Keywords
dental bleaching - dental materials - glass ionomer - composite resins - toothpastes
- blue covarine
Introduction
Tooth color is an important parameter that plays a role in facial beauty. Some recent
studies have shown that 17% to 53% of people from different populations are not satisfied
with their tooth color.[1]
[2]
[3]
The available techniques to improve the appearance of discolored teeth include tooth
bleaching, placement of crowns and veneers, professional cleaning by scaling and polishing
to remove stains and tartar, and use of whitening toothpastes. The aforementioned
techniques improve tooth color and dental esthetics via different mechanisms.[4]
[5]
[6]
[7] The tooth bleaching techniques include in-office bleaching and at-home bleaching
with the use of over-the-counter products that possess oxidizing properties. In the
process of tooth bleaching, oxidizing agents penetrate into the enamel and dentin
structure and become involved in chemical reactions. The goal of all bleaching agents,
irrespective of their specific mechanism of action, is to deliver active components
into the discolored parts of the tooth structure to eliminate the stains or bleach
them.[8]
Whitening toothpastes have been designed for daily use to physically and chemically
clean the tooth structure by removing stains or preventing their deposition.[9]
[10] Toothpastes have several components to remove the stains or prevent their accumulation
including abrasives,[11] surfactants, calcium chelators, enzymes, and polymers. Recent studies have shown
that abrasives are the primary cleaning agent in the composition of toothpastes.[7]
[11]
The literature is rich regarding the whitening toothpastes and evidence confirms their
safety and different grades of efficacy. For instance, perlite was added to silica
and calcium carbonate toothpastes as a cleanser and polisher and enhanced the stain
removal efficacy of these toothpastes compared with nonwhitening toothpastes. Also,
it did not cause unnecessary abrasion of enamel and dentin.[9]
[12]
Knowledge about the color science in dentistry and the relevant tools has led to advances
in technology for dental bleaching and tooth whitening.[7]
The Commission Internationale de l’Eciairage (CIE) introduced the three–dimensional
(3D) color space in 1975 to enhance color perception. This system uses the three axes
of L*, a*, and b*. The L* parameter indicates lightness while the a* and b* parameters
indicate the redness-greenness and yellowness-blueness, respectively.[13]
Studies on tooth bleaching with peroxide products have demonstrated that changes in
yellowness-blueness axis of tooth color are important and should be taken into account
to assess the degree of tooth whitening. For instance, Gerlach et al[14] evaluated the whitening response of two teeth to bleaching with products containing
hydrogen peroxide after 2 weeks. They measured the tooth color before and after the
treatment and filled out a questionnaire after the intervention. Data were compared
with a model and they concluded that individual whitening responses to bleaching and
patient satisfaction were significantly correlated with the changes in b* value and
not the L* value or a* value. Thus, changes in yellowness-blueness axis are important
to assess the efficacy of vital tooth whitening products.[15] Moreover, Kleber et al[16] in an in vitro study used 1% hydrogen peroxide and showed that reduction in b* value
was greater and occurred faster than the changes in L* value. Evidence shows that
the b* value is a more important parameter in tooth whitening. Goodson et al, in their
clinical study on tooth whitening, stated that the bleaching agents significantly
decreased the b* value (yellowness) while they caused an increase in L* value.[1]
[17]
Researchers believe that application of blue-colored substances on the tooth surface
causes the desired changes in terms of optical properties of the teeth and particularly
causes a color shift from yellow to blue. Thus, a spectrum of blue colors and pigments
are commonly tested in laboratories for use in oral hygiene products to assess their
effect on the b* value and its alterations.
Blue covarine is the most effective substance used for significant reduction of b*
value. Chemically-analyzed samples have shown that blue covarine deposits on the enamel
surface. Further in vitro studies on extracted teeth have shown that treatment with
blue covarine causes a significant reduction in b* value compared with the control
group.
Changes in CIE Laboratory color parameters can be used to assess the efficacy of tooth
whitening. A previous study showed that blue covarine significantly enhanced tooth
whitening compared with the control group. Optical measurements after treatment with
blue covarine demonstrated that teeth treated with blue covarine were whiter compared
with their baseline state. Thus, blue covarine causes optical changes in color parameters,
conferring a whiter appearance to the teeth.
Tooth whitening agents are available in different forms in the market. Blue covarine
has been added to silica-based toothpastes in different concentrations in a laboratory.[1] A previous study used extracted human teeth and brushed them with blue covarine
dissolved in water and measured the color parameters. They indicated that high concentrations
of blue covarine significantly decreased the yellowness and increased the whiteness
of teeth.[1]
[7]
In 2008, Joiner et al evaluated the cleaning efficacy of a silica-based whitening
toothpaste containing blue covarine and the associated abrasion of enamel and dentin.
