Novel finite element-based plate design for bridging mandibular defects:Reducing mechanical failure

Introduction: When the application of a free vascularised flap is not possible, a segmental mandibular defect is often reconstructed using a conventional reconstruction plate. Mechanical failure of such reconstructions is mostly caused by plate fracture and screw pull-out. This study aims to develop a reliable, mechanically superior, yet slender patient-specific reconstruction plate that reduces failure due to these causes. Patients and Methods: Eight patients were included in the study. Indications were as follows: fractured reconstruction plate (2), loosened screws (1) and primary reconstruction of a mandibular continuity defect (5). Failed conventional reconstructions were studied using finite element analysis (FEA). A 3D virtual surgical plan (3D-VSP) with a novel patient-specific (PS) titanium plate was developed for each patient. Postoperative CBCT scanning was performed to validate reconstruction accuracy. Results: All PS plates were placed accurately according to the 3D-VSP. Mean 3D screw entry point deviation was 1.54 mm (SD: 0.85, R: 0.10–3.19), and mean screw angular deviation was 5.76° (SD: 3.27, R: 1.26–16.62). FEA indicated decreased stress and screw pull-out inducing forces. No mechanical failures appeared (mean follow-up: 16 months, R: 7–29). Conclusion: Reconstructing mandibular continuity defects with bookshelf-reconstruction plates with FEA underpinning the design seems to reduce the risk of screw pull-out and plate fractures

Design optimisation of patient-specific implants and total joint replacements in oral & maxillofacial surgery

This thesis focuses on the development, implementation, evaluation, and optimization of 3D-virtual surgical planning (VSP) workflows and patient specific implants (PSI) for oral and maxillofacial surgery (OMFS). The studied fields are: head and neck reconstructive surgery (Section I) and temporomandibular joint (TMJ) replacement surgery (Section II). Section III of this thesis focuses on optimisation and validation workflows and intertwines with both aforementioned fields. Current conventional osteosynthesis reconstruction plates (RPs) and PSIs are accompanied by complications, such as, mechanical instability, screw loosening, plate fracture and inaccurate positioning. In TMJ total joint replacement (TMJ-TJR) surgery, correct positioning of TMJ-TJR prostheses and their movement behaviour are focus areas. The general aim of the research described in this thesis was to solve these complications and focus areas by means of mechanical reconsiderations, developing patient-specific (PS) solutions to be used in guided surgery and optimising current workflows in order to enhance the current generation of PS-RPs and TMJ-TJR prostheses by increasing their level of patient-specificity, making them more specific to the patient than currently is the case.Improvements were made by developing patient specific alternatives, which were experimentally and clinically validated. Furthermore, by presenting workflows that allow for improvements in the development of patient specific implants and temporomandibular joint total joint replacements, and by presenting enhanced mechanical testing methodologies, the research presented in this thesis will come together in a next, even more patient specific generation of patient specific implants and temporomandibular joint total joint replacements

Biomechanical analysis of bone remodeling following mandibular reconstruction using fibula free flap

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Whilst the newly established biomechanical conditions following mandibular reconstruction using fibula free flap can be a critical determinant for achieving favorable bone union, little has been known about their association in a time-dependent fashion. This study evaluated the bone healing/remodeling activity in reconstructed mandible and its influence on jaw biomechanics using CT data, and further quantified their correlation with mechanobiological responses through an in-silico approach. A 66-year-old male pa- tient received mandibular reconstruction was studied. Post-operative CT scans were taken at 0, 4, 16 and 28 months. Longitudinal change of bone morphologies and mineral densities were measured at three bone union interfaces (two between the fibula and mandibular bones and one between the osteotomized fibulas) to investigate bone healing/remodeling events. Three-dimensional finite element models were created to quantify mechanobiological responses in the bone at these different time points. Bone mineral density increased rapidly along the bone interfaces over the first four months. Cortical bridging formed at the osteotomized interface earlier than the other two interfaces with larger shape discrepancy between fibula and mandibular bones. Bone morphology significantly affected mechanobiological responses in the osteotomized region ( R 2 > 0.77). The anatomic position and shape discrepancy at bone union affected the bone healing/remodeling process.This work was supported by the Australian Research Council (ARC) through the Discovery and Fellowship schemes ( DP160104602 and FT120100947 )

Finite element study of fractured mandible in human and sheep

Osteosynthesis is one of the most discussed and investigated subjects in the orthopaedic literature. Mandible fractures are reported as one of the main causes of facial injury and their impact on patient life may bring serious consequences, compromising masticatory function, speech and facial aesthetics. Current treatments for mandibular simple fractures include the use of load-sharing devices such as titanium miniplates and screws, which have the role of fixing the fracture ends and restore the facial continuity. Fixation systems ultimately aim to generate the optimum mechanical strains within the fracture region, which will promote the bone healing process. However, there is not a clear understanding of the influence of fixation stability on the biomechanics of stabilized mandibular fractures, particularly when using biomaterials different from titanium. The aim of this study is to investigate the biomechanical response of fractured mandible using traditional titanium miniplates and alternative fixation systems made of magnesium alloys. With a view on future preclinical evaluation of these new devices, both human and sheep models are investigated

