Abstract: Objective: To study the effect of orthodontic movement of maxillary first molar on the structure of zygomatic pillar and the correlation between structural alteration and occlusal changes. Methods: Fifty patients with malocclusion (control group) and 50 patients receiving orthodontic treatment with extraction (experimental group) were selected, and the occlusal contact characteristics of two groups were analyzed with the Teetester,. Twenty-five patients with complete CBCT images were selected from the experimental group, and the CBCT images were analyzed with Mimics 21.0. The cross-sectional area of the zygomatic pillar, the movement of surface markers and the maxillary first molar, and the thickness and density of the alveolar bone and the cortical bone of the zygomatic pillar were measured. Results: The maxillary first molar showed changes in three-dimensional directions after orthodontic treatment, with significant mesial movement. The cross-sectional area of the lower section of the zygomatic pillar became smaller, the zygomatic point and the lowest point of the zygomaticomaxillary suture were displaced posteriorly, the thickness of the alveolar bone and the cortical bone decreased, and the above changes were correlated with the movement of the maxillary first molar. Total occlusal contact area (TCA), total occlusal force (TOF), and occlusal force of the maxillary first molar were reduced in the experimental group. Conclusion: Before and after orthodontic treatment with extraction, there was a correlation between the movement of maxillary first molar in three-dimensional directions and the modification of the structure of zygomatic pillar in the middle and lower segments. These alterations may affect the magnitude and the distribution of occlusal force.

Key words: orthodontic treatment with extraction, zygomatic pillar, the maxillary first molar, occlusal fforce