A pilot study in the application of texture relief for digitally designed facial prostheses

Trueness and precision of skin surface reproduction in digital workflows for facial prosthesis fabrication

STATEMENT OF PROBLEM

How much skin surface details of facial prostheses can be transferred throughout the digital production chain has not been quantified.

PURPOSE

The purpose of this in vitro study was to quantify the amount of skin surface details transferred from the prosthesis virtual design through the prototype printing with various additive manufacturing (AM) methods to the definitive silicone prosthesis with an indirect mold-making approach.

MATERIAL AND METHODS

Twelve test blocks with embossed wrinkles of 0.05 to 0.8 mm and 12 test blocks with applied earlobe skin structures were printed with stereolithography (SLA), direct light processing (DLP), and PolyJet methods (n=4). DLP and SLA prototype specimens were duplicated in wax. All specimens were then transferred into medical-grade silicone. Rz values of the wrinkle test blocks and the root mean square error (RMSE) of the earlobe test blocks were evaluated by laser topography to determine the trueness and precision of each stage.

RESULTS

For the earlobe test blocks, the PolyJet method had superior trueness and precision of the final skin surface reproduction. The SLA method showed the poorest trueness, and the DLP method, the lowest precision. For the wrinkle test blocks, the PolyJet method had the best wrinkle profile reproduction level, followed by DLP and SLA.

CONCLUSIONS

The indirect mold-making approach of facial prostheses manufacturing may be associated with 7% of skin surface profile loss with SLA, up to 20% with DLP, and no detail loss with PolyJet.

Toward Mass Customization Through Additive Manufacturing: An Automated Design Pipeline for Respiratory Protective Equipment Validated Against 205 Faces

Respiratory protective equipment (RPE) is traditionally designed through anthropometric sizing to enable mass production. However, this can lead to long-standing problems of low-compliance, severe skin trauma, and higher fit test failure rates among certain demographic groups, particularly females and non-white ethnic groups. Additive manufacturing could be a viable solution to produce custom-fitted RPE, but the manual design process is time-consuming, cost-prohibitive and unscalable for mass customization. This paper proposes an automated design pipeline which generates the computer-aided design models of custom-fit RPE from unprocessed three-dimensional (3D) facial scans. The pipeline successfully processed 197 of 205 facial scans with <2 min/scan. The average and maximum geometric error of the mask were 0.62 mm and 2.03 mm, respectively. No statistically significant differences in mask fit were found between male and female, Asian and White, White and Others, Healthy and Overweight, Overweight and Obese, Middle age, and Senior groups.

Simplifying the digital workflow of facial prostheses manufacturing using a three-dimensional (3D) database: setup, development, and aspects of virtual data validation for reproduction

PURPOSE

To set up the digital database (DDB) of various anatomical parts, skin details and retention elements in order to simplify the digital workflow of facial prostheses manufacturing; and to quantify the reproduction of skin wrinkles on the prostheses prototypes with stereolithography (SLA) and direct light processing (DLP) methods.

METHODS

Two structured light scanners were used to obtain the nasal and auricle forms of 50 probands. Furthermore, the ala nasi and scapha areas were captured with the digital single lens reflex camera and saved in jpeg format. The four magnetic retention elements were remodeled in computer aided design (CAD) software. The 14 test blocks with embossed wrinkles of 0.05-0.8mm were printed with SLA and DLP methods and afterwards analyzed by means of profilometry and confocal microscopy.

RESULTS

The introduced DDB allows for production of customized facial prosthesis and makes it possible to consider the integration of concrete retention elements on the CAD stage, which makes the prosthesis modelling more predictable and efficient. The obtained skin structures can be applied onto the prosthesis surface for customization. The reproduction of wrinkles from 0.1 to 0.8mm in depth may be associated with the loss of 4.5%-11% of its profile with SLA or DLP respectively. Besides, the reproduction of 0.05mm wrinkles may be met with up to 40% profile increasement.

CONCLUSIONS

The utilization of DDB may simplify the digital workflow of facial prostheses manufacturing. The transfer of digitally applied skin wrinkles till the prostheses' prototypes may be associated with deviations from 11 to 40%.

