Effect of bleaching on color change and refractive index of dental composite resins.

Abstract

This study investigated the effects of three bleaching agents (Whiteness Perfect, Whiteness Super, and Whiteness HP) on the color change and refractive index of three dental composites (Admira, Durafill VS, and Gradia Direct). Twenty disk-shaped specimens (10 x 2 mm) of each composite were prepared and divided into four subgroups (n=5). An unbleached group was used as a control, while the remaining specimens in the three subgroups were bleached with one of the bleaching agents respectively. Color change was assessed according to CIELAB color system and refractive indices were determined by phase modulated spectroscopic ellipsometry. Color differences between bleaching and baseline value (DeltaE) were less than 3.3 for all groups. However, bleaching with Whiteness HP led to noticeable color changes for Admira and Durafill VS. While this agent had no effect on the refractive indices of these composites, the other two agents containing carbamide peroxide increased their refractive indices. Therefore, results suggested that replacement of such composite restorations may be required after bleaching.

Full text

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Dental Materials Journal 27(1)：105－116, 2008
Effect of Bleaching on Color Change and Refractive Index of Dental Composite Resins
İhsan HUBBEZOGLU1, Barış AKAOĞLU2, Arife DOGAN3, Selda KESKİN4, Giray BOLAYIR5,
Süleyman ÖZÇELİK2 and Orhan Murat DOGAN5
1Department of Endodontics, Faculty of Dentistry, Cumhuriyet University, Sivas, Turkey
2Department of Physics, Gazi University, Ankara, Turkey
3Department of Prosthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey
4Department of Chemistry, Middle East Technical University, Ankara, Turkey
5Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, Sivas, Turkey
Corresponding author, Arife DOĞAN; E-mail: adogan@gazi.edu.tr, adogan1956@yahoo.com
Received June 16, 2007/Accepted August 28, 2007
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　
This study investigated the effects of three bleaching agents (Whiteness Perfect, Whiteness Super, and Whiteness HP) on
the color change and refractive index of three dental composites (Admira, Durafill VS, and Gradia Direct). Twenty disk-
shaped specimens (10×2 mm) of each composite were prepared and divided into four subgroups (n=5). An unbleached
group was used as a control, while the remaining specimens in the three subgroups were bleached with one of the bleach-
ing agents respectively. Color change was assessed according to CIELAB color system and refractive indices were deter-
mined by phase modulated spectroscopic ellipsometry. Color differences between bleaching and baseline value (ΔE) were
less than 3.3 for all groups. However, bleaching with Whiteness HP led to noticeable color changes for Admira and Durafill
VS. While this agent had no effect on the refractive indices of these composites, the other two agents containing carbamide
peroxide increased their refractive indices. Therefore, results suggested that replacement of such composite restorations
may be required after bleaching.
Keywords: Bleaching, Composites, Color
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　
INTRODUCTION
Bleaching is a relatively non-invasive approach to
lightening teeth stained extrinsically or intrinsically.
Bleaching techniques may be classified by whether
they involve vital or　non-vital teeth or whether the
procedure is performed in-office or has an at-home
component1-3).
　　Bleaching agents usually contain some form of
peroxide (generally carbamide and hydrogen perox-
ide) in gel or liquid form to be in contact with teeth
for several minutes to several hours, depending
on the formulation of material used3-6). It has been
reported that bleaching effect is directly related to
the exposure time and concentration of active bleach-
ing ingredient2,7). The longer the exposure time and
the higher the concentration of whitening mate-
rial, the greater will be the oxidation process and
color change. The associated side effects are namely
porosity, increased surface roughness, and reduction
in surface hardness of the existing composite resto-
rations2,8). Previous investigations reported that the
color change of resin composites was caused by many
factors such as the chemical structure, chemical acti-
vator, resin initiator and inhibitor, activator process,
polymer quality, type and quantity of filler, oxidation
of unreacted C=C bonds, UV illumination, heat, and
water9,10).
　　Color assessments of teeth and composite mate-
rials after bleaching have been made using value-
oriented shade guides, colorimeters, and digitized
photographs ― each with their own advantages and
disadvantages4,11). The use of a colorimeter gives
more objective results than shade tabs4,7,11), but it is
affected by some factors including translucency of the
material tested11).
　　Translucency is essential for dental restorative
materials. Most of the organic molecules present in
the matrix phase of dental composites and glasses
(frequently used as fillers) do not effectively absorb
visible light. As a result, scattering of light might
be considered as the main reason for low translu-
cency. Magnitude of light scattered depends on the
dimensions and surface area of the dispersed phase
(fillers), their segregation, microporosity, and surface
roughness. These properties of the microstructure
also affect the overall refractive index of the com-
posite material. It should be noted that in general,
magnitude and direction of scattering depends on
the average magnitude of refractive index fluctuation
in the composite material12). Therefore, individual
refractive indices of the dispersed phase (fillers) and
matrix phase (resin) should be perfectly matched in
order to obtain transluceny close to that of tooth tis-
sue12,13). If this were not so, the tooth would have
poor esthetical properties and reduced cure depth
with visible light14). In this respect, refractive indi-
ces are extensively used for the selection of compos-
ite materials.
　　Very often in daily dental practice, tooth-colored
restorations exist in the teeth that are planned to be
bleached1). Therefore, unintended application of the

