Effect of remineralizing agents on the bleaching efficacy of gels

Tooth Whitening/Bleaching
Effect of remineralizing agents on the
bleaching efficacy of gels
Alessandra Buhler Borges, DDS, PhD n Rafaela Lantyer Marques Dantas n Taciana Marco Ferraz Caneppele, DDS, PhD Alexandre Luis Souto Borges, DDS, PhD n Carlos Rocha Gomes Torres, DDS, PhD
Adding remineralizing agents to bleaching gels has been proposed to reduce the mineral loss of enamel and tooth sensitivity. This study sought
to investigate the efficacy of hydrogen peroxide (HP) gel after the addition of calcium and fluoride. Ninety enamel-dentin discs were prepared
from bovine incisors. The specimens were divided into 3 groups: a negative control group (nonbleached) and 2 experimental groups, 1 bleached
with 7.5% HP (at-home bleaching) and the other with 35% HP (in-office
bleaching). Each group was subdivided into 3 subgroups, according to
the addition of remineralizing agents on gels: no remineralizing agents,
addition of 2% calcium gluconate, and addition of 2% sodium fluoride.
For 14 days, the gels were applied 1 hour/day for at-home bleaching
H
ydrogen peroxide (HP) is the main
active agent in bleaching products.
The basic process of bleaching
involves an oxidation reaction that
converts the organic pigment to carbon
dioxide and water.1,2 This reaction produces free radicals that react with the
organic molecules responsible for tooth
pigmentation.3 Due to its low molecular
weight, HP readily penetrates the interior of enamel and dentin and is easily
biodegradable, which allows it to react
with the components of the tooth.4
Demineralization and calcium loss are
changes that can occur with bleached
enamel. Laboratory studies have observed
a loss of calcium in bleached enamel,
although this was not considered clinically significant.5-7 A decrease in concentrations of calcium and phosphorus in
enamel bleached with carbamide peroxide
has also been observed.8,9
After bleaching is complete, fluoride is
recommended to increase the wear resistance of enamel and promote the repair of
structural changes in bleached enamel. The
loss of enamel hardness could be reversed
postbleaching by using fluoride gels or calcium/fluoride gels.10,11 The use of fluoride
after bleaching has been proven effective,
due to an interaction between the sodium
fluoride (present in topical fluoride gel)
and the calcium of the tooth, which forms
calcium salts (carbonates) and phosphate.
The interaction with fluoride, calcium,
and 50 minutes/week for in-office bleaching. Between bleaching, the
specimens were immersed in artificial saliva.
The results showed significant differences in all bleached groups
compared to the nonbleached negative control group. No significant
differences were observed for any parameters tested when the different
treatments were compared using 2-way ANOVA. It was concluded that
adding remineralizing agents to the gels did not interfere with their
whitening effect and that both concentrations tested offered similar
bleaching outcomes.
Received: May 10, 2012
Accepted: September 24, 2012
and phosphate produces a layer of calcium
fluoride, which acts to inhibit demineralization and enhance remineralization.12
The possible decrease of enamel hardness
could also be overcome by adding fluoride
and calcium to the bleaching agent, increasing gel saturation, and decreasing mineral
loss and ion exchange during the bleaching
procedures.13,14 However, there is concern
that these remineralizing agents could interfere with the efficacy of bleaching gels, since
calcium and fluoride in the bleaching agent
could be related to a decrease in the permeability of HP and increase the inorganic
content of enamel, even though Chen et al
added fluoride to 10% carbamide peroxide
and reported that the results of bleaching
were unaffected.15,16 Adding fluoride to
more concentrated bleaching agents has
not been evaluated, nor has the influence of
adding calcium to bleaching gels. Due to the
short time associated with the use of highly
concentrated bleaching agents, their potential to penetrate through the tooth structure
is essential to ensure their whitening effect;
therefore, any reduction in permeability
could interfere with dental bleaching.
Given the beneficial effects associated
with adding remineralizing agents to bleaching gels, the present study added calcium
and fluoride to 7.5% and 35% HP gels
(used in at-home and in-office techniques,
respectively). The null hypothesis tested was
that adding remineralizing agents to bleaching gels would not affect the gels’ efficacy.
