Received: 4 December 2017

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Revised: 28 February 2018

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Accepted: 1 March 2018

DOI: 10.1002/col.22224

RESEARCH ARTICLE

Color stability of denture shade tabs is affected by exposure
to daylight and decontamination protocols
Eduardo Jos
e Soares | Rafaella Tonani | Marta Maria Martins Giamatei Contente |
Carolina Noronha Ferraz Arruda | Fernanda de Carvalho Panzeri Pires-de-Souza
Department of Dental Materials and
Prosthodontics, Ribeir~ao Preto School of
Dentistry, University of S~ao Paulo,
Avenida do Caf
e, s/n, 14040-904,
Ribeir~ao Preto, SP, Brazil
Correspondence
Fernanda de Carvalho Panzeri Pires-deSouza, Department of Dental Materials
and Prosthodontics, Ribeir~ao Preto
School of Dentistry, University of S~ao
Paulo, Avenida do Caf
e, s/n, 14040-904,
Ribeir~ao Preto, SP, Brazil.
Email: ferpanzeri@usp.br
Funding information
FAPESP (Sao Paulo Research
Foundation—Brazil), Grant/Award
Number: 2015/00848-5

Abstract
The purpose of this study was to investigate the effect of light exposure and decontamination protocols on the color stability of denture shade guide tabs. Fifty tabs for
shades 62, 66, and 69 (Biotone IPN, Dentsply Sirona) were submitted to baseline
L*a*b* measurements (EasyShade, Vita), separated into 5 experimental groups
(n 5 10), and subjected to one of the following conditions: G1–distilled water (DWH2O)–control; G2 270% alcohol; G3–sodium hypochlorite 1% (NaClO); G4–no light
exposure; G5–natural light exposure for 6 months. The experimental conditions were
designed to simulate 6 months of clinical use. After the test period, final color measurements were recorded. The mean tristimulus coordinate difference (DL*,Da*,Db*)


) were analyzed using 2-way ANOVA and the
and total color difference values (DEab
Tukey test, a 5 .05. G2 (alcohol) produced less (P < .05) color change in shade 69
than G3 (NaClO). G5 (light exposure) affected the color stability for all shades, producing a statistical difference (P < .05) from G4 (no light exposure). It was
concluded that natural light changes the color stability of the shade guides and that
decontamination with 70% alcohol had the least impact on the color stability of the
shade guide tabs.
KEYWORDS
color, decontamination protocols, denture teeth, natural light, shade guide

1 | INTRODUCTION
New materials and restorative protocols were developed and
incorporated to dentistry, thereby promoting higher quality
and longevity for patients’ oral health treatments.
Life expectancy has increased, and a greater number of
elderly people require complete or partial dentures. Additionally, tooth loss is a significant public health problem in many
countries. Dentistry has progressed in designing improved
artificial replacements for natural dentition.
The perfect smile is valued greatly because of media
exposure,1 and patients are more critical of the quality of
esthetic restorations, especially their color.2–4 Any perceptible color alteration when compared with natural teeth is significant for patient acceptance.5
Color Res Appl. 2018;1–6.

Accurately selected denture tooth shades are important to
satisfy increasing demands for esthetic dental prostheses.
The color matching used to decide these shades is a complicated process4 because of the subjectivity of color perception6,7; the psychosocial and psychological factors of the
person making the selection8,9; and environmental factors
such as lighting conditions.10
The most common color matching method is a comparison of shade tabs from commercial shade guides11,12 with
the patient’s remaining teeth. A recent report of the National
Dental Practice-Based Research Network13 demonstrated
that 98% of 365 dentists indicated that they frequently use
commercial shade tabs for their patients’ shade selection.
However, even when shade guides are made from the same
material as those used in restorations, they do not necessarily

