Techno-economic assessment of process chains for the manufacturing of external maxillofacial prostheses for the South African ethnic demography using digital and Additive Manufacturing technologies

Abstract

Introduction: Maxillofacial trauma can significantly impact a person's life, affecting vital functions such as vision, smell, hearing, speech, breathing, eating, and facial appearance. Treating such trauma is challenging since the face plays a key role in expressing emotions and identity. In South Africa, the impact of facial trauma is extensive, not only for individuals but also for their families. Many patients, especially those reliant on government healthcare, lack the funding to access advanced technologies for the manufacturing of external maxillofacial prostheses. Therefore, given the high costs, research is needed to identify cheaper production options that still produce quality prostheses. To improve access for patients with limited financial resources, identifying cost-effective alternatives is crucial while ensuring the quality of these prostheses matches industry-benchmarks. In this study, process chains incorporating medical image processing (MIP) and computer-aided design (CAD) software using computed tomography (CT) volumetric data were evaluated against the industry-benchmark, which combines Mimics and Geomagic Freeform software applications. Additionally, process chains using surface scan data in conjunction with CAD software were tested and compared to the industry-benchmark. Main research question: The main research question probed in this study was: “Which process chain(s) can produce external maxillofacial prostheses of acceptable quality at a price relevant to the South African demography?” The answer to this question was explored by employing a design science research approach to find practical solutions to real-world problems, aligning with the pragmatic goal of generating useful, actionable knowledge with tangible outcomes. Methods: The objective was to determine which process chains could effectively meet the requirements for designing external maxillofacial prostheses. To systematically explore and validate affordable alternatives to the industry-benchmark, the research was divided into four distinct phases. In Phase 1, MIP and CAD software with potential for inclusion in the test process chains were identified through a comprehensive systematic literature review. In Phase 2, MIP software was selected based on its features and ability to segment CT data obtained from two human subjects. Errors in the segmented geometries were evaluated using Meshmixer, while the alignment of the test geometries with the control mesh was analysed and compared using CloudCompare. In Phase 3, the selected CAD software was tested for its features and sculpting capabilities. Sculpting functionality was evaluated using an anti-oloid mesh as the test object. Meshmixer was also used to detect any errors introduced during the sculpting process. Finally, in Phase 4, 3D models of human ears and noses were designed using the potential alternative process chains, which combined the selected MIP and CAD software and compared them to the industry benchmark. Additionally, the process chains that used surface scan data and CAD software to design ears and noses were also compared to the industry-benchmark. The ears and noses produced by the different process chains were analysed using Meshmixer, CloudCompare, and Geomagic Control X. To further assess the performance of each process chain, an Unweighted Standardised Rating Index was calculated to rate the various process chains based on quality. The process chains were also compared based on cost. Results: Following a thorough examination of over 700 scholarly publications, 73 were found to be suitable for identifying MIP and CAD software that may be suitable for testing in process chains related to the manufacturing of external maxillofacial prostheses. By applying a stepwise process of excluding software that did not fit the criteria, five MIP (out of 21) and nine CAD software applications (out of 37) were chosen for testing besides the industry-benchmarks. After testing the MIP software mainly for their segmenting capabilities, 3D Slicer and InVesalius were selected for testing in process chains. The systematic comparison of CAD software for digital sculpting in the manufacturing of external maxillofacial prostheses revealed that 3D Coat and ZBrush should be tested in process chains. The study's findings showed that the four test process chains combining MIP software with CAD software, and the two chains using scanned data with CAD software, produced products of comparable quality to those created by the control process chains. Among these, the combination of 3D Slicer with either 3D Coat or ZBrush resulted in the highest quality products. In contrast, the combinations of InVesalius with ZBrush, as well as surface scan data with 3D Coat or ZBrush, yielded lower-quality outcomes. In terms of cost, surface scan data combined with 3D Coat was the most affordable option for the South African demographic. For CT data, however, the combination of 3D Slicer or InVesalius with 3D Coat was the most cost-effective. Significance: By identifying alternative, cheaper, and more readily available processes to produce maxillofacial prostheses, more patients suffering from facial trauma will be able to access these life-changing technologies. When patients undergo reconstructive interventions, their self-esteem improves, which in turn helps them to reintegrate into society more quickly.