Role of expansion screw in treatment of skeletal Class Ⅲ malocclusion with maxillary protraction in mixed dentition

Objective To investigate the effect of anterior protraction with expansion screw in the treatment of skeletal Class Ⅲ malocclusion in mixed dentition. Methods Thirty-two children with skeletal Class Ⅲ malocclusion were randomly divided into two groups.Sixteen patients of group A received simple protraction,while the other sixteen patients of group B received the rapid maxillary expansion for two weeks followed by maxillary protraction.The treatment time was six to nine months.After the treatment,the cephalometric measurement in lateral X-ray film was done to compare the difference using t-test by SPSS. Results ①In group A,the anterior teeth of both jaws met along their incisal edges in 3 cases,and crossbite was relieved,anterior overbite and override recovered in 13 cases;While in group B,crossbite was relieved,anterior overbite and override recovered in all 16 cases.②After the treatment,SNA,Ptm-A,ANB,Wits,U1-SN,ANS-Me,FH-MP increased significantly in both groups(P<0.05).Wits,ANS-Me,FH-MP in group A increased more significantly when compared with group B(P<0.05).The increase of U1-SN and the decrease of SN-PP and L1-MP in group B changed more significantly as compared with group A. Conclusion The maxillary protraction,with or without rapid expansion,can obtain significant effect in the treatment of skeletal Class Ⅲ malocclusion.The combined treatment can reduce the labial axial inclination of anterior teeth,and mandibular counterclockwise rotation.