Failure location prediction by finite element analysis for an additive manufactured mandible implant

• An accurate three-dimensional geometrical computer model of a human mandible was constructed from computed-tomography images.
• Stress analysis in the mandible implant was performed by way of finite element simulations, with the geometrically characterized mandible and implant subjected to realistic muscular forces.
• The location of implant failure correlated with the location of the highest stress concentration predicted by the numerical simulations.
• Additive manufacturing, patient computed tomography and finite element simulations provide possibilities of significantly improved patient-specific design of implants of high structural integrity.

In order to reconstruct a patient with a bone defect in the mandible, a porous scaffold attached to a plate, both in a titanium alloy, was designed and manufactured using additive manufacturing. Regrettably, the implant fractured in vivo several months after surgery. The aim of this study was to investigate the failure of the implant and show a way of predicting the mechanical properties of the implant before surgery. All computed tomography data of the patient were preprocessed to remove metallic artefacts with metal deletion technique before mandible geometry reconstruction. The three-dimensional geometry of the patient's mandible was also reconstructed, and the implant was fixed to the bone model with screws in Mimics medical imaging software. A finite element model was established from the assembly of the mandible and the implant to study stresses developed during mastication. The stress distribution in the load-bearing plate was computed, and the location of main stress concentration in the plate was determined. Comparison between the fracture region and the location of the stress concentration shows that finite element analysis could serve as a tool for optimizing the design of mandible implants.