Additive Manufacturing: A Comparative Analysis of Dimensional Accuracy and Skin Texture Reproduction of Auricular Prostheses Replicas

PURPOSE

The use of computer-aided design/computer-aided manufacturing (CAD/CAM) and additive manufacturing in maxillofacial prosthetics has been widely acknowledged. Rapid prototyping can be considered for manufacturing of auricular prostheses. Therefore, so-called prostheses replicas can be fabricated by digital means. The objective of this study was to identify a superior additive manufacturing method to fabricate auricular prosthesis replicas (APRs) within a digital workflow.

MATERIALS AND METHODS

Auricles of 23 healthy subjects (mean age of 37.8 years) were measured in vivo with respect to an anthropometrical protocol. Landmarks were volumized with fiducial balls for 3D scanning using a handheld structured light scanner. The 3D CAD dataset was postprocessed, and the same anthropometrical measurements were made in the CAD software with the digital lineal. Each CAD dataset was materialized using fused deposition modeling (FDM), selective laser sintering (SLS), and stereolithography (SL), constituting 53 APR samples. All distances between the landmarks were measured on the APRs. After the determination of the measurement error within the five data groups (in vivo, CAD, FDM, SLS, and SL), the mean values were compared using matched pairs method. To this, the in vivo and CAD dataset were set as references. Finally, the surface structure of the APRs was qualitatively evaluated with stereomicroscopy and profilometry to ascertain the level of skin detail reproduction.

RESULTS

The anthropometrical approach showed drawbacks in measuring the protrusion of the ear's helix. The measurement error within all groups of measurements was calculated between 0.20 and 0.28 mm, implying a high reproducibility. The lowest mean differences of 53 produced APRs were found in FDM (0.43%) followed by SLS (0.54%) and SL (0.59%)--compared to in vivo, and again in FDM (0.20%) followed by SL (0.36%) and SLS (0.39%)--compared to CAD. None of these values exceed the threshold of clinical relevance (1.5%); however, the qualitative evaluation revealed slight shortcomings in skin reproduction for all methods: reproduction of skin details exceeding 0.192 mm in depth was feasible.

CONCLUSION

FDM showed the superior dimensional accuracy and best skin surface reproduction. Moreover, digital acquisition and CAD postprocessing seem to play a more important role in the outcome than the additive manufacturing method used.

Fabrication of low cost soft tissue prostheses with the desktop 3D printer

Soft tissue prostheses such as artificial ear, eye and nose are widely used in the maxillofacial rehabilitation. In this report we demonstrate how to fabricate soft prostheses mold with a low cost desktop 3D printer. The fabrication method used is referred to as Scanning Printing Polishing Casting (SPPC). Firstly the anatomy is scanned with a 3D scanner, then a tissue casting mold is designed on computer and printed with a desktop 3D printer. Subsequently, a chemical polishing method is used to polish the casting mold by removing the staircase effect and acquiring a smooth surface. Finally, the last step is to cast medical grade silicone into the mold. After the silicone is cured, the fine soft prostheses can be removed from the mold. Utilizing the SPPC method, soft prostheses with smooth surface and complicated structure can be fabricated at a low cost. Accordingly, the total cost of fabricating ear prosthesis is about $30, which is much lower than the current soft prostheses fabrication methods.

Evaluation of direct and indirect additive manufacture of maxillofacial prostheses

The efficacy of computer-aided technologies in the design and manufacture of maxillofacial prostheses has not been fully proven. This paper presents research into the evaluation of direct and indirect additive manufacture of a maxillofacial prosthesis against conventional laboratory-based techniques. An implant/magnet-retained nasal prosthesis case from a UK maxillofacial unit was selected as a case study. A benchmark prosthesis was fabricated using conventional laboratory-based techniques for comparison against additive manufactured prostheses. For the computer-aided workflow, photogrammetry, computer-aided design and additive manufacture (AM) methods were evaluated in direct prosthesis body fabrication and indirect production using an additively manufactured mould. Qualitative analysis of position, shape, colour and edge quality was undertaken. Mechanical testing to ISO standards was also used to compare the silicone rubber used in the conventional prosthesis with the AM material. Critical evaluation has shown that utilising a computer-aided work-flow can produce a prosthesis body that is comparable to that produced using existing best practice. Technical limitations currently prevent the direct fabrication method demonstrated in this paper from being clinically viable. This research helps prosthesis providers understand the application of a computer-aided approach and guides technology developers and researchers to address the limitations identified.