Dimensional Airway Changes due to the Use of Fixed Functional Appliances in Class II Malocclusion in Growing Patients: A Systematic Review

Aim: To determine the dimensional changes of the airways with the use of fixed functional appliances (FFA) in growing individuals with Class II malocclusion. Materials and Methods: The search was performed in five electronic databases (PubMed, Scopus, Embase Cochrane Library, and LILACS) until April 2022. Volume, area, or distance measurements of the global airway or by retropalatal (RP), nasopharynx (NP), oropharynx (OP), hypopharynx, and laryngopharynx (LP) regions were analyzed with intragroup or intergroup radiographs versus fixed orthodontic treatment (FOT) or no treatment (NT). Risk of bias was assessed with the Newcastle-Ottawa scale. Results: Out of 754 articles, six cohort studies were included. At least one airway parameter was found to increase with FFA, with better results in the oropharyngeal airway. In six studies, airway dimensions significantly increased with Herbst with or without FOT (ShortUpArrow 12.9%-139.2%), Forsus with FOT (ShortUpArrow28.7%) and mandibular anterior repositioning appliance (MARA) with FOT (ShortUpArrow22.6%-61%), with five studies reporting significant results (P < 0.05). The increase was in volume (14.8%-139.2%), areas (24.1%-61%), and distances (12.9%-39.3%) and in the RP (26.2%-100.7%), NP (7.8%-20.4%), OP (5.3%-139.2%), and LP (24.8%-94.7%) regions. Four cohorts showed significantly higher values of OP and LP volume and distance and cross-sectional areas with Herbst with or without FOT and MARA with FOT compared to FOT or NT (P < 0.05). Low risk of bias was more frequent (n = 4) than high risk (n = 2). Conclusion: Airway measurements were not standard between studies, thus limiting the group comparison. Various measurements of airway regions limit intergroup comparisons, and thus, a standard protocol is needed in future studies. Herbst, MARA, and Forsus FFAs used in growing patients with Class II malocclusion and showed benefits in the airways, especially by increasing the volume of OP in comparison to NT or FOT.