RESEACH ARTICLE
Effect of Light-Activated Tooth Whitening on Color Change Relative to Color of Artificially Stained Teeth SO RAN KWON, DDS, MS, PhD, MS*, STEVEN R. KURTI JR., PhD†, UDOCHUKWU OYOYO, MPH‡, YIMING LI, DDS, MSD, PhD§
ABSTRACT Purpose: There is still controversy as to the efficacy of light activation used in tooth whitening. The purpose of this study was to evaluate the effect of light activation on tooth color change relative to the artificial dye color. Materials and Methods: Extracted human third molars (160) were randomly distributed into eight groups of 20 specimens each based on artificial staining and use of light activation. All groups received three 45-minute sessions of in-office whitening at 3-day intervals. Color measurements were performed with an intraoral spectrophotometer at baseline prior to staining (T0), after artificial staining (T1), 1-day—(T2), and 1-week—(T3) post-whitening. Color differences were calculated relative to after artificial staining color parameters (L*1, a*1, b*1) with the use of a software analysis program enabling synchronization of two images. Results: Within the same staining groups, the light-activated samples exhibited a greater color change than their nonlight-activated counterparts. However, only in the case of the yellow-stained samples at 1-day post-whitening was there a significant difference between the nonlight-activated and light-activated groups (Tukey’s post hoc multiple comparison test for pairwise comparisons, p < 0.05). Conclusions: Light activation is a valid method for enhancing the efficacy of tooth whitening with respect to overall color change and works best with yellow stains.
CLINICAL SIGNIFICANCE Light activation is a valid method for enhancing the efficacy of tooth whitening with respect to overall color change and works best with yellow stains. (J Esthet Restor Dent 27:S10–S17, 2015)
INTRODUCTION In-office whitening using concentrated whitening material is a common alternative to home whitening, especially in cases of severe discoloration, single discolored teeth, lack of patient compliance, or if a rapid treatment is desired.1 However, dental offices commonly use light-activating devices in
combination with in-office whitening materials, and their effectiveness is currently the subject of debate. Whereas several in vitro and clinical trials have indicated that light activation does not affect the change in color produced by whitening,2–6 other studies have provided evidence that it significantly enhances the degree of lightening and the reduction of chroma.7–12
*Associate Professor, Department of Operative Dentistry, University of Iowa College of Dentistry, Iowa City, IA, USA † Associate Professor, Center for Dental Research, Loma Linda University School of Dentistry, Loma Linda, CA, USA ‡ Assistant Professor, Dental Education Services, Loma Linda University School of Dentistry, Loma Linda, CA, USA § Professor and Director, Center for Dental Research, Loma Linda University School of Dentistry, Loma Linda, CA, USA
This work was presented at the American Academy of Dental Research Annual Meeting, Charlotte, NC, USA March, 2014.
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This controversy is partly based on our current lack of knowledge of the basic mechanism underlying tooth whitening, with respect to both the hydrogen peroxide diffusion into the enamel and dentin, and the interaction of peroxide radicals with particular chromogens in the tooth. It has been speculated that light activation may lead to direct whitening by breaking bonds in the chromogen when sufficient energy is transferred. Alternatively, the absorption of photons could raise the energy status of conjugated bonds in the chromogens, making these molecules more reactive to hydrogen peroxide molecules and radicals.12 Energy absorption by chromogens is dependent on the spectrum that are present, with yellow chromogens absorbing light at 425 nm, and other dyes having their own characteristic frequency of absorption, depending on where they fall in the color spectrum.13 Based on the theory of Young and colleagues,12 yellow stains should absorb more photons from a light-activating unit with a peak wavelength of 466 nm than a red or blue stain and the latter would preferably absorb photons at peak wavelengths of 504 and 625 nm, respectively.14 The purpose of this study was to evaluate the effects of light activation on changes in tooth color when three distinct artificial dyes were used to stain the teeth: yellow, red, and blue. Two hypotheses were tested: first, that light activation would affect the change in tooth color; and second, that changes in tooth color that occur in the context of light activation would be influenced by the color of the artificial dye employed for tooth staining.
METHODS AND PROCEDURES Sample Selection and Preparation Sound human third molars extracted from patients (N = 160) were collected and stored in 0.2% sodium azide solution at 4°C. The Loma Linda University Institutional Review Board approved the use of extracted human teeth with no identifiers in this study. Teeth were examined for the existence of cracks and
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defects under a stereomicroscope (Nikon SMZ-2, Tokyo, Japan) and sectioned 1 mm apical to the cementoenamel junction. Any remaining pulp tissue was removed and the coronal surface was cleaned with fine, plain pumice and rubber cups.
Artificial Staining Once measurements of baseline color were completed, the teeth were artificially stained with yellow, red, or blue dye. Teeth in the various groups were immersed in one of the following solutions: 1% acid yellow 23 phosphate buffered saline (PBS) solution (Tartrazine, molar mass: 534.36 g/mol, Sigma-Aldrich, St. Louis, MO, USA); 1% red 40 PBS solution (Allura Red AC, molar mass: 496.42 g/mol, TCI America, Portland, OR, USA); or 1% acid blue 9 PBS solution (Eriglaucine disodium salt, molar mass: 792.85 g/mol, Acros Organics, New Jersey, NY, USA). The teeth were incubated in the dyes in a shaking water bath (Lab-Line Shak-R-Bath 3580, Waltham, MA, USA) for 7 days at 37°C. After artificial staining was completed, the teeth were cleaned with pumice and rubber cups and then immersed in artificial saliva for 1 day. Further dye loss was prevented by painting the sectioned surface with grey nail varnish (Sally Hansen, New York, NY, USA).
