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JJOD-2109; No. of Pages 6
Coverage error of commercial skin pigments ascompared to human facial skin tones
Elizabeth Hungerford a, Mark W. Beatty a,b,*, David B. Marx c,Bobby Simetich a, Alvin G. Wee d
aUniversity of Nebraska Medical Center College of Dentistry, 40th & Holdrege, Lincoln, NE 68583-0740, USAbVA Nebraska-Western Iowa Healthcare System, Omaha, NE 68105, USAcDepartment of Statistics, University of Nebraska-Lincoln, 340 Hardin Hall, Lincoln, NE 68583-0963, USAdCreighton University School of Dentistry, 2500 California Plaza, Omaha, NE 68178, USA
j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x . e 1 – x x x . e 6
a r t i c l e i n f o
Article history:
Received 9 April 2013
Received in revised form
15 July 2013
Accepted 18 July 2013
Available online xxx
Keywords:
Maxillofacial elastomer
Prosthesis colouring
Colour differences
Aesthetics
a b s t r a c t
Objectives: It is unknown if present-day pigments used for intrinsic colouration of maxillo-
facial prostheses are representative of human facial skin tones. This study’s purpose was to
measure L*a*b* values of pigmented elastomers coloured by eleven skin tone pigments and
determine coverage error (CE) when the pigments were compared to human facial lip and
nose colour data.
Methods: 11 skin tone pigments were combined at 0.1%, 1% and 10% by weight with A-2186
elastomer (n = 3). L*a*b* values were measured with a spectrophotometer and group means
were used to calculate DE* colour differences with each L*a*b* value obtained for human nose
and lip. Pigmented elastomer CEs were calculated for nose and lip. Results were compared to
CEs for proposed shade guide colours obtained from clustering analyses of facial skin
colours.
Results: L* values of pigmented elastomers generally were higher than those measured for
nose and lip, whereas a* values were lower. CEs for pigmented elastomers were higher than
those obtained from the proposed shade guide obtained from clustered skin measurements.
Conclusions: Overall, the current commercial elastomers appeared to be too white and not
red enough to adequately match the skin tones of the subject population. Adjustments must
be made to the existing pigmenting system in order to adequately match the skin colours of
the study population.
Clinical significance: The creation of a shade guide and a collection of intrinsic pigments
representing the realm of human facial skin colours would greatly decrease the time a
patient must sit while the clinician is obtaining an acceptable colour match for the silicone
to be used for processing the final prosthesis, thereby increasing both patient satisfaction
and clinician productivity.
Published by Elsevier B.V.
Available online at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
1. Introduction
Craniomaxillofacial defects arise from congenital malforma-
tion, severe head trauma or radical surgery for treatment of
* Corresponding author. Tel.: +1 402 472 1261; fax: +1 402 472 6681.E-mail address: [email protected] (M.W. Beatty).
Please cite this article in press as: Hungerford E, et al. Coverage error of
Journal of Dentistry (2013), http://dx.doi.org/10.1016/j.jdent.2013.07.010
0300-5712/$ – see front matter. Published by Elsevier B.V.http://dx.doi.org/10.1016/j.jdent.2013.07.010
head and neck cancer. Rising numbers of craniomaxillofacial
defect cases are attributed to non-fatal injuries that now
comprise 30% of all battlefield injuries1,2 and increases in both
the incidence and survivability of head and neck cancer.3
Reconstructive surgery often cannot correct these defects, and
commercial skin pigments as compared to human facial skin tones.
