Facial scans of the patients eligible for the functional appliance treatment (Twin Block appliance) will be taken prior to and after the end of treatment. Also, a facial scan of the predicted final outcome will be taken, and compared to the actual final outcome. Parents / caregivers will fill out the Pediatric Sleep Questionnaire (PSQ) prior to and upon the end of treatment to asses perceived influence on sleep related breathing problems in their children.

The harmonious growth of the upper and lower jaw enables further favorable development of the orofacial region and the functions of breathing, chewing, swallowing and speaking, as well as the general growth and development of the child. Translation into Croatian and administration of the questionnaire for early detection of sleep disorders related to breathing in children (PSQ) will enable triage and early recognition of children with sleep disorders, which also affect general psycho-physical development. The impact of functional appliance therapy (FA) on changes in craniodentofacial characteristics, dimensions of the upper airway and sleep problems in children will be determined. The non-invasive three-dimensional representation of the face surface provides information about the surface and volume of the observed object, which is used for better diagnostics and therapy planning. Class II is a frequent malocclusion, characterized by a discrepancy of sagittal interjaw relationships. The diagnostic method, which helps in deciding on a therapeutic approach, is the so-called Fränkel maneuver (FM). By comparing the observation of the soft tissue profile of the subjects at rest and after the application of FM, a decision is made on the therapeutic approach. Previous research indicates the validity of using FM in making a decision about FN therapy, with high reliability and consistency. The analysis of latero-lateral (LL) X-ray cephalograms in numerous studies has provided a series of data, which is used, among other things, to assess the remaining growth in order to apply FN therapy in a timely manner, but also to expect a desirable response. The evaluation of the success of therapy based on FM don't exist, because a reliable 2D analysis through LL cephalogram would require additional radiation of the subjects. Research indicates that the analysis of scan surfaces is more appropriate than the analysis of anatomical points for detection of the area and amount of changes.

Inclusion Criteria:

• retrognathic mandible, increased overjet

Exclusion Criteria:

• craniodentofacial deformities

Data contain identifiable biometric data, and will be disclosed only upon reasonable request.