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Materials and methods
Freshly extracted intact bovine incisors
were stored in a 0.1% thymol solution
and refrigerated at 5°C. Using a trephine
mill (Dentoflex), 2 enamel-dentin samples
(3 mm diameter) were prepared from the
labial surface of each tooth. The labial
and pulpal sides of each specimen were
ground flat and polished with sandpaper
(1200, 2400, and 4000 grit). The samples
were trimmed to a thickness of 2 mm; the
enamel and dentin portions of the samples
were each 1 mm thick.17,18
After preparation, the specimens were
stored in a thymol solution to avoid
dehydration. Prior to treatment, the
color of each specimen was assessed at
standardized ambient conditions using a
Spectrophotometer CM-2600d (Konica
Minolta), which was set to small area
view, with a reading area of 3 mm and
a lighting area of 6 mm. The color and
spectral distributions were measured
according to the CIE L*a*b* system,
through the Spectramagic NX system
(Konica Minolta); the standard D65
illuminant with the reflectance mode and
ultraviolet light was used. The observer
angle was set to 2 degrees and the specular
component included. The samples were
carefully dried (not desiccated) and placed
on the base of the spectrophotometer.
The results of color measurement
were quantified in terms of 3 coordinate
values (L*, a*, b*), as established by the
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Tooth Whitening/Bleaching Effect of remineralizing agents on the bleaching efficacy of gels
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November/December 2013
Chart 1. Mean (±SD) ∆L parameters.
6
5
4
∆L
3
2
1
0
-1
-2
Negative
pH 7.5
pH 7.5/Ca pH 7.5/F
pH 35
pH 35/Ca pH 35/F
(control)
(control)(control)
Groups
Abbreviations: ∆L, change in the degree of light within a sample; Ca, calcium; F, fluoride.
Chart 2. Mean (±SD) ∆a parameters.
1.4
1.0
0.6
∆a
Commission International de l’Eclariage
(CIE), which locates the color of an object
in a 3-dimensional color space. The L* axis
represents the degree of lightness within a
sample and ranges from 0 (black) to 100
(white). The a* plane represents the degree
of green/red color, while the b* plane
represents the degree of blue/yellow color
within a sample. The spectrophotometer
was set to perform 3 consecutive readings,
automatically calculating the mean values
of L*, a*, and b*. The mean L* value of
each enamel-dentin specimen was used for
a stratified allocation into the groups.
The specimens were divided into 3
groups. A negative control group (n =
18) consisting of nonbleached specimens
were kept in artificial saliva during the
study period. Two experimental groups
(n = 54, each group) were bleached, one
with 7.5% HP gel (White Class, FGM
Produtos Odontologicos), and the other
with 35% HP gel (Whiteness HP Blue,
FGM Produtos Odontoligicos). Each
experimental group was subdivided into
3 subgroups (n = 18): 1 subgroup containing no remineralizing agents, 1 with 2%
calcium gluconate added, and 1 with 2%
sodium fluoride added. The experimental
bleaching agents were manipulated in an
industrial laboratory.
The specimens were positioned on
individual silicone molds (Xantopren VL
Plus, Heraeus Kulzer), so that only the
flat enamel surface was exposed to the
gel. For the at-home bleaching technique
(7.5% HP), a 2 mm layer of bleaching gel
was deposited over the enamel surface,
remaining in contact with the specimens for 1 hour at 37°C. The gel was
removed using a suction tube connected
to a vacuum pump and the specimens
were washed with a water/air spray
and immersed in artificial saliva for 23
hours. This gel application protocol was
repeated every day for 14 days; at that
point, the specimens were immersed in
artificial saliva for 24 hours and the final
color measurements were performed.
For the in-office bleaching technique
(35% HP), a 2 mm layer of bleaching gel
was deposited over the enamel surface. The
gel remained in contact with the specimens for a period of 50 minutes at 37°C.
Following the same procedure for at-home
bleaching, the gel was removed and the
specimens were washed and immersed in
0.2
-0.2
-0.6
-1.0
Negative
pH 7.5
pH 7.5/Ca pH 7.5/F
pH 35
pH 35/Ca pH 35/F
(control)
(control)(control)
Groups
Abbreviations: ∆a, degree of change in green/red color; Ca, calcium; F, fluoride.
artificial saliva for 7 days. The gel was then
applied again for 50 minutes as described
above, simulating a 2-session treatment.
The specimens were kept in artificial saliva
for 24 hours and the final color measurements were performed.
