Simplifying the Digital Workflow of Facial Prostheses

journal of prosthodontic research 63 (2019) 313–320

Journal of Prosthodontic Research

Original article

Simplifying the digital workﬂow of facial prostheses manufacturing

using a three-dimensional (3D) database: setup, development, and

aspects of virtual data validation for reproduction

a,b, c a c

Alexey Unkovskiy *, Ariadne Roehler , Fabian Huettig , Juergen Geis-Gerstorfer ,

d e c

Joern Brom , Constanze Keutel , Sebastian Spintzyk

Department of Prosthodontics at the Centre of Dentistry, Oral Medicine, and Maxillofacial Surgery with Dental School, Tuebingen University Hospital,

Tuebingen, Germany

Department of Dental Surgery, Sechenov First Moscow State Medical University, Moscow, Russia

Section Medical Materials and Science, Tuebingen University Hospital, Tuebingen, Germany

Brom Epithetik, Heidelberg, Germany

Department of Oral and Maxillofacial Surgery, and Head of Radiology Department at the Centre of Dentistry, Oral Medicine and Maxillofacial Surgery with

Dental School, Tuebingen University Hospital, Tübingen, Germany

A R T I C L E I N F O A B S T R A C T

Article history: Purpose: To set up the digital database (DDB) of various anatomical parts, skin details and retention

Received 24 September 2018

elements in order to simplify the digital workﬂow of facial prostheses manufacturing; and to quantify the

Received in revised form 8 January 2019

reproduction of skin wrinkles on the prostheses prototypes with stereolithography (SLA) and direct light

Accepted 17 January 2019

processing (DLP) methods.

Available online 18 February 2019

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

Keywords:

saved in jpeg format. The four magnetic retention elements were remodeled in computer aided design

Nasal prostheses

(CAD) software. The 14 test blocks with embossed wrinkles of 0.05–0.8 mm were printed with SLA and

Auricular prostheses

DLP methods and afterwards analyzed by means of proﬁlometry and confocal microscopy.

Silicone prostheses

Anaplastology Results: The introduced DDB allows for production of customized facial prosthesis and makes it possible

Additive manufacturing 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 0.8 mm in depth may be associated

with the loss of 4.5%–11% of its proﬁle with SLA or DLP respectively. Besides, the reproduction of 0.05 mm

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%.

1. Introduction to enhance the workﬂow of facial prostheses manufacturing in

terms of efﬁciency, ease of production and patients burdens [2].

Patients afﬂicted by facial defects experience immense Various protocols of AM utilization have been introduced,

psychological pressure and usually undergo a long lasting featuring direct mold making (DMM) [3], indirect mold making

treatment process in order to camouﬂage their mutilation by (IMM) [4], and also rapid manufacturing (RM) with direct silicone

means of a prosthetic appliance [1]. The utilization of computer printing of the ﬁnal prostheses [5,6]. The last mentioned approach

aided design (CAD) and additive manufacturing (AM) was reported remains to be a potentially valid option for the future, but can be

considered only for provisional solutions, today [7]. The approach

of IMM was shown to achieve a more predictable rehabilitation

outcome in terms of overall esthetics [8].

* Corresponding author at: Department of Prosthodontics at the Centre of

Whichever AM approach is chosen, a virtual prosthesis has to be

Dentistry, Oral Medicine, and Maxillofacial Surgery with Dental School, Tubingen

constructed ﬁrst and commonly in standard tessellation language

University Hospital, Osianderstr. 2-8, 72076 Tübingen, Germany.

E-mail address: [email protected] (A. Unkovskiy). (STL) format. In case of unilateral loss of an auricle the native

https://doi.org/10.1016/j.jpor.2019.01.004

314 A. Unkovskiy et al. / journal of prosthodontic research 63 (2019) 313–320

anatomy can be captured with a surface scanner and adopted from consideration such categories as administration, functionality,

the opposite side with the use of a “mirror-imaging technique” [9]. query, storage, safety and easiness of use.

However, a bilateral auricle absence and also facial defects, which The open access software package XAMPP (Version 5.2.7. for MS

cross the facial midline, would restrict such an approach. Windows) developed by a non-proﬁt project Apache Friends [17]

Thus, the three dimensional (3D) design calls for experience was chosen. It is SQL-based and imitates server functionality on a

with complex software solutions for free-form sculpting. This local computer. This way it provides an opportunity to load local

requires not only technical skills and artistic vision, but also plenty saved data in a web browser through the administration service

of time. with the use of phpMyAdmin [18].

