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Image and Design Stage in 3D Printing Facial Prostheses


By using color 3D printing technology, it is possible to detail facial soft tissue prostheses in semi-automatic and accurate additive manufacturing systems. A protocol for three-dimensional color image generation is designed based on six steps of processing. For this special application, the development protocols required for each sub-process and the details of each technique applied are discussed, and the quality of facial prostheses is evaluated by objective measurement and subjective evaluation.
The results show that the proposed color reproduction system can be used effectively to produce accurate skin color with fine textures on a 3D shape, with significant savings in both time and cost compared to traditional techniques.

3D Image Design

Raw data from 3D camera systems usually requires further processing before 3D printing. Depending on the anatomical location of the prosthesis, prototype editing may include the following steps.

Data PreparationImage and Design Stage in 3D Printing Facial Prostheses

CAD production of the missing faceplate can take a variety of forms. Data capture of unaffected areas of the face can be performed, and images can be projected to virtually replace those that are affected or missing. This may be appropriate for missing ears or orbital areas where there are usually bilateral structures. However, this may not be appropriate or possible for single or isolated structures, including nasal structures, or where surgery is performed to remove the affected part. Alternatively, open source CAD databases are becoming more and more available now. Databases such as www.turbosquid.com and these can offer CAD users direct links to downloadable content.
These can include non-specific face shapes that cover a wide variety of anatomical forms, from those that are generally considered to have interesting or characteristic features. Although easily accessible, there are some issues with these resources. Although geometrically correct, the peripheral area can be quite variable and may not be suitable to cover the affected areas in certain patients. Additionally, surface detail can be quite versatile and not suitable for direct modeling. However, these files can provide good starting points for CAD design and allow adaptation to suit the affected area.
Various software can be used to modify captured or obtained data files, including 3-Matic (Materialize, Leuven, Belgium). These can then be used to change the surface detail and improve the geometry to provide individual and bespoke features for the missing facial portion (peripheral area can be highly variable and not suitable to cover affected areas in certain patients. However, these files can provide good starting points for CAD design and allow adaptation to suit the affected area.

Data processing

The obtained and adjusted model can then be mixed into the affected area, creating a smooth margin that will come into contact with facial tissues. Moreover, CAD prostheses occasionally require gouging and tapering until the thickness of the prosthesis is between 2 and 3 mm, and this can also be done with various software packages. Finally, the model is cropped to remove all unnecessary data before printing. As mentioned earlier, attachment information can then be imported and combined with the prepared CAD prosthesis and precisely aligned to ensure a good holding element and fit.

Precision Attachment DesignImage and Design Stage in 3D Printing Facial Prostheses

Often facial prostheses are held using precision attachments, including magnets with osseointegrated implant retainers, rods, and clips. In these cases, external markers or headers are used to determine the position, angle and direction of any crop that should be included in the data included in the process. Their position can then be translated into the final prosthesis through the design and manufacturing process.

Data Detailing

Natural openings such as nasal openings and auditory canals should be designed to ensure that the prosthesis has the correct anatomical form and, if necessary, should be modeled to provide the appropriate function. While it allows air to pass through during breathing through the nose, it provides unimpeded hearing through direct access to the external auditory hole (canal), although the external shape for the ear is lacking. Similar considerations can be made when designing orbital prostheses, as an artificial glass or acrylic sphere enclosure will be required within the palpebral fissure (eyelids). It should be borne in mind that in some cases the provision of attachments may affect these design features and therefore optimal modeling and detailing should be done to hide these issues.

Completing the Design

After the final model has been produced, additional details need to be added to produce a satisfactory prosthesis. All of the final details can be done before printing, including the softening of the circumferential extensions, feathered edges, all necessary reinforcing buttresses, and seams and joints on the inner surface of the model. The color calibration image is then applied to the entire model before production.

3D Printing Facial Implants Results

To increase the peripheral fit of the prosthesis, practices and protocols developed to allow for a durable seal where appropriate and the manufacture of a prosthesis with fine hairy edges or well-defined edges should also be considered. The next points can be determined according to the condition of the current area, the surgery the patient has undergone, or the preference of the prosthetician. Given the accuracy of the procedure and the flexibility to produce both types of periphery, the protocols developed will be suitable for both adhesive and anchor-retained prostheses.
The process described in this section has several key advantages. By printing the prosthesis directly using biocompatible materials, several steps can be taken from the traditional process, including impression making, mold making, placement of the prosthesis in silicone, and intermediate placement. Current methods require two to four patient visits over several weeks and significant man hours to produce the final prosthesis. Existing molds should be used for replacements or the process should be restarted, and considering that old molds may not be accurate due to changes in disease state or other patient factors, they may not be suitable for replicating prostheses. Also, the method described is non-contact, except for the final fitting of the prosthesis. As a result, the patient experiences minimal discomfort and discomfort and data capture is faster than traditional methods. Moreover, it enables the prostheticist to electronically store these data for future use and record keeping.
Using this digital process, the imaging and color reference appointment takes approximately 10-15 minutes. In addition, manufacturing time is significantly reduced to approximately 48-72 hours between imaging and placement of the finished prosthesis and, in detail, this process has the potential to produce multiple parts (60-80) at the same time scale, thus significantly increasing production times for each relative prosthesis. . The process is limited to CAD input only (ie image manipulation and model design / manipulation), but the process is also highly automated.
CAD programs can be used individually, or integrated into a bespoke software that seamlessly passes the model between programs. Single human intervention occurs during CAD input, design, and post-process penetration stages. Another benefit of developing and using this technology is its significant cost advantages. The average cost for the healthcare system to produce soft tissue prostheses using traditional methods in the UK is around £ 2,000-6,000, and the cost remains largely the same for each prosthesis. Image and Design Stage in 3D Printing Facial Prostheses
The cost per unit of 3D printed parts with attachments is significantly reduced due to the reduction in labor costs and the number that can be produced at any time. Considering that the average prosthesis life is 1-2 years and the population is increasingly aging, long-term time and cost savings will be significant when using this new technology. However, this methodology has some limitations. The process will depend on practitioners acquiring new skills such as software and CAD usage, which will again become highly specialized. However, in recent years this technology has been available for conventional hard tissue and dental prostheses, such as custom-made dental crowns, bridges, implant abutments, and a variety of other hard tissue prostheses.
Given that the software associated with these developments is widely accepted and is user-friendly and intuitive, it should not be difficult to introduce such technology for soft tissue prostheses. Another issue to consider may be the limited availability of virtual CAD models that might be required if there is no available patient data. However, these are becoming more accessible, and once patients have the parts, existing electronic data can be reused for prostheses for the same patient or adapted for new patients. Another limitation can be start-up costs that are not insignificant. Currently, equipment costs are high, but with the development of new printing techniques and the emergence of a large number of manufacturers in the market, costs are falling significantly.
Moreover, the manufacturing process can be centralized in several specialist manufacturing centers, while collaborative or ‘hub and nodes’ arrangements mean that data capture and manipulation of missing parts can be performed at a local or regional level. Given that data will be stored electronically, electronic communication is largely effortless,
As a result, the use of modern manufacturing technologies, including 3D printing, can provide a quality product quickly and with significantly reduced cost, labor, and patient inconvenience. In detail, this is a convenient method for manufacturing prostheses using commercially available equipment and software, and can be easily applied clinically.

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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