Abstract: Objective To analyze the three-dimensional(3D) changes of the morphology and structure of the temporomandibular joint (TMJ）after the establishment of a new steady-state through Twin-Block-induced mandibular advancement with 3D reconstruction of cone beam computed tomography (CBCT). Methods  Fifteen adolescent patients treated with Twin-Block appliances at the Department of Orthodontics, Shandong University School of Stomatology from June 2023 to July 2025 were selected. Pre- and post-treatment CBCT images were collected. Mimics 21.0 software was utilized for 3D reconstruction of the TMJs. Landmark identification and data measurement of condylar morphology and joint space were performed on the 3D models. Statistical analysis of pre- and post-treatment measurements was conducted. Results  Compared with pre-treatment values, significant increases were observed in post-treatment condylar mediolateral dimension, anteroposterior dimension, height, surface area, total volume, and head volume  (P<0.05). The superior joint space was significantly widened (P<0.05), and positional changes of the condyle were detected. Conclusion  Twin-Block mandibular advancement therapy induced adaptive growth remodeling of the condyle, characterized with increased height, volume and surface area, along with anterior and inferior displacement of the condyle relative to the glenoid fossa. The temporomandibular joint achieved a balanced state of structural and functional coordination at the new leading position.

Key words: Twin-Block appliance, mandibular advancement, temporomandibular joint, steady-state reconstruction, three-dimensional reconstruction analysis, cone-beam computed tomography