CLINICAL REPORT

Direct 3D printing of silicone facial prostheses: A preliminary

experience in digital workflow
Alexey Unkovskiy, DMD,a Sebastian Spintzyk, MSc,b Joern Brom,c Fabian Huettig, DMD,d and
Constanze Keutel, MD, DMDe

In the last decade, additive ABSTRACT

manufacturing has been widely
Direct silicone printing may be applied to the fabrication of maxillofacial prostheses, although
used for the production of facial its clinical feasibility is unknown. The present clinical report shows an early application of a
1,2
prostheses. Because printable directly printed silicone prosthesis for the rehabilitation of a nasal defect. Two extraoral
silicone materials have been scanning systems were used to capture the face and the defect. The virtual construction of the
unavailable, most approaches nasal prosthesis was performed with free-form software. Two prostheses were printed in sili-
have concentrated on direct or cone and post-processed by manual sealing and coloring. The clinical outcome was acceptable
indirect mold making for for an interim prosthesis; however, the marginal adaptation and color match were not satis-
manual fabrication of definitive factory without further individualization. (J Prosthet Dent 2018;120:303-8)
prostheses from conventional silicone.3,4 Direct manu- surgery at the Centre of Dentistry, Oral Medicine, and
facturing of definitive prostheses has also been attempted, Maxillofacial Surgery with Dental School at Tübingen
but only in terms of printing a basic shape from an University Hospital. She received 3 implants (Vistafix 2;
acrylate-based material coated with a colored silicone Cohlear Ltd) in the nasal cavity floor, 2 of which were
layer.5 Another company (Fripp Design Ltd) developed a initially exposed surgically for prosthesis retention (Fig. 1).
starch powderebased 3-dimensional (3D) printing system, A conventionally fabricated interim silicone prosthesis was
which was subsequently vacuum-infiltrated with medical- provided during the healing phase of the implants. The
grade silicone.6 Recently, the development of direct- prosthesis was fixed to the nasal remnant with skin ad-
printable silicone has been reported.7,8 However, reports hesive. When the patient received an additional interim
about its clinical application are lacking. The present prosthesis, she was informed orally and in writing about
clinical report demonstrates the outcome of a nasal defect the newly developed 3D scanning and silicone printing
rehabilitation with a directly printed silicone prosthesis in systems as options for patients with maxillofacial defects.
a digital workflow. She consented to undergo, in addition to her conventional
treatment, a treatment with this digital workflow to eval-
uate 2 directly printed nasal prostheses.
CLINICAL REPORT
The patient was scanned with 2 scanning systems:
A 40-year-old woman with a poorly differentiated squa- first, with a stationery 3D photogrammetry system (pri-
mous cell carcinoma of the entire nose presented after tiface; pritidenta GmbH) with her eyes closed to obtain

J.B. holds shares of Technovent Ltd, and owns Cosmesil/BromFX Comp.

a
Dentist, Department of Prosthodontics at the Centre of Dentistry, Oral Medicine, and Maxillofacial Surgery with Dental School, Tübingen University Hospital,
Tübingen, Germany.
b
Material Science Engineer, Section of Medical Materials and Science, Tübingen University Hospital, Tübingen, Germany.
c
Anaplastologist, Brom Epithetik, Heidelberg, Germany.
d
Assistant Medical Director, Department of Prosthodontics at the Centre of Dentistry, Oral Medicine, and Maxillofacial Surgery with Dental School,
Tübingen University Hospital, Tübingen, Germany.
e
Senior Associate, Department of Oral and Maxillofacial Surgery, and Head of Radiology Department at the Centre of Dentistry, Oral Medicine and Maxillofacial
Surgery with Dental School, Tübingen University Hospital, Tübingen, Germany.

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Figure 1. Patient referred after resection of poorly differentiated Figure 2. Extensive 3-dimensional (3D) image from matched scans
squamous cell carcinoma of entire nose. obtained by 3D photogrammetry and structured light scanning systems
and computer-aided design (CAD) design of nasal prosthesis.

