Three-dimensional pharyngeal airway and hyoid bone changes in skeletal class I malocclusion treated with extraction and non-extraction protocols: a comparative study of fixed orthodontic appliance and clear aligners.

Objectives: This study aimed to provide a comprehensive three-dimensional (3D) evaluation of fixed appliances (FAs) and clear aligners (CAs) on pharyngeal airway (PA) dimensions and hyoid bone (HB) positioning in skeletal Class I malocclusion patients treated with extraction and non-extraction protocols, comparing the effects within each protocol.

Materials and methods: This retrospective study involved 120 adult patients divided into extraction and non-extraction groups, each further subdivided equally into those treated with FAs and CAs. PA segmentation and measurements were conducted with Dolphin 11.8 (Dolphin Imaging and Management Solutions, Chatsworth, CA). The PA was analyzed in the nasopharyngeal (NP), oropharyngeal (OP), and hypopharyngeal (HP), total pharyngeal (TP) airway, while HB parameters were measured using InVivo 6.0.3 (Anatomage, San Jose, CA). Descriptive and analytical statistics were performed, with a significance level set at P < 0.05.

Results: None of the evaluated parameters showed a significant difference in the baseline, indicating almost comparable groups. Inter-group comparisons showed that within the non-extraction group, FAs caused greater decreases in OP sagittal width and HP lateral width and more significant increases in vertical hyoid position (H-FH) compared to CAs (P < 0.05). In the extraction group, FAs resulted in greater decreases in OP lateral width and volume, HP volume, and more significant H-FH increases than CAs (P < 0.05).

Conclusion: Fixed appliances caused greater reductions in oropharyngeal and hypopharyngeal dimensions and more significant changes in hyoid bone position compared to clear aligners, particularly in extraction cases. Clinicians should consider these effects when selecting treatment modalities, especially for patients with airway concerns.

Clinical relevance: Fixed appliances significantly impact pharyngeal airway dimensions and hyoid bone positioning, while clear aligners have milder effects, emphasizing the need for careful treatment planning.