j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x . e 1 – x x x . e 6e2
JJOD-2109; No. of Pages 6
a disfigured appearance produces disability through profound
quality of life issues that include a loss of self-esteem,
depression and withdrawal from society.4,5 Consequently, a
facial prosthesis that replaces missing structure and
aesthetically blends with surrounding facial features is critical
to restoring self-esteem and eventual re-integration into
everyday life.6
One of the challenges in constructing a facial prosthesis is
the determination of a shade that serves as a base colourant
within an elastomer. A common technique is to mix a
combination of pigments into a siloxane polymer and hold
the pigmented elastomer next to the face to assess the
accuracy of the mixture. This trial-and-error method is time
consuming, as it may require multiple trials to achieve the
proper shade. Needed in this process is a group of base
colourants representative of the range of facial shades present
within the human population. Pre-mixed skin shades are
marketed for this purpose, but their ranges of shades have not
previously been compared to facial skin measured in a human
population. Recently it was reported that through clustering
analyses, five base shades could be identified to represent lip
and nose skin colours for a group of 119 human subjects, and
therefore serve as a basis for a potential shade guide.7 With
these data available, the purpose of this study was to compare
human facial skin colours in this population with eleven
cosmetic pigments currently available from Factor II, Inc., as
intrinsic colourants for maxillofacial prostheses.8 CIELab
colour differences between pigmented elastomers and facial
skin measurements were used to compare coverage errors of
pigmented elastomers with those calculated for the five
shades obtained from clustered skin colours.
2. Materials and methods
This study tested a platinum-catalyzed, vinyl-terminated
poly(dimethyl siloxane) elastomer (A-2186, Factor II, Lakeside,
AZ) combined with a functional intrinsic cosmetic pigment.8
The vinyl elastomer was combined with a polymethyl
hydrogen siloxane cross-linking agent at a 10:1 ratio by
weight. Once elastomer components were combined and
thoroughly mixed, one of eleven pigments (Table 1) was added
in three different concentrations by weight: 0.1%, 1.0%, and
10%. For each concentration the sample size was three (n = 3),
Table 1 – Functional intrinsic skin pigments evaluated inthis study.
Name Product code Lot number
1. Bisque FI-SK05 S 070111
2. Blush FI-SK13 B 021511
3. Cream FI-SK07 SB 081611
4. Dark Brown FI-SK21 BS 081711
5. Dusk FI-SK17 TK 080509
6. Honey FI-SK09 BS 082510
7. Ivory FI-SK03 BT 042210
8. Mocha FI-SK19 T 042909
9. Naturelle FI-SK01 B 062311
10. Santa Fe FI-SK11 SB 052711
11. Soft Brown FI-SK15 BS 052011
Please cite this article in press as: Hungerford E, et al. Coverage error of
Journal of Dentistry (2013), http://dx.doi.org/10.1016/j.jdent.2013.07.010
thus yielding a total of 99 samples. The elastomer – pigment
combination was placed under 5 � 10�3 torr vacuum for
10 min to remove air from the system, then poured into three
disc-shaped moulds with dimension 6 mm thick-
ness � 34 mm diameter. The moulds were placed into a
convection oven and held at 74 degrees Celsius for 1 h to
achieve full polymerization. The moulds were removed and
allowed to cool to room temperature, then a specimen number
was scribed on the side of the disc with an indelible marker.
A colour reflectance spectrophotometer with a 1 cm
aperture (CM-2002, Konica Minolta) was used to measure
the colour of each elastomer disc on standard black and white
background tiles using the CIEL*a*b* colour space. The
instrument’s repeatability was DE* < 0.01 and validity com-
pared to British Ceramic Research Association colour tiles was
0.025 < DE* < 0.219. A D65 illuminant and a viewing angle of
108 were chosen. After calibration, colour was measured first
on white (L*: 97.256, a*: 0.307, b*: 2.360) and second on black (L*:
4.53, a*: �0.86, b*: �1.17) background tiles in a darkened room.
L*a*b* coordinates and spectral curve data were recorded.
Since comparisons only between pigments and human
skin colours were desired, visible differences caused by
elastomer translucency were considered unacceptable. There-
fore, during colour measurement of a test sample, the
influence of background colour for a translucent sample
had to be removed. Translucency parameter (TP) was
calculated for each disc using the equation9,10
TP ¼ ½ðLb � LwÞ2 þ ðab � awÞ2 þ ðbb � bwÞ2�1=2;
where the subscripts b and w refer to colour coordinates mea-
sured on black and white backgrounds, respectively. Group
means and standard errors of the mean (s.e.m.) were calculated
for each elastomer formulation. Since the threshold for 50:50
colour difference perceptibility has been reported to be for
approximately DE* = 1.1,11 groups demonstrating TP greater
than 1.1 were excluded from skin comparison measurements.
