Effect of maxillary molars distalization using clear aligners and fixed orthodontic appliances on the positional and dimensional temporomandibular joint parameters: a three-dimensional comparative study

Objective: The use of clear aligners (CAs) for orthodontic treatment has substantially increased in recent decades. However, limited empirical evidence exists regarding their potential effects on the temporomandibular joint (TMJ). The aim of this study was to assess the effect of maxillary molar distalization on the positional and dimensional TMJ parameters between CAs and conventional fixed orthodontic appliances (FAs) in skeletal class II malocclusion.

Methods: This is a retrospective cohort study examined 70 adult patients with skeletal class II malocclusion with similar baseline characteristics based on American Board of Orthodontics (ABO) discrepancy index scores. The patients were treated by maxillary distalization movement by CAs or FAs, of which there were two equal groups of 35 patients were included in each group. CBCTs on TMJs were performed before and after treatment through Anatomage Invivo Dental 6.0. The measured parameters included inclination, position, condyle and articular fossa dimensions, and the volumetric joint spaces.

Results: In both groups, linear measurements of the maxillary molar position revealed significant improvement after treatment (P < 0.001). Regarding TMJ parameters, intra-group comparisons revealed significant changes in FA group in the anterioposterior condylar inclination and condylar position across the three planes. Additionally, the pretreatment-centric condylar position in the glenoid fossa was 45.7% and 40% in the CA and FA groups, respectively. After treatment, these percentages changed to 51.4% and 31.4%, respectively. In inter-group comparisons, significant changes were noted in the mediolateral condylar position, which was more inward in the FA group than the CA group.

Conclusion: The FA group had more significant dimensional and positional changes in the mandibular condyle than the CA group; nevertheless, the changes are considered clinically negligible.