Fracture of dental implants: literature review and report of a case.

Fracture of dental implants is a rare phenomenon with severe clinical results. In this article, the literature is reviewed and various causative factors that may lead to fracture are presented. Galvanic activity has not been mentioned before as a possible cause for implant fracture, yet, it can occur at the level of contact with the superstructure. This is illustrated by the case of a titanium implant restored with a non-precious porcelain-fused-to-metal cemented crown that fractured 4 years after loading. The radiographs show alveolar bone resorption around the fixture. Metallurgical analysis of the implant indicated that the fracture was caused by metal fatigue and that the crown metal, a nickel-chromium-molybdenum alloy, exhibited corrosion. These findings suggest a new explanation for implant fractures; cytotoxic nickel ions, leaching from the base metal alloy may cause bone resorption. This in turn leads to increased mobility, facilitating washout of the luting cement. Contact of the base metal with titanium in the presence of oral fluids produces galvanic currents that hasten corrosion and leaching out of nickel ions, thus leading to further bone resorption. Loss of bone support allows lateral bending moments that cause metal fatigue, eventually leading to fracture. Therefore, good treatment planning and appropriate case selection might have prevented this fracture. Furthermore, the use of nonprecious metal alloy for the crown's infrastructure had further contribution to the chain of events that led to the implant's fracture.