Finite element analysis of shape and thickness variations in patient-specific implants for t-shaped genioplasty.

Background: T-shaped genioplasty is a versatile surgical technique used to correct chin deformities by altering its vertical, transverse, and sagittal dimensions. Despite numerous advancements in patient-specific implants (PSIs), the biomechanical impact of PSI thickness and the number of screws used for fixation remain unexplored. This study aims to evaluate the effects of PSI thickness and screw configurations on fixation stability in T-shaped genioplasty using finite element analysis.

Material and methods: Mandibular computed tomography data were used to construct 12 three-dimensional models with varying PSI thicknesses (0.6 mm, 0.9 mm, and 1.2 mm) and screw configurations (five, six, seven, and eight screws). T-shaped osteotomies were applied to create narrowing and widening genioplasty models, with iliac bone grafts placed in widening scenarios. Horizontal forces of 50 N were applied bilaterally, and fixation stability was evaluated using von Mises stress and bone displacement. Fixation was considered stable when bone displacement amounts were below 1 mm.

Results: In narrowing models, fixation stability was achieved with five screws and a 1.2 mm PSI or seven screws with a 0.9 mm or 1.2 mm PSI, showing stress values within titanium's yield strength limits. For widening models, stable fixation was achieved with six screws and a 0.9 mm or 1.2 mm PSI, or eight screws across all tested thicknesses. Bone displacement was minimal with thicker PSIs and higher screw counts, demonstrating improved stability.

Conclusions: This study highlights the importance of PSI customization in optimizing fixation stability in T-shaped genioplasty. A minimum of five screws with a 1.2 mm plate or seven screws with a 0.9 mm plate is suggested for narrowing, while six screws with a 0.9 mm plate or eight screws with any tested thickness are sufficient for widening. Future research should address combined movements, dynamic loading, and long-term outcomes to refine PSI fixation strategies further.