History of Mandibular Advancement Treatment Is Associated with Cranio-Cervico-Hyoid Biomechanical Alterations in Young Women with Class II Division 1 Malocclusion: An Exploratory Cross-Sectional Study

Abstract

Background: Orthodontic treatment is widely performed in young populations, yet its post-treatment functional associations beyond dental occlusion remain poorly understood. The cranio-cervico-hyoid complex plays a central role in posture, swallowing, and airway function, and may be sensitive to developmental or treatment-related influences. This study investigated whether, among otherwise healthy young women with a diagnosis of Class II division 1 malocclusion, a history of orthodontic treatment with mandibular advancement is associated with altered passive mobility of this system. Methods: A cross-sectional observational study was conducted on 170 women aged 18–30 years with a diagnosis of Class II division 1 malocclusion (104 treated with mandibular advancement for 6–12 months (ortho group); 66 with the same diagnosis who had never undergone orthodontic treatment (ctrl group)). Anthropometric, epidemiological, clinical, and psychosocial variables were collected, including VAS, FIQR, CSI, and DASS-42. Passive mobility of the hyoid bone, C0–C1, and C2–C3 segments (primary outcome) was assessed by an experienced blinded examiner. Group differences were analyzed using chi-square, Fisher’s exact test, Welch’s t test, or Wilcoxon tests, with effect sizes and multiple-comparison corrections (Benjamini–Hochberg and Bonferroni). At the time of examination, all treated participants presented Class I occlusion, whereas all controls retained Class II division 1 malocclusion. Results: Groups were comparable in baseline anthropometric and epidemiological characteristics. The orthodontic group reported higher FIQR scores and greater pain intensity on the VAS, although these differences did not remain significant after multiple-comparison correction. Marked biomechanical differences emerged: reduced passive mobility of the hyoid bone, C0–C1, and C2–C3 was significantly more frequent in orthodontically treated subjects, with moderate to strong effect sizes. The composite variable “at least one dysfunction” was present in 74% of orthodontic subjects versus half of controls. These associations remained significant after multiple-comparison correction. Because all treated participants had been corrected to Class I while all controls remained in Class II division 1, the effect of treatment could not be separated from that of the corrected occlusion. Conclusions: Young women with Class II division 1 malocclusion previously treated with mandibular advancement showed a higher prevalence of altered passive mobility of the cranio-cervico-hyoid complex, and differences in cervical pain intensity and functional impact were small and did not remain significant after multiple-comparison correction. Because treatment history and current occlusion were completely confounded, the findings cannot establish whether these differences are attributable to mandibular advancement, occlusal correction, or pre-existing factors. Given the cross-sectional design and the lack of consistent data on retention period and exact time since treatment completion, these findings should be interpreted as post-treatment associations rather than causal or long-term effects. Further longitudinal studies are needed to clarify the temporal relationship and clinical relevance of these alterations.

The authors' abstract, as published at the source. Bioengineering, 2026 · DOI ↗