That is why an alternative data source i.e. a digital database

(DDB) of facial parts with organ-speciﬁed anatomy would ease the 2.1.1. Integrated anatomical forms

CAD process. Ciocca et al. highlighted potential beneﬁts of a DDB In order to preliminarily populate the DDB with nasal and

utilization [10]. auricular anatomy, 50 probands aged from 19 to 62 years gave

Such DDB for facial prosthetics should not only provide their informed consent to undergo the light scanning pro-

“custom” facial parts, but also customized supportive objects cedure and the usage of their 3D data free of charge. The ethical

and soft tissue surface textures to improve function and esthetics. committee of the Tuebingen University Hospital voted afﬁrma-

As far as prosthesis function is concerned, the virtual tively (037/2018BO1).

implementation of retention elements is crucial in a digital For the auricular forms, mastoid area was isolated from hair

workﬂow of facial prostheses manufacturing [11]. Following the with a medical cap and the left auricle of each proband was

bone availability, the transdermal implant position might be defatted with 80% ethanol. In order to capture the complex ear

suboptimal for the prosthetic supply. In order to predict and cope anatomy with its numerous undercuts and adjacent tissue portion

with shortage of space, a virtual set of commonly utilized retention the portable Artec Spider scanner (Artec 3D, Luxembourg,

elements (i.e. magnet or bars) would allow the best choice during Luxembourg) was used. The gathered raw data underwent the

the prosthetic CAD design. post-processing stage with Artec Studio software (ver. 11, Artec

With regard to the esthetical outcome and camouﬂage, skin 3D). The output ﬁle in STL-format was assigned with an ID: “O-DB-

structure details must be applied onto the prosthesis surface [12]. ###” and sent to Zbrush software (Pixologic, Inc., Angeles, CA,

The facial skin wrinkles have been measured to range between USA) for the further CAD preparation. Therefore, each virtual

0.06 to 0.94 mm in depth, and their full reproduction by means of a model was cut with a digital knife tool leaving 1 cm of adjacent

digital workﬂow might be hardly feasible [13,14]. Neither is the tissue around the auricle. The areas between helix and scapha,

resolution of CT with its voxel size of 0.2–0.5 mm, nor the light helix and antihelix, tragus and antitragus as well as ear canal were

scanners with an accuracy of 0.02 mm are able to capture and revisited, whether they were captured distinctively. Further

describe wrinkles of 0.1 mm or less in depth [15]. Thus, it may be artefacts and surfaces depiction shortcomings were edited with

useful to apply the desired amount of skin details out from a DDB following digital brush tools listed in Table 1.

set during the CAD process. For the capturing of the nasal anatomy each proband was

In the topical literature only one DDB for nasal anatomy was scanned with pritimirror system (pritidenta GmbH, Leinfelden-

found [16]. Thus, the ﬁrst aim of the present study was to generate Echterdingen, Germany) following the manufactures speciﬁcations

an extensive DDB for facial prosthetics including auricular and with support of pritiimaging software (pritidenta GmbH). The 3D

nose anatomy, exemplary custom retention elements as well as a image of the whole face was exported in a native OBJ format and

preliminary set of skin wrinkles and skin surface textures. imported to Zbrush software where the nose was cut out with 1 cm

These efforts should make a digital workﬂow of facial prosthesis of adjacent tissue portion. The nostrils were cut through the nose

manufacturing more applicable in a daily routine and more bulk and the inner surface was smoothed out to be ready for the

attractive for maxillofacial technicians. alignment to a defect side. Each virtual model was assigned with an

Furthermore, the set of skin wrinkles should be validated by a ID: “N-DB-###” and saved in STL-format. All gathered nose and

quantiﬁcation of skin wrinkles reproduction with two 3D printing auricular 3D models were preliminarily labeled with age (years)

systems based on stereolithographie (SLA) and digital light and gender (female/male) as a later search criteria for the user.

processing (DLP) in context of IMM approach. It was hypothesized

that these AM machines with a printing resolution of 0.025 mm 2.1.2. Implementation of retention elements

both are able to reproduce faithfully the skin wrinkles starting As a ﬁrst example for the database it was decided to implement

from 0.05 mm. the magnetic retention elements (Technovent Limited, Bringend,

South Wales, UK) that are frequently used in Department of Oral

2. Materials and methods and Maxillofacial Surgery of the University Clinic, Tuebingen. After

clearance with the patent owner, the original parts were measured

2.1. Populating the database with a digital caliper (DIGI-MET 0–25 mm, Helios-Preisser,

Gammertingen, Germany) and their dimensions were recon-

Considering the complexity of a database concept a suitable structed in NX software (NX 10.0, Siemens Product Lifecycle

database management system must be found, taking into Management Software Inc.) (Fig. 1). The imported STL-ﬁles were

Table 1. Digital tools in the Zbrush software and their preferences for processing of raw scan data of facial anatomy.