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Effect of bleaching on color change106
bleaching products on existing restorations by the
patients cannot be excluded if bleaching is not per-
formed and monitored by the dentist15). The change
of color and loss of shade match of composite resto-
rations with surrounding tooth structure are perhaps
the most frequent reasons for replacement of existing
restorations after bleaching6).
　　Many studies have evaluated the effect of bleach-
ing agent on composite resin properties. One such
investigation used a colorimeter to show that 10％
carbamide peroxide gels somewhat lightened the
color of composite resins16). In the same vein, analy-
sis of surface reflectance showed significant changes
in microfilled and hybrid resin composites after
application of highly concentrated tooth whiteners
with 30－35％ hydrogen peroxide17).
　　Due to significant advances in adhesive den-
tistry, resin composite materials have demonstrated
ongoing improvements in strength, wear resistance,
handling properties, and esthetics3,12). Besides, the
introduction of ormocers has also brought on a range
of highly esthetic composites. Ormocer is the term
for organically modified ceramics. This class of
material is characterized by incorporation of novel
organic-inorganic copolymers in the formulation
that allow a modification of the mechanical proper-
ties over a wide range3). Although some studies7,18-20)
have compared the effect of carbamide peroxide
against hydrogen peroxide on resin composites
ranging from microcomposite to polyacrylic resins,
ormocers’ bleaching-related changes in color have
not yet been fully documented. It should be high-
lighted that drastic color changes in existing resto-
rations may compromise esthetics. Therefore, it is
also important to understand the effect of bleach-
ing agents on the color of ormocer-based restorative
materials.
　　This study was conducted to compare color
changes and also refractive indices of a microfill, a
microhybrid, and an ormocer-based resin composite
exposed to bleaching agents of different formulation
and concentrations.
MATERIALS AND METHODS
Composites
To examine the effects of three bleaching agents on
the color change of resin composites, one product
from each type of contemporary resin-based filling
material was chosen to investigate if the composition
Whiteness PerfectWhiteness Super Whiteness HP
Composition16% carbamide peroxide,
glycol, distilled water, potassium
nitrate, sodium fluoride
37% carbamide peroxide,
neutralized carbopol, potassium
ions, glycerin, deionized water
35% hydrogen peroxide,
mixture of pigments, glicol,
thickener, deionized water
Regime
daily application
(3-4 hours)
for 14 days
3 application
(20 minutes each)
with a 7 day interval
2 application
(15 minutes each)
with a 7 day interval
Table 2 Bleaching agents used
AdmiraDurafill VSGradia Direct
ManufacturerVoco,
Cuxhaven, Germany
Heraeus Kulzer,
Wehrheim, Germany
GC Corpo.,
Tokyo, Japan
Typeormocer-based resin compositemicrofill resin compositemicrohybrid resin composite
Organic Martrixanorganic-organic copolymers
(ormocers), aliphatic and aromatic
dimethacrylates
bisphenol-A dimethacrylate,
urethane dimethacrylate
urethane dimethacrylate
Filler type Ba-Al-B-silicate glass, SiO2
pyrogenic SiO2, splinter polymerFluoro-alumino silicate glass,
silica and pre-polymerized fillers
Average
particle size
0.04-1.2 μm
(mean 0.7 μm)
pyrogenic SiO2: 20-70 nm
splinter polymer: 10-20 μm
0.85 μm
Filler volume % 564064-65
Data are according to manufacturers’ infomation.
Table 1 Restorative materials used

