Novel Design and Optimization of Porous Titanium Structure for Mandibular Reconstruction

A preliminary study of the mechanical properties of 3D-printed personalized mesh titanium alloy prostheses and repair of hemi-mandibular defect in dogs

This study is a preliminary investigation exploring the mechanical properties of three-dimensional (3D)-printed personalized mesh titanium alloy prostheses and the feasibility of repairing hemi-mandibular defects. The ANSYS 14.0 software and selective laser melting (SLM) were used to produce personalized mesh titanium alloy scaffolds. Scaffolds printed using different parameters underwent fatigue property tests and scanning electron microscopy (SEM) of the fracture points. Models of hemi-mandibular defects (encompassing the temporomandibular joint) were created using beagle dogs. Freeze-dried allogeneic mandibles or 3D-printed personalized mesh titanium alloy prostheses were used for repair. Gross observation, computed tomography (CT), SEM, and histological examinations were used to compare the two repair methods. The prostheses with filament diameters of 0.5 and 0.7 mm could withstand 14,000 times and >600,000 cycles of alternating stresses, respectively. The truss-structure scaffold with a large aperture and large aperture ratio could withstand roughly 250,000 cycles of alternating forces. The allogeneic mandible graft required intraoperative shaping, while the 3D-printed mesh titanium alloy prostheses were personalized and did not require intraoperative shaping. The articular disc on the non-operated sides experienced degenerative changes. No liver and kidney toxicity was observed in the two groups of animals. The 3D-printed mesh titanium alloy prostheses could effectively restore the shape of the mandibular defect region and reconstruct the temporomandibular joint.

Design and evaluation of mechanical strength of multi-material polymeric implants for mandibular reconstruction

Reconstruction of mandible implants to address segmental abnormalities is still a challenging task, both in vitro and in vivo. The mechanical strength of the materials used is a critical factor that determines how well bone is regenerated. The reconstruction technique of mandibular abnormalities widely uses polymeric implants. It is critical to evaluate the mechanical resilience under different load cases, including axial, combined, and flexural loading conditions. This study developed implants for mandibular defects using a combination of four materials: polylactic acid (PLA), polyethylene terephthalate glycol (PETG), thermoplastic polyurethane (TPU), and polycaprolactone (PCL), with the aim of mimicking the inherent characteristics of cortical and cancellous bone structures and evaluating their mechanical properties to support bone Osseo integration. The eleven of these combinations of structures result below the micro strain threshold level of <3000 µε, and the five combinations of the structures result in micro strain above the threshold value. The intact bone study results show that the stress under axial, combined, and flexural loading conditions is 27.6, 38.9, and 64.9 MPa, respectively. This study's stress results are lower than those from the intact bone study. The study found that the combinations of PLA and TPU material were most preferred for the cortical and cancellous bone regions of polymeric implants. These materials are also compatible with 3D printing. The results of this study can be used to find multi-material combinations that are strong and flexible.

Computational models and their applications in biomechanical analysis of mandibular reconstruction surgery

Advanced head and neck cancers involving the mandible often require surgical removal of the diseased parts and replacement with donor bone or prosthesis to recreate the form and function of the premorbid mandible. The degree to which this reconstruction successfully replicates key geometric features of the original bone critically affects the cosmetic and functional outcomes of speaking, chewing, and breathing. With advancements in computational power, biomechanical modeling has emerged as a prevalent tool for predicting the functional outcomes of the masticatory system and evaluating the effectiveness of reconstruction procedures in patients undergoing mandibular reconstruction surgery. These models offer cost-effective and patient-specific treatment tailored to the needs of individuals. To underscore the significance of biomechanical modeling, we conducted a review of 66 studies that utilized computational models in the biomechanical analysis of mandibular reconstruction surgery. The majority of these studies employed finite element method (FEM) in their approach; therefore, a detailed investigation of FEM has also been provided. Additionally, we categorized these studies based on the main components analyzed, including bone flaps, plates/screws, and prostheses, as well as their design and material composition.

A Novel Design Method of Gradient Porous Structure for Stabilized and Lightweight Mandibular Prosthesis

Compared to conventional prostheses with homogenous structures, a stress-optimized functionally gradient prosthesis will better adapt to the host bone due to its mechanical and biological advantages. Therefore, this study aimed to investigate the damage resistance of four regular lattice scaffolds and proposed a new gradient algorithm for stabilized and lightweight mandibular prostheses. Scaffolds with four configurations (regular hexahedron, regular octahedron, rhombic dodecahedron, and body-centered cubic) having different porosities underwent finite element analysis to select an optimal unit cell. Meanwhile, a homogenization algorithm was used to control the maximum stress and increase the porosity of the scaffold by adjusting the strut diameters, thereby avoiding fatigue failure and material wastage. Additionally, the effectiveness of the algorithm was verified by compression tests. The results showed that the load transmission capacity of the scaffold was strongly correlated with both configuration and porosity. Scaffolds with regular hexahedron unit cells can withstand stronger loads at the same porosity. The optimized gradient scaffold showed higher porosity and lower maximum stress than the target stress value, and the compression tests also confirmed the simulation results. A mandibular prosthesis was established using a regular hexahedron unit cell, and the strut diameters were gradually changed according to the proposed algorithm and the simulation results. Compared with the initial homogeneous prosthesis, the optimized gradient prosthesis reduced the maximum stress by 24.48% and increased the porosity by 6.82%, providing a better solution for mandibular reconstruction.