Brush code Draw size (units) Focal shift (units) Z intensity (units) Application

BMV 0–20 0 50 Deepen folds

BPO 20 À40 20 Smoothing

BTD 20 À50 40 Remove blobs

BCB 15–30 À50 30 Treating undercuts

BDS 17 40 23 Draw ﬁne wrinkles

BIN 0–20 0 10 Closing holes

BNO 0–20 0 10 Applying texture

BST 1000 À100 25 Applying texture

A. Unkovskiy et al. / journal of prosthodontic research 63 (2019) 313–320 315

Fig. 1. Technovent magnets constructed in NX software to be implemented in a

database.

labeled in the database with information about width/diameter,

height, and the order number of the manufacturer.

2.1.3. Implementation of skin textures and wrinkles

In order to create a library of skin texture details, probands’ skin

surface was captured chairside with the use of digital single-lens

Fig. 2. (A) Overview to the virtual design of the 40 Â 20 mm test block with

reﬂex camera (DSLR) (Nikon D300s, Nikon Corp., Tokio Japan) with

wrinkles (lines) of 0.05, 0.1, 0.2, 0.4, 0.6, 0.8 mm in depth, designed with the BDS

a macro lens (AF-S Dx Micro Nikkor 85 mm 1:3,5G ED VR, Nikon tool. (B) Side aspect in magniﬁcation of the 0.4 mm wrinkle. Measuring of the

Corp.), tele converter (Kenko N-AF 2x Teleplus Pro 300, Nikon wrinkle depth in Zbrush software from the deepest point to the wrinkle margin

with a use of “transpose tool” (BTS).

Corp.) and ﬂash unit (Mecablitz 15 MS-1, Metz, Zirndorf, Germany).

The ala nasi area was chosen to capture nose skin surface and the

scapha area was captured for auricles skin surface. Additionally,

2.2.2. Wrinkle proﬁle measurements

the peel of a naval orange was photographed with the same camera

The wrinkle depth on each test block was examined in cross

in a light box. All these structure images were saved in JPG-format

section under microscope (M 400 Photomakroskop, Wild-Heer-

categorized with the respective area to the database.

brugg AG, Heerbrugg, Switzerland) with 64Â magniﬁcation and

captured with a camera (Canon Eos 700D, Canon Inc., Tokio, Japan).

2.2. Validation tests for the reproduction on example of wrinkles

The wrinkles depth was measured software-based on the screen

(Datinf Measure, Datinf GmbH, Tuebingen, Germany) (Fig. 3).

2.2.1. Preparing the test blocks

Three repeated measurements of each wrinkle were recorded.

In order to deﬁne the level of skin surface reproduction by

Further surface analysis was performed with proﬁlometer

means of modern AM methods a test block 40 Â 20 Â 5 mm was

(Mahr S6E, Mahr GmbH, Goettingen, Germany). In order to ensure

designed in Zbrush software. Wrinkles ranging from 0.05 to

the reproducibility of all measurements a retainer was designed

0.8 mm in depth, according to the classiﬁcation of Lemperle, were

and printed with fused deposition modelling (FDM) printer

embossed evenly on the test blocks [13]. Holding the “Shift” button

(Replicator, MakerBot Industries, Brooklyn, NY, USA) to ﬁx the

ensured the horizontal position of the test block. A line was

test blocks on the proﬁlometer testing area.

dragged downwards from the upper block border in 90 angle with

Due to the probes’ amplitude limitation of 0.25 mm, only

the Damian Standard Brush (BDS) — ensured by holding the “Shift”

wrinkles below that value – namely 0.05, 0.1 and 0.2 mm in depth –

button (Fig. 2A). The brush preferences listed in Table 1 were used

could be analyzed this way. The measuring probe drove

for the creation of various wrinkles depth. To ensure a precise

perpendicular to the wrinkle orientation. Three repeated proﬁles

depth of each wrinkle all digital tools were calibrated in mm ﬁrst. A

for each test block were recorded. The acquired data was analyzed

cube form with deﬁned dimension (1 Â1 Â1 mm) was designed in

in measuring software (MountainsMap universal 7.3, Digital Surf,

NX software and uploaded in Zbrush. The Transpose Brush (BTS)