Skin colour measurements used for this study were taken
from those reported previously.7 Briefly, colour measurements
were recorded from the vermilion border of the lip and the tip
of the nose for 119 human subjects (IRB #2003H0001, The Ohio
State University). The population was stratified by age (18–29,
30–39, 40–49, 50–59, 60–85), gender (female, male), and race/
ethnicity (Asian/Pacific Islander, Black, White, Other). Written
informed consent was secured and skin colour measurements
were obtained with a spectroradiometer (PR 705; Photo
Research, Inc., Chatsworth, CA) and Xenon arc lamp (300 W;
Oriel Instruments, Stratford, CO) that were set up in an optical
configuration of 08 observation and 458 illumination. Reflec-
tance measurements were obtained between 380 and 780 nm
in 2 nm bandwidth intervals, and the data converted to L*a*b*
(CIELAB) colour coordinates.
For comparison of elastomers with skin colours, mean
� s.e.m. L*, a* and b* values were determined for each
elastomer group. The colour difference (DE*) between each
elastomer group mean and each skin colour measured for
nose or lip was calculated from the following equation:
DE� ¼ ½ðDL�Þ2 þ ðDa�Þ2 þ ðDb�Þ2�1=2:
For evaluation of colour differences between elastomers
and skin, minimum, maximum and average DE* values were
commercial skin pigments as compared to human facial skin tones.
Table 2 – Translucency parameters (mean W s.e.m.) of 11pigments at three concentrations.
0.10% 1% 10%
Bisque 10.526 � 0.1265 0.09 � 0.0099 0.06 � 0.0037
Blush 17.485 � 0.3366 0.405 � 0.0278 0.085 � 0.0168
Cream 13.879 � 0.2152 0.213 � 0.0166 0.088 � 0.0085
Dark Brown 9.539 � 0.0979 0.07 � 0.0023 0.163 � 0.0072
Dusk 12.259 � 0.2561 0.048 � 0.0006 0.055 � 0.0202
Honey 11.564 � 0.2311 0.05 � 0.0032 0.038 � 0.0157
Ivory 10.110 � 0.1943 0.082 � 0.0250 0.084 � 0.0184
Mocha 7.466 � 0.1993 0.061 � 0.0074 0.083 � 0.0141
Naturelle 10.687 � 0.0294 0.23 � 0.0203 0.061 � 0.0066
Santa Fe 20.032 � 0.4108 0.944 � 0.0819 0.042 � 0.0061
Soft Brown 11.185 � 0.2359 0.063 � 0.0064 0.102 � 0.0102
j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x . e 1 – x x x . e 6 e3
JJOD-2109; No. of Pages 6
compared to those reported for the threshold of 50:50
perceptibility (DE* = 1.1) and 50:50 acceptability (DE* = 3.0).11
Coverage error was used as an index for estimating the
relative error between the pigmented elastomers and skin
colours of the human population. For each pigmented
elastomer group, mean L*a*b* values were calculated for the
three discs. DE* was calculated for colour differences occurring
between each pigmented elastomer group’s mean L*a*b* value
and the L*a*b* value for each of the 119 lip and nose
measurements. From this, the smallest DE* was determined
for each elastomer group. The average minimum DE* for the
pigmented elastomers was then calculated for lip and nose.
The coverage error (CE), was calculated by the expression12,13
CE ¼P
DEmin
n¼P
MinffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðDL�Þ2 þ ðDa�Þ2 þ ðDb�Þ2
q
n;
where n = 119, the number of lip or nose measurements. The
coverage error, therefore, was the average difference between
a lip or nose colour and the nearest pigmented elastomer
colour. Likewise, CE was calculated for the five skin shade
cluster centroids, with CE representing the average difference
between a lip or nose colour and the nearest clustered skin
shade.