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replicate the same color.14–16 In addition, some materials
change color after exposure to light.17
Shade guides can be fabricated from ceramics, but denture tooth shade tabs are usually based on polymethyl methacrylate or other polymeric materials. The shade guide tabs
are considered noninvasive instruments because there is no
direct contact with oral tissues during handling.18 However,
they may become contaminated with saliva, and appropriate
decontamination procedures are recommended after each use
by the Occupational Safety and Health Administration
(OSHA).19 Biosafety practice is essential to prevent crossinfection.
Decontamination protocols have been reported to cause
color changes in shade guides in studies using visual20 or
instrumental methods.4,19,21 In one study, a 17.8% change in
color of guides was found after 2 years and 28.9% after 3
years. Changes of this magnitude are considered perceptible,21 although consensus on the most appropriate acceptability/perceptibility color changes for aesthetic restorations22–24
has not yet been reached.
Exposure to light can change the color of shade guides
and denture teeth over time.25 Shade guides are frequently
stored in readily accessible location and often exposed to natural light containing ultraviolet (UV) wavelengths that can
cause color alterations, especially if the shade guides are
polymeric.26–28 However, there are few studies exploring
this issue.
Therefore, the purpose of this study was to evaluate the
color stability of shade guides subjected to decontamination
protocols and exposed to natural light, with the null hypothesis that no color alteration would be found in the shade guide
tabs after the treatments.

2 | MATERIALS AND METHODS
Fifty anterior denture shade tabs (Biotone IPN®, Dentsply
Sirona, Petr

opolis, RJ, Brasil) with 3 sets of colors tabs (62,
66, and 69) were selected for the study. To ensure that the
color measurements would be in the same central region of
the tooth and that the repeatability of the handheld measuring
tip of the spectrophotometer (Easy Shade, VITA Zahnfabrik,
Bad Sckingen, Germany), a 2-piece template (6 mm in diameter) for precise placement was fabricated (Figure 1) from
colorless autopolymerized acrylic resin (VIPI Flash, VIPI
Produtos Odontol
ogicos, Pirassununga, SP, Brazil).
An initial color reading was made of all of the shade
guides. The simulated observation standard follows the CIE
L*a*b* system, which consists of 2 axes, a* (1 red; 2
green) and b* (1 yellow; 2 blue), at right angles to one
another representing the saturation level and color dimension. The third axis is lightness, L*, perpendicular to plane
a*b*, and represents the luminosity of the color from white

SOARES

FIGURE 1

ET AL.

Spectrophotometer positioned on the acrylic jig and

shade tab

(100) to black (0). Three color measurements were made for
each shade tab, against a white background, and the mean
values were considered the initial baseline values for all the
coordinates of the CIE L*a*b* system.
The shade guide tabs were divided into 5 experimental
groups (n 5 10) considering 3 decontamination protocols and
2 different degrees of light exposure, as described in Table 1.
For decontamination (groups 1, 2, and 3), 6 mL of each
solution was sprayed onto the facial surface of each shade
guide tab and left for 3 min before drying by rubbing with 3
3 3 mm gauze. After each decontamination protocol, the
specimens were washed with distilled water and dried. This
procedure was performed 5 days a week for 24 weeks, corresponding to 6 months of clinical use of shade guides.4,21 The
specimens were stored in a dry and dark environment
between solution treatments.
TA B L E 1

Five experimental treatment groups

Groups
(n 5 10,
3 shades)

Experimental
conditions

Experimental
Treatment

G1

Solution exposure

Distilled water (DW-H2O)

G2

Alcohol 70%

G3

Sodium hypochlorite 1%
(NaClO 1%)

G4

Enclosed black
box, dry

No light exposure

G5

Light exposure

Natural daylight

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The shade guide tabs in Group 4 (negative control) were
stored in black boxes and kept totally protected from light
exposure or external influence. The shade guide tabs in Group
5 were fixed in a white box with the facial surfaces facing
upwards. The box, containing all of the tabs, was fixed in clear
glass and exposed to natural light during the day. Both groups
were maintained in these conditions for 6 months.
After the experimental treatments, the color of the shade
guide tabs was re-recorded, as previously described for the