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HUBBEZOGLU et al.107
influenced the results. For all the chosen resin com-
posites, shade A3 was used. Table 1 lists the com-
posite materials and their details. Included were
a microfill resin composite, Durafil VS; a microhy-
brid composite, Gradia Direct; and a ormoser-based
composite, Admira.
Bleaching agents
The bleaching agents used were Whiteness Perfect
(16％ carbamide peroxide), Whiteness Super (37％
carbamide peroxide), and Whiteness HP (35％ hydro-
gen peroxide) (Table 2). All the selected bleaching
agents were marketed by the same manufacturer
(FGM Produtos Odontológicos, Joinville, SC, Brasil)
for different applications and claimed not to bleach
restorative materials. Whiteness Perfect was to be
applied daily at home by the patients for 3－4 hours
per day for 14 days consecutively. As for the other
two products, they were recommended for in-office
use by dentists for non-vital and vital teeth. It was
recommended that Whiteness HP be applied for 15
minutes each for two sessions, whereas Whiteness
Super for 20 minutes each for three sessions.
Specimen preparation
Twenty disk-shaped specimens from each resin com-
posite material (60 specimens in total), 10 mm in
diameter and 2mm in depth, were prepared in Tef-
lon molds. The materials were handled according to
manufacturers’ instructions. The mold was placed
on a transparent polyester film strip (3M Flip-Frame,
3M Visual Systems Division, Austin, TX, USA) and
a glass microscope slide. The composite was packed
into the mold until it was intentionally overfilled.
The material was covered with another polyester
film strip and a glass microscope slide. Excess mate-
rial was extruded by light pressure, and resin com-
posites were polymerized using a blue light-emitting
diode (LED) unit (UltraLight PB-070, Fine Vision
Electronics Co., Sanchung City, Taipei County,
Taiwan). This source emitted light at 440－480 nm,
and had an intensity of 1000 mW/cm2. Curing time
was set at 20 seconds. Distance between the light
source and specimen was standardized by the use of
a 1-mm glass slide. The end of the light guide was
in contact with the cover glass during polymeriza-
tion. After light curing, all specimens were stored
in distilled water for 24 hours at 37℃ to ensure
complete polymerization. The top surfaces of the
specimens were then polished flat using a sequence
of 600-, 800-, and 1200-grit silicon carbide papers
and Sof-Lex (3M ESPE, USA) disks.
Bleaching procedure
Twenty specimens from each composite group were
randomly divided into four subgroups. For control,
five specimens of each composite were immersed in
distilled water. Then, five specimens in each sub-
group were bleached by one of the bleaching agents.
To simulate the bleaching process, the first subgroup
was immersed in Whiteness Perfect (16％ carbamide
peroxide gel) for three hours for 14 consecutive
days; the second subgroup immersed in Whiteness
Super (37％ carbamide peroxide gel) for 20 minutes
for three sessions; the third subgroup immersed
in Whiteness HP (35％ hydrogen peroxide gel) for
15 minutes for two sessions. Whiteness Super and
Whiteness HP were applied in intervals of seven
days. Throughout the experiment, specimens were
stored in a dark environment at room temperature
(23±1℃). During test intervals, the specimens were
rinsed with tap water for one minute to remove the
bleaching agents, blotted dry, and placed in Petri
dishes filled with distilled water for storage. For
each new session, bleaching agents were replenished
accordingly.
Color assessment
Before and after treatment with each of the bleaching
agents, the surface of each specimen was inspected
to determine whether any changes in the color of
the specimen’ s surface were visible to the naked
eye. Before baseline color measurement, specimens
were rinsed under tap water for one minute and blot-
ted dry. A colorimeter (Mercury™ 2000, Datacolor,
Lawrenceville, NJ, USA) was used to record the color
variables according to the CIELAB (Commission
Internationale de I’ Eclairage L*, a*, b*) system.
　　Aperture size diameter was 5 mm and illuminat-
ing and viewing configurations were CIE diffuse/8°.
The illumination source was provided by a pulsed
xenon lamp filtered to D65, and a white calibration
ceramic was used (CIE L* = 95.93, a* = －0.41, and
b* = 1.56). The specimens were positioned so that
their surfaces were in contact with the aperture head
of the colorimeter. Each specimen was measured
twice by the same person, and the average baseline
values of L*, a*, and b* were calculated. L* repre-
sents the degree of gray and corresponds to a value
of brightness, such that high L* values are obtained
from bright or white specimens. The value a* repre-
sents the red-green axis, and the value b* represents
the blue-yellow axis.
　　After bleaching, the same procedure was
repeated to determine the chromatical values. Mag-
nitude of total color difference (ΔE*) was calculated
using the following equation21):
　ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2]1/2
where ΔL*, Δa*, and Δb* are changes in L*, a*,
and b* after bleaching, respectively. ΔE* values >1
were considered to be visible to the naked eye, and
ΔE* ≥3.3 was considered as clinically unacceptable9).