Besançon, France) and converted into proﬁle curves. The absolute

was used to measure the uploaded cube in standard for this

proﬁle depth (Rv) value was obtained for each wrinkle (Fig. 4).

software “units” and so to deﬁne the “unit-to-mm” ratio. This

allowed calibrating transpose tool (BTS) scale in mm. The proﬁle of

2.2.3. Statistical methods for quantiﬁcation and comparison of the

each wrinkle was measured by dragging the “BTS” line from the

data

deepest wrinkle proﬁle point up to the test block upper border,

All gathered data was analyzed with JMP 13.1 software package

which was the nil level for each wrinkle. Holding the “Shift” button

(SAS Corp., Heidelberg, Germany). The distributions of the

ensured the vertical position of the test block and the same vertical

measurements (wrinkle depth; dependent variable) were grouped

direction of BTS line. This also allowed stopping the BTS line right

by the AM machine (DLP and SLA; independent variable) and

on the nil level of the test block automatically (Fig. 2B).

The constructed digital test block with embossed wrinkle

proﬁles were printed 14 times each with streolithography (SLA)

(Form 2, Formlabs, Somerville, MA, USA) from “Grey Resin”

material (Formlabs) and direct light processing (DLP) (Solﬂex 650,

W2P, Klosterneuburg, Austria) from “V-print model” material

(VOCO, Cuxhaven, Germany) with 45 printing orientation to the

build platform. For both 3D printers the printing resolution was set

on 0.025 mm. The printed test blocks were post-processed

immediately as follows: 6 min storing in isopropanol 80%, drying

for 30 min in room air, and lightcuring with 2 Â 2000 ﬂashes

(Otoﬂash G171, VOCO). In order to get rid of any printing artefacts

on the test block edges, 5 mm were cut off orthogonally with the

Fig. 3. Wrinkle depth measurement in Datinf software. Three repeated measure-

micro saw (Accustom-50, Strues, Willich, Germany) exhibiting the

ments were carried out from the deepest wrinkle points to the wrinkle margin and

wrinkles cross-section for the further analysis.

the average was used for calculation.

316 A. Unkovskiy et al. / journal of prosthodontic research 63 (2019) 313–320

auricle, was adopted from a DDB by entering patient’s sex and age

(Æ5 years) (Fig. 5C). The picked image in STL format was then

properly positioned to the defect side and its margins were aligned

to the adjacent soft tissue (Fig. 5D). The prosthesis form can be also

manipulated with a bunch of digital tools to align symmetry and

reach facial harmony in an overview picture, as described

elsewhere [14].

Fig. 4. Winkle depth proﬁlometrical measurement in MountainsMap software. The

As seen here and found in most cases, a shortage of space may

green line represents the wrinkle depth from the deepest proﬁle point to the

lead to “digital” perforation of the retention elements to the

wrinkle margin.

prosthesis outer surface (Fig. 6A). Hence, a virtual clay tool is used

for a selective build-up of the prosthesis bulk (Fig. 6B).

The uploaded virtual magnet construction serves like a

tested for normality of distribution by goodness of ﬁt with placeholder (Fig. 6C), as it can be then cut out from the prosthesis

Shapiro–Wilk test [19] and homoscedasticity of the compared bulk with a Boolean function, providing thereby the socket of

distributions with the Barlett test, using p < 0.05 for both. corresponding geometry congruent to the prosthesis magnet

In case of a non-normal distribution within a set of chosen (Fig. 6D).

comparisons, the Wilcoxon rank sum test was used to evaluate Once the prosthesis is adjusted in terms of form and relation

statistical difference using alpha = 0.05; otherwise ANOVA Tukey– (Fig. 7A), the skin details can be applied. This is for example

Kramer post-hoc test was applied on the same alpha level of 0.05. possible in the ZBrush software by uploading the jpeg ﬁle from the

DDB, which can be embossed onto the prosthesis surface (Fig. 7B).

3. Results Interestingly, application of the naval orange peel yielded a

naturally looking skin surface.

3.1. Application of the database After ﬁnishing these stages the prosthesis is ready for

materialization (CAM). If not printed directly in silicone, a

The DDB called “Epi-Database” for the digital workﬂow of facial prosthesis prototype is printed in wax for a chairside try-in

prostheses manufacturing was set up on a 2TB HDD (WD Elements session. Such prototypes can be transferred to silicone prosthesis

portable, San Jose, CA, USA). After the CAD stage 21 post-processed using the conventional molding technique (Fig. 8A), including the

virtual auricles and 48 noses were implemented as labeled integration of magnets into prosthesis bulk, according to their

datasets (categorized by age and sex) within the database. position in the CAD (Fig. 8B).