) was
baseline measurements, and the color difference (DEab
calculated using the formula:
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi


DEab
5 ðDL
 Þ2 1 ðDa
 Þ2 1 ðDb
 Þ2
where
DL
 5 L
 F – L
 I
Da
 5 a
 F – a
 I
Db
 5 b
 F – b
 I
and where L*F, a*F, and b*F are the final readouts and L*I,
a*I, and b*I are color baseline measurements. The values
were analyzed by 2-way ANOVA and the Tukey post hoc
test (a 5 .05).

3 | RESULTS


The mean DEab
values were compared separately between
solutions (Figure 2) and light environments (Figure 3).



F I G U R E 3 Mean DEab
values for denture shade tabs after 6 months


5 2) for
exposure to light or no light. The red line indicates the level (DEab
which color differences are visually detectable 100% of the time by dental
professionals29



treatment, which exhibited the highest DEab
, values above


the acceptability threshold of color change (DEab
5 2).29 No
statistical difference (P > .05) was found between the other
studied shade tabs, regardless of the decontamination protocol used.
The mean values for DL*, Da*, and Db* can be seen in


) of the specimens between
Table 2. The color change (DEab
baseline and 6 months resulted from alterations in coordinate
b*, the only parameter that presents variations with similar


(Figure 2).
effects on DEab
The control solution (DW-H2O) presented greater DL
and Db* changes considering all 3 shade tabs.

Mean DL*, Da*, and Db* values after decontamination
protocols over 6 months (2-way ANOVA, Tukey, P < .05) note the
standard deviation 6 in all cases

TA B L E 2

3.1 | Comparison between solutions
The lowest color change was demonstrated for shade 69 after
decontamination with alcohol, a result that was statistically
different (P < .05) from that of sodium hypochlorite

Shade

DI H2O

Sodium
hypochlorite

Alcohol

62

0.8 (60.71)

0.9 (60.44)

0.9 (60.51)

66

0.8 (61.11)

1.0 (60.58)

1.2 (60.29)

69

0.9 (60.96)

0.8 (60.38)

1.0 (60.29)

62

0.4 (60.24)

0.0 (60.18)

0.0 (60.22)

66

0.0 (60.31)

0.3 (60.26)

0.1 (60.64)

69

0.0 (60.22)

0.1 (60.22)

0.0 (60.13)

62

0.8 (60.96)

0.5 (60.69)

0.8 (60.50)

66

1.0 (61.50)

0.7 (60.72)

0.5 (60.62)

69

1.0 (61.22)

0.8 (63.05)

0.4 (60.38)

DL*

Da*

Db*


Mean DEab
values and the standard deviations for 3 denture shades subjected to 1 of 3 decontaminant protocols over 6 months.
Columns with different symbols indicate statistically significant differen

5 2) for which color difces (P < .05). The red line shows the level (DEab
ferences are visually detectable 100% of the time by dental professionals29

3

FIGURE 2

For all comparisons, P > .05.

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Mean DL*, Da*, and Db* values for shade tabs with
light exposure or no light exposure (2-way ANOVA, Tukey, P < .05)

T A BL E 3

Shade

No light

Light
exposure

62

0.8 (60.40)a

0.1 (60.51)b

66

0.9 (60.30)a

0.3 (60.82)b

69

0.9 (60.37)a

0.4 (60.36)a

62

20.2 (60.12)b

0.8 (60.41)a

66

20.1 (60.11)b

0.8 (60.23)a

69

20.1 (60.16)b

0.8 (60.39)a

62

0.2 (60.37)b

1.6 (60.76)a

66

0.4 (60.48)b

1.8 (60.62)a

69

0.5 (60.69)b

1.6 (60.89)a

DL*

Da*

Db*

Different letters in the row, for each tristimulus parameter, indicate a statistically significant difference (P < .05). For all comparisons in columns, P > .05.