Whitening Specimens from each staining group were divided into two samples—one to be activated with light and the other not to be activated with light. Thus, in total, there were eight groups of 20 specimens each, based on the staining protocol applied (NS, no staining; YS, yellow staining; RS, red staining; BS, blue staining) and whether or not light was applied (NL, no light activation; WL, with light activation), as illustrated in Figure 1. All groups received three 45-minute treatments with 25% hydrogen peroxide (Zoom Chairside Whitening Gel, Philips Oral Healthcare, Los Angeles, CA, USA) at 3-day intervals. During each treatment, the whitening material was replenished every 15 minutes according to the manufacturer’s directions. The light-activated teeth were continuously exposed to a light-emitting diode lamp (Zoom WhiteSpeed, Philips Oral Healthcare; peak wavelength: 466 nm) set at high
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(L*1, a*1, b*1), with the analysis program enabling synchronization of the two images (MHT Software Analysis version 2.43, Niederhasli, Switzerland). Tooth color was measured prior to staining (T0, i.e., baseline), after staining (T1), and 1 day (T2) and 1 week (T3) after whitening.
Statistical Analysis
FIGURE 1. Schematic illustration of staining and whitening protocol used in this study.
intensity (190 mw/cm2). Throughout the period of whitening, the specimens were stored in artificial saliva at 37°C, which was prepared and refreshed daily (modified Fusayama solution, as described in the International Organization for Standardization Spec 4115).
Descriptive and statistical analysis was performed for change in lightness (ΔL*), change in chroma in the yellow-blue axis (Δb*), change in chroma in the red-green axis (Δa*), and change in overall color (ΔE*); the findings for 1-day and 1-week post-staining are summarized in Tables 1 and 2. Rank-based analysis of covariance was performed to compare overall color change (ΔE*) among the groups and Tukey’s post hoc multiple comparisons test was performed to evaluate pairwise comparisons (Table 3). Tests of hypotheses were two-sided, with an alpha level of 0.05. Analysis was conducted using SAS Software version 9.2 (SAS Institute, Cary, NC, USA).
Measurement of Changes in Tooth Color
RESULTS Tooth color was measured using a noncontact type intraoral spectrophotometer (Spectroshade Micro, MHT, Niederhasli, Switzerland), which produces the entire spectrum of visible at different intervals. The colors are carried along a light path divided into two optic guides that illuminate the target tooth simultaneously, converging light symmetrically on the target area. The image illuminated by the colored light is then reflected onto a sensor that reads the data in the visible range, i.e., from about 400 nm to 700 nm. The color difference as measured with the spectrophotometer was expressed as overall color change (ΔE*) from the Commission Internationale de l’Eclairage, using the following equation:
ΔE * = ([ L*2 − L*1 ]2 + [ a*2 − a*1 ]2 + [ b*2 − b*1 ]2 )
12
The color differences were calculated relative to the parameters for the color produced by the artificial stain
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Baseline color parameters measured before staining, indicated as L*0, a*0, b*0, did not differ significantly among the groups, indicating that the specimens in each group were randomized effectively (p > 0.05). The color change after staining is summarized in Table 2. Overall color change in the stained groups was significantly higher than in the nonstained control groups (p < 0.05). The greatest change in color was observed in the blue-stained group. This effect can be attributed to the great negative shift in the yellow-blue axis (Tukey’s post hoc test for multiple comparisons, p < 0.05). Overall color change (ΔE*) after whitening, as measured 1-day and 1-week post-whitening, is summarized in Table 2 and illustrated as box plots in Figures 2 and 3. Regardless of staining protocol, all groups showed significant tooth whitening, with an increase in lightness and changes in chroma (p < 0.05),
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TABLE 1. Descriptors (mean/SD) of change in lightness and chroma by group, at 1-day and 1-week post-whitening Group
1-day post-whitening
1-week post-whitening
Δa*1d
ΔL*1d
Δb*1d
ΔL*1w
Δa*1w
Δb*1w
NS-NL
3.43/1.69
−2.61/0.73
−9.35/1.79
1.73/1.62
−2.22/0.76
−7.99/1.23
NS-WL
7.54/2.14
−2.78/0.51
−12.32/2.07
5.32/1.33
−2.54/0.74
−11.91/1.91
YS-NL
6.17/1.43
−1.64/1.29
−17.08/6.35
4.10/1.48
−1.34/1.40
−16.83/7.45
YS-WL
9.00/1.10
−1.37/1.35
−24.15/7.57
5.44/1.85
−1.68/1.56
21.91/7.71
RS-NL
8.66/4.04
−8.21/5.60
−10.05/6.73
6.02/4.40
−8.58/5.35
−9.31/7.13
RS-WL
11.67/5.44
−9.52/7.13
−14.53/8.11
9.48/6.11
−9.64/7.38
−13.90/8.53
BS-NL
8.98/1.94
4.94/1.65
−3.35/2.04
7.23/1.94
5.57/2.24
−2.07/2.41
BS-WL
12.95/2.32
6.16/1.97
−5.65/2.22
10.25/2.34
6.32/2.26
−4.66/2.30
1d = 1-day; 1w = 1-week; BS = blue staining; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining.
