Topological optimization for designing patient-specific large craniofacial segmental bone replacements.

Restoring normal function and appearance after massive facial injuries with bone loss is an important unsolved problem in surgery. An important limitation of the current methods is heuristic ad hoc design of bone replacements by the operating surgeon at the time of surgery. This problem might be addressed by incorporating a computational method known as topological optimization into routine surgical planning. We tested the feasibility of using a multiresolution three-dimensional topological optimization to design replacements for massive midface injuries with bone loss. The final solution to meet functional requirements may be shaped differently than the natural human bone but be optimized for functional needs sufficient to support full restoration using a combination of soft tissue repair and synthetic prosthetics. Topological optimization for designing facial bone tissue replacements might improve current clinical methods and provide essential enabling technology to translate generic bone tissue engineering methods into specific solutions for individual patients.

Topology optimization of fixed complete denture framework.

The functionality of a denture is directly related to the quality of life of the edentulous patients because treatment failure results in demoralizing consequences including difficulties in oral activities. Framework for fixed complete dentures plays a crucial role by transferring loads from the denture to the implants, which are integrated into the remaining bones and gingiva, thereby providing stability to the denture. Current techniques utilize 3D scan data of the implant site to capture the locations and soft tissue contours to design customized framework using computer-aided design (CAD) and computer-aided manufacturing (CAM) technology to properly support the denture teeth in their position. The performance and efficiency of these frameworks may be enhanced by incorporating a design optimization in the design process. We tested the feasibility of using the topology optimization to design patient-specific dental frameworks. The shapes of the optimized frameworks may be significantly different from the traditional designs, but better structural integrity is likely to be achieved with potentially less material. The numerical study reveals that commercially available dental framework would experience 16% less maximum stress when topology optimized even with a compliance minimization formulation with 50% volume fraction constraint. Topology optimization for designing dental frameworks might improve current clinical methods and provide better long-term patient satisfaction.

Design of complex bone internal structure using topology optimization with perimeter control.

Large facial bone loss usually requires patient-specific bone implants to restore the structural integrity and functionality that also affects the appearance of each patient. Titanium alloys (e.g., Ti-6Al-4V) are typically used in the interfacial porous coatings between the implant and the surrounding bone to promote stability. There exists a property mismatch between the two that in general leads to complications such as stress-shielding. This biomechanical discrepancy is a hurdle in the design of bone replacements. To alleviate the mismatch, the internal structure of the bone replacements should match that of the bone. Topology optimization has proven to be a good technique for designing bone replacements. However, the complex internal structure of the bone is difficult to mimic using conventional topology optimization methods without additional restrictions. In this work, the complex bone internal structure is recovered using a perimeter control based topology optimization approach. By restricting the solution space by means of the perimeter, the intricate design complexity of bones can be achieved. Three different bone regions with well-known physiological loadings are selected to illustrate the method. Additionally, we found that the target perimeter value and the pattern of the initial distribution play a vital role in obtaining the natural curvatures in the bone internal structures as well as avoiding excessive island patterns.

Designing patient-specific 3D printed craniofacial implants using a novel topology optimization method.

Large craniofacial defects require efficient bone replacements which should not only provide good aesthetics but also possess stable structural function. The proposed work uses a novel multiresolution topology optimization method to achieve the task. Using a compliance minimization objective, patient-specific bone replacement shapes can be designed for different clinical cases that ensure revival of efficient load transfer mechanisms in the mid-face. In this work, four clinical cases are introduced and their respective patient-specific designs are obtained using the proposed method. The optimized designs are then virtually inserted into the defect to visually inspect the viability of the design . Further, once the design is verified by the reconstructive surgeon, prototypes are fabricated using a 3D printer for validation. The robustness of the designs are mechanically tested by subjecting them to a physiological loading condition which mimics the masticatory activity. The full-field strain result through 3D image correlation and the finite element analysis implies that the solution can survive the maximum mastication of 120 lb. Also, the designs have the potential to restore the buttress system and provide the structural integrity. Using the topology optimization framework in designing the bone replacement shapes would deliver surgeons new alternatives for rather complicated mid-face reconstruction.