Design Criteria for Patient-specific Mandibular Continuity Defect Reconstructed Implant with Lightweight Structure using Weighted Topology Optimization and Validated with Biomechanical Fatigue Testing

Chun-Li Lin; Yu-Tzu Wang; Chun-Ming Chang; Cheng-Hsien Wu; Wei-Heng Tsai

doi:10.18063/ijb.v8i1.437

Design Criteria for Patient-specific Mandibular Continuity Defect Reconstructed Implant with Lightweight Structure using Weighted Topology Optimization and Validated with Biomechanical Fatigue Testing

Int J Bioprint. 2021 Dec 10;8(1):437. doi: 10.18063/ijb.v8i1.437. eCollection 2022.

Authors

Chun-Li Lin¹, Yu-Tzu Wang², Chun-Ming Chang³, Cheng-Hsien Wu⁴, Wei-Heng Tsai¹

Affiliations

¹ Department of Biomedical Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan.
² Department of Mechanical and Electro-Mechanical Engineering, TamKang University, New Taipei City, Taiwan.
³ National Applied Research Laboratories, Instrument Technology Research Center, Hsinchu, Taiwan.
⁴ Department of Oral and Maxillofacial Surgery, Taipei Veterans General Hospital, School of Dentistry, National Yang Ming Chiao Tung University, Hsinchu, Taiwan.

Abstract

This study developed design criterion for patient-specific reconstructed implants with appearance consideration and structural optimization of various mandibular continuity defects. The different mandible continuity defects include C (from left to right canines), B (from 1^st premolar to 3^rd molar), and A (from 3^rd molar to ramus) segments defined based on the mandible image. The finite element (FE) analysis and weighted topology optimization methods were combined to design internal support beam structures within different reconstructed implants with corresponding occlusal conditions. Five continuity mandibular defects (single B/C/A+B and combination of B+C and B+C+B segments) were restored using additive manufacturing (AM) reconstructed implant and bone plate to confirm reasonable design criterion through biomechanical fatigue testing. The worst mandible strength was filtered based on the material mechanics and results from segmental bone length, thickness, and height statistics from the established database containing mandible images of 105 patients. The weighted optimization analysis results indicated that the sizes and positions of internal supporting beams within the reconstructed C, B, and A+B implants can be defined parametrically through corresponding segmental bone length, width, and height. The FE analysis found that the weight variation percentage between the parametric designed implants and original core solid implants in the C, B, and A+B was reduced by 54.3%, 63.7%, and 69.7%, respectively. The maximum stress values of the reconstructed implant and the remaining bone were not obviously reduced but the stress values were far lower than the material ultimate strength. The biomechanical fatigue testing indicated that all cases using the AM reconstructed implant could pass the 250,000 dynamic load. However, condyle head, bone plate fracture, and bone screw loosening could be found in cases using bone plates. This study developed a design criterion for patient-specific reconstructed implants for various mandibular continuity defects applicable for AM to further clinical use.

Keywords: Additive manufacturing; Biomechanical testing; Finite element analysis; Mandibular continuity defect; Patient-specific implant; Topology optimization.