In vitro evaluation of two whitening regimens using color-analyzing methods

145_AlMachot_ArcariQUINTESSENCE INTERNATIONAL
response to patients’ demands for both
healthy and attractive smiles. Since the intro-
duction by Haywood and Heymann of at-
home bleaching in 1989,2 the profession has
sought to compare how well one product in a
similar category compares with another, as
well as how categories compare in terms of
efficacy. The American Dental Association
(ADA) convened a panel of experts in
December 1993 to develop guidelines for eval-
uating peroxide-based at-home whiteners.
then revised in 1998.3,4 Cate gories of whiten-
ing techniques now include at-home bleach-
ing, in-office bleaching with and without
various thermocatalytic lights, and over-the-
counter whitening products in a variety of
delivery options and material concentrations.
Whitening products often contain hydro-
gen peroxide or carbamide peroxide (a
source of hydrogen peroxide) as active ingre-
dients. Both of these agents have been used
for many years to improve intrinsic tooth
color and whiten teeth.2 Chemically, car-
bamide peroxide contains approximately
and it decomposes to form H2O2 and urea in
In vitro evaluation of two whitening regimens using color-analyzing methods Elyan Al Machot, DDS1/Barbara Noack, Dr Med2/
Thomas Hoffmann, Prof Dr Med Habil3
Objectives: To determine in vitro the effect of prophylaxis before tooth whitening and to
evaluate a paint-on home whitening product using two methods of color analysis. Method
and Materials: Ninety extracted human maxillary anterior teeth were randomly separated
into a prophylaxis group or nonprophylaxis group of 45 teeth. The prophylaxis group
received debridement and polishing before whitening. The two groups were randomly
separated into three subgroups of 15 teeth each: placebo group, test group (Easy White,
Dental Kosmetik), and positive control group (Colgate Simply White, Colgate-Palmolive).
The 2-week whitening treatment consisted of applying one of the three gels twice daily
according to the manufacturers’ instructions. In vitro measurements included tooth color
assessment using digital imaging analysis and evaluation of tooth shade by a colorimeter.
Measurements were taken at baseline, after prophylaxis, and after whitening. Results:
While whitening was effective with or without prophylaxis, prior prophylaxis contributed
to improved posttreatment outcomes. Both test gel and positive control gel resulted in
greater shade reductions and tooth color improvements compared to placebo gel
(P < .05). The positive control gel was not superior to test gel. Conclusions: Prophylaxis
is highly recommended before use of paint-on home whitening gels. Colorimetric meas-
urements and digital imaging analysis with a gray card are options to record the efficacy
of whitening products. Digital imaging analysis has advantages: Numeric data can be eval-
uated, and an image of the outcome of the whitening procedure is available.
(Quintessence Int 2010;41:145–156)
card, prophylaxis, tooth color, tooth whitening
1Postgraduate and research assistant, Medical Faculty,
Department of Conservative Dentistry, Periodontology, TU
Dresden, Germany.
3Professor and Chair, Medical Faculty, Department of
Conservative Dentistry, TU Dresden, Germany.
Correspondence: Dr Elyan Al Machot, University of Technology,
Medical Faculty, Department of Conservative Dentistry,
Fetscherstrasse 74, 01307 Dresden, Germany. Fax: 49-351-
4585341. Email: [email protected]
© 2009 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF THIS ARTICLE MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
146 VOLUME 41 • NUMBER 2 • FEBRUARY 2010
QUINTESSENCE INTERNATIONAL
aqueous solution.5 The bleaching process of
hydrogen peroxide involves the diffusion of
peroxide through enamel,6,7 causing bleach-
ing of the pigments found in the enamel-
dentin junction and dentin areas.6,8 This
process makes the tooth appear whiter and
less yellow.9
ly administered but are increasingly available
for in-home use. Home-use product types
include peroxide gels applied in leave-on
trays, gel-impregnated strips, and paint-on
gels with a brush applicator.2,10–12 The paint-
on approach is reported to offer some spe-
cific advantages over other delivery systems,
particularly in the area of convenience.13
It is important to understand what makes
up the color of the teeth and how to measure
this color. This color is due to the combined
effects of intrinsic and extrinsic colorations.14
Intrinsic tooth color is the result of the color
of the enamel and underlying dentin. Tooth
discolorations result from a number of fac-
tors including injury, antibiotic use, fluorosis,
and aging.14,15 Extrinsic tooth color is derived
from staining on the tooth surface and the
staining of the salivary pellicle that readily
forms on enamel. Extrinsic stains form from
a variety of sources including tea, coffee, red
wine, smoking, metal salts, and, above all,
poor oral hygiene. Because the extrinsic
stains are on the tooth surface, these can be
thoroughly removed by the abrasive action of
a dental prophylaxis16 and controlled by the
regular use of dentifrice.17 Both extrinsic and
intrinsic tooth color can be influenced by
whitening treatment. Current protocols gen-
erally mandate the provision of a dental pro-
phylaxis to remove all surface stains before
initiation of the tooth-whitening regimen.