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Effect of bleaching on color change108
Determination of refractive index
Refractive indices of specimens were determined
by phase modulated spectroscopic ellipsometry at a
70° angle of incidence (HORIBA UVISEL, Jobin
Ivon, Chilly Mazarin, France). The measurements
were performed in configuration II where the modu-
lator and analyzer angles were fixed to 0° and
45° respectively. All measurements were performed
with a spot size of 2.9 mm2. The ratio of complex
reflection coefficients of an incident light polarized
parallel (rp) and perpendicular (rs) to the plane of
incidence was expressed in terms of ellipsometric
angles Ψ and Δ as
∆
Ψ==
i
s
p
e
r
r
)tan(
ρ
. The refractive
index n of specimen was determined by assuming a
simple air/material (one interface) model and that
the material was assumed as nonabsorbing22). Within
the frame of this method, refractive index was deter-
mined using the following equation23):














Ψ+
Ψ−
+=
∆
∆
2
0
2
0
2
tan1
tan1
tan1 sin
i
i
e
e
n
φφ
where φ0 is the angle of incidence and
angles Ψ and Δ determine the changes in amplitude
and phase, respectively, of the p (parallel) and s (per-
pendicular) components of a wave upon reflection. ρ
is equivalent to the ratio of the polarization states of
reflected and incident waves.
1
−=
i
. The
Scanning microscope analysis
For the evaluation of topography and surface struc-
ture, a total of 12 specimens were examined. One
specimen from each bleaching agent and one con-
trol specimen was selected for each resin compos-
ite. After sputter-coating with 25 to 30 μm of gold
(Hummer VII, Analect, USA), the specimens were
examined at ×2000 magnification with a scanning
electron microscope (SEM) (Jeol JSM 6400, Noran
Instruments, Tokyo, Japan).
Statistical analysis
After data collection, mean values and standard devi-
ations were calculated by using a SPSS statistical
software program (version 13.0, SPSS Inc., Chicago,
USA). The data were subjected to statistical analysis
using two-way analysis of variance (ANOVA). Where
significant differences were present, Tukey’ s post hoc
test was applied to make pairwise comparison at a
significant level of 0.05.
RESULTS
Table 3 and Figs. 1a－c show the chromatical val-
ues of resin composites before and after bleaching.
For the L* values, it could be seen that Admira and
Durafill VS ― not Gradia Direct ― showed increase
in brightness with the different bleaching agents.
For the a* values, all the bleached specimens of
Admira showed small shifts when compared to the
control. By contrast, Durafill VS and Gradia Direct
resin composite specimens bleached with White-
ness Perfect (16％ carbamide peroxide) revealed a
relatively larger shift in a* value when compared
to the controls and their other own bleached speci-
mens. For the b* values, all resin composites tended
to shown an increase with the use of Whiteness HP
(35％ hydrogen peroxide). This led to a yellow shade
of the specimens that was visible to the naked eye.
　　A complete evaluation of color changes based on
ΔE* values by two-way ANOVA revealed an interac-
tion between the bleaching agents and resin compos-
ites (F=141.229). The highest score was recorded for
Admira bleached with Whiteness HP, while micro-
hybrid resin composite Gradia Direct bleached with
Whiteness Super (37％ carbamide peroxide) ranked
the lowest among the materials (Table 4, Fig. 1(d)).
　　To clarify the effect of different bleaching agents
on the same resin composite, Tukey’ s test revealed
that the color of each composite did not change sta-
tistically when bleached with Whiteness Perfect and
Whiteness Super (p>0.05). However, when com-
pared against Whiteness HP for Admira and Durafill
VS specimens, the use of the former two bleaching
agents registered statistically significant differences
(p<0.05) respectively. For Gradia Direct specimens
bleached with Whiteness Super and Whiteness HP,
the color change was found to be significant when
comparing the mean ΔE* values of the specimens
(p<0.05). Conversely, for Gradia Direct specimens
bleached with Whiteness Perfect and Whiteness HP,
no statistically significant differences were noted
(p>0.05).
　　Bleaching with 16％ and 37％ of carbamide per-
oxides led to statististically significant differences
among the resin composites (p<0.05). Color change
was found to be statistically significant for all the
resin composites except for Admira and Durafill VS.
On the other hand, the color changes of the three
resin composites tested were found to be statistically
different from each other after bleaching with 35％
hydrogen peroxide (p<0.05).
　　Figure 2 shows the refractive indices of the
composites before and after bleaching. The refrac-
tive indices of unbleached specimens of Admira and
Durafill VS resin composites were found to be higher
than those of Gradia Direct (1.425, 1.425, and 1.375
respectively). The refractive indices of Admira and
Durafill VS resin composites increased as they were
bleached with both carbamide peroxide gels, being
more so with 37％ carbamide peroxide. As for
Gradia Direct, bleaching with both carbamide per-