Figure 3. Working principle of ACEO Drop-on-Demand technology. A-D, Printing without supporting structures. A, After design in computer-aided
design (CAD) software, object meshed from STL format. B, Software creates print instructions. C, General principle: droplets applied in X- and Y-position
and each layer immediately polymerized with ultraviolet light, layering object in Z-direction. D, Final dimension. E-F, Printing with supporting
structures. E, Silicone and support material (light blue) printed at same time. F, Printed to final object dimension. G, Support material washed out with
water. H, Object fully polymerized at 200 C.

an image of the whole face and measure its general unaware of the design of the conventional interim
proportions; and then with a portable structured light prosthesis.
scanner (Artec Spider; Artec 3D) to render the anatomy The availability of the whole facial anatomy with open
of the nasal defect and the undercuts of the nasal cavity. eyes aided the proper positioning and formation of the
Both scans were matched, resulting in a 3D image of the prosthesis. The prosthesis edges were aligned to the
whole face, including a highly detailed defect anatomy virtual soft tissue adjacent to the defect. The nasal cavity
(Fig. 2). The prosthesis was free-formesculpted by using a and airways were formed. The prosthesis construction
computer-aided design (CAD) system (Zbrush Software; was exported in standard tessellation language (STL)
Pixologic Inc) and without any standard templates. The format and sent for direct printing (Drop-on-Demand
design was based on photographs provided by the pa- ACEO; Wacker Chemie AG). This technology is based
tient. The operator (A.U.) who performed the CAD was on platinum-catalyzed addition polymerization, which

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August 2018 305

(USP) class VI are still in process. The printing technol-

ogy specifies that single droplets are dosed onto the
working surface according to the STL mesh, and each
single layer of 0.4 mm is polymerized with ultraviolet
(UV) light (Fig. 3). A summary of the printer hardware is
shown in Figure 4.
Two prostheses in a flesh-tone color were printed and
evaluated on the patient. Finishing was necessary to
remove the staircase effect and to improve the color
match. Therefore, the first prosthesis was sealed with a
silicone coating material (G531 RTV Silicone; Technovent
Ltd). The second prosthesis was first superficially finished
with a fine milling cutter and subsequently sealed in the
same manner (Fig. 5). Both sealants included coloring with
Figure 4. Printing hardware. Printing head (A) moves in a coloration set (Xtrinsic Farben KIT; Cosmesil Co). Both
X-, Y-directions and doses droplets (B) onto printing table (C) to finished prostheses fitted well into the patient’s defect and
layer object in Z-direction. set passively in position. The patient felt comfortable and
experienced no compression pain. The prostheses were
means the crosslinker’s Si-H groups react with the vinyl fixed with a skin adhesive (B-530 Secure Adhesive; Cos-
groups of the polymer to form a 3D network.9 A pure mesil Co), and both showed an acceptable marginal
silicone free of solvents (ACEO Silicone General Purpose; adaptation to the adjacent skin (Figs. 6, 7); however, the
Wacker Chemie AG) with a Shore hardness of 40 A was color match was better in the second one. In terms of
used to fabricate the prosthesis. The biological compati- overall esthetics, the second prosthesis was comparable to
bility tests according to the International Organization for the traditionally fabricated one (Fig. 8). Information about
Standardization10 and United States Pharmacopeia the process and production times can be found in Table 1.

Figure 5. Directly printed silicone prostheses. A, Without post-processing. B, Sealed with silicone coating and colored. C, Polished with fine milling
cutter, sealed with silicone coating, and colored.

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Figure 6. First finished directly printed prosthesis. Sealed with silicone coating and colored. A, Frontal view. B, Profile view.

Figure 7. Second finished directly printed prosthesis. Polished with fine milling cutter, sealed with silicone coating, and colored. A, Frontal view.
B, Profile view.

DISCUSSION superficially ground prior to the silicone sealing and

showed a better color match. Apparently, the roughened
This clinical report showed that a digital workflow from
silicone surface helps the paint pigments better infiltrate
defect acquisition to definitive prosthesis is possible.
the prosthesis structures. In addition to printing accuracy,
However, as manual finishing was necessary to reach an
such interventions on the prosthesis surface prevent
acceptable esthetic outcome, the prosthesis was

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August 2018 307

Figure 8. Nasal prostheses in place. A, Traditionally made. B, Second 3-dimensionaleprinted silicone. Color match to adjacent tissue comparable.

sophisticated surface instructions (such as wrinkles and Table 1. Time needed for workflow
furrows) applied in the CAD software. These manual Stage Substage Time (min*)
efforts might not be necessary in the future with de- 3D scanning of face Pritidenta 10
and defect
velopments in silicone printing.7,8 Artec Spider 15
The fit of the directly printed prosthesis was found to Subtotal: 25
be clinically acceptable, which demonstrates the reli- Free-form 3D design Matching of initial images 10
ability and precision of the digital process. However, the (CAD)
marginal adaptation was lacking in some areas. The main Construction of bulk 20
reason for this drawback was the layer thickness of 0.4 Alignment to defect 10
mm, which represents a major limitation of the technique Customization 10
Subtotal: 50
as compared with thicknesses below 0.1 mm in the
Direct printing Regardless of number of 10 h for each order
conventional process. Improvement of the manufacturing prostheses including shipping
technology must address this point to achieve a smoother Manual post-processing Prosthesis no. 1 15
transition of the prosthesis margins to the soft tissue. At Prosthesis no. 2 25
the current stage of silicone printing technology, the Total time: 12:30/12:40 h
prosthesis was only suitable as an interim postsurgical Total time without 2:30/2:40 h
appliance. Even so, the prosthesis must be made from a printing:

medical grade (certified) silicone, which is not yet avail- 3D, 3-dimensional; CAD, computer-aided design. *Unless otherwise designated.

able for 3D printing.