Artificial saliva (pH 7.4-7.8) was prepared using the formulation described
by Gohring et al: hydrogen carbonate
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(22.1 mmol/L), potassium (16.1 mmol/L),
sodium (14.5 mmol/L), hydrogen phosphate (2.6 mmol/L), boric acid (0.8
mmol/L), calcium (0.7 mmol/L), thiocyanate (0.2 mmol/L), and magnesium
(0.2 mmol/L).19 Differences in L* (DL), a*
(Da), and b* (Db) values, and the general
change of color (DE) was calculated automatically using Spectramagic NX.
Chart 3. Mean (±SD) ∆b parameters.
3
1
∆b
-1
-3
-5
-7
-9
Negative
pH 7.5
pH 7.5/Ca pH 7.5/F
pH 35
pH 35/Ca pH 35/F
(control)
(control)(control)
Groups
Abbreviations: ∆b, degree of change in blue/yellow colors; Ca, calcium; F, fluoride.
Chart 4. Mean (±SD) ∆E parameters.
10
8
∆E
6
4
2
0
Negative
pH 7.5
pH 7.5/Ca pH 7.5/F
pH 35
pH 35/Ca pH 35/F
(control)
(control)(control)
Groups
Abbreviations: ∆E, general change of color; Ca, calcium; F, fluoride.
For the statistical analysis, 2-way
ANOVA was used to compare the factors of
HP concentration (7.5% and 35%), remineralizing agents (calcium and fluoride), and
their interaction. Dunnett’s test was applied
to compare the negative control group with
the experimental test groups. The significance level was determined to be 5%.
Results
Charts 1-4 present the means and standard
deviations for the tested groups. The
application of 2-way ANOVA revealed no
significant differences for any of the
tested groups (Table 1). Dunnett’s test
revealed significant differences for all groups
compared to the nonbleached samples when
all parameters were evaluated (Table 2).
Discussion
The null hypothesis—that the addition of
remineralizing agents to the bleaching gels
has no influence on their efficacy—was
accepted because there were no significant
differences among the experimental groups.
Studies have investigated combining
remineralizing agents with bleaching
gels to reduce the possible adverse effects
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on dental tissues related to the bleaching
procedures. According to the literature,
adding remineralizing agents during or
after bleaching procedures reduces the
demineralization caused by bleaching
agents on enamel and/or aids in the remineralization process.11,14,20-22
Studies have previously confirmed that
adding fluoridated agents to bleaching gels
has a positive effect in terms of preventing
mineral loss on bleached enamel and that
calcium serves as a remineralizing agent
when added to bleaching gel.14,16,21,22 It is
believed that the addition of remineralizing
agents leads to saturation of the bleaching
gels with these ions, which become incorporated into the enamel, increasing the
enamel resistance to demineralization.22
In addition to reducing the deleterious
effects on the enamel mineral content,
adding remineralizing agents to bleaching
gels may reduce enamel solubility and
decrease sensitivity due to mineral deposition in the enamel crystals.23 In the present
study, the effectiveness of the at-home and
in-office bleaching agents was not affected
by the addition of fluoride or calcium.
External dental bleaching increases
enamel porosity and permeability.24,25
Conversely, fluoride’s role in caries
prevention has been attributed to its
reducing the permeability of enamel.26 As
described earlier, the availability of high
levels of calcium as a soluble salt leads to
precipitation of calcium-phosphate on the
enamel surface.27
It has been reported that adding bleaching agents such as carbamide peroxide to
a whitening gel may reduce the uptake
of fluoride by bleached enamel.28 There
may be an interaction between the free
radicals derived from the decomposition
of HP and the fluoride added to the gel
that reduces the enamel incorporation of
fluoride.28 Additional research is necessary to determine if this interaction also
occurs with calcium.
The literature has described different
methods of measuring color changes,
including using a shade guide and a colorimeter.16,23 In the present study, a spectrophotometer with an integrated sphere
assembly was used with the CIE L*a*b*
color model. Colorimeters and spectrophotometers allow for objective measurement. Previous studies have determined
that human evaluation of tooth color was
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Tooth Whitening/Bleaching Effect of remineralizing agents on the bleaching efficacy of gels
Table 1. Results of 2-way ANOVA for all parameters evaluated.