They concluded that the toothpaste was effective for stain removal and did not cause
unnecessary abrasion of enamel and dentin compared with similar products.[18]
Covarine is a pigment used in hygienic and cosmetic products. Blue covarine (CI 74160;
pigment blue 15, phthalocyanine blue) is incorporated in the composition of optical
whitening toothpastes such as Signal, Colgate and Close Up.
On the other hand, to the best of authors’ knowledge, there is a gap of information
regarding the effect of long-term use of these toothpastes on color of teeth and restorative
materials. Considering the high demand for tooth bleaching, high cost of this treatment
and the need for retreatment after 1 to 3 years, it seems imperative to assess the
efficacy of alternative treatments such as the use of whitening toothpastes. These
toothpastes are low cost and easy to use, and preserve the tooth color for a longer
period of time after the bleaching treatment. Thus, this study aimed to assess the
effect of a toothpaste containing blue covarine on color stability of microfilled,
nanofilled, and microhybrid composite resins and resin-modified glass ionomer (RMGI)
cement at 0, 1, 7, 30, and 90 days after use. The null hypotheses were (1) type of
toothpaste would have no significant effect on color of restorative materials at 0,
1, 7, 30, and 90 days after use and (2) type of restorative material would have no
significant effect on color change at 0, 1, 7, 30, and 90 days after use.
Materials and Methods
Microhybrid, microfilled, and nanofilled composite resins and RMGI cement were used
in this in vitro, experimental study ([Table 1]).
Table 1
Characteristics of the materials used in this study
|
Material
|
Type
|
Content
|
Manufacturer
|
|
Filtek Z250
|
Microhybride metacrylate-based composite
|
BisGMA (bisphenol A diglycidyl ether dimethacrylate) and a low-viscosity resin called
TEGDMA, UDMA (urethane dimethacrylate), and bis-EMA (bisphenol A polyethylene glycol
diether dimethacrylate)
|
3M ESPE, St. Paulm, MN, United States
|
|
Filtek Z350 XT Enamel
|
Nanofilled metacrylate–based composite
|
Bis-GMA, UDMA,
TEGDMA, and bis-EMA(6)
The fillers are a combination of nonagglomerated/nonaggregated 20 nm silica filler,
nonagglomerated/nonaggregated 4–11 nm zirconia filler, and aggregated zirconia/silica
cluster filler (comprised of 20 nm silica and 4–11 nm zirconia particles).
|
3M ESPE, St. Paulm, MN, United States
|
|
Anterior Gradia
|
Microfilled Hybrid Composite Resin
|
7,7,9 (or 7,9,9)-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-diyl bismethacrylate
|
GC Fuji II LC, Corporation, Japan
|
|
Resin-modified Glass ionomer
|
Resin-modified
|
2-hydroxyethyl methacrylate
tartaric acid
7,7,9 (or 7,9,9)-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diazahexadecane-1,16-diyl bismethacrylate
|
GC Fuji II LC, Corporation, Japan
|
|
Colgate fluoride toothpaste
|
Maximum cavity protection
|
Calcium carbonate, aqua, sorbitol, sodium lauryl sulfate, sodium monofluorophosphate,
aroma, cellulose gum, sodium bicarbonate, tetrasodiumpyrophosphate, benzyl alcohol,
sodium saccharin, sodium hydroxide, limonene
|
Colgate- Palmolive (Thailand) Limited
|
|
Colgate antibacterial and fluoride toothpaste (Colgate Total)
|
Whitening
|
Aqua, glycerin, hydrated silica, pvm/ma copolymer, sodium lauryl sulfate, aroma, cellulose
gum, microcrystalline cellulose, sodium hydroxide, carrageenan, sodium fluoride, triclosan,
sodium saccharin, mica, limonene, CI 77891, CI 42090
|
Colgate- Palmolive (Poland)
|
|
Colgate
|
Optic White
|
Aqua, hydrated silica, glycerin, sorbitol, PEG-12, pentasodium triphosphate, tetrapotassium
pyrophosphate, sodium lauryl sulfate, aroma, cellulose gum, cocamidopropyl betaine,
sodium flouride, sodium saccharin, xanthan gum, sodium hydroxide, limonene, CI74160
|
Colgate- Palmolive (Poland)
|
A2 shade disc-shaped composite samples with 2 mm thickness and 10 mm diameter were
fabricated using a plexiglass mold. The mold was placed on a glass slab and a Mylar
strip and filled with composite. Another glass slab was placed over it and compressed
to eliminate voids. The samples were light-cured using a light curing unit (Valo;
Ultradent, United States) with a light intensity of 1100 mW/cm2 for 20 seconds from each side of the mold.