TABLE 2. Descriptors (mean/SD) of overall color change (ΔE*) by group at post-staining, 1-day, and 1-week post-whitening Group
ΔE*s
ΔE*1d
ΔE*1w
NS-NL
1.17/0.47
10.41/2.00
8.63/1.39
NS-WL
1.04/0.42
14.87/2.05
13.37/1.93
YS-NL
20.38/10.05
18.42/6.07
17.57/7.23
YS-WL
21.17/7.82
26.02/7.00
22.89/7.30
RS-NL
22.83/7.72
15.90/9.11
14.43/9.29
RS-WL
21.63/11.13
21.16/11.65
19.69/12.33
BS-NL
30.41/4.24
11.07/1.98
9.86/2.10
BS-WL
31.08/5.77
15.69/2.28
13.30/2.27
1d = 1-day; 1w = 1-week; BS = blue staining; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining.
in accordance with the International Organization for Standardization guidelines (ISO 28399) for color change after tooth whitening.16 Within the same staining groups, the light-activated samples exhibited a higher mean change in color than their nonlight-activated counterparts. However, only in the case of the yellow-stained samples at 1-day post-whitening was there a significant difference between the nonlight-activated and light-activated groups (YS-NL
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versus YS-WL, Tukey’s post hoc test for multiple comparisons, p < 0.05). With regard to differences by staining group, at 1-day post-whitening, those for NS-WL versus YS-WL, NS-WL versus RS-WL, and YS-WL versus BS-WL were significant (Table 3). By 1-week post-whitening, only those for NS-WL versus YS-WL and YS-WL versus BS-WL were significant (Table 4) (Tukey’s post hoc test for multiple comparisons, p < 0.05).
DISCUSSION Throughout the years, staining models for evaluating whitening efficacy have evolved into standardized in vitro tests. Such models generally employ the use of common comestible stains such as tea,12,17,18 whole blood,19 red dye,20 chlorhexidine,21 and tetracycline.22,23 Recently, Kurti and colleagues24 developed a model for directly measuring whitening efficacy as change in dye mass, using optical absorption spectrums. They found that the use of solution density and optical absorption spectrums made it possible to directly calculate the mass of dye retained in the extracted teeth and to evaluate the whitening efficacy based on the change in dye mass. Our study introduces a staining model that uses three different Food and Drug Administration-approved food dyes, based on the assumption that the response to light activation varies
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TABLE 3. Tukey’s post hoc multiple comparisons test of pairwise comparisons of color change (ΔE*) at 1-day post-whitening Comparison
Mean difference
95% CI (lower limit, upper limit)
*NS:NL versus YS:WL
−15.61
(−21.77, −9.44)
*YS:WL versus BS:NL
14.95
*NS:WL versus YS:WL
−11.16
(−17.32, −5.00)
*NS:NL versus RS:WL
−10.74
(−16.91, −4.58)
*YS:WL versus BS:WL
10.33
(4.17, 16.50)
*YS:WL versus RS:NL
10.12
(3.96, 16.29)
*RS:WL versus BS:NL
10.09
(3.93, 16.25)
*NS:NL versus YS:NL
−8.005
(−14.17, −1.84)
*YS:NL versus YS:WL
−7.601
(−13.77, −1.44)
*YS:NL versus BS:NL
7.35
(8.79, 21.12)
(1.19, 13.51)
*NS:WL versus RS:WL
−6.297
(−12.46, −0.133)
NS:NL versus RS:NL
−5.482
(−11.65, 0.68)
RS:WL versus BS:WL
5.473
(−0.69, 11.64)
NS:NL versus BS:WL
−5.271
(−11.44, 0.89)
RS:NL versus RS:WL
−5.262
(−11.43, 0.90)
YS:WL versus RS:WL
4.862
(−1.30, 11.03)
RS:NL versus BS:NL
4.827
(−1.34, 10.99)
BS:NL versus BS:WL
−4.616
(−10.78, 1.55)
NS:NL versus NS:WL
−4.447
(−10.61, 1.72)
NS:WL versus BS:NL
3.792
(−2.37, 9.96)
NS:WL versus YS:NL
−3.558
(−9.72, 2.61)
YS:NL versus RS:WL
−2.739
(−8.91, 3.43)
YS:NL versus BS:WL
2.733
(−3.43, 8.90)
YS:NL versus RS:NL
2.522
(−3.64, 8.69)
NS:WL versus RS:NL
−1.036
(−7.20, 5.13)
NS:WL versus BS:WL
−0.8246
(−6.99, 5.34)
NS:NL versus BS:NL
−0.655
(−6.82, 5.51)
RS:NL versus BS:WL
0.2109
(−5.95, 6.38)
BS = blue staining; CI = confidence interval; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining. *p < 0.05.
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FIGURE 2. Box plots of overall color change by group at 1-day post-whitening.