Additionally, retention magnets of four sizes and various skin

details were generated. 3.1.2. Nasal prosthesis

The following pathway describes the utilization of the database Rehabilitation of a nasal defect and constructing a nasal

on two clinical examples. prosthesis in a digital workﬂow has some peculiarities. Thus,

not only the organ outer anatomy must be restored but also the

3.1.1. Auricular prosthesis inner one, considering the reestablishment of breathing entrances.

A virtual image of the deﬁcient side with implant magnetic This case demonstrates schematically the utilization computed

attachments (VF-MC1-S, Mini Magnacap, Technovent) being tomography (CT) as the main virtual data source of the deﬁcient

screwed onto the implants has been obtained with Artec Spider area. Once a CT has been obtained the bony and soft tissue

scanner and uploaded in Zbrush software. This way the magnetic structure can be easily segmented in a special software (Invesalius,

attachments act as scan bodies and allow for locating their position Renato Archer CTI, Campinas, Brasil) (Fig. 9A), which allows for

in the CAD software, the same way it is done for the intraoral translation of DICOM data in STL format. The extracted STL model

caption of implant position. For this purpose the three cylinders of of the facial (soft tissue) with a nasal defect and the skull anatomy

the same geometry and dimensions are put over the obtained were then uploaded into the Zbrush freeform software (Fig. 9B).

virtual images of the original magnetic attachments. (Fig. 5A). The suitable anatomical form of a female nose aged between 35

Three suitable prosthesis magnets in STL format, in this case ML-2S and 50 was appended and aligned to the adjacent soft tissue. The

magnets (Technovent), were appended onto the screwed implant nasal anatomy was checked to ﬁt the overall facial proportions and

attachments (Fig. 5B). Afterwards a missing facial part, in this case shown to the patient (Fig. 9C). Once the position and form were

Fig. 5. CAD of auricle prosthesis. (A) Locating the implant position on the defect side; (B) placement of magnets of the chosen geometry onto the implants; (C) adoption of a

suitable auricle anatomy out from the database according to patients’ sex and age; (D) adjustment of auricle position and alignment of prosthesis margins.

A. Unkovskiy et al. / journal of prosthodontic research 63 (2019) 313–320 317

Fig. 6. CAD individualization of auricular prosthesis. (A) Perforation of the chosen

Fig. 9. (A) Segmentation bony structures and soft tissues using the CT data in the

magnets size through the surface. (B) Coverage of the magnets with a virtual build

Invesalius software; (B) the STL ﬁle of bony structures and soft tissue being exported

up; (C) cut out of the deﬁnitively positioned magnets from the prosthesis bulk with

in the Zbrush software; (C) applying of the nasal prosthesis from a DDB according to

a Boolean function; (D) ﬁnally the prosthesis bulk owes a placeholder box

the age and gender and its further alignment to the adjacent soft tissue; (D)

congruent to the chosen magnet proﬁle.

blending of the soft tissue mask and virtual implant (gold bar) placement following

both the bone availability and the adjusted prosthesis position.

Fig. 7. Auricle prosthesis after being aligned virtually to the adjacent tissue (A) and

after application of skin details onto its surface (B).

Fig. 10. (A) The implant (gold bar) position and relation to prosthesis bulk was

approved; (B) the ML-2S magnet (Technovent) was appended over the implant and

ﬁxed virtually in the prosthesis bulk; (C) the magnet was cut out with the Boolean

function, leaving thereby a socket of corresponding geometry.

function allowed for creation of a corresponding socket for a future

real magnet (Fig. 10C). As ﬁnal stage of CAD the photographs of

orange peel and ala nasi were embossed onto the prosthesis

surface to add some details the same way it was done for the

auricular prosthesis.

3.2. Validation of the digital wrinkles after materialization

The mean values of the wrinkles depth reproduced with SLA

Fig. 8. (A) a ﬁnished auricle prosthesis manufactured with a use of the RP approach;

ﬁ

(B) magnets (Technovent) being integrated into prosthesis bulk, according to their and DLP methods gathered by an optical and pro lometrical

position in the virtual design. analysis are shown in Table 2.

