Abstract: Objective To evaluate the effects of combined application of rapid maxillary expansion and fixed appliance on dental arch,basal bone sagittal and vertical. Methods Rapid maxillary expansion and fixed appliances were used in nonextraction treatment on 30 mild to moderate crowding cases of permanent dentition and they are divided into two groups:a hyperdivergent group (mandibular plane angle >32 °; n=20) and a normal vertical dimension group (mandibular plane angle ≥22 ° and ≤ 32 °; n=10). Cephalometric analysis was done at T1 (pretreatment),T2 (rapid maxillary expansion after 3 months) and T3 (after fixed appliance treatment). Results No significant differences in treatment effects were found in vertical dentoskeletal variables examined in two groups. There were significant differences in mandibular plane angle at the 3 time points.Y axis,total facial height,upper anterior facial height increased significantly during T1T2 and T1T3. Conclusions Rapid maxillary expansion will lead to downward rotation of the maxillary and mandibular,but there is no clinical significance due to the small variation of the absolute value. Hyperdivergent is not a contraindication for rapid maxillary expansion therapy.

Key words: rapid maxillary expansion, hyperdivergent, cephalometrics analysis