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FIGURE 3. Box plots of overall color change by group at 1-week post-whitening.
in relation to the inherent absorption spectrum of each dye. The color parameters post-staining demonstrating a decrease in lightness and a strong increase in chroma confirmed the validity of this staining model. It is noteworthy that the discoloration exceeded the normal range and could not be evaluated using conventional shade guides such as the Vita Classic or the Vita Bleachedguide 3D Master (VITA Zahnfabrik, Bad Sackingen, Germany). Such evaluation was also beyond the abilities of a commonly used intraoral
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TABLE 4. Tukey’s post hoc multiple comparisons test of pairwise comparisons of color change (ΔE*) at 1-week post-whitening Comparison
Mean difference
95% CI (lower limit, upper limit)
*NS:NL versus YS:WL
−14.26
(−20.77, −7.75)
*YS:WL versus BS:NL
13.03
(6.514, 19.54)
*NS:NL versus RS:WL
−11.06
(−17.57, −4.55)
*RS:WL versus BS:NL
9.83
(3.32, 16.34)
*YS:WL versus BS:WL
9.59
(3.07, 16.10)
*NS:WL versus YS:WL
−9.52
(−16.03, −3.01)
*NS:NL versus YS:NL
−8.94
(−15.46, −.43)
*YS:WL versus RS:NL
8.46
(1.94, 14.97)
*YS:NL versus BS:NL
7.71
(1.20, 14.22)
RS:WL versus BS:WL
6.39
(−0.12, 12.90)
NS:WL versus RS:WL
−6.32
(−12.83, 0.19)
NS:NL versus RS:NL
−5.81
(−12.32, 0.71)
YS:NL versus YS:WL
−5.32
(−11.83, 1.20)
RS:NL versus RS:WL
−5.26
(−11.77, 1.26)
NS:NL versus NS:WL
−4.74
(−11.25, 1.77)
NS:NL versus BS:WL
−4.67
(−11.19, 1.84)
RS:NL versus BS:NL
4.57
(−1.94, 11.08)
YS:NL versus BS:WL
4.27
(−2.24, 10.78)
NS:WL versus YS:NL
−4.20
(−10.72, 2.31)
NS:WL versus BS:NL
3.51
(−3.01, 10.02)
BS:NL versus BS:WL
−3.44
(−9.95, 3.07)
YS:WL versus RS:WL
3.20
(−3.31, 9.71)
YS:NL versus RS:NL
3.14
(−3.37, 9.65)
YS:NL versus RS:WL
−2.12
(−8.63, 4.39)
NS:NL versus BS:NL
−1.23
(−7.75, 5.28)
RS:NL versus BS:WL
1.13
(−5.38, 7.64)
NS:WL versus RS:NL
−1.07
(−7.58, 5.45)
NS:WL versus BS:WL
0.07
(−6.45, 6.58)
BS = blue staining; CI = confidence interval; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining. *p < 0.05.
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spectrophotometer, the Vita Easyshade Compact (VITA Zahnfabrik, Bad Sackingen, Germany). Thus, it was necessary to use a full tooth spectrophotometer with the ability to capture a broader color spectrum. However, discoloration of this magnitude is not unprecedented clinically; it can arise in the case of severe tetracycline staining. Color change was measured at both 1-day and 1-week post-whitening to rule out potential misinterpretation because of dehydration of the teeth that may occur immediately after whitening, especially when light activation is used. Increased lightness and a reduction of chroma were observed in all groups. Although the mean overall color change tended to be higher in the light-activated groups, it was significantly higher only in the yellow-stained samples and at 1-day post-whitening. This observed benefit of light activation in tooth whitening for yellow stains supports our first hypothesis, i.e., that light activation enhances changes in tooth color. Our second hypothesis was also supported. The yellow-stained samples showed a better effect in the context of light activation than the nonstained and blue-stained samples, at both 1-day and 1-week post-whitening. This also supports the theory of Young and colleagues that yellow stain may absorb energy transferred from the light source and thus may be particularly susceptible to tooth whitening by hydrogen peroxide.12 An interesting aspect of this study was the observation of differences in the extent of the change in color with respect to the artificial stains. Yellow and orange stains have been reported to respond well to tooth whitening, whereas grayish-blue stains have not.25 Despite the well-established evidence that the more chromatic the tooth the greater the color change in response to whitening agent,26 this did not apply for the acid 9 blue stain; the color change in this case was significantly less dramatic than that for the yellow and red stains. This may be explained by the differences in molecular weight (MW) and water solubility of the dyes, with Tartrazine and Allura red having lower MW and being more water-soluble. Future studies measuring
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the energy required to create excitation stages for molecules that commonly cause staining (thus making them more reactive to hydrogen peroxide) would provide information useful in improving the application of light activation in tooth whitening.
6.
7.
CONCLUSION
8.
Within the limitations of this study, it can be concluded that light activation is a valid method for enhancing the efficacy of tooth whitening with respect to overall color change and that current protocols work best with yellow stains. In addition, the application of commonly used food dyes in staining models facilitated the evaluation of whitening materials in relation to color change of specific dye molecules.
9.
10.
11.
DISCLOSURE AND ACKNOWLEDGEMENTS 12.
The authors of this manuscript certify that they have no proprietary, financial, or other interest in any products presented in this article. The authors thank Patricia Conrad at Technology and Media Services for designing the illustrations and Philips Oral Healthcare for kindly providing the whitening materials used in this study.
13.
14. 15.