3.2 | Comparison between light conditions
The mean color change values for the shade guide tabs
exposed to natural light or kept in the dark are presented in


) occurred when
Figure 3. The smallest color change (DEab
the shade guides were protected from natural light, with statistically different results (P < .05) from shade guide tabs
exposed to light. With light-exposure, shade 66 demonstrated
more color change than shades 62 or 69, it was above the


5 2) estabacceptability threshold of color change (DEab
29
lished by Seghi et al.
The mean color parameters (DL*, Da*, and Db*) for G4
and G5 groups are presented in Table 3. For all parameters, a
significant difference (P < .05) was found when the storage
environments (light/dark) were analyzed; however; no significant difference (P > .05) was when shade tabs were compared.
The greatest change in DL* occurred when the shade
tabs were stored in the absence of light. However, for the
other 2 color coordinates (Da* and Db*), the highest color
differences were found when the shade guides were exposed
to natural light. For the specimens stored in the dark, negative Da* values were recorded and positive Da* values for
those exposed to natural light.

4 | DISCUSSION
The aim of this study was to evaluate the effect of light exposure and 3 decontamination protocols on the color stability

ET AL.

of denture shade guide tabs. After analysis of the results, the
null hypothesis was rejected, as significant color changes
were found when the decontamination protocols were compared, and, noticeable and statistically significant changes
were observed depending on whether the shade guides were
stored in the presence of natural light or kept in the dark.
Shade guides are generally made of plastic, and their
decontamination can cause color alterations.4 Thus, the color
stability of shade guides should be checked regularly.21
When sprayed, solutions can interfere with the optical and
mechanical properties of the shade guide materials.24,25
The results of this study demonstrated that the alcohol


) when comsolution led to the lowest color change (DEab
pared with other solutions, different (P < .05) from sodium
hypochlorite for shade 69. These findings contrast with those
found by Alshethri,19 who reported a greater color change in
denture teeth treated with 70% alcohol. Decontamination
protocols that contain organic solvents, such as alcohol, can
degrade plastics and resins.19,27
Most dental offices use various shade guides at least
twice a day, 5 days a week, 48 weeks a year.4 Thus, the 240
decontaminations correspond to 6 months of shade guide
cleaning. The 62 and 66 shades were tested because they are
2 of the most commonly selected for dentures. Shade 69 was
also chosen because it is a darker shade and might behave
differently from the lighter colors.
Although the decontamination protocols caused color
changes in the shade tabs, no color differences were found
among the shades when decontaminated with the same solution. The color changes, however, did not surpass the maxi

5 2). However,
mum threshold for clinical acceptance (DEab
some shades did exceed the visually detectable level of


5 1 reported by Seghi et al.29 A standard for patient
DEab
shade selection should adhere to the highest standard for the
most accurate results. Although recent studies have been
concerned with the acceptability/perceptibility of color
changes in aesthetic restorations,22–24 the color difference
found by the observers in Seghi et al.’s29 study were correctly judged by the observer group 100% of the time, while
the others only 50% of the time.
The color changes observed may have occurred because
of the chemical effects of the decontamination liquids or the
cleaning action during the decontamination protocols.
Repeated application and cleaning with disinfectant spray
may abrade the surface of the plastic, resulting in color
change. In addition, disinfectant components could remain
on the surface of the tabs after multiple decontamination protocols, which could cause color changes.19 If this were the
cause, lower DL* values and an increase in chromaticity
would be expected,4 as observed in the control group (Table
2). Thus, this phenomenon can explain the color change of
specimens after cleaning with distilled water. As alcohol is

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volatile, the repeated use of this agent would have less effect
on the material, resulting in lower color differences.
The authors are unaware of recommendations or literature
references for shade guide storage. This study evaluated ideal
shade guide storage by measuring the effect of 6 months of
natural light exposure on their color stability. The results demonstrated that the denture shade tabs stored in natural light


