Abstract: Objective　To evaluate the effects of three kinds of rapid maxillary expansion with protraction appliances on maxilla and teeth using three-dimensional finite element method, and provide reference for clinical treatment. Methods　The three-dimensional finite element model of Hyrax with tooth-borne protraction appliance, MSE(Maxillary Skeletal Expander) with tooth-borne protraction appliance, MSE with bone-borne protraction appliance and cranial-maxillary complex was established. The expander screw was activated by 0.25 mm and the traction force of 500 g per side was applied to the traction site of the appliance. The direction of the force was 30°downward and forward to the occlusion plane. The displacement trend and stress distribution of maxilla and teeth under the three kinds of appliances were evaluated. Results　The stress distribution and the displacement trend of the three types of appliances were similar, but the lateral displacement of the maxilla under the two kinds of MSE with protraction appliance was 2.7 times as much as that of the Hyrax’s, and 2.6 times in sagittal displacement, and its stress value was much higher than that of the Hyrax’s. The tooth displacement trend of the three models was similar, but the tooth stress distribution pattern was different. MSE with bone-borne protraction appliance still affected the anchored molar. Conclusion　①MSE with protraction appliance is a better choice for adults or patients who need a large amount of maxilla movement.②MSE with protraction appliance needs to be improved.

Key words: Rapid maxillary expansion, Protraction of Skeletal anchorage, Finite element analysis