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Reprint requests: So Ran Kwon, DDS, MS, PhD, MS, Department of Operative Dentistry, University of Iowa College of Dentistry, 801 Newton Road #45, S235 DSB, Iowa City, IA 52242-1001, USA; Tel.: 319-335-8871; Fax: 319-335-7267; email: [email protected]
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Effect of Light-Activated Tooth Whitening on Color Change Relative to Color of Artificially Stained Teeth SO RAN KWON, DDS, MS, PhD, MS*, STEVEN R. KURTI JR., PhD†, UDOCHUKWU OYOYO, MPH‡, YIMING LI, DDS, MSD, PhD§
ABSTRACT Purpose: There is still controversy as to the efficacy of light activation used in tooth whitening. The purpose of this study was to evaluate the effect of light activation on tooth color change relative to the artificial dye color. Materials and Methods: Extracted human third molars (160) were randomly distributed into eight groups of 20 specimens each based on artificial staining and use of light activation. All groups received three 45-minute sessions of in-office whitening at 3-day intervals. Color measurements were performed with an intraoral spectrophotometer at baseline prior to staining (T0), after artificial staining (T1), 1-day—(T2), and 1-week—(T3) post-whitening. Color differences were calculated relative to after artificial staining color parameters (L*1, a*1, b*1) with the use of a software analysis program enabling synchronization of two images. Results: Within the same staining groups, the light-activated samples exhibited a greater color change than their nonlight-activated counterparts. However, only in the case of the yellow-stained samples at 1-day post-whitening was there a significant difference between the nonlight-activated and light-activated groups (Tukey’s post hoc multiple comparison test for pairwise comparisons, p < 0.05). Conclusions: Light activation is a valid method for enhancing the efficacy of tooth whitening with respect to overall color change and works best with yellow stains.
CLINICAL SIGNIFICANCE Light activation is a valid method for enhancing the efficacy of tooth whitening with respect to overall color change and works best with yellow stains. (J Esthet Restor Dent 27:S10–S17, 2015)
INTRODUCTION In-office whitening using concentrated whitening material is a common alternative to home whitening, especially in cases of severe discoloration, single discolored teeth, lack of patient compliance, or if a rapid treatment is desired.1 However, dental offices commonly use light-activating devices in
combination with in-office whitening materials, and their effectiveness is currently the subject of debate. Whereas several in vitro and clinical trials have indicated that light activation does not affect the change in color produced by whitening,2–6 other studies have provided evidence that it significantly enhances the degree of lightening and the reduction of chroma.7–12
*Associate Professor, Department of Operative Dentistry, University of Iowa College of Dentistry, Iowa City, IA, USA † Associate Professor, Center for Dental Research, Loma Linda University School of Dentistry, Loma Linda, CA, USA ‡ Assistant Professor, Dental Education Services, Loma Linda University School of Dentistry, Loma Linda, CA, USA § Professor and Director, Center for Dental Research, Loma Linda University School of Dentistry, Loma Linda, CA, USA
This work was presented at the American Academy of Dental Research Annual Meeting, Charlotte, NC, USA March, 2014.
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This controversy is partly based on our current lack of knowledge of the basic mechanism underlying tooth whitening, with respect to both the hydrogen peroxide diffusion into the enamel and dentin, and the interaction of peroxide radicals with particular chromogens in the tooth. It has been speculated that light activation may lead to direct whitening by breaking bonds in the chromogen when sufficient energy is transferred. Alternatively, the absorption of photons could raise the energy status of conjugated bonds in the chromogens, making these molecules more reactive to hydrogen peroxide molecules and radicals.12 Energy absorption by chromogens is dependent on the spectrum that are present, with yellow chromogens absorbing light at 425 nm, and other dyes having their own characteristic frequency of absorption, depending on where they fall in the color spectrum.13 Based on the theory of Young and colleagues,12 yellow stains should absorb more photons from a light-activating unit with a peak wavelength of 466 nm than a red or blue stain and the latter would preferably absorb photons at peak wavelengths of 504 and 625 nm, respectively.14 The purpose of this study was to evaluate the effects of light activation on changes in tooth color when three distinct artificial dyes were used to stain the teeth: yellow, red, and blue. Two hypotheses were tested: first, that light activation would affect the change in tooth color; and second, that changes in tooth color that occur in the context of light activation would be influenced by the color of the artificial dye employed for tooth staining.
METHODS AND PROCEDURES Sample Selection and Preparation Sound human third molars extracted from patients (N = 160) were collected and stored in 0.2% sodium azide solution at 4°C. The Loma Linda University Institutional Review Board approved the use of extracted human teeth with no identifiers in this study. Teeth were examined for the existence of cracks and
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defects under a stereomicroscope (Nikon SMZ-2, Tokyo, Japan) and sectioned 1 mm apical to the cementoenamel junction. Any remaining pulp tissue was removed and the coronal surface was cleaned with fine, plain pumice and rubber cups.
Artificial Staining Once measurements of baseline color were completed, the teeth were artificially stained with yellow, red, or blue dye. Teeth in the various groups were immersed in one of the following solutions: 1% acid yellow 23 phosphate buffered saline (PBS) solution (Tartrazine, molar mass: 534.36 g/mol, Sigma-Aldrich, St. Louis, MO, USA); 1% red 40 PBS solution (Allura Red AC, molar mass: 496.42 g/mol, TCI America, Portland, OR, USA); or 1% acid blue 9 PBS solution (Eriglaucine disodium salt, molar mass: 792.85 g/mol, Acros Organics, New Jersey, NY, USA). The teeth were incubated in the dyes in a shaking water bath (Lab-Line Shak-R-Bath 3580, Waltham, MA, USA) for 7 days at 37°C. After artificial staining was completed, the teeth were cleaned with pumice and rubber cups and then immersed in artificial saliva for 1 day. Further dye loss was prevented by painting the sectioned surface with grey nail varnish (Sally Hansen, New York, NY, USA).