A total of 108 samples were fabricated as such (27 samples from each material). After
removal of the Mylar strip, one operator polished the samples using 1,000, 2,000,
3,000, and 5,000-grit silicon carbide papers. For completion of polymerization, the
samples were immersed in distilled water for 24 hours. Samples made of each composite
were randomly divided into three subgroups for toothbrushing with conventional whitening
and whitening containing blue covarine toothpastes (n = 9) ([Table 1]). The amount of toothpaste used was 0.25 g, which was diluted with water in 1:3
ratio. One operator brushed the samples twice a day, each time for 30 seconds. An
electric toothbrush with circular motion was used for this purpose. The samples were
then rinsed under running water. After the two tooth-brushing procedures, the artificial
saliva was refreshed. The samples were stored in artificial saliva in a dark glass
vial at room temperature during the experiment. Baseline colorimetry was performed
by measuring the baseline L*, a*, and b* parameters using a spectrophotometer (X-Rite;
Grandville, Michigan, United States). The color of samples was measured at 0, 1, 7,
30, and 90 days after toothbrushing with the respective toothpastes.
Calculation of Change in Color Parameters
The color of samples was measured according to the CIE L*a*b* color parameters using
a spectrophotometer at the abovementioned time points. The L* parameter indicates
lightness, the a* parameter indicates redness-greenness, and the b* parameter indicates
yellowness-blueness. The overall color change (∆E) of the samples was calculated using
the formula below:
Statistical Analysis
Data were analyzed using SPSS version 18 (IBM cooperation, New York, United States).
The measures of central dispersion including the mean, standard deviation, minimum,
and maximum values of color parameters of different restorative materials at different
time points were reported and the relevant tables and graphs were drawn. Two-way ANOVA
was applied to assess the effect of type of restorative material, time, and the interaction
of the two on different color parameters as well as ∆E. In case of presence of a significant
difference, pairwise comparisons were performed using Tukey’s HSD test. Level of significance
was set at 0.05.
Results
Assessment of ∆E at baseline (time 0) and 1 day revealed no significant difference
(p > 0.05). In other words, type of toothpaste had no significant effect on ∆E1–0 (p = 0.78). However, the effect of type of restorative material on ∆E was significant
(p < 0.05).
The three toothpastes were significantly different in terms of their effect on ∆E
of Z250 (p < 0.05) except for ∆E30–0 (p = 0.106). Comparison of the effects of toothpastes on ∆E of Z250 revealed that the
difference between the whitening toothpaste and whitening toothpaste containing blue
covarine on ∆E7–0 was not significant (p = 0.197). Comparison of toothpastes revealed no significant difference in their effect
on ∆E30–0 (P > 0.05). Comparison of the conventional toothpaste and the whitening
toothpaste containing blue covarine revealed no significant difference in their effect
on ∆E90–0 (p = 0.126). However, the difference in this respect between the conventional toothpaste
and the whitening toothpaste containing blue covarine was significant. For Z250 samples,
the whitening toothpaste was able to cause clinically perceivable change in color
at 90 days (∆E90–0).
The three toothpastes were significantly different regarding their effect on ∆E of
Z350 (p < 0.05). Comparison of toothpastes revealed a significant difference with regard
to ∆E7–0 (p < 0.05) but no significant difference was noted for ∆E30–7. The difference between
the whitening toothpaste and the one containing blue covarine was not significant
with regard to ∆E30–0 (p = 0.448). The difference between the whitening toothpaste and the blue covarine toothpaste
was not significant for ∆E90–0 (p = 0.188). For Z350 samples, only the conventional toothpaste caused clinically perceivable
color change (∆E = 3.9) at 90 days (∆E90–0).
The three toothpastes were significantly different in terms of their effect on ∆E
of Gradia at all time points (p < 0.05). The three toothpastes were significantly different with regard to their
effect on ∆E7–0 (p < 0.05) and ∆E30–0 (p < 0.05) for Gradia. However, the difference between the whitening and the conventional
toothpastes was not significant for ∆E90–0 (p = 0.317). None of the ∆E values for Gradia were within the acceptability threshold
range (∆E < 3.3).
For RMGI samples, the toothpastes were not significantly different regarding their
effect on ∆E7–0 (p = 0.43) and ∆E90–0 (p = 0.52). The whitening toothpaste caused color change out of acceptability threshold
(∆E = 3.7) in RMGI samples on day 1 (∆E1–0) ([Figs. 1]
[2]
[3]
[4]).
Fig. 1 The 95% CI of color change (∆E) of materials at different time points. CI, confidence
interval.
