Statement of problem: The press-fit (Morse taper) implant system is commonly used to restore edentulous areas. However, abutment screws in this system may be damaged because of the 2- or 3-piece design, consequently causing complications. How these damaging situations occur is unclear. Purpose: The purpose of this in vitro and finite element analysis (FEA) study was to elucidate the mechanisms of the press-fit implant system underlying abutment screw damage. Material and methods: The ANKYLOS implant system was used as a simulation model and for experimental test specimens. The experimental test was performed by using a material test system, and the obtained data were used to validate the FEA outcome. In the FEA simulation, the bilinear material property and nonlinear contact conditions were applied to simulate the process of tightening the abutment screw between the abutment and implant. A force of 300 N was then applied to the abutment to investigate the stress distribution and deformation of the implant system. Results: In the experimental test, the fracture site of all specimens was observed at the abutment-screw thread. All implants and abutments exhibited permanent bending deformation. The results of the FEA simulation generally concurred with the experimental outcomes. Conclusions: The abutment torque used to generate the press-fit contact interface between the abutment and implant induced stresses within the implant components, substantially increasing the failure probability of the conical implant system during function.
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