Whitening Specimens from each staining group were divided into two samples—one to be activated with light and the other not to be activated with light. Thus, in total, there were eight groups of 20 specimens each, based on the staining protocol applied (NS, no staining; YS, yellow staining; RS, red staining; BS, blue staining) and whether or not light was applied (NL, no light activation; WL, with light activation), as illustrated in Figure 1. All groups received three 45-minute treatments with 25% hydrogen peroxide (Zoom Chairside Whitening Gel, Philips Oral Healthcare, Los Angeles, CA, USA) at 3-day intervals. During each treatment, the whitening material was replenished every 15 minutes according to the manufacturer’s directions. The light-activated teeth were continuously exposed to a light-emitting diode lamp (Zoom WhiteSpeed, Philips Oral Healthcare; peak wavelength: 466 nm) set at high
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(L*1, a*1, b*1), with the analysis program enabling synchronization of the two images (MHT Software Analysis version 2.43, Niederhasli, Switzerland). Tooth color was measured prior to staining (T0, i.e., baseline), after staining (T1), and 1 day (T2) and 1 week (T3) after whitening.
Statistical Analysis
FIGURE 1. Schematic illustration of staining and whitening protocol used in this study.
intensity (190 mw/cm2). Throughout the period of whitening, the specimens were stored in artificial saliva at 37°C, which was prepared and refreshed daily (modified Fusayama solution, as described in the International Organization for Standardization Spec 4115).
Descriptive and statistical analysis was performed for change in lightness (ΔL*), change in chroma in the yellow-blue axis (Δb*), change in chroma in the red-green axis (Δa*), and change in overall color (ΔE*); the findings for 1-day and 1-week post-staining are summarized in Tables 1 and 2. Rank-based analysis of covariance was performed to compare overall color change (ΔE*) among the groups and Tukey’s post hoc multiple comparisons test was performed to evaluate pairwise comparisons (Table 3). Tests of hypotheses were two-sided, with an alpha level of 0.05. Analysis was conducted using SAS Software version 9.2 (SAS Institute, Cary, NC, USA).
Measurement of Changes in Tooth Color
RESULTS Tooth color was measured using a noncontact type intraoral spectrophotometer (Spectroshade Micro, MHT, Niederhasli, Switzerland), which produces the entire spectrum of visible at different intervals. The colors are carried along a light path divided into two optic guides that illuminate the target tooth simultaneously, converging light symmetrically on the target area. The image illuminated by the colored light is then reflected onto a sensor that reads the data in the visible range, i.e., from about 400 nm to 700 nm. The color difference as measured with the spectrophotometer was expressed as overall color change (ΔE*) from the Commission Internationale de l’Eclairage, using the following equation:
ΔE * = ([ L*2 − L*1 ]2 + [ a*2 − a*1 ]2 + [ b*2 − b*1 ]2 )
12
The color differences were calculated relative to the parameters for the color produced by the artificial stain
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Baseline color parameters measured before staining, indicated as L*0, a*0, b*0, did not differ significantly among the groups, indicating that the specimens in each group were randomized effectively (p > 0.05). The color change after staining is summarized in Table 2. Overall color change in the stained groups was significantly higher than in the nonstained control groups (p < 0.05). The greatest change in color was observed in the blue-stained group. This effect can be attributed to the great negative shift in the yellow-blue axis (Tukey’s post hoc test for multiple comparisons, p < 0.05). Overall color change (ΔE*) after whitening, as measured 1-day and 1-week post-whitening, is summarized in Table 2 and illustrated as box plots in Figures 2 and 3. Regardless of staining protocol, all groups showed significant tooth whitening, with an increase in lightness and changes in chroma (p < 0.05),
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TABLE 1. Descriptors (mean/SD) of change in lightness and chroma by group, at 1-day and 1-week post-whitening Group
1-day post-whitening
1-week post-whitening
Δa*1d
ΔL*1d
Δb*1d
ΔL*1w
Δa*1w
Δb*1w
NS-NL
3.43/1.69
−2.61/0.73
−9.35/1.79
1.73/1.62
−2.22/0.76
−7.99/1.23
NS-WL
7.54/2.14
−2.78/0.51
−12.32/2.07
5.32/1.33
−2.54/0.74
−11.91/1.91
YS-NL
6.17/1.43
−1.64/1.29
−17.08/6.35
4.10/1.48
−1.34/1.40
−16.83/7.45
YS-WL
9.00/1.10
−1.37/1.35
−24.15/7.57
5.44/1.85
−1.68/1.56
21.91/7.71
RS-NL
8.66/4.04
−8.21/5.60
−10.05/6.73
6.02/4.40
−8.58/5.35
−9.31/7.13
RS-WL
11.67/5.44
−9.52/7.13
−14.53/8.11
9.48/6.11
−9.64/7.38
−13.90/8.53
BS-NL
8.98/1.94
4.94/1.65
−3.35/2.04
7.23/1.94
5.57/2.24
−2.07/2.41
BS-WL
12.95/2.32
6.16/1.97
−5.65/2.22
10.25/2.34
6.32/2.26
−4.66/2.30
1d = 1-day; 1w = 1-week; BS = blue staining; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining.
