Abstract: Objective： To use the cone-beam computed tomography (CBCT) to evaluate the three-dimensional (3D) changes of maxillary landmarks in the maxillary protraction with alternating rapid palatal expansion and constriction and with rapid palatal expansion, and to provide some clinical suggestions for the early treatment of Class Ⅲ malocclusion. Methods: A total of 36 maxillary retrusive patients were included and randomized in a 1 ∶1 ratio to either the intervention group (alternating rapid palatal expansion and constriction group, RPE/C) or the control group (rapid palatal expansion group, RPE). Randomization was accomplished with permuted block randomization based on participation sequence. The patients in the RPE/C were treated for 10 weeks (0.5 mm/d ) with the repetition of two-week palatal expansion and two-week palatal constriction. The patients in the RPE were taught to complete rapid palatal expansion for 2 weeks (0.5 mm/d ).The patients were instructed to come to the office for the follow-up to ensure the correct procedures. Damaged expanders were repaired (or replaced) and rebanded quickly. Sequential CBCT images including pretreatment (T1), postexpansion (T2) and post-protraction (T3) were required for 3D reconstruction, establishment of landmarks, measurement and analysis by Mimics 10.01. Results: There was significant forward movement of subspinale (A) in the RPE/C after the treatment with (3.06±1.29) mm, compared with RPE (2.16±1.27) mm, P<0.05. There were more symmetrical changes of the landmarks in the RPE/C and there was no statistic significance of the entire treatment time between the two groups. Moreover, the maxillary skeletal landmarks had the following 3D changes of a forward and downward movement during the expansion stages T2-T1, a forward and upward movement during the protraction stages T3-T2 and a forward and downward movement during the total treatments T3-T1 compared with the control group. And the width between the bilateral landmarks increased during the expansion stages T2-T1, narrowed down during the protraction stages T3-T2 and increased during the total treatments T3-T1. Conclusion: The maxillary protraction with alternating rapid palatal expansion and constriction provided clinical benefits on maxillary advancement and symmetrical changes in the orthopedic treatment of the patients with maxillary retrognathism and it required further study on the orthodontic analysis and measurements of CBCT.

Key words: Maxillary retrognathism, Maxillary expansion, Maxillary protraction, Cone-beam computed tomography, Maxillary landmarks