Biological and technical failures of implants have already been reported. Mechanical factors are certainly of importance in implant failures, even if their exact nature has not yet been established. The abutment screw fracture or loosening represents a rare, but quite unpleasant failure. The aim of the present research is an analysis and structural examination of screw thread or abutment. In this study broken screws were excluded. A total of 58 screw thread loosening were observed, 5 Branemark, (Nobel Biocare, Gothenburg, Sweden) 4 Implant Innovation (Riverside Drive Palm Beach Gardens, FL, USA) and 7 Restore (Lifecore Biomedical, Chaska, Minnesota, USA) and 42 T.B.R. implant (Benax, Ancona, Italy). The loosened abutment screws were retrieved and analyzed under SEM. Many alterations and deformations were present in concavities and convexities of screw threads.
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