TABLE 2. Descriptors (mean/SD) of overall color change (ΔE*) by group at post-staining, 1-day, and 1-week post-whitening Group
ΔE*s
ΔE*1d
ΔE*1w
NS-NL
1.17/0.47
10.41/2.00
8.63/1.39
NS-WL
1.04/0.42
14.87/2.05
13.37/1.93
YS-NL
20.38/10.05
18.42/6.07
17.57/7.23
YS-WL
21.17/7.82
26.02/7.00
22.89/7.30
RS-NL
22.83/7.72
15.90/9.11
14.43/9.29
RS-WL
21.63/11.13
21.16/11.65
19.69/12.33
BS-NL
30.41/4.24
11.07/1.98
9.86/2.10
BS-WL
31.08/5.77
15.69/2.28
13.30/2.27
1d = 1-day; 1w = 1-week; BS = blue staining; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining.
in accordance with the International Organization for Standardization guidelines (ISO 28399) for color change after tooth whitening.16 Within the same staining groups, the light-activated samples exhibited a higher mean change in color than their nonlight-activated counterparts. However, only in the case of the yellow-stained samples at 1-day post-whitening was there a significant difference between the nonlight-activated and light-activated groups (YS-NL
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versus YS-WL, Tukey’s post hoc test for multiple comparisons, p < 0.05). With regard to differences by staining group, at 1-day post-whitening, those for NS-WL versus YS-WL, NS-WL versus RS-WL, and YS-WL versus BS-WL were significant (Table 3). By 1-week post-whitening, only those for NS-WL versus YS-WL and YS-WL versus BS-WL were significant (Table 4) (Tukey’s post hoc test for multiple comparisons, p < 0.05).
DISCUSSION Throughout the years, staining models for evaluating whitening efficacy have evolved into standardized in vitro tests. Such models generally employ the use of common comestible stains such as tea,12,17,18 whole blood,19 red dye,20 chlorhexidine,21 and tetracycline.22,23 Recently, Kurti and colleagues24 developed a model for directly measuring whitening efficacy as change in dye mass, using optical absorption spectrums. They found that the use of solution density and optical absorption spectrums made it possible to directly calculate the mass of dye retained in the extracted teeth and to evaluate the whitening efficacy based on the change in dye mass. Our study introduces a staining model that uses three different Food and Drug Administration-approved food dyes, based on the assumption that the response to light activation varies
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TABLE 3. Tukey’s post hoc multiple comparisons test of pairwise comparisons of color change (ΔE*) at 1-day post-whitening Comparison
Mean difference
95% CI (lower limit, upper limit)
*NS:NL versus YS:WL
−15.61
(−21.77, −9.44)
*YS:WL versus BS:NL
14.95
*NS:WL versus YS:WL
−11.16
(−17.32, −5.00)
*NS:NL versus RS:WL
−10.74
(−16.91, −4.58)
*YS:WL versus BS:WL
10.33
(4.17, 16.50)
*YS:WL versus RS:NL
10.12
(3.96, 16.29)
*RS:WL versus BS:NL
10.09
(3.93, 16.25)
*NS:NL versus YS:NL
−8.005
(−14.17, −1.84)
*YS:NL versus YS:WL
−7.601
(−13.77, −1.44)
*YS:NL versus BS:NL
7.35
(8.79, 21.12)
(1.19, 13.51)
*NS:WL versus RS:WL
−6.297
(−12.46, −0.133)
NS:NL versus RS:NL
−5.482
(−11.65, 0.68)
RS:WL versus BS:WL
5.473
(−0.69, 11.64)
NS:NL versus BS:WL
−5.271
(−11.44, 0.89)
RS:NL versus RS:WL
−5.262
(−11.43, 0.90)
YS:WL versus RS:WL
4.862
(−1.30, 11.03)
RS:NL versus BS:NL
4.827
(−1.34, 10.99)
BS:NL versus BS:WL
−4.616
(−10.78, 1.55)
NS:NL versus NS:WL
−4.447
(−10.61, 1.72)
NS:WL versus BS:NL
3.792
(−2.37, 9.96)
NS:WL versus YS:NL
−3.558
(−9.72, 2.61)
YS:NL versus RS:WL
−2.739
(−8.91, 3.43)
YS:NL versus BS:WL
2.733
(−3.43, 8.90)
YS:NL versus RS:NL
2.522
(−3.64, 8.69)
NS:WL versus RS:NL
−1.036
(−7.20, 5.13)
NS:WL versus BS:WL
−0.8246
(−6.99, 5.34)
NS:NL versus BS:NL
−0.655
(−6.82, 5.51)
RS:NL versus BS:WL
0.2109
(−5.95, 6.38)
BS = blue staining; CI = confidence interval; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining. *p < 0.05.
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FIGURE 2. Box plots of overall color change by group at 1-day post-whitening.