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HUBBEZOGLU et al.109
Resin
composite
Admira
GroupsL* a*b*
Control
WP
WS
WHP
Control
WP
WS
WHP
Control
WP
WS
WHP
72.95±0.18
73.64±0.12
73.68±0.12
74.28±0.13
75.44±0.20
75.78±0.15
76.20±0.06
76.14±0.05
74.30±0.15
74.35±0.03
74.67±0.03
74.51±0.02
0.65±0.02
0.59±0.01
0.76±0.02
0.65±0.02
0.14±0.05
0.70±0.02
0.30±0.02
0.23±0.02
0.92±0.07
1.40±0.02
1.05±0.01
1.06±0.01
3.55±0.02
3.61±0.02
3.63±0.10
4.02±0.02
3.52±0.22
3.69±0.02
3.74±0.07
4.38±0.02
4.64±0.24
4.52±0.01
4.70±0.02
5.17±0.02
Durafill VS
Gradia Direct
n=5 specimens per experimental condition
Groups depicted as WP, WS and WHP are the speciments bleached with Whiteness Perfect, Whiteness Super, and Whiteness HP, respec-
tively.
Table 3 ANOVA analysis results of the chromatical values of L*, a*, and b*
AdmiraDurafill VSGradia Direct
Bleaching Agents
Whiteness Perfect
Whiteness Super
Whiteness HP
n=5 specimens per experimental condition
By two-way ANOVA: F=141.229, p=0.000, p<0.05.
Tukey’ s test indicates statisticl difference (p<0.05) for means followed by the same letters; small letters in the column are for the compari-
son of different bleaching agents within the same material; capital letters in the rows are for the comparison of the composites bleached
with the same agent.
Mean ± SD
0.6956 ± 0.1250a,A
0.7496 ± 0.1255b,C
1.4117 ± 0.1180a,b,E,F
Mean ± SD
0.6893 ± 0.0794c,B
0.8073 ± 0.0606d,D
1.1133 ± 0.0290c,d,F,G
Mean ± SD
0.4962 ± 0.0168A,B
0.4007 ± 0.0288e,C,D
0.5874 ± 0.1400e,E,G
Table 4 Color changes (ΔΕ*) of restorative materials after bleaching
77
76
75
74
73
72
(a)
ⅣⅠⅡⅢ
L
5.5
5
4.5
4
3.5
3
(c)
ⅣⅠⅡⅢ
b
(b)
ⅣⅠⅡⅢ
a
1.5
1
0.5
(d)
ⅡⅢⅣ
ΔE
1.5
1
0.5
0
Fig. 1 Chromatical values (a) L*, (b) a*, (c) b* and (d) ΔΕ* of the specimens. I, II, III, and IV show
unbleached and bleached specimens with Whiteness Perfect, Whiteness Super, and Whiteness HP
respectively. Resin composites Admira, Durafill VS, and Gradia Direct are denoted by squares,
triangles, and circles respectively. Magnitude of standard deviation is within the marker size.