Computational fluid dynamics analysis of the respiratory function of orthodontic patients. A scoping review.

BACKGROUND: Computational fluid dynamics (CFD) has been increasingly applied to simulate airflow behavior in the upper airway, enabling the assessment of airflow-related changes following orthodontic and orthognathic treatments that modify airway dimensions and shape. Such changes may influence ventilation and, potentially, the risk of sleep-disordered breathing. Therefore, the aim of this scoping review was to map and characterize the use of CFD to assess upper airway airflow and ventilation in orthodontic patients treated with or without orthognathic surgery. METHODS: A literature search was conducted up to March 2025 in five databases: Cochrane, EMBASE, PubMed, Web of Science, and Scopus. The Selection criteria were: Population: Healthy patients or patients with sleep-breathing disorders, without any age restrictions. Concept: All patients underwent orthodontic treatment, either associated with orthognathic surgery or not. Context: Articles that evaluated the upper airway airflow (nasal cavity, nasopharynx, oropharynx, hypopharynx) after orthodontic and/or orthognathic intervention, using CFD, were included. Studies that included CFD in patients diagnosed with or without Obstructive Sleep Apnea were included. Study types: randomized and non-randomized trials, analytical, and descriptive studies were included. No limitations on the year of publication or language were imposed. Articles that met eligibility criteria were assessed using the PRISMA-ScR. Data were charted and synthesized descriptively according to treatment modality, airway region assessed, imaging protocols, CFD modelling characteristics, and reported airflow outcomes. RESULTS: Forty-three articles met the inclusion criteria. In general, CFD results have shown that treatments that could reduce the upper airway dimension, such as premolar extraction or mandibular setback surgeries, worsened the ventilation in patients. Conversely, treatments that might increase the upper airway dimension (i.e. functional appliances, rapid maxillary expansion, mandibular advancement device, maxillo-mandibular advancement surgery, and postero-superior repositioning of the maxilla) improved ventilation and possibly improved obstructive sleep apnea (OSA) signs and symptoms. Although more robust studies are needed. CONCLUSION: This scoping review maps the expanding application of CFD for the evaluation of upper airway airflow in orthodontic and orthognathic contexts. CFD appears to be a valuable exploratory tool for characterizing airflow patterns and identifying potential trends related to different treatment modalities. Nevertheless, due to methodological variability and limited longitudinal data, CFD findings should be interpreted descriptively. Future research should prioritize standardized imaging and CFD protocols, validation against in vivo respiratory measures, and clinically relevant outcome reporting to better define the translational role of CFD in orthodontic airway assessment.