The Shapiro–Wilk test revealed non-normal distributions for

the data gathered with the stereomicroscopy. For this reason the

approved, the soft tissue mask could be blended, so that the Wilcoxon test was used to evaluate statistical difference using

relation of the prosthesis to the bony structures was clearly seen alpha = 0.05; for the data gather with proﬁlometry a normal

(Fig. 9D). This allowed for the implant position planning, taking distribution was observed. Therefore the Tukey–Kramer post-hoc

into consideration both, bone availability and future prosthesis test was applied on the alpha level of 0.05.

position. As nowadays there is no digital database for the According to the optical analysis, the wrinkles from 0.1 to

commonly used extraoral implants, the cylinder of a corresponding 0.8 mm reproduced by both printers were not able to reach the

geometry with the same cross section was appended and acted as reference values. Interestingly, the wrinkles of 0.05 mm became

an implant. Once the implant was virtually placed (Fig. 10A), the even more pronounced (18–40% “deeper” than the reference

magnet (in this case ML-2S, Technovent) could be put upon it and values with both SLA and DLP). The wrinkles from 0.1 to 0.8 mm

checked once again, whether it ﬁts in a prosthesis bulk (Fig. 10B). were reproduced more precisely with DLP, having the maximum

The virtual extraction of the magnet 3D model with a Boolean deviation of À4.5% to the reference value. In case of SLA deviations

318 A. Unkovskiy et al. / journal of prosthodontic research 63 (2019) 313–320

Table 2. Mean values of wrinkle depth for the test blocks made with stereolithography (SLA) and digital light processing (DLP). The ﬁrst row represents the mean wrinkle

depth gathered by stereomicroscopy and proﬁlometry, followed by standard deviation and relative deviation of the mean measurements to the reference value in percent (%).

Shapiro–Wilk test was used for the assessment of data normality and Barlett test for homoscedasticity. As in case of stereomicroscopy the Shapiro–Wilk test revealed a non-

normal data distribution, the non-parametric Wilcoxon analysis was used for statistical comparison. For proﬁlometry due the normal data distribution the statistical

signiﬁcance was analyzed with Tukey Kramer test.

Wrinkles depth in mm

0.05 0.1 0.2 0.4 0.6 0.8

Stereomicroscopy

Mean Ry SLA; SD (mm); relative deviation to 0.059; 0.008; 0.088; 0.010; 0.178; 0.008; 0.364; 0.014; 0.548; 0.024; 0.747; 0.032;

reference (%) +18% À8% À11% À9% À8.7% À6.4%

Shapiro–Wilk test W = 0.88 W = 0.89 W = 0.95 W = 0.96 W = 0.93 W = 0.93

p = 0.0004 p = 0.001 p = 0.056 p = 0.257 p = 0.013 p = 0.011

Mean Ry DLP; SD (mm); relative deviation to 0.070; 0.010; 0.10; 0.007; 0 0.191; 0.010; 0.390; 0.016; 0.595; 0.018; 0.797; 0.021;

reference (%) +40% À4.5% À2.5% À0.8% À0.4%

Shapiro–Wilk test W = 0.97 W = 0.96 W = 0.91 W = 0.96 W = 0.97 W = 0.9

p = 0.283 p = 0.247 p = 0.0027 p = 0.284 p = 0.387 p = 0.017

Comparison mean Ry SLA/DLP

Barlett-Test F = 2.63 F = 5.35 F = 1.97 F = 0.91 F = 3.26 F = 7.51

p = 0.11 p = 0.021 p = 0.159 p = 0.34 p = 0.071 p = 0.006

Wilcoxon rank sum test α = 0.05 Z = À4.85 Z = À5.11 Z = À5.74 Z = À6.33 Z = À7.21 Z = À6.64

p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001 p < 0.0001

Proﬁlometry

Mean Ry SLA; SD (mm); relative deviation to 0.047; 0.005; 0.085; 0.009; 0.171; 0.007;

reference À6% À15% À14.5%

Shapiro–Wilk test W = 0.86 W = 0.86 W = 0.88

p = 0.067 p = 0.078 p = 0.132

Mean Ry DLP; SD (mm); relative deviation to 0.064; 0.011; 0.105; 0.012; +5% 0.195; 0.009;

reference +28% À2.5%

Shapiro–Wilk test W = 0.85 W = 0.94 W = 0.97

p = 0.64 p = 0.56 p = 0.88

Comparison mean Ry DLP/SLA

Barlett-Test F = 3.65 F = 0.7 F = 0.83

p = 0.56 p = 0.41 p = 0.36

Tukey Kramer α = 0.05 p < 0.0004 p < 0.0009 p < 0.0001

ranged between À6 and À11% not reaching the true value. The [2,3], some researches today have concentrated rather on the

results of the proﬁlometry coincided with the optical analysis and expediency and easiness of its application [11,20]. The main

are presented in Table 2. limitations highlighted in the topical literature are the high costs