However, the importance of prophylaxis
before beginning whitening for positive treat-
ment outcomes has not been established.18
The color and appearance of teeth are a
complex phenomenon. The determination of
tooth color presents many challenges. Factors
such as lighting conditions, translucency,
opacity, light scattering, and gloss, as well as
the human eye and brain, influence the over-
all perception of tooth color. The measure-
ment of tooth color is possible via a number of
methods including visual assessment with
shade guides, spectrophotometry, colorime-
cedures that must be followed to assess the
therapeutic outcome of tooth-whitening pro-
cedures. However, none of the methods
seems to be ideal.19,20 For evaluating effects
on intrinsic tooth color, in vitro models gener-
ally use the natural color of extracted human
teeth and monitor changes in color by visual
or instrumental assessments.20–22
on the whitening regime, the product used,
and the color measurement method. Thus,
the aim of this investigation was threefold:
first, to examine whether prophylaxis before
the home use of paint-on gels is beneficial in
terms of the efficacy of the whitening prod-
uct; second, to evaluate the effects of a
tooth-whitening mass-market product con-
stain and intrinsic tooth color; and third, to
determine suitability of two color measure-
ment approaches to allow the assessment of
the therapeutic outcome of tooth-whitening
procedures.
rized in Fig 1. Ninety extracted human maxil-
lary anterior teeth were randomly assigned to
either a prophylaxis or a nonprophylaxis
group, each of 45 teeth (regimen A and regi-
men B, respectively). Inclusion criteria were
no restorations and no caries. Additionally, the
teeth were required to have a minimum Vita
shade score of A3 or darker (Vita Zahnfabrik).
To obtain standard measurements, the root of
each tooth was intruded in a standard block
of Flextime Easy Putty (Heraeus Kulzer). The
purpose was to standardize the tooth position
during the color measurements.
men A) received prophylaxis, which included
debridement with ultrasonic instruments and
brushing using a nylon bristle (Kerr Hawe) with
a green Prophy Paste CCS (CCS) followed by
final polishing using a soft rubber cup (Kerr
Hawe) with a yellow Prophy Paste CCS (CCS).
VOLUME 41 • NUMBER 2 • FEBRUARY 2010 147
Afterward, groups A and B were randomly
separated into three whitening subgroups of
15 teeth each: (1) positive control group
(receiving Colgate Simply White gel, Colgate-
Palmolive, group X), (2) test group (receiving
Easy White gel, Dental Kos metik, group Y),
and (3) placebo group (receiving methylhy-
droxyethylcellulose gel [100.0 g, containing
methylhydroxyethylcellulose 4.0 g, anhydrous
served water 71.0 g], group Z). The test gel
contained 7.0% hydrogen peroxide, whereas
the positive control gel contained 5.9% hydro-
gen peroxide.
The 2-week whitening treatment consist-
ed of applying one of the three gels—X, Y, or
Z—to the teeth in each group. The gels were
applied twice daily, morning and evening,
with 8 hours between the two applications,
according to the manufacturers’ instructions.
At the end of the 15-minute whitening proce-
dure, the teeth were rinsed with water and
placed in fresh artificial saliva at 37°C to sim-
ulate remineralizing conditions. For blinding,
all products were covered with a nonremov-
able white label. Thus, the examiner was
blind to the treatment group.
