ABSTRACT
Objective:To simulate the instantaneous distal moving trend of the maxillary first molar based on the three-dimensional finite element mode(l3-FEM)of Forsus distalizing the maxillary first molar with some visco-elastic-plastic characters and explore the favorable loading mode of molar distal movement in Forsus in order to provide biomechanical basis for clinical practice.Methods:A male patient with ClassⅡmalocclusion was selected.The 3-FEM of Forsus distalizing the maxillary first molar was built through spiral CT scanning,Mimics8.0,and Abaqus6.5 software.This study simulated instantaneous distal moving process of the maxillary first molar under three dif-ferent loading modes(loading force was 300 g,point of force was on the center of the crown's buccal surface,loading time was 1s),which included a distalizing force,a distalizing force+counterrotation moment,a distalizing force+countertipping moment+counterrotation moment.Results:When Forsus distalized the maxillary first molar,different loading modes lead to different PDL stress distributions.When the model was added by a distalizing force,the maxillary first molar would be relatively seriously inclined;when added by a distalizing force +counterrotation moment(Mt/F=9),the maxillary first molar would be relatively seriously rotated and when added by a distalizing force+ countertipping momen(tMt/F=9)+counterrotation momen(tMr/F=5),the distal surface of the PDL would bear the lightest stress,and the first molar would achieve approximate translation movement.Conclusion:When mandible is guided forward by Forsus,the maxillary first molar would achieve better molar translation effect if added certain countertipping and counterrotation moment