3. Results
Mean translucency parameter values of the 11 pigments at 3
concentrations are reported in Table 2. All 0.1% pigment
concentration samples exhibited translucency parameters
exceeding 3.0, which demonstrated that translucency visibly
affected colour for this concentration. Therefore, the 0.1%
specimens could not be considered for comparison with
Table 3 – Colour differences and coverage error between lip d
Pigment Concentration Mean DE*
Colour difference (DE*)
Bisque 1% 27.712
Bisque 10% 27.152
Blush 1% 26.724
Blush 10% 26.075
Cream 1% 27.183
Cream 10% 26.648
Dusk 1% 14.743
Dusk 10% 15.321
Dark Brown 1% 19.701
Dark Brown 10% 18.907
Honey 1% 24.266
Honey 10% 23.523
Ivory 1% 26.743
Ivory 10% 26.924
Mocha 1% 17.473
Mocha 10% 16.828
Naturelle 1% 30.390
Naturelle 10% 30.799
Soft Brown 1% 24.021
Soft Brown 10% 23.841
Santa Fe 1% 21.674
Santa Fe 10% 20.096
Coverage error (DE*) 13.272
Please cite this article in press as: Hungerford E, et al. Coverage error of
Journal of Dentistry (2013), http://dx.doi.org/10.1016/j.jdent.2013.07.010
human skin measurements and were removed from further
analysis. The translucency parameters for the 1.0% and 10%
specimens ranged from 0.006 to 0.9 which remained below the
50:50 threshold for perceptibility (DE* = 1.1) and could thus be
investigated further.
DE* colour differences between the 1% and 10% pigmented
elastomer groups and the lip and nose data were analyzed and
the results are presented in Tables 3 and 4. In both tables, the
range of DE* colour differences are presented as the minimum,
maximum and average DE* values for each lip and nose
comparison with the elastomers. For lip comparisons (Table
3), minimum colour differences ranged 4.793 � DE* � 15.988.
The closest colour match with a single human lip measure-
ment occurred with 10% Mocha (DE* = 4.793). Maximum DE*
values ranged 31.313 � DE* � 56.755 and coverage error ranged
3.459 � DE* � 28.094.
In Table 4, DE* comparisons between pigmented elastomers
and nose measurements demonstrated minimum colour
ata and pigmented elastomer specimens.
s.e.m. Minimum Maximum
6.737 13.756 52.578
7.035 11.169 53.418
6.808 12.290 52.123
7.299 7.976 53.701
5.853 15.553 48.871
6.135 12.959 50.016
4.019 6.668 34.094
3.842 7.540 33.556
5.205 7.832 39.505
5.241 7.120 39.516
6.244 10.612 48.697
6.307 8.599 48.826
6.233 12.179 50.636
6.408 10.765 51.753
4.825 5.516 31.968
4.817 4.793 31.313
6.734 15.988 54.759
7.104 13.955 56.755
6.280 13.115 47.606
7.237 9.446 51.157
5.809 10.951 44.378
5.824 10.064 43.895
0.348 3.459 28.094
commercial skin pigments as compared to human facial skin tones.
Table 4 – Colour differences and coverage error between nose data and pigmented elastomer specimens.
Pigment Concentration Mean DE* s.e.m. Minimum Maximum
Colour difference (DE*)
Bisque 1% 21.253 7.496 8.057 42.035
Bisque 10% 20.215 7.964 6.231 41.912
Blush 1% 20.059 7.643 6.607 41.158
Blush 10% 18.721 8.351 4.737 41.148
Cream 1% 19.714 6.515 9.475 38.331
Cream 10% 18.598 7.120 7.311 38.472
Dusk 1% 9.766 4.114 1.008 19.154
Dusk 10% 10.700 4.386 0.236 19.819
Dark Brown 1% 15.216 4.618 7.434 30.180
Dark Brown 10% 14.005 4.802 6.043 29.514
Honey 1% 16.209 7.338 4.852 36.691
Honey 10% 14.850 7.645 3.101 35.905
Ivory 1% 18.461 7.327 6.886 38.722
Ivory 10% 18.262 7.667 6.361 39.138
Mocha 1% 15.925 2.924 9.959 24.087
Mocha 10% 15.275 2.959 9.190 22.906
Naturelle 1% 23.883 7.477 10.657 44.527
Naturelle 10% 23.819 7.993 9.913 45.482
Soft Brown 1% 19.678 6.444 9.090 38.565
Soft Brown 10% 18.611 7.737 5.753 40.156
Santa Fe 1% 15.369 6.182 5.972 33.821
Santa Fe 10% 12.934 6.481 4.221 32.168
Coverage error (DE*) 7.523 0.303 0.236 17.927
j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x . e 1 – x x x . e 6e4
JJOD-2109; No. of Pages 6
differences ranging 0.236 � DE* � 10.657, maximum differ-
ences ranging 19.154 � DE* � 45.482 and coverage errors
ranging 0.236 � DE* � 17.927. Pigmented elastomers with
colours closest to those measured for human noses were
10% dusk, 1% dusk and 10% honey (DE* = 0.236, 1.008 and 3.101,
respectively).
