Abstract
One of the possible complications of dental implant treatment is fracture of implant components. Metal fatigue and biomechanical overload seem to be the most common causes of fractured implant components.
We experienced a case of retaining screw loosening and consequent fracture of an implant. In this case, implants had been installed in the mandibular molar region, with an inferior alveolar nerve repositioning procedure. Five years after functional loading, a fracture of the distally placed implant fixture was observed.
The fractured surface was observed by scanning electron microscope(SEM). The SEM analysis showed evidence of metal fatigue, which is thought to be the most common cause of implant fracture.The finite element methods(FEM)model was established based on this case, and then the stress distribution in and around the implants was investigated. The results showed that the non-fractured fixture had a higher concentration of stresses than the fractured one. Higher tensile stress concentration was observed at the abutment-superstructure interface of the non-fractured implant. Clinically,the superstructure is connected to the abutment with a retaining screw. Therefore, the retaining screw in the non-fractured implant might have loosened, resulting in a fracture of the other fixture due to the anterior cantilever condition.
It is important to check for screw loosening during the maintenance period, to prevent serious damage, such as implant fracture.
