Evaluation and comparison of airway changes in skeletal Class II patients treated with Twin Block and Forsus FRD: a systematic review

Objective This study aims to compare and evaluate the effects of two functional appliances—Twin Block and Forsus Fatigue Resistant Device (FRD)—on changes in airway dimensions in patients with skeletal Class II malocclusion. Methods A search was conducted in four electronic databases (PubMed, Web of Science, Scopus, and Cochrane Library) for articles published up to November 2025. Six clinical studies (five retrospective and one prospective) that evaluated airway changes following treatment with Twin Block and Forsus FRD were included. Data extracted included study design, sample characteristics, intervention details, cephalometric airway measurements and dimensions, and pre- and post-treatment outcomes. Risk of bias was assessed using ROBINS-I, and the certainty of evidence was evaluated using GRADE. Results Both Forsus FRD and Twin Block appliance therapies were associated with improvements in selected airway parameters, including increases in the upper, middle, and lower pharyngeal airway widths, anterior repositioning of the hyoid bone, and changes in nasopharyngeal and oropharyngeal sagittal dimensions. Some studies reported more pronounced airway changes and greater skeletal advancement with the Twin Block appliance, particularly in the oropharyngeal region, whereas other studies found similar airway effects with no statistically significant intergroup differences. Twin Block was associated with greater skeletal mandibular advancement in some studies, whereas Forsus FRD tended to produce more pronounced dentoalveolar effects, particularly mandibular incisor proclination. Overall, airway changes were modest and variable, with differences in age, growth stage, appliance protocol, treatment duration, and measurement techniques contributing to heterogeneity. Conclusion Both Twin Block and Forsus FRD therapies may be associated with modest improvements in selected pharyngeal airway dimensions in patients with skeletal Class II malocclusion. Although Twin Block was associated with greater skeletal mandibular advancement in some studies and Forsus FRD tended to produce more pronounced dentoalveolar effects, particularly mandibular incisor proclination, these comparative patterns were not consistent across all studies. Consistency of statistically significant differences between the appliances in airway outcomes was not demonstrated. More high-quality prospective comparative studies are required to clarify the comparative skeletal, dentoalveolar, and airway effects of Twin Block and Forsus FRD and their clinical significance. Systematic Review Registration identifier: CRD420251207653.