Fig. 2 The 95% CI of change in L* parameter of materials at different time points. CI, confidence
interval.
Fig. 3 The 95% CI of change in a* parameter of materials at different time points. CI, confidence
interval.
Fig. 4 The 95% CI of change in b* parameter of materials at different time points. CI, confidence
interval.
Discussion
This study aimed to assess the effect of three types of toothpastes, namely, a conventional
toothpaste, a whitening toothpaste, and another whitening toothpaste containing blue
covarine on color stability of four types of restorative materials, namely, a nanofilled
(Z350 XT), a microhybrid (Z250), a microfilled (Gradia) composite, and an RMGI cement
(Fuji II LC).
The color of samples was measured at 0, 1, 7, 30, and 90 days after toothbrushing
with the abovementioned toothpastes. As shown in [Fig. 1], the ∆E of all composite samples was within acceptability threshold range at all
time points (∆E < 3.3). This finding shows that these toothpastes do not cause a significant
change in color of composite resins. However, they caused a significant change in
color of RMGI samples at 1 and 7 days.
In this study, baseline colorimetry of samples revealed a significant difference among
them, which may be due to their different composition. A previous study that individual
whitening responses to bleaching and satisfaction of patients were significantly associated
with changes in b* value but not L* value or a* value. In the present study, use of
whitening toothpastes did not cause a significant color change in composite samples;
however, the whitening toothpaste and the toothpaste containing blue covarine both
caused a reduction in b* value in almost all composite and RMGI samples. This indicates
the optimal efficacy of these toothpastes in decreasing the yellowness of composite
resins used in this study. However, this was not the case for the effect of conventional
toothpaste on Gradia composite and RMGI since the whitening toothpastes increased
the yellowness of these samples. This finding can be due to the aging of these composites
over time and the consequent changes in their color parameters including the b* value.
Application of whitening toothpastes on RMGI samples did not decrease the b* value;
instead, it increased the yellowness of samples. This finding was probably attributed
to the structural differences of RMGI and composite resins. Composite resins are composed
of organic polymer matrix and inorganic filler particles, which are attached to each
other via the coupling agents and form a polymer network after polymerization. However,
glass ionomers have an aqueous base and fluoroaluminosilicate glass fillers. They
have a polymer or copolymer matrix of carboxylic acids and have acid-base setting
reaction. A methacrylate component has been added to this composition in RMGI cement.
In general, the physical and mechanical properties of glass ionomers such as their
wear resistance and dimensional stability are inferior to those of composite resins.[19] It seems that water sorption and aging due to passage of time also had an effect
on the results obtained for RMGI samples in the present study.
Al-Shalan showed that application of Colgate, Aqua Fresh Ultimate White, and Crest
3D white toothpastes twice a day for 2 minutes for a total of 15 days caused a significant
color change in Z250XT, GC Fuji II LC, and Ketac Molar Quick Aplicap.[20] In our study, color change occurred at a longer time (90 days) in Z250 and Z350XT.
Teixeira et al (2005)[21] applied restorative materials in standard molds to standardize the size and shape
of samples and placed the molds between two Mylar strips and glass slabs. The same
methodology was adopted in our study. Also, we stored the samples in artificial saliva,
similar to the study by Joiner et al.[18]
For assessment of color stability, colorimetry was performed using a spectrophotometer,
which displayed ∆E of each sample on a display monitor. Use of spectrophotometer for
this purpose in our study was similar to previous studies.[22]
[23] However, some other studies measured the change in color by analyzing digital images
or use of a colorimeter.[1]
[18]
[24]
[25] In the present study, different toothpastes caused color change in acceptability
threshold or out of acceptability threshold after 90 days (Z350 showed perceivable
color change after brushing with the conventional toothpaste for 90 days and Z250
showed perceivable color change after brushing with the whitening toothpaste for 90
days). It appears that this finding is more related to aging due to long-term immersion
rather than the composition of toothpastes.
In vitro design was a limitation of this study, which has differences with the intraoral environment.[26] However, we tried our best to standardize the study settings and simulated long-term
use of toothpastes and their effect on color of restorations.
Danying Tao et al, in 2017, concluded that toothpastes containing blue covarine or
a combination of blue covarine and FD&C blue No.1 significantly increase the whiteness
of teeth immediately after tooth brushing both in vitro and in the clinical setting.[27] Our study revealed clinically perceivable color change after 90 days, but no changes
were noticed at 1, 7, or 30 days.
Conclusion
The color change of composite samples at all time points evaluated in this study was
within the acceptable threshold range (<3.3). This finding indicates that these toothpastes
do not cause a significant color change in composite restorations. However, a significant
color change occurred in RMGI samples at 1 and 7 days after using the whitening toothpastes.