Degree of
freedom (Df)
Mean
square
Df error
F value
P value
No remineralizing agent
1
0.41
102
0.16
0.68
Parameter
Factors
∆L
∆a
∆b
∆E
2% calcium gluconate
2
2.73
102
1.10
0.33
2% sodium fluoride
2
2.50
102
1.01
0.36
No remineralizing agent
1
0.44
102
0.40
0.52
2% calcium gluconate
2
0.08
102
0.79
0.45
2% sodium fluoride
2
0.14
102
0.13
0.87
No remineralizing agent
1
5.04
102
1.72
0.19
2% calcium gluconate
2
6.17
102
2.11
0.12
2% sodium fluoride
2
4.47
102
1.53
0.22
No remineralizing agent
1
2.55
102
0.79
0.35
2% calcium gluconate
2
1.40
102
0.43
0.64
2% sodium fluoride
2
3.45
102
1.07
0.34
Abbreviations: ∆L, difference in the degree of lightness within a sample; ∆a, degree of change in green/red color;
∆b, degree of change in blue/yellow color; ∆E, general change of color.
Conclusion
Table 2. Results of Dunnett’s test for comparison of negative control group with
experimental groups.
According to the limitations of the present
study, it can be concluded that the remineralizing agents calcium and fluoride can
be added to gels containing 7.5% HP or
35% HP without impairing their bleaching efficacy. Both bleaching methods
presented similar whitening effects.
Groups
pH
ΔL
Δa
Δb
ΔE
Author information
No remineralizing agent
7.5
0.001528
0.000003
0.000003
0.000003
2% calcium gluconate
7.5
0.001836
0.000003
0.000003
0.000003
2% sodium fluoride
7.5
0.002907
0.000003
0.000003
0.000003
No remineralizing agent
35
0.026418
0.000003
0.000003
0.000003
2% calcium gluconate
35
0.000063
0.000003
0.000003
0.000003
2% sodium fluoride
35
0.024784
0.000003
0.000003
0.000003
Significant difference for all groups, 5%.
not reliable and that a spectrophotometer
could prove to be a more predictable and
refined method for evaluating the in
vitro color of a tooth.29,30
The ΔL, Δa, Δb, and ΔE (representing
the difference between readings before
and after bleaching) were calculated.31
There has been debate concerning which
methods of color evaluation best indicate
the effectiveness of bleaching. Previous
studies observed that the greatest
changes after bleaching occur in the
values of the coordinates L* and b*, and
that b* is the most relevant for evaluating
bleaching treatment.32-34 However, ∆E did
70
evaluated concentrations of HP were
compared, indicating that both bleaching
techniques produced similar whitening
outcomes after 14 days of treatment. In
fact, the results from low-concentration
bleaching agents used for a long time
are compatible with high-concentration
gels used for shorter time periods.35,36 A
2010 study by da Costa et al compared
at-home (10% calcium phosphate) and
in-office bleaching (35% HP) techniques
and observed that the results from 5 days
of home bleaching corresponded to 1
in-office bleaching session.37 Auschill et
al reported bleached teeth could be whitened by 6 shades from 1 in-office whitening treatment (utilizing 38% HP) or after
7 days of at-home whitening utilizing
10% calcium phosphate.38
November/December 2013
not express the total change in color, and
it was more appropriate to evaluate ∆E
in association with L*.32-34 An increase in
L* after bleaching indicates that the teeth
tended toward white, while a reduction in
b*, indicates that the teeth tended to be
less yellow. In the present study, all experimental samples demonstrated an increase
in ΔL and a reduction in Δb.
The significant difference between the
experimental groups when compared with
the negative control group confirmed the
bleaching efficacy among the samples
in the tested groups. Similar bleaching results were obtained when the 2
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Drs. A.B. Borges, Caneppele, and Torres
are assistant professors, Department
of Restorative Dentistry, Sao Jose dos
Campos Dental School, Sao Paulo State
University, Brazil, where Dantas is an
undergraduate student, and Dr. A.L.
Borges is an assistant professor.
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Manufacturers
Dentoflex, Sao Paulo, Brazil
55.11.2065.2155, www.dentoflex.com.br
FGM Produtos Odontologicos, Joinville, Brazil
55.47.3441.6100, www.fgm.ind.br
Heraeus Kulzer, South Bend, IN
800.485.1735, www.heraeus-dental-us.com
Konica Minolta, Ramsey, NJ
888.473.2656, www.konicaminolta.us
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