Abstract: Objective To evaluate the clinical effects of maxillary protraction with repetitive rapid expansion and constriction or maxillary protraction with rapid expansion only on treating skeletal class III patients with maxillary dysplasia.Methods 34 cases of skeletal class III children with maxillary dysplasia were randomly divided into two groups:the observation group and the control group.The observation group contained 17 cases treated with maxillary repetitive rapid expansion and constriction combined with maxillary protraction,which were further divided into the low angle group (12 cases) and the high angle group (10 cases).The control group contained 17 cases treated with simple rapid maxillary expansion combined with maxillary protraction.Cephalometric radiographs of all cases were taken before and after treatment,and data were given projection measurement analysis.Results Anterior displacement of maxilla,as well as downward and backward rotation of mandible was found after maxillary protraction in both groups.To compare the two groups:in the observation group,A-NP and A-Y distance increased by 2.50 mm and 3.47 mm respectively,which were greater than 1.37 mm and 2.05 mm in the control group.Conclusions Maxillary repetitive rapid expansion and constriction combined with maxillary protraction can obtain larger amount of anterior displacement in maxilla than simple rapid expansion combined with maxillary protraction.Besides,the former had more effect on the low angle patients.

Key words: repetitive expansions and constrictions, rapid maxillary expansion, maxillary protraction, maxillary dysplasia