Abstract: 【Objective】 To investigate the influence of neck design of mini-implant on the primary stability after loading with torque force using three-dimension finite element analysis. 【Methods】 After established new mini-implants and bone block models

a torque force equaling to 6 N·mm was applied on the top of mini-implants. Set the range of the enlarged mini-implant neck parameters value: height 0 ~ 2 mm

diameter 1.3 ~ 1.6 mm and taper 0~60°. Fixed two variables and investigated the action of cortical bone maximum equivalent stress (Max EQV)

cancellous bone maximum equivalent stress (Max EQV)

and maximum displacements (Max DM) of mini-implants as another variable changing under torque force. 【Results】 With the increase of H

Max EQV in cortical bone and Max DM of mini-implant showed a trend of decrease

but the variation amplitude decreased when H exceeds the thickness of cortical bone. There was a decrease in the cortical bone Max EQV and mini-implant Max DM as D increased. In this research range

the stability was good when T equaled to 15°. 【Conclusion】 The neck of new mini-implant should be designed with large diameter

enough height not less than cortical bone thickness and appropriate taper angle under torque force.