Skeletal and Dentoalveolar Changes Following the Functional Treatment of Skeletal Class II Growing Patients: A Systematic Review and Meta-Analysis

This systematic review was conducted to critically assess the effects of removable and fixed functional appliances (FFAs) on skeletal and dentoalveolar outcomes in growing patients with skeletal Class II malocclusion. In September 2025, a comprehensive literature search was performed across eight electronic databases. Randomized controlled trials (RCTs) and controlled clinical trials (CCTs) evaluating skeletal and dentoalveolar changes after treatment with removable functional appliances (RFAs) or FFAs were considered eligible. The included studies involved patients aged 9-14 years who underwent treatment with either RFAs or FFAs. Treatment outcomes were evaluated using cephalometric radiographic measurements. Study selection, data extraction, and risk-of-bias evaluation were independently conducted using the Cochrane risk-of-bias tools, while the certainty of the evidence was assessed according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) methodology. A total of six studies, including four RCTs and two CCTs, comprising 276 patients, fulfilled the eligibility criteria and were included in the final analysis. Overall, both RFAs and FFAs were effective in improving skeletal Class II malocclusion following active treatment, with correction resulting from combined skeletal and dentoalveolar changes. Most appliances, including Activator, Twin-block, and Aesthetic Twin-block (ATB), produced favorable sagittal changes, primarily mediated by mandibular advancement and modest restriction of maxillary growth, in conjunction with dentoalveolar adaptations. In contrast, the Trainer (T4K®) exhibited limited skeletal effects, suggesting that its mechanism of action is predominantly dentoalveolar. With regard to vertical changes, no clinically significant effects were observed for the Activator, Twin-block, ATB, or Trainer (T4K®), indicating minimal impact on lower facial height during the course of treatment. Conversely, the Bite-Jumping Appliance (BJA) was associated with increased facial height. The overall certainty of the evidence ranged from low to moderate, primarily due to methodological limitations and inter-study heterogeneity. In conclusion, both RFAs and FFAs - excluding the Trainer (T4K®) - are effective in the correction of skeletal Class II malocclusion in growing patients, primarily through maxillary growth restriction, increased mandibular length, and favorable dentoalveolar adaptations. No clinically significant short-term vertical changes were observed for most appliances; however, the certainty of this finding remains limited. Further well-designed, long-term RCTs directly comparing these treatment modalities are required to strengthen the evidence base and inform clinical decision-making. This systematic review was prospectively registered in the PROSPERO database (ID: CRD42025633113).