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FIGURE 3. Box plots of overall color change by group at 1-week post-whitening.
in relation to the inherent absorption spectrum of each dye. The color parameters post-staining demonstrating a decrease in lightness and a strong increase in chroma confirmed the validity of this staining model. It is noteworthy that the discoloration exceeded the normal range and could not be evaluated using conventional shade guides such as the Vita Classic or the Vita Bleachedguide 3D Master (VITA Zahnfabrik, Bad Sackingen, Germany). Such evaluation was also beyond the abilities of a commonly used intraoral
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TABLE 4. Tukey’s post hoc multiple comparisons test of pairwise comparisons of color change (ΔE*) at 1-week post-whitening Comparison
Mean difference
95% CI (lower limit, upper limit)
*NS:NL versus YS:WL
−14.26
(−20.77, −7.75)
*YS:WL versus BS:NL
13.03
(6.514, 19.54)
*NS:NL versus RS:WL
−11.06
(−17.57, −4.55)
*RS:WL versus BS:NL
9.83
(3.32, 16.34)
*YS:WL versus BS:WL
9.59
(3.07, 16.10)
*NS:WL versus YS:WL
−9.52
(−16.03, −3.01)
*NS:NL versus YS:NL
−8.94
(−15.46, −.43)
*YS:WL versus RS:NL
8.46
(1.94, 14.97)
*YS:NL versus BS:NL
7.71
(1.20, 14.22)
RS:WL versus BS:WL
6.39
(−0.12, 12.90)
NS:WL versus RS:WL
−6.32
(−12.83, 0.19)
NS:NL versus RS:NL
−5.81
(−12.32, 0.71)
YS:NL versus YS:WL
−5.32
(−11.83, 1.20)
RS:NL versus RS:WL
−5.26
(−11.77, 1.26)
NS:NL versus NS:WL
−4.74
(−11.25, 1.77)
NS:NL versus BS:WL
−4.67
(−11.19, 1.84)
RS:NL versus BS:NL
4.57
(−1.94, 11.08)
YS:NL versus BS:WL
4.27
(−2.24, 10.78)
NS:WL versus YS:NL
−4.20
(−10.72, 2.31)
NS:WL versus BS:NL
3.51
(−3.01, 10.02)
BS:NL versus BS:WL
−3.44
(−9.95, 3.07)
YS:WL versus RS:WL
3.20
(−3.31, 9.71)
YS:NL versus RS:NL
3.14
(−3.37, 9.65)
YS:NL versus RS:WL
−2.12
(−8.63, 4.39)
NS:NL versus BS:NL
−1.23
(−7.75, 5.28)
RS:NL versus BS:WL
1.13
(−5.38, 7.64)
NS:WL versus RS:NL
−1.07
(−7.58, 5.45)
NS:WL versus BS:WL
0.07
(−6.45, 6.58)
BS = blue staining; CI = confidence interval; RS = red staining; NL = no light activation; NS = no staining; WL = with light activation; YS = yellow staining. *p < 0.05.
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spectrophotometer, the Vita Easyshade Compact (VITA Zahnfabrik, Bad Sackingen, Germany). Thus, it was necessary to use a full tooth spectrophotometer with the ability to capture a broader color spectrum. However, discoloration of this magnitude is not unprecedented clinically; it can arise in the case of severe tetracycline staining. Color change was measured at both 1-day and 1-week post-whitening to rule out potential misinterpretation because of dehydration of the teeth that may occur immediately after whitening, especially when light activation is used. Increased lightness and a reduction of chroma were observed in all groups. Although the mean overall color change tended to be higher in the light-activated groups, it was significantly higher only in the yellow-stained samples and at 1-day post-whitening. This observed benefit of light activation in tooth whitening for yellow stains supports our first hypothesis, i.e., that light activation enhances changes in tooth color. Our second hypothesis was also supported. The yellow-stained samples showed a better effect in the context of light activation than the nonstained and blue-stained samples, at both 1-day and 1-week post-whitening. This also supports the theory of Young and colleagues that yellow stain may absorb energy transferred from the light source and thus may be particularly susceptible to tooth whitening by hydrogen peroxide.12 An interesting aspect of this study was the observation of differences in the extent of the change in color with respect to the artificial stains. Yellow and orange stains have been reported to respond well to tooth whitening, whereas grayish-blue stains have not.25 Despite the well-established evidence that the more chromatic the tooth the greater the color change in response to whitening agent,26 this did not apply for the acid 9 blue stain; the color change in this case was significantly less dramatic than that for the yellow and red stains. This may be explained by the differences in molecular weight (MW) and water solubility of the dyes, with Tartrazine and Allura red having lower MW and being more water-soluble. Future studies measuring
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the energy required to create excitation stages for molecules that commonly cause staining (thus making them more reactive to hydrogen peroxide) would provide information useful in improving the application of light activation in tooth whitening.
6.
7.
CONCLUSION
8.
Within the limitations of this study, it can be concluded that light activation is a valid method for enhancing the efficacy of tooth whitening with respect to overall color change and that current protocols work best with yellow stains. In addition, the application of commonly used food dyes in staining models facilitated the evaluation of whitening materials in relation to color change of specific dye molecules.
9.
10.
11.
DISCLOSURE AND ACKNOWLEDGEMENTS 12.
The authors of this manuscript certify that they have no proprietary, financial, or other interest in any products presented in this article. The authors thank Patricia Conrad at Technology and Media Services for designing the illustrations and Philips Oral Healthcare for kindly providing the whitening materials used in this study.
13.
14. 15.
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Reprint requests: So Ran Kwon, DDS, MS, PhD, MS, Department of Operative Dentistry, University of Iowa College of Dentistry, 801 Newton Road #45, S235 DSB, Iowa City, IA 52242-1001, USA; Tel.: 319-335-8871; Fax: 319-335-7267; email: [email protected]
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