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3D Printing Facial Prosthesis Printing and Manufacturing Phase


Traditional prosthesis manufacturing methods are well established and are used even today. These include making an impression, producing a plaster, and ultimately hand-crafting a prosthesis from a silicone-based or similar material. Providing prostheses in this way has provided many patients with considerable comfort and support for years and allows them to continue their normal daily activities and improve social interactions.

Despite the advantages that this method can provide, its application has shown some limitations and shortcomings. These are primarily concerned with machining strategy, required technical expertise, time, effort, cost and retention issues. In addition, there are durability issues due to material degradation and discoloration after a relatively short service period due to general wear and tear and exposure to ultraviolet radiation. For these reasons, facial prostheses require renewal and periodic replacement, which is a costly and time-consuming process that burdens both patients and prosthetic specialists.3D Printing Facial Prosthesis Printing and Manufacturing Phase

In the last decade, additive manufacturing technology has evolved significantly, including three-dimensional (3D) printing. Color 3D printing has also been developed to produce full spectrum colored solid objects using a range of materials. With the evolution of various 3D imaging techniques, target object geometric data can be accurately captured and converted into 3D digital models. By combining 3D image capture and printing techniques, there is great potential to get the same printing or rendering of something seen. More importantly, it has the ability to directly link with advanced manufacturing techniques, allowing highly accurate customization, saving both time and costs.

It has been widely used in rapid prototyping, has been successfully applied in medical sciences, and has gained popularity in multidisciplinary applications. For medicine, captured digital 3D models are of great accuracy and have been used effectively for the diagnosis of facial disfigurement, surgical planning and evaluation of treatment results for several years. Additionally, there is potential to improve this automated additive manufacturing technology for facial prostheses.

Compared to traditional image capture technology, image processing between 3D imaging devices has much more complex operating processes. For 3D printing, the quality of 3D printed objects is affected not only by the printing itself, including binder / substrate interaction and printer resolution, but also by the printing material and any post processing or finishing steps. Therefore, without a specific protocol, 3D objects can often be produced with low reliability, accuracy, and quality. Moreover, in terms of 3D image production, image processing methods for converting 3D images from a 3D camera to a 3D printer are much less advanced than existing processes using 2D technology.

Also, accurate color reproduction for facial prostheses is highly desirable and the quality of skin color reproduction can significantly affect the overall quality of facial prostheses. Therefore, correct color management processes are not only necessary, but also need to be executed in conjunction with the specific 3D fabrication processes used. Recently, new and innovative methods for the manufacture of facial soft tissue prostheses that prioritize precise 3D color image reproduction have been developed, and a framework and protocol for custom 3D processing has been designed. In addition, color management processes have been improved and successfully applied to 3D imaging devices and production processes.

3D Color Printing Stage

Full color 3D printing is considered to be advanced technology, with different 3D color printing technologies that are constantly being developed and improved. A common full color 3D printing technology is 3DPTM printing, also known as powder-binder printing. It was developed at the Massachusetts Institute of Technology and licensed by Z Corporation and 3D Systems, the process itself is based on inkjet printing where powder is deposited in successive layers and then optionally combined with the color binder by inkjet. A three (CMY) or four (CMYK) color binder is mixed together with a clear binder, printing the powder material layer by layer in a full-color spectrum. After 3D printing, finishing, including removal of excess unused dust and infiltration, often needs to be done to produce the final model.

Powders can be made from different types of materials. Gypsum is primarily used with plastic powder. However, starch, ceramic, glass and other powdered materials can also be processed. To manufacture facial prostheses, 3D printers, including the Z Corp Z510 3D printer (3D Systems Inc., Rock Hill, SC, USA), can be used to color the biocompatible starch powder. In this case, post-printing is required. Infiltration can then be carried out with the appropriate elastomeric polymer to produce a flexible, lightweight and realistic soft tissue prosthesis. More recently, there has been improvement in other elastomeric 3D printing processes, including direct deposition and filament printing. However, its main drawback is the limited color spectrum that they can print.3D Printing Facial Prosthesis Printing and Manufacturing Phase

Leakage Foundation Design in Facial Prosthesis

The printing process itself will produce a highly accurate solid pattern of the missing facet and will consist of printed powder and tan binder. Given the resulting structure, the post-printing needs to infiltrate the required role into the model with a suitable material that is inherently light, flexible and durable – with properties to lend itself to. Because of the post-pressure processing required for direct denture printing, an infiltration base modeled from the affected and adjacent area must be created.

The site of the affected area is transferred to the process as a single surface using an appropriate CAD software program. Using the final prosthesis as a guide, the infiltration base can then be trimmed to support any peripheral extensions needed to support the prosthesis and define the contact point or provide a hairy edge for final insertion. Each requirement of the prosthesis can be developed in support with the exact nature of the environment, depending on the type of face part to be replaced and the characteristics of the surrounding tissue. Smooth peripheral surfaces will be better suited to feathered edges, while well-defined wrinkles or surgical margins with a well-defined edge will be more suitable for closer placement. The final design features of the infiltration base will depend on the geometry of the missing face portion.

Production

Following CAD manipulation of the design of the model and the final prosthesis, the data can be converted into .zpr files for printing to the printer. Again, this can be accomplished using appropriate software. Using additive manufacturing with biocompatible powder and color binder, the denture can be printed ready for any finishing process, including infiltration with a suitable elastomeric polymer. In most cases, the resulting printed pattern needs to rest for a while to allow the binder to dry completely, and gentle removal of excess powder allows for accurate finishing. As detailed earlier, for large models designed to replace significant portions of facial tissue, an infiltration base may be required to prevent distortion or sagging during this procedure.

Prosthesis Infiltration

3D printing produces models with excess dust closely related to the final structure. The resulting powder should be gently removed before being filtered with a suitable material. The prosthesis can then be dipped into the infiltrant with or without the infiltration base and a period of time is allowed for full saturation. This process will depend on the thickness of the printed pattern and the viscosity and setting characteristics of the leak.

All will need to be evaluated before the definitive prostheses can be manufactured. Ideally, materials with properties and properties similar to those used in current manufacturing methods should be used to make a comparable prosthesis. Normally the materials used will be silicone, acrylic or polyvinyl in nature. Given the variability in the properties of these materials, prolonged immersion or leakage under pressure should be considered. Following this process, excess leakage must be removed from key areas such as openings, holes, and connectors, and then allowed to cure and dry completely. This process normally takes about 24 hours.3D Printing Facial Prosthesis Printing and Manufacturing Phase

Final Preparations

Following the manufacture of the prosthesis, it can be delivered to the anaplastologist for final application. Given the nature of the environment produced and the infiltration with a comparable material, adjustments can be made to both the peripheral matched surface and the color to achieve complete harmony and color matching in normal posture and function. In addition to these changes, the connection components can be fixed in place within the prosthesis using appropriate adhesives.

Finally, minor changes in texture and surface appearance can also be made by adding matting agents or external colorants. Second, it will allow for a more natural finish. The prosthesis can then be attached to the patient. It shows a 3D printed nasal prosthesis held by magnet attachments. Using this contactless approach, production and final delivery are carried out within 48 hours. Considering that any single impression can produce up to 60-80 prostheses at a time, the relative time required to produce a facial prosthesis for multiple patients can be significantly reduced.

References:
https://www.researchgate.net/publication/323144729_Direct_3D_printing_of_silicone_facial_prostheses_A_preliminary_experience_in_digital_workflow
https://www.nature.com/articles/s41598-020-67945-z

Writer: Ozlem Guvenc Agaoglu


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