AbstractThe objective of this study was to investigate the influence of implant/abutment joint designs on abutment screw loosening in a dental implant system, using nonlinear dynamic analysis of the finite element method (FEM). This finite element simulation study used two dental implant systems: the Ankylos implant system (Degusa Dental, Hanau, German) with a taper joint (taper joint‐type model), and the Bränemark implant system (Nobel Biocare, Gothenburg, Sweden) with an external hex joint (external hex joint‐type model). The nonlinear dynamic analysis was performed using three‐dimensional finite element analysis. In comparing the movement of the taper type‐joint model and external hex type‐joint model, it was found that the external hex type‐joint model had greater movement than the taper type‐joint model. The external hex joint‐type model showed rotation movement, whereas the movement of the taper joint‐type model showed no rotation. It was concluded that the nonlinear dynamic analysis used in this study clearly demonstrated the differences in rotation of components in dental implant systems with taper or external hex joints. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005