Purpose: This study evaluated the mechanism of an abutment fracture by means of a case-based finite element (FE) stress analysis.
Materials and methods: A patient presented with a complaint of fracture of an implant-retained single posterior restoration that had been in place for 6 years. The retrieved restoration was examined on the original working cast and subjected to microscopic observation for fracture surface analysis. A case-based FE analysis was conducted to detect the location and magnitude of stress concentration in the implant structures.
Results: The fracture occurred at the concave neck of the abutment, with an evidence of fatigue fracture on the titanium surface. Ratchet marks were shown at the distal lingual edge, indicating that the crack proceeded from distolingual to mesial direction. The highest maximum tensile stress at the distolingual concave neck of the abutment was shown when the load was directed on the internal and external surfaces of the mesial buccal cusp.
Conclusions: It is suggested that an offset loading because of the cantilever structure caused a high tensile stress on the distolingual edge, resulting in the fatigue fracture of the abutment.