Background/purpose: This study investigated in seven patients the main causes of accidental fractures of various implant components. Materials and methods: We used a scanning electron microscope and transmission electron microscope to observe the fracture interfaces of four fixtures, six abutment screws, and nine gold screws retrieved from patients with prosthetic problems. Results: In all fixtures and some abutment screws, parafunctional force and a cantilever design ultimately resulted in movement of low-angle grain boundaries (LAGBs) at most fracture surfaces. Fractographic observations showed that overloading deformed the grain sizes, and the no precipitates were present on the high-angle grain boundaries (HAGBs) or matrices of some abutment screws and most gold screws. Conclusion: To avoid implant fracture, certain underlying mechanical risk factors should be noted such as patients with a habit of bruxism, bridgework with a cantilever design, or two implants installed in a line in the posterior mandible.
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