Failure analysis of an in-vivo fractured patient-specific Ti6Al4V mandible reconstruction plate fabricated by selective laser melting

Preclinical study of additive manufactured plates with shortened lengths for complete mandible reconstruction: Design, biomechanics simulation, and fixation stability assessment

“…Clinical recommendations call for three or four screws on the side of a plate to provide adequate fixation stability [23]. Following this recommendation, four screw holes with 7 mm spacing were assigned at the condyle end of the plate, as the highest stress is expected to accumulate at that location under masticatory activities [10].…”

“…The building orientation of the MRPs and subsequent support generation were selected considering the optimal printing condition of titanium and the quality requirement for the MRPs. For example, the upper surface quality of the MRPs should be prioritised during the SLM to guarantee fatigue performance, since a fatigue crack is highly likely to initiate from the upper surface due to high tensile stress [10]. Therefore, the building of the MRPs during the SLM started from the chin end and ended at the condyle end, and the entire support structure was generated on the bottom surface of the MRPs (Fig.…”

“…J o u r n a l P r e -p r o o f An engineering safety factor (SF), defined as the ratio of the fatigue strength of the Ti-6Al-4V prepared by SLM (510 MPa) to the maximum tensile stress on the MRP [10], was used to evaluate the implant safety.…”

“…Although SLM-fabricated PSCIs have a great reputation in biomedical applications, the non-uniform heat input under its inherent domain-by-domain localised formation tends to produce high tensile residual stress on the implant. The tensile residual stress not only accelerates fatigue crack growth under cyclic loading but also causes macroscale implant deformation, reducing implant placement precision [10,11]. Such implant deformation is particularly significant in bar-like structures due to relatively large stress accumulation along the length compared with that oriented along the thickness and width [12].…”

“…The maximum von Mises stress on the MRP under incisor clenching (183.2 MPa in Design 2, Fig.7b) and under left molar clenching (371.71 MPa in Design 4, Fig.8d) are both lower than 870 MPa (Ti-6Al-4V yield strength from SLM) and 510 MPa (Ti-6Al-4V fatigue strength from SLM), theoretically indicating the safety of customised MRPs during masticatory activities. However, implant fracture is still likely to occur due to metallurgical defects and hydrogen embrittlement induced by biological fluid[10].…”