Aim: The aim of this study was to perform the Croatian translation of the Parental-Caregiver Perception Questionnaire (P-CPQ), Family Impact Scale (FIS) and their short forms, and to analyze their psychometric properties for the Croatian population. Only valid questionnaires could then enable the following goals: (1) to define the predictors of family impacts, (2) to assess the levels of agreement between parents and adolescents about young adolescents' orthodontic treatment demand, (3) to evaluate to what extent was the treatment demand under the influence of family and psychosocial impacts as well as oral function and (4) to determine factors that could be classified as the predictors of treatment success (including the assessment of the impact of the family on cooperation) during treatment of Class II/1 malocclusion with removable functional appliances. Materials and methods: A forward-backward translation of the P-CPQ and FIS was made as a first step in the testing of psychometric properties of the Croatian instruments, which was then followed by a validation study of the previously mentioned questionnaires. The sample size that was obtained to assess the validity and internal reliability of the measures equaled 334 participants (children aged 11-14 years; 53% female and their parents). For the assessment of test-retest reliability, 26 participants were included in the study, while 46 participated in the testing of responsiveness of the measures. For the part where the agreement between adolescents and parents on the orthodontic treatment demand of adolescents was evaluated, and for the assessment of predictors of orthodontic treatment demand in young adolescents, a sample size of 221 subjects (dyads of children (11-14 years; 54% female) and their parents) was used. A sample of 88 participants (aged 11-13; 47% female) who presented with a Class II division 1 malocclusion with a distal molar relationship, overjet equal or greater than 6 millimeters, and confirmed pubertal growth spurt were included in a randomized controlled trial meant to evaluate possible predictors of orthodontic treatment success of young adolescents. Patients were treated with removable functional appliances (50% twin-block, 50% Sander bite jumping appliance) with built-in maxillary expansion screws. The follow-up period was 1 year. The CPQ, P-CPQ and FIS were self-administrated to assess emotional well-being (EW), social well-being (SW), oral symptoms (OS), functional limitations (FL), parental emotions (PE), family activities (FA), family conflicts (FC), and financial burden (FB). Participants additionally responded to questions related to self-perceived oral health, well- being, satisfaction with appearance, treatment need and treatment demand on a five-point Likert-type scale. Malocclusion severity was assessed using the Index of Orthodontic Treatment Need Dental Health Component (IOTN DHC), while caries severity was assessed using the Decayed, Missing, Filled Teeth Index (DMFT). Sex and overjet were also recorded. Exploratory and confirmatory factor analysis, Pearson correlation, Cronbach alpha coefficient, inter-item correlation, intraclass correlation coefficient, Cohen's kappa coefficient, MannWhitney, Wilcoxon, Fisher, Kruskal Wallis test, linear and logistic regression and discriminant analysis were used in the statistical analysis. Results: Exploratory factor analysis of the P-CPQ initially indicated an eight-factor structure with interference of all original dimensions. However, when the analysis was fixed to four factors, it indicated a mixing of the EW and SW subscales as well as the OS and FL subscales. Additionally, a two-factor model was also evaluated, but overall, the four-factor structure was found to be more appropriate for the Croatian population than the two-factor structure explaining 52.5% of variability. Confirmatory factor analysis confirmed the findings of exploratory factor analysis. The instrument moderately correlated with all dimensions of oral health related quality of life (OHRQoL) reported by children (r=0.345-0.506; p<0.001). Higher P-CPQ scores in all subscales were detected in subjects with caries lesions, while only EW and SW scores differed between participants with low and high malocclusion severity. Internal consistency of original four factors ranged α=0.66-0.89. All subscales of the overall measure were stable over time, while the temporal stability results for the 16- and 8-item P-CPQ were not satisfactory. The questionnaire showed adequate responsiveness to change as a consequence of Class II/1 treatment with removable functional appliances, mostly in the EW domain. Short forms of P-CPQ (16 and 8-items) had lower psychometric properties than long form instrument. On the other hand, the exploratory factor analysis of the FIS with 14 items showed a four-factor structure of the instrument with mixing of all original dimensions – PE, PA, FC and FB, accounting for 56% of variance. FIS correlated greatly with parental reporting of impaired EW and SW of their children (r=0.656-0.694; p<0.001) and the overall P-CPQ (r=0.716-0.736; p<0.001). Higher family impacts were detected in young adolescents affected with caries lesions and severe malocclusions, mostly PE and PA (p<0.05). The Cronbach alpha values of the unidimensional FIS and 8-item short-form FIS were found to be better (α=0.81 and 0.73) compared to the individual dimensions (α=0.60-0.69). Repeatability of family impact reporting was good for the summary FIS scale, PA and PE subscales. The questionnaire was responsive to change that happened as a consequence of Class II/1 treatment, mostly in the PE domain. According to the linear regression analysis, parental perception of child's emotional state, OS, and social relationships were significant predictors of family impacts (p<0.001). The agreement between parents and their children on young adolescents’ orthodontic treatment demand was weak, concording in 67.4% of cases. The most common reasons why adolescents demanded orthodontic treatment came from a psychosocial background for both informants. In linear regression, the adolescent's reporting of an impaired EW and an objective treatment need were the only significant linear predictors of the orthodontic treatment demand. There were more patients with successful than unsuccessful result (58% vs. 42%). Low functional limitations of the child as noted by the parent before starting the treatment increased the odds of the treatment success 3.3 times (95% CI 1.2-9.0; p=0.020), as did the twin-block appliance compared to the Sander bite jumping appliance (95 % CI 1.2-8.6; p=0.016). Conclusion: Among the evaluated questionnaires, the four-factor structure of the P-CPQ showed the best metric properties, while the one-dimensional FIS instrument had better properties for orthodontic scenarios compared to other questionnaire forms. Overall, the role of family in orthodontic treatment of young adolescents was not big. Parents were not able to properly assess the demand for orthodontic treatment of their children and had little influence on that request. However, parents did play a role in the treatment success as the treatment was considered to be more successful in those patients whose parents perceived a low impairment of oral function, as well as in those treated with the twin block appliance.