within the physiological limits of the muscles and joints [14]. The quality of 2D images was also considered, as well as the possibility  
Figure 1: Study enrolment flow chart.  
for their most precise analysis. The sample size was calculated with a power of 90% and a significance level of 0.05, using an online calculator and previous published studies. It was calculated that a minimum of 14 participants was needed [12].  
The inclusion criteria for participants in the study were as follows: individuals of both genders with the presence of skeletal Class II with a retrogathic mandible, overjet > 6 mm, ANB > 2.5\({}^{\circ}\), Wits > 2.5 mm, Class II on the first permanent molars and canines, and patients who were undergoing orthodontic treatment for the first time. Additionally, participants included in the study had to have lateral cephalograms taken before and after therapy. All subjects were Class II, division 1; six of them had a horizontal growth pattern (SN:GoGn \(\leq\) 26\({}^{\circ}\)), ten had a neutral growth pattern (SN:GoGn \(>\) 26\({}^{\circ}\) \(<\) 37\({}^{\circ}\)), and two exhibited a vertical growth pattern (SN:GoGn \(>\) 37\({}^{\circ}\)). The treatment choice for the functional appliance was made upon performing the Frankel maneuver.  
The exclusion criteria for the study were as follows: the presence of hypodontia, temporomandibular joint disorders, obstructive airway disorders, craniofacial syndromes, congenital malformations, severe facial asymmetries, or systemic diseases that could affect facial morphology.