Based on results from clustering analyses, previous
research identified five colours capable of serving as a shade
guide for this same human population.7 Each colour repre-
sented the centroid of a population cluster. Table 5 presents
colour difference and coverage error results for the five shades
and each of the 119 lip and nose colour measurements. For
Table 5 – Colour differences and coverage error betweencluster centroids and lip and nose data.7
Cluster Mean DE* s.e.m. Minimum Maximum
Lip colour difference (DE*)
1 17.097 0.568 7.064 44.366
2 13.384 0.406 4.240 36.165
3 9.206 0.510 1.872 34.270
4 14.321 0.569 1.709 33.736
5 11.190 0.616 1.304 40.744
Lip coverage
error (DE*)
5.603 0.278 1.304 22.199
Nose colour difference (DE*)
1 9.239 0.663 1.520 30.344
2 8.557 0.402 1.121 21.367
3 14.334 0.377 2.478 22.618
4 17.727 0.556 5.976 28.805
5 12.184 0.480 3.901 28.570
Nose coverage
error (DE*)
4.759 0.174 1.121 10.769
Please cite this article in press as: Hungerford E, et al. Coverage error of
Journal of Dentistry (2013), http://dx.doi.org/10.1016/j.jdent.2013.07.010
both lip and nose measurements, three cluster centroids
demonstrated minimum DE* values less than 2.5. Coverage
error values ranged 1.304 � DE* � 22.199 for lip and
1.121 � DE* � 10.769 for nose.
To gain a better understanding of the spatial relationship of
colour coordinates among 22 pigmented elastomers, 119 lips
and noses, and 5 cluster centroids, colour data were plotted.
Results are presented in Fig. 1. Fig. 1(a) presents an overall
three-dimensional view of data, and Fig. 1(b)–(d) present two-
dimensional views along primary colour axes. Generally,
pigmented elastomers were clustered at higher L* values and
lower a* values compared to lip and nose measurements.
Cluster centroids, as expected, demonstrated L*a*b* values
that were representative of the subject population.
4. Discussion
Until now, there has been no research comparing the
commercially available intrinsic pigments with human skin
data. Previous research7 identified five colours that represent a
subject population based on clustering analysis and proposed
the use of these colours to form a shade guide for silicone
facial prostheses. This research provides colour comparisons
of intrinsic pigments both with human skin and the five
proposed shade guide colours.
As has been recognized during clinical construction of a
prosthesis, pigment concentration can affect the final appear-
ance of the elastomer. During construction, pigments are
mixed in variable amounts in order to achieve a custom match
with the surrounding facial tissues for each patient. Since the
effect of pigment concentration was unknown for this
pigmenting system, a 10-fold difference in concentration
was chosen as a starting point. Also, since the aim of this
commercial skin pigments as compared to human facial skin tones.
Fig. 1 – Scatter plots of colour coordinates for 22 pigmented elastomer groups, 119 human noses, 119 human lips and 5
cluster centroids proposed as shade guide colours for this population: (a) 3D L*a*b* plot, (b) 2D a* vs. b* plot, (c) 2D L* vs. a*
plot and (d) 2D L* vs. b* plot. Due to the number of data points shown, certain symbols are not visible.
j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x . e 1 – x x x . e 6 e5
JJOD-2109; No. of Pages 6
research was to evaluate the pigmenting system based solely
on colour, any visually detectable contribution by translucen-
cy had to be eliminated. By measuring the translucency
parameter at each pigment concentration for a test sample of
constant thickness, it was possible to determine that
translucency contributed to the visual appearance of 0.1%
pigmented elastomers. Consequently, these samples had to be
removed from further analysis for colour comparisons with
human skin and proposed shade guide colours.