3D Innovations in Personalized Surgery

Current practice involves the use of 3D surgical planning and patient-specific solutions in multiple surgical areas of expertise. Patient-specific solutions have been endorsed for several years in numerous publications due to their associated benefits around accuracy, safety, and predictability of surgical outcome. The basis of 3D surgical planning is the use of high-quality medical images (e.g., CT, MRI, or PET-scans). The translation from 3D digital planning toward surgical applications was developed hand in hand with a rise in 3D printing applications of multiple biocompatible materials. These technical aspects of medical care require engineers’ or technical physicians’ expertise for optimal safe and effective implementation in daily clinical routines.The aim and scope of this Special Issue is high-tech solutions in personalized surgery, based on 3D technology and, more specifically, bone-related surgery. Full-papers or highly innovative technical notes or (systematic) reviews that relate to innovative personalized surgery are invited. This can include optimization of imaging for 3D VSP, optimization of 3D VSP workflow and its translation toward the surgical procedure, or optimization of personalized implants or devices in relation to bone surgery

Radiological Society of North America (RSNA) 3D printing Special Interest Group (SIG): Guidelines for medical 3D printing and appropriateness for clinical scenarios

Este número da revista Cadernos de Estudos Sociais estava em organização quando fomos colhidos pela morte do sociólogo Ernesto Laclau. Seu falecimento em 13 de abril de 2014 surpreendeu a todos, e particularmente ao editor Joanildo Burity, que foi seu orientando de doutorado na University of Essex, Inglaterra, e que recentemente o trouxe à Fundação Joaquim Nabuco para uma palestra, permitindo que muitos pudessem dialogar com um dos grandes intelectuais latinoamericanos contemporâneos. Assim, buscamos fazer uma homenagem ao sociólogo argentino publicando uma entrevista inédita concedida durante a sua passagem pelo Recife, em 2013, encerrando essa revista com uma sessão especial sobre a sua trajetória

Finite Element Analysis and Its Applications in Dentistry

Finite Element Analysis or Finite Element Method is based on the principle of dividing a structure into a finite number of small elements. It is a sophisticated engineering tool, which has been used extensively in design optimization and structural analysis first originated in the aerospace industry to study stress in complex airframe structures. This method is a way of getting a numerical solution to a specific problem, used to analyze stresses and strains in complex mechanical systems. It enables the mathematical conversion and analysis of mechanical properties of a geometric object with wide range of applications in dental and oral health science. It is useful for specifying predominantly the mechanical aspects of biomaterials and human tissues that cannot be measured in vivo. It has various advantages, can be compared with studies on real models, and the tests are repeatable, with accuracy and without ethical concerns

DESIGN, ANALYSIS AND FABRICATION OF POROUS TITANIUM IMPLANTS USING ELECTRON BEAM MELTING FOR CRANIOFACIAL APPLICATIONS

Patient specific implants for the reconstruction of craniofacial defects have gained importance due to better performance over their generic counterparts. This is due to, the precise adaptation to the region of implantation, reduced surgical times, and better cosmesis. Titanium implants built using traditional manufacturing processes are often heavy compared to the parts they replace and can cause discomfort to the patients. The variation in mechanical properties as elastic modulus between the implant and bone reduces the longevity of the implant. In mandible reconstruction, post implant dental reconstruction poses additional problems. Recent introduction of direct digital manufacturing technologies as electron beam melting (EBM) and Selective Laser Melting for processing of titanium has led to a one step fabrication of near net shape porous custom titanium implants with controlled porosity to meet the requirements of the anatomy and functions at the region of implantation.The first part of this research is directed towards development of a design strategy using representative volume element based technique, in which precisely defined porous implants with customized stiffness values are designed to match the stiffness and weight characteristics of surrounding healthy bone tissue. Dental abutment structures have been incorporated into the mandibular implant. Finite element analysis is used to assess the performance of the implant under masticatory loads. This design strategy lends itself very well to rapid manufacturing technologies such as Selective Laser Sintering (SLS) and Electron Beam Melting (EBM) processes.The second part of the research consists of an image based micro-structural analysis and mechanical characterization of porous Ti6Al4V structures fabricated using the EBM rapid manufacturing process. SEM studies have indicated complete melting of the powder material with no evidence of poor inter-layer bonding. Micro-CT scan analysis of the samples indicate well formed titanium struts and fully interconnected pores with porosities varying from 49.75 - 70.32%. Compression tests of the samples showed effective stiffness values ranging from 0.57 (+0.05) - 2.92(+0.17) GPa and compressive strength values of 7.28(+0.93) - 163.02(+11.98) MPa. For nearly the same porosity values of 49.75% and 50.75%, with a variation in only the strut thickness in the sample sets, the compressive stiffness and strength decreased significantly from 2.92GPa to 0.57GPa (80.5% reduction) and 163.02MPa to 7.28MPa (93.54 % reduction) respectively. Grain density of the fabricated Ti6Al4V structures was found to be 4.423g/cm3 equivalent to that of dense Ti6Al4V parts fabricated using conventional methods.In conclusion, a methodology for fabrication of craniofacial implants that would have better aesthetics, and improved masticatory functions, enhancing patient comfort and compliance, has been developed. From a mechanical strength viewpoint, we have found that the porous structures produced by the electron beam melting process presents a promising rapid manufacturing process for the direct fabrication of customized titanium implants for enabling personalized medicine with reduced lead time and cost