Furthermore, the deviations of relative differences for each off soft- and hardware solutions for data acquisition, CAD and

value gathered with stereomicroscopy were depicted in Fig. 11. It materialization. These technologies call not only for technical

can be seen again, that the wrinkles from 0.1 to 0.8 mm were experience, but also for digital sculpting skills to perform the CAD

generally reproduced better with the DLP and became rather stage and for a certain structured pathway to translate the CAD

smoothed. Whereas the wrinkles of 0.05 mm became even more data into a ﬁnal prosthesis

pronounced and were reproduced nearly with the same accuracy

with both SLA and DLP. 4.1. Signiﬁcance of a database

As the certain deviations in wrinkles reproduction were

revealed, the hypothesis of the present study can be rejected. As demonstrated in this study, a database for virtual facial parts

and skin details could be setup by open access solutions. Such a

4. Discussion database could support a free-form software, such as ZBrush,

during the CAD stage. Moreover, the content of this database may

Since the general feasibility of digital workﬂow for facial also allow the usage of patients’ CBCT datasets instead of STL-ﬁles

prostheses manufacturing has been successfully demonstrated delivered by costly and sophisticated surface scanners, such as

Artec Spider, which is priced about 20.000 USD plus 500 USD

annual software license [21,22]. Obviously, the CBCT with its voxel

size ranging from 0.2 to 0.4 mm is not able to describe the skin

surface structure faithfully, however may provide sufﬁcient

information about the general facial proportion and anatomy of

the defect and donor-organ. Thus, the skin details can be adopted

from the database and embossed on a prosthesis pattern on a CAD

stage, as it was demonstrated in the second clinical case.

For basic CAD manipulations, i.e. adjusting the prosthesis

position and adjustment of prosthesis edges a row of free software

solutions such as MeshLab (http://www.meshlab.net/) can be

found in web and successfully used for virtual data editing in

maxillofacial prosthetics [23]. Surely the pre-saved anatomical

forms from the database need to be adapted to the patients’

Fig. 11. Deviations of mean relative differences for each value gathered with the

general facial proportions and to the soft tissues adjacent to the

stereomicroscopy. The black line represents the reference value of each wrinkles

defect. However, these reﬁnements and adjustments may be not

depth (0.05, 0.1, 0.2, 0.4, 0.6, 0.8 mm). The blue spots represent the relative mean

that time-consuming, as sculpting of prosthesis from the very

differences of each value gathered by each single measurement of the DLP

reproduced wrinkles and the red spots — of SLA. beginning. The free-form sculpting of a nose, for instance, begins

A. Unkovskiy et al. / journal of prosthodontic research 63 (2019) 313–320 319

with the appendence of a cube as a basic pattern, which should be 4.3. Skin surface reproduction

then transformed with the virtual clay tool in to a nasal anatomy.

According to authors’ experience such manipulations may cost The wrinkles from 0.05 to 0.8 mm in depth were visible on the

time, especially the creation of nostrils and achieving of a smooth AM-manufactured test blocks. However, the present study

surface adjacent to the defect site, without affecting the prosthesis disclosed certain shortcomings in their reproduction by means

form and overall wall-thickness. The utilization of a database may of SLA and DLP printers. Generally, the SLA-reproduced wrinkles

allow for time-savings here, as demonstrated in a clinical case. showed greater deviations to original wrinkle depth values than

To the authors’ best knowledge, all existing databases today DLP, as they became less pronounced. This may be attributed to the

include only nasal anatomy [16]. The present study shows a pathway wise the layers are cured together. Thus, in case of SLA a laser beam

how to create and utilize the more extensive DDB, which covers also travels the layer surface curing the particles step by step in a

the attachments, auricle anatomy, and skin surface details. Anyhow, sequence deﬁned by a printing software, whereas in case of DLP a

the categorization of the datasets with descriptors included to the whole layer is cured at once. The earlier studies showed that the

database has to be reﬁned further. For attachments this is most easy wrinkles of 0.1 can be faithfully reproduced on a visible level with

due to its manufacturer, item number as well as their dimensions. the use of Thermojet printer and a 0.04 mm printing accuracy [15].