For 1.0% and 10% pigment concentrations, the results
demonstrated that the ranges of colour difference between
pigmented elastomers and human lips were higher than those
observed for human noses. Minimum colour differences
(which represented the closest matches between elastomers
Please cite this article in press as: Hungerford E, et al. Coverage error of
Journal of Dentistry (2013), http://dx.doi.org/10.1016/j.jdent.2013.07.010
and human skin) were 4.557–5.331 DE* units lower for noses,
and maximum colour differences were 11.273–12.159 DE* units
lower. Coverage errors, the average differences between lip or
nose colours and the nearest pigmented elastomer colours,
were 4.977–6.916 DE* units lower for noses than for lips.
Collectively these results demonstrated that the pigmenting
system more closely approximated human nose colours than
the human lip colours. This implies that additional pigments
are likely needed to match lip colours more closely.
Comparison of mean coverage errors for clustered cen-
troids (which represented proposed shade guide colours) with
those for pigmented elastomers demonstrated that the
centroid values were 2.764 and 8.513 DE* units lower for nose
and lip colours, respectively. Also, results displayed in Fig. 1
commercial skin pigments as compared to human facial skin tones.
j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x . e 1 – x x x . e 6e6
JJOD-2109; No. of Pages 6
illustrate that cluster centroid positions were located closer to
human nose and lip colours than were the group of pigmented
elastomers studied here, which was expected since the
centroids were derived from observations taken from the
study population. However, Fig. 1(b) and (c) also shows that the
group of 1% and 10% pigmented elastomers represented
colours that were too low in redness (a*) or blackness (L*) to
effectively cover the study population. These results strongly
suggest that future development of more accurate intrinsic
colourants rely upon shades that represent the spectrum of
skin colours present within the human population. Future
research should focus on conducting an expanded, properly
powered clinical study capable of identifying pigment colours
that adequately span the realm of human skin colours that can
be incorporated into a usable shade guide for facial prosthesis
construction.
Although this research provided first-time information
regarding the ability of commercial pigments to cover lip and
nose colours in a study population, a number of limitations
should be noted. An obvious limitation is that the reported
results pertained only to this human population, and a larger
population is warranted for future research. A second
limitation is that the results were based on measurements
taken from only two facial locations. Future research also
should include measurements taken from other locations,
particularly forehead, cheek and ear. It is noteworthy that
different equipment was used to provide illumination and
measure colour for human skin (non-contact spectroradi-
ometer) and pigmented elastomers (spectrophotometer). This
drawback enhanced the importance of removing translucency
as a component of perceived colour. Similar future studies
should employ identical equipment for illumination and
colour measurement for skin and elastomers. It is important
to note that only one commercial pigmenting system was
evaluated here; different colour coverage parameters for
human skin may be identified for different commercial
pigmenting systems. Finally, colour measurements for pig-
mented elastomers were conducted only on freshly mixed
materials. Colour changes produced by ageing and weathering
would be expected to produce colour shifts accompanied by a
different range of coverage for human skin colour. This
phenomenon should be considered when engineering
changes into future facial prosthetic materials.
5. Conclusions
Within the limitations of this study, the following conclusions
could be drawn:
1. Elastomers containing 0.1 wt.% pigment produced trans-
parency parameters above the threshold limits for 50:50
perceptibility and acceptability, whereas elastomers
containing 1.0 and 10.0 wt.% pigment produced transpar-
ency parameters below the threshold limit for 50:50
perceptibility.
2. The commercial pigmenting system examined in this
project produced colours that were low in redness and
Please cite this article in press as: Hungerford E, et al. Coverage error of
Journal of Dentistry (2013), http://dx.doi.org/10.1016/j.jdent.2013.07.010
blackness, as compared to colours measured for lips and
noses within a human subject population.
3. Colours derived from clusters of measured skin colours
produced lower coverage errors than did colours produced
by a commercial pigmenting system.
4. A large-scale human subject study that measures colour at
several facial locations is needed for further development of
a shade guide for facial prosthetic materials.
Conflict of interest statement
The authors deny any conflict of interest and hold no
association with any of the products or manufacturers,
financial or otherwise, as stated in the manuscript.
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commercial skin pigments as compared to human facial skin tones.