Purpose: To investigate the causes for internal implant fractures, which is suggested to be one of the reasons for marginal bone loss. Materials and Methods: From a 14-year database of 6051 implants, 10 single implant vertical fractures were identified and the abutments were all castable abutments. The abutments presented contamination and irregularities at the internal connecting areas. The hypothesis was that perfect fit was disturbed by laboratory polishing procedures, and finite element analysis (FEA) using overcorrected and undercorrected castable abutment models were created and tested against a perfect fit model Results: The results from the FEA presented that both overcorrected and undercorrected models presented nonuniform excessive plastic strain distribution in the neck portion of the implants where clinically an implant fracture was noted Conclusions: The results suggested that laboratory procedures could induce plastic strain of the implant-abutment complex, which increases the risk of fracture