The selection via age and gender is a limitation that might be However the reproduction capability was not quantiﬁed for this

overcome with the implementation of height-length ratios as well as stage of digital workﬂow.

sophisticatedanatomical features.Such a setofdescriptorsshouldbe The present study allows for identifying the level of texture

condensed by experts (MFTs together with maxillofacial surgeons). details loss while transferring them from CAD to AM. Thus,

Same should be performed for skin structures and wrinkles. reproduction of wrinkles from 0.1 to 0.8 mm in depth may be

The least but not last aspect of CAD in maxillofacial prosthetics is associated with the loss of 4.5%–11% of its proﬁle, dependent on a

the planning of the prosthesis anchoring [11]. The recent technical printer used — DLP or SLA respectively. Besides, the reproduction of

digital protocols reported, disregard this aspect, and this technical 0.05 mm wrinkles may be met with up to 40% proﬁle incensement.

step is accomplished rather in analog way. The utilization of the It must be emphasized that reproduction of only skin wrinkles

digitalizedretentionelements mayallow ﬁnding anoptimal position does not cover fully the aspect of reproduction accuracy (both

in the limited space of a prosthesis pattern on the CAD stage prior to trueness and precision). The skin surface is more complex

the chairside try-in session. The use of CT also allows here for the structure, than just a sum of wrinkles and includes also ﬁne

backwards-planning, which begins with the virtual placementof the furrows and pores. These anatomical structures, however, may be

implant. This manipulation is, however still very raw, as no database difﬁcult to quantify and reproduce on a CAD stage in order to use

(including the created one) and software include the virtual images them as a referent value. For this reason in the present study the

of the commonly used implants in various dimensions, as it is done, wrinkles of a predetermined proﬁle were chosen in order to assess

for instance, in the intraoral rehabilitation to perform a backwards- the reproduction capabilities of CAM with the chosen AM methods.

planning [24].Inthose cases,where the implantsare insertedpriorto The reproduction of more complex surface proﬁles may be

the facial scanning, the so-called scan bodies are required for a considered in further studies and calls for utilization of a more

consistent capturing of the implant position. accurate hardware for the surface analysis, such as laser

For this reason in the ﬁrst clinical case the implants were microscopy, for instance.

scanned with the magnet attachments being screwed on, which

acted this way as scan bodies. As far as the structured light scanner 5. Conclusion

used was not able to capture the magnetics attachments faithfully,

the cylinders of the same dimensions and the same cross section The digital workﬂow in maxillofacial prosthetics still can not be

were aligned with their virtual images in the CAD software. This considered as state of the art in this brunch of rehabilitation. The

may lead to certain discrepancies between the real and virtual utilization of DDB may aid for its more spread application and a

implants positions. The same problem is true in the ﬁeld of more consistent utilization by primarily decreasing the invest-

intraoral rehabilitation, but its discussion can be found in ments and simplifying the CAD stage.

corresponding researches [25]. Reproduction of digitally applied skin wrinkles may be

associated with deviations of 11–40% details depending on the

4.2. Signiﬁcance of surface structures reproduction initial wrinkle depth. The virtual application of skin details have to

consider the concrete later AM machine and therefore a single set

It was shown that the reproduction of skin structure depends of skin details is not enough for a DBB.

on the AM method chosen. The clinical relevance of the encountered deviations of

The simple validation of only wrinkles’ reproduction in this wrinkles’ proﬁle is difﬁcult to assess on the stage of prosthesis

study may not represent the reproduction of the real skin surface. prototype, as it remains unclear which amount of skin details could

The findings of the present study suggest that more complex be transferred till the final silicone prosthesis. The quantification of

structures, such as pores or furrows, may be also affected skin details amount that could be seen from private and social

throughout the digital workﬂow. Furthermore, this study follows distances must be addressed in future researches.

the skin wrinkles reproduction till the prosthesis prototype in

context of IMM approach, but not till the ﬁnal silicone prosthesis. Acknowledgement

This should be clariﬁed in further studies, including the impact of

processing of prototypes (wax casting of a prototype replica and its The present study was ﬁnancially supported by the “Research

transfer into medical silicone), which may impair the surface Foundation Dental e.V.”. Furthermore, the authors thank the W2P

structure in the ﬁnal prosthesis. Engineering GmbH and VOCO GmbH for the hardware and

This implies two rationales. First, the users of the database have materials supply.

to validate the outcome of applied structures and wrinkles towards

their reproduction with the speciﬁc CAM. Second, and conse-

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