Purpose To assess the effects of rapid maxillary expansion (RME) treatment on the zygomatic bone complex (ZBC). Methods In this single-center retrospective study, pre-and posttreatment cone-beam computed tomography (CBCT) images of 38 patients treated with RME were analyzed to investigate changes in the coordinates of the ZBC landmarks. At the start of treatment (T0), the patients’ mean age was 11.1±3.8 years (range 8.3–14.9 years). Cohen’s d test was used to evaluate statistical differences.

Results There were statistically significant differences between T0 and T1 (P< 0.01) in the measurement values for the maxillary transverse width (ΔT: 3.18±2.58, d: 1.23), frontozygomatic sutures (ΔT: 1.09±0.56, d: 0.43), lowest point of the zygomaticomaxillary sutures (ΔT: 3.16±1.78, d: 0.78), frontomaxillary angular parameter (right side ΔT: 2.81±1.63, d: 1.73; left side ΔT: 2.52±1.20, d: 2.10), frontozygomatic angular parameter (right side ΔT: 2.81±1.63d: 1.07; left side ΔT: 2.21±2.79, d: 0.61), anterior intermaxillary distance (ΔT: 2.11±1.42, d: 0.99), interzygomaticotemporal distance (ΔT: 2.00±2.42, d: 0.99), and zygomatic angular parameter (right side ΔT: 2.06±1.29, d: 1.6; left side ΔT: 2.02±1.86, d: 1.09). Conclusions After RME in growing patients, the zygomatic bone showed pyramidal expansion in the coronal plane and parallel palatal expansion in the axial plane. In addition, significant lateral relocation of the zygomatic bone occurred. The zygomatic bone tended to rotate outward in conjunction with the maxilla, with a typical center of rotation close to the superior side of the frontozygomatic suture. These results shed light on the patterns of skeletal expansion in the zygomatic bone associated with RME in growing patients.