Objective To investigate the effects of time varied stress on the shape-alteration of myoblast in rats and to provide a theoretic base to determine the mechanics of myoblast in orthodontic therapy. Methods Based on the pulsatile mechanical system our group founded, this study loaded different strain（2.5 kPa、5.0 kPa and 10.0 kPa） to the myoblast of lateral pterygoid muscle. The alterations in shape under time varied stress of 6 h and 12 h were assessed by phase-contrast microscopy, scanning electron microscope. Results The orientation of myoblast seemed no obvious orderliness before loading. But after loading the lower time varied strain（2.5 kPa, 5.0 kPa）, they were changed their orientation to paralel with the direction of strain along with the membrane. Meanwhile, there had one trend to set the shape of myoblast more upright along with the membrane after loading the higher time varied stress（10.0 kPa）. Conclusion It was proved that the different time varied stress in vitro expressed the different influence on the remolding of myoblast.
