Three-dimensional changes of the zygomaticomaxillary complex after mini-implant assisted rapid maxillary expansion.

INTRODUCTION: The aim of this study was to investigate 3-dimensional changes of the zygomaticomaxillary complex (ZMC) after mini-implant assisted rapid maxillary expansion (MARME). METHODS: A total of 15 pairs of cone-beam computed tomography 3-dimensional images taken before expansion (T0) and after expansion (T1) were analyzed by measuring changes in the coordinates of the landmarks of the ZMC. RESULTS: Changes in the x coordinates of the landmarks showed significant expansion (P <0.01) and greater expansion at the lower than upper portion of the ZMC (P <0.05) in the transverse dimension. All y coordinates of the landmarks except the jugal point (J) showed forward displacement (P <0.05), and the z coordinates of ANS, PNS, Alare, A, and ectocanine showed downward displacement (P <0.01) in the sagittal and vertical dimensions. Also, z coordinates of the landmarks that were closer to the midsagittal plane and in a more posterior portion of the ZMC displaced further downward (P <0.05). SNA and ANB angles increased (P <0.05 and P <0.001, respectively) and the SNB angle decreased (P <0.01). There was a significant correlation between changes in the x coordinates of the ectomolare and ectocanine and the amount of expansion measured from the center of resistance of the maxillary first molars (CR6; P <0.05). There was no significant correlation between the amount of CR6 expansion and changes in y and z coordinates of the landmarks. CONCLUSIONS: 3-Dimensional changes of the ZMC after MARME showed expansion in a pyramidal shape from the coronal view, downward and forward displacement from the sagittal view, and parallel palatal expansion from the axial view. These findings might be useful for understanding skeletal expansion patterns using MARME.