) than those stored
would undergo greater color change (DEab
in the dark. No significant difference was found in the color
stability of different shades under the same storage conditions.
Polymers are susceptible to photodegradation,26 a process called photolysis. The chemical bond is broken down
by a photochemical reaction caused by the absorption of
light energy corresponding to an electronic transition or an
energy transfer from a sensitizer in its excited state.26 In this
kind of degradation, only absorbed light can cause the photochemical effect.27 Thus, energy provided to the system, but
not absorbed as electronic excitation would have no effect.
In polymers, the most common chemical groups responsible for light absorption in the solar spectrum region are
conjugated C5C double bonds, C5O bonds, and aromatic
rings. The first 2 are present in the composition of methyl
(methyl methacrylate),28 the shade guide base. Carbonyl
groups (C5O), even at low concentration, can initiate selfcatalytic reactive processes. The absorption of light by the
molecules leads to the formation of free radicals, which bind
to oxygen and initiate oxidative chain reactions, causing
breaks in the main carbon chain, followed by the breaking of
C–H bonds and the formation of C5C double bonds.27
Thus, there is a marked change in their chemical and physical properties.27
The exposure of polymers to the UV radiation present in
solar radiation causes photo oxidative degradation of the
material, which results in the breaking of polymer chains,
radical production, and molecular weight reduction. These
processes discolor the dyes and pigments in the materials
and cause yellowing and loss of gloss on plastics.27
The color changes in the specimens of this study were a
result of chromaticity changes in the different shade guides.
As seen in Table 2, natural light did not alter the lightness
(DL*) of the specimens in a significant manner. However, a
substantial increase in Da* and Db* was noted when the
specimens were exposed to natural light, indicating reddening and yellowing. Guides stored in the dark demonstrated
little change in these coordinates, demonstrating that light is
the cause of changes in the chromaticity of the shade guides.
Another reason for these changes could be an increased
opacity caused by the formation of microcracks at the polymer surface, resulting in light scattering due to approaching
the polymeric chains.26
Clinicians must store shade guides correctly to prevent
changes in their color over time and to maintain standards of
accurate color selection for restorative materials.

5

5 | CONCLUSIONS
The storage of shade guides under natural light increased the
chromaticity of the shade tabs. Regarding decontamination,
alcohol caused the lowest color change in a dark shade tab
compared with sodium hypochlorite.
AC K NO WLE DG M E NTS
Authors thank Allyson Barrett for the limit of perception
or acceptance threshold suggestions. This study was supported by grant No. 2015/00848-5 from FAPESP (Sao
Paulo Research Foundation—Brazil).
CO N FLI CT OF I N TER EST
No conflict of interest.
O RC ID
Fernanda de Carvalho Panzeri Pires-de-Souza
orcid.org/0000-0002-1455-1538

http://

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AU TH O R BI O GR A PH IE S
EDUARDO J. SOARES is a graduated student in the Department
of Dental Materials and Prosthodontics, Ribeir~ao Preto
School of Dentistry, University of S~ao Paulo, Ribeir~ao Preto,
SP, Brazil.
RAFAELLA TONANI is a laboratory technician in the same
department.
MARTA M. M. G. CONTENTE is a researcher in the same
department.
CAROLINA N. F. ARRUDA doctoral student in the same
department.
FERNANDA CARVALHO PANZERI PIRES‐DE‐SOUZA is an associate professor, Department of Dental Materials and Prosthodontics, Ribeir~ao Preto School of Dentistry, University of S~ao
Paulo, Ribeir~ao Preto, SP, Brazil.

How to cite this article: Soares EJ, Tonani R, Contente MMMG, Arruda CNF, Pires-de-Souza FCP.
Color stability of denture shade tabs is affected by
exposure to daylight and decontamination protocols.
Color Res Appl. 2018;00:1–6. https://doi.org/10.1002/
col.22224