Biomechanical validation of structural optimized patient-specific mandibular reconstruction plate orienting additive manufacturing

A New Method to Design and Manufacture a Low-Cost Custom-Made Template for Mandible Cut and Repositioning Using Standard Plates in BSSO Surgery

In this study, a new methodology for designing and creating a custom-made template for maxillofacial surgery has been developed. The custom-made template can be used both for cutting and repositioning of the mandible arches for executing a BSSO (bilateral sagittal split osteotomy) treatment. The idea was developed in order to give the possibility of using a custom-made template with standard plates, thus reducing long times, high costs and low availability of custom-made plates; this represents the proof of novelty of the proposed template, based on a well-established methodology. The methodology was completely developed in the CAD virtual environment and, after the surgeons' assessment, an in-vitro experiment by a maxillofacial surgeon was performed in order to check the usability and the versatility of the system, thanks to the use of additive manufacturing technologies. When computer-aided technologies are used for orthognathic surgery, there are significant time and cost savings that can be realised, as well as improved performance. The cost of the whole operation is lower than the standard one, thanks to the use of standard plates. To carry out the procedures, the proposed methodology allows for inexpensive physical mock-ups that enable the BSSO procedure to be performed.

To what extent can mastication functionality be restored following mandibular reconstruction surgery? A computer modeling approach

STATEMENT OF PROBLEM

Advanced cases of head and neck cancer involving the mandible often require surgical removal of diseased sections and subsequent replacement with donor bone. During the procedure, the surgeon must make decisions regarding which bones or tissues to resect. This requires balancing tradeoffs related to issues such as surgical access and post-operative function; however, the latter is often difficult to predict, especially given that long-term functionality also depends on the impact of post-operative rehabilitation programs.

PURPOSE

To assist in surgical decision-making, we present an approach for estimating the effects of reconstruction on key aspects of post-operative mandible function.

MATERIAL AND METHODS

We develop dynamic biomechanical models of the reconstructed mandible considering different defect types and validate them using literature data. We use these models to estimate the degree of functionality that might be achieved following post-operative rehabilitation.

RESULTS

We find significant potential for restoring mandibular functionality, even in cases involving large defects. This entails an average trajectory error below 2 mm, bite force comparable to a healthy individual, improved condyle mobility, and a muscle activation change capped at a maximum of 20%.

CONCLUSION

These results suggest significant potential for adaptability in the masticatory system and improved post-operative rehabilitation, leading to greater restoration of jaw function.

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.

Biomechanical feasibility of non-locking system in patient-specific mandibular reconstruction using fibular free flaps

Mandibular reconstruction with free fibular flaps is frequently used to restore segmental defects. The osteosythesis, including locking and non-locking plate/screw systems, is essential to the mandibular reconstruction. Compared with the non-locking system that requires good adaption between plate and bone, the locking system appears to present a better performance by locking the plate to fixation screws. However, it also brings about limitations on screw options, a higher risk of screw failure, and difficulties in screw placement. Furthermore, its superiority is undermined by the advancing of patient-specific implant design and additive manufacturing. A customized plate can be designed and fabricated to accurately match the mandibular contour for patient-specific mandibular reconstruction. Consequently, the non-locking system seems more practicable with such personalized plates, and its biomechanical feasibility ought to be estimated. Finite element analyses of mandibular reconstruction assemblies were conducted for four most common segmental mandibular reconstructions regarding locking and non-locking systems under incisal biting and right molars clenching, during which the influencing factor of muscles' capacity was introduced to simulate the practical loadings after mandibular resection and reconstruction surgeries. Much higher, somewhat lower, and similar maximum von Mises stresses are separately manifested by the patient-specific mandibular reconstruction plate (PSMRP), fixation screws, and reconstructed mandible with the non-locking system than those with the locking system. Equivalent maximum displacements are identified between PSMRPs, fixation screws, and reconstructed mandibles with the non-locking and locking system in all four reconstruction types during two masticatory tasks. Parallel maximum and minimum principal strain distributions are shared by the reconstructed mandibles with the non-locking and locking system in four mandibular reconstructions during both occlusions. Conclusively, it is feasible to use the non-locking system in case of patient-specific mandibular reconstruction with fibular free flaps based on the adequate safety, comparable stability, and analogous mechanobiology it presents compared with the locking system in a more manufacturable and economical way.

Biomechanical behavior of the three-dimensionally printed surgical plates for mandibular defect reconstruction: a finite element analysis

The aim of the study was to investigate the biomechanical behavior of three-dimensionally (3D)-printed surgical plates used for mandibular defect reconstruction, compare them with conventional surgical plates, and provide experimental evidence for their clinical application. Three-dimensional models were created for the normal mandible and for mandibular body defects reconstructed using free fibula and deep circumflex iliac artery flaps. Three-dimensional finite element models of reconstructed mandibles fixed using 3D-printed and conventional surgical plates were established. Vertical occlusal forces were applied to the remaining teeth and the displacement and Von Mises stress distributions were studied using finite element analysis. The normal and reconstructed mandibles had similar biomechanical behaviors. The displacement distributions for the surgical plates were similar, and the maximum total deformation occurred at the screw hole of the anterior segment of the surgical plates. However, there were differences in the Von Mises stress distributions for the surgical plates. In reconstructed mandibles fixed using 3D-printed surgical plates, the maximum equivalent Von Mises stress occurred at the screw hole of the posterior segment, while in those fixed using conventional surgical plates, the maximum equivalent Von Mises stress was at the screw hole of the anterior segment. In the mandible models reconstructed with the same free flap but fixed with different surgical plates, the plates had similar biomechanical behaviors. The biomechanical behavior of 3D-printed surgical plates was similar to conventional surgical plates, suggesting that 3D-printed surgical plates used to reconstruct mandibular body defects with vascularized autogenous bone grafts could lead to secure and stable fixation.

Comparison of Two Types of Patient Specific Implants (PSI) and Quad Zygoma Implant (QZI) for Rehabilitation of Post-COVID Maxillary Mucormycosis Defect (PCMMD): Finite Element Analysis

Introduction

The residual post-COVID maxillary mucormycosis defect (PCMMD) were extensive, due to unilateral or bilateral maxillectomies. The Goal of rehabilitation of PCMMD is to deliver a prosthetically driven reconstruction. FEA was to evaluate the biomechanical response of PSI struts (PSI 1), PSI Screw retained (PSI 2) and QZI to masticatory load on virtual simulation to improve accuracy and enhance the design.

Aim

To validate and compare the Biomechanical benefit of the PSI struts, PSI Screw retained, QZI in a case of rehabilitation of post-COVID maxillary mucormycosis defect (PCMMD) by FEA study.

Methodology

The result of stress to masticatory load on virtual simulation for (1) Maximum and minimum stress (Von Mises stress); (2) the Displacement (in three positions) and (3) the Deformation (Plastic strain) was compared on virtual simulation for PSI 1 and PSI 2 and QZI.

Conclusion

The FEA and comparative evaluation of PSI 1, PSI 2 and QZI showed a good resistance to displacement. The stress and strain values are low and acceptable. In comparison QZI shows more stress in the anterior region.