Functional appliances and airway in class II malocclusion

Abstract Purpose The potential influence of functional appliances on respiratory health has recently gained attention, though evidence remains inconsistent. This umbrella review and meta-analysis evaluated the impact of functional appliances on the upper airway area and volume as primary aims, and any patient-centered reported outcomes in the literature as a secondary aim. Methods The protocol was registered in PROSPERO (CRD42024540778). Systematic reviews and meta-analysis including patients as individuals in the prepubertal or circumpubertal growth phases. Specifically, this refers to growing patients in the mixed to early permanent dentition, cervical vertebral maturation (CVM) stages II–IV, with class II malocclusion treated with removable or fixed functional appliances were selected. Studies involving noninterventional designs, craniofacial syndromes, major comorbidities, or diagnosed obstructive sleep apnea were excluded. A comprehensive search was performed across MEDLINE, Cochrane, Scopus, Web of Science, LILACS, and Ovid up to October 2024, following PRISMA guidelines. Grey literature was screened via OpenGrey. Risk of bias was assessed using ROBIS. Study overlap was evaluated through corrected covered area (CCA) and GROOVE indices. Quantitative re-analysis of three CBCT-based meta-analyses was conducted using random effects models. Results Nine reviews met the inclusion criteria, eight with low risk of bias and moderate-to-high overlap (CCA = 10.97%). Functional appliances significantly increased oropharyngeal airway volume, especially the Herbst (up to 7759 mm 3 ) and Twin Block (up to 1727 mm 3 ) appliances. Meta-regression analysis indicated that with each additional year of patient age, the treatment-induced increase in posterior airway space decreased by an average of 0.36 mm. Conversely, for each additional month of treatment with the functional appliance, the superoposterior airway space increased by 0.12 mm and the inferior airway space by 0.29 mm. Re-analysis of the three meta-analyses showed a large significant effect for oropharyngeal changes (standardized mean difference [SMD] = 1.41; 95% confidence interval [CI] 0.57–2.26) and a moderate effect for total airway volume (SMD = 0.71; 95% CI 0.31–1.11). No studies described any patient-centered reported outcomes. Conclusion Functional appliances demonstrated consistent effects in increasing the volume of the oropharyngeal region. However, variability among studies highlights the need for standardized protocols using volumetric assessments and adequate follow-up periods to determine treatment stability in a multidisciplinary approach for young patients.