As no prototype or forerunner of the prosthesis was retaining magnet copings in such a prosthesis requires
fabricated, the clinical evaluation stage was dispensed investigation.
with. Therefore, the clinical evaluation session for the
patient was omitted. However, it is not possible to
SUMMARY
evaluate position and marginal adaptation before
definitive delivery of the prosthesis. The 2 directly This clinical report shows the clinical outcome of nasal
printed nasal prostheses were retained adhesively and defect rehabilitation by means of a directly printed silicone
mechanically with the aid of the nasal remnant. The prosthesis. This approach may become a valid treatment
feasibility of transfer, adaptation, and integration of option with a reduced number of appointments for the

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308 Volume 120 Issue 2

patient compared with a conventional approach while still 8. Jindal SK, Sherriff M, Waters MG, Smay JE, Coward TJ. Development of a 3D
printable maxillofacial silicone. Part II: Optimization of moderator and
providing acceptable esthetics. thixotropic agent. J Prosthet Dent 2018;119:299-304.
9. ACEO Technology GmbH. Available at: https://www.aceo3d.com/
technology. (Accessed November 11, 2017.)
10. International Organization of Standardization. Biological evaluation of
REFERENCES medical devices - Part 1: Evaluation and testing within a risk management
process. ISO 10993-1:2009. Geneva: International Organization of Stan-
1. He Y, Xue GH, Fu JZ. Fabrication of low cost soft tissue prostheses with the dardization; 2009. Available at: http://www.iso.org/standard/44908.html.
desktop 3D printer. Sci Rep 2014;4:6973.
2. Unkovskiy A, Spintzyk S, Axmann D, Engel E, Weber H, Huettig F. Additive
manufacturing: A comparative analysis of dimensional accuracy and skin Corresponding author:
texture reproduction of auricular prostheses replicas. J Prosthodont 10 Dr Alexey Unkovskiy
November 2017. doi: 10.1111/jopr.12681. [Epub ahead of print.] Department of Prosthodontics
3. Unkovskiy A, Huettig F, Brom J, Keutel C. Auricular prostheses produced by Centre of Dentistry, Oral Medicine, and Maxillofacial Surgery
means of conventional and digital workflows: A clinical report on esthetic Dental School, Tübingen University Hospital
outcomes. Int J Prosthodont 2018;31:63-6. Osianderstr. 2-8, 72076 Tübingen
4. Yadav S, Narayan AI, Choudhry A, Balakrishnan D. CAD/CAM-assisted GERMANY
auricular prosthesis fabrication for a quick, precise, and more retentive Email: Alexey.Unkovskiy@med.uni-tuebingen.de
outcome: A clinical report. J Prosthodont 2017;26:616-21.
5. Eggbeer D, Bibb R, Evans P, Ji L. Evaluation of direct and indirect additive Acknowledgments
manufacture of maxillofacial prostheses. Proc Inst Mech Eng H 2012;226: The authors thank ACEO Technology GmbH and especially Mrs Dr V. Seitz for
718-28. their support in terms of silicone printing; Pritidenta GmbH for providing their 3D
6. Xiao K, Zardawi F, van Noort R, Yates JM. Color reproduction for advanced photogrammetry system; Prof Dr Geis-Gerstorfer for his ideas for the topic; Priv-
manufacture of soft tissue prostheses. J Dent 2013;41 Suppl 5:e15-23. Doz Dr E. Engel and Prof Dr H. Weber for their financial support; the patient; and
7. Jindal SK, Sherriff M, Waters MG, Coward TJ. Development of a 3D printable Mrs Ursula Gonser, MPho, for photography.
maxillofacial silicone: Part I. Optimization of polydimethylsiloxane chains and
cross-linker concentration. J Prosthet Dent 2016;116:617-22. Copyright © 2017 by the Editorial Council for The Journal of Prosthetic Dentistry.

THE JOURNAL OF PROSTHETIC DENTISTRY Unkovskiy et al