Three-dimensional condylar changes in the surgery first approach: A comparison of fixed orthodontics vs. Invisalign therapy

Objectives: Analyze skeletal changes and condylar resorption, remodeling, and positional changes in patients with Surgery First Approach (SFA) during orthodontics with fixed braces or aligner therapy. Methods: This retrospective longitudinal study, approved by the University of the Pacific IRB (#2021-70), compared skeletal changes between fixed orthodontics and Invisalign® therapy in patients undergoing the surgery-first approach (SFA). The study included 46 patients (28 fixed, 18 Invisalign). Cone-beam computed tomography (CBCT) scans were obtained at three timepoints: pre-surgery (T1), post-surgery (T2), and after orthodontic treatment (T3). Using InViVo 3- Dimensional Software, AI-based landmark identification, and standardized reference planes were employed for dental and skeletal measurements. Regional registration at the condylar level was also performed using 3D Slicer. Custom analyses were performed to assess anterior-posterior, vertical, and transverse changes. Statistical analysis included Spherical Harmonics (SPHARM) mesh statistics to assess condylar shape changes. Student's t-test and Mann-Whitney tests were used to compare the results between the groups and Spearman correlations. Results: Both groups presented similar skeletal movements during surgery (T2-T1). Frankfort Mandibular Plane (MP-FH) increased in the fixed group while decreased in the Invisalign group when comparing T3-T2. No significant dental changes were observed between the two groups. Mandibular body length (Gonion to Pogonion) decreased more in the fixed group. There were no significant condylar positional changes between the two groups (T2-T1) and no differences in remodeling (T3-T2). Conclusion: Most skeletal variables did not show statistically significant differences between the two groups, and the condylar changes were also similar when comparing T2-T1 and T3-T2. This study’s findings suggest that both techniques are safe and provide similar skeletal, dental, and condylar outcomes.