Abstract: Objective　To determine the changes after maxillary skeletal expansion(MSE) in adults with narrow upper arch by cone-beam CT(CBCT). Methods　This study included 13 patients(6 males, 7 females; range 18-24 years old, mean age 20.7) with narrow upper arch treated with MSE. CBCT images were taken before， after expansion. The following items were compared and measured:upper arch width, the midpalatal suture width, maxillary basal bone width, nasal cavity width, and other measurements. Statistical analyses were performed using paired t-test. Results　Except for 1 patient who failed because of the infection, all the other 12 patients obtained good effects. The CBCT measurements were as follows:① upper arch width was obviously expanded(P<0.05）; ② the midpalatal suture width, maxillary basal bone width and nasal cavity width were expanded respectively with significant statistical difference(P<0.05）; ③ the inclination of upper first molar was slightly increased with no significant statistical difference(P>0.05）. Conclusion　MSE is an effective method for maxillary expansion in adult patients with narrow upper arch.

Key words: rapid maxillary expansion, mid-palatalsuture, micro-implant anchorage, cone-beam computed tomography