Cervical spine changes with functional appliance treatment: A systematic review and meta-analysis

Objective: Cervical spine posture is related to craniofacial morphology, airway, gait and body posture. This posture may be influenced by the changes in the mandibular position brought about by functional appliance therapy. Therefore, this systematic review aimed to assess the changes in the cervical spine posture with functional appliance treatment in Skeletal Class II subjects. Methods: A search of studies in six electronic databases - Medline (via Pubmed), the Cochrane Library, OVID, LILACS, Scopus and Web of Science were performed until January 18, 2024 without any restriction in date or language of publication. Eligibility screening, study selection, and data extraction were performed by two reviewers independently. The risk of bias assessment of the included studies was performed with the Newcastle Ottawa scale and Cochrane RoB 2.0. Meta-analysis was performed using random effects model for assessment of changes in the cervical spine with removable and fixed functional appliances. Results: Twelve articles that satisfied the eligibility criteria were included for systematic review and nine articles for meta-analysis. Five studies showed a low risk of bias, one as moderate and six as high risk of bias. GRADE assessment revealed a low quality evidence. Meta-analysis revealed a decrease of the upper cervical inclination by 1.16° (95 % CI of −2.68 to 0.35, I2 = 6 %), an increase of the middle cervical inclination by 2.20° (95 % CI of 0.46–3.94, I2 = 49 %), an increase in cervical curvature angle by 1.60° (95 % CI of 0.12–3.09, I2 = 89 %) and a decrease in cervical lordosis angle by 1.54° (95 % CI of −4.16 to 1.08, I2 = 0 %). Conclusions: Minimal uprighting of the cervical spine was noted with functional appliances. Fixed functional appliances exerted a greater effect than removable functional appliances. Cervical hyperlordosis was reduced with removable functional appliance treatment. Though these changes are minimal, the clinical orthodontist should be aware that functional therapy also influences cervical spine posture. Due to the heterogeneity and low quality of evidence, the results are to be considered critically.