Measurement of tooth color Tooth color was measured using two meth-
ods: a digital imaging analysis (with a “gray
standard”) and the tooth shade using colori-
metric measurements (X-Rite Shade Vision
System, X-Rite).
affect color and brightness and cannot be
excluded completely. Therefore, a photo-
graphic procedure was proposed and validat-
ed that includes a piece of gray card in the
picture as a neutral reference object.23 In this
way, color casts can be eliminated and image
brightness can be fine-tuned using a standard
image-editing program (Adobe Photoshop,
mal gray cards available in photography
stores are too big to be included in a 1:1 shot,
only a small piece of gray card was used. It
was punched out using an office hole punch
and fixed beside the surface of a tooth with a
small amount of petroleum jelly (Fig 2). Digital
photos were taken using a Canon camera
(EOS D60 with macro lens 100 mm, Canon).
90 teeth
Color measurementColor measurement
Nonprophylaxis
Fig 1 Flow chart depicting the study experimental design. Test group received Easy White gel); positive control received Colgate Simply White gel; negative control received placebo gel.
The digital images were analyzed with
commercial software (Adobe Photoshop).
ness (L) and yellowness (b) of each tooth
were taken from the Photoshop histogram.
The range of these values is different when
compared to the Commission Internationale
d’Eclairage (CIE) L* and b* values. In Photo -
shop, the range of the mean L* (L [PM]) and
b* (b [PM]) values, respectively, is 0 to 255.
The CIE L* value ranges from 0 to 100, and
the CIE b* value ranges from –120 to +120.
A transformation can be figured using a spe-
cific formula.23
assessment of tooth shade (SH) using a spe-
cial colorimeter (Shade Vision). This instru-
ment is designed to measure tooth color by
the handheld method24 without a custom
alignment device. Therefore, taking measure-
ments needs to follow procedures recom-
mended usually, eg, repositioning the aperture
in all single measurements for each tooth. The
Shade Vision device is capable of expressing
the color of a surface in various parameters by
comparison with standards (Vitapan Classical,
Vita Zahnfabrik; and Vita 3D-Master, Vident).
In the current study, shades have been related
to the Vitapan Classical shade guide. The
Fig 2 Example of treatment results in the prophylaxis group (for test gel). (a to c) Measured with digital imaging analysis; (d to e) measured with X-Rite Shade Vision). (a, d) Baseline; (b, e) after prophylaxis; (c, f) after whitening.
a b c
d e f
C4 D2 B1
shade values were ranked from 1 to 16, as
suggested by the manufacturer, for statistical
analysis.25 Value 1 was assigned to the dark-
est shade (C4), and value 16 was assigned to
the lightest shade (B1).
teeth of each subgroup before the whitening
procedure was started (baseline), after pro-
phylaxis, and at the end of the 2-week
whitening period. These measurements
care was taken to avoid dehydration of the
teeth during the measurements. Allowing
teeth to dry has been shown to make the
teeth appear whiter.26,27
firmed before each measurement. The
reproducibility was very high (96%). This
value is based upon reexamining 20% of
teeth at the time of the measurements. A sin-
gle, neutral-color laboratory was used to
standardize the tooth-color measurements.
and shade improvement per tooth over base-
line for each of the groups.
Color measurement Baseline After prophylaxis P values (Wilcoxon test)
L 155.91 ± 9.89 160.85 ± 8.15 < .001 b 150.74 ± 4.22 149.83 ± 3.91 .004 SH 5.31 ± 4.29 6.02 ± 4.17 .09
(L) Lightness, (b) yellowness, (SH) shade.
Table 1 Prophylaxis outcome prebleaching, regimen A (mean ± SD)
P value* After bleaching prophylaxis vs bleaching
Group (n = 15) After prophylaxis (2-week data) (paired t test)
L X 162.53 ± 7.85 168.26 ± 6.80 < .001 Y 158.75 ± 9.89 165.76 ± 8.40 < .001 Z 161.27 ± 6.43 160.42 ± 6.76 .28 P value (ANOVA) .44 .02
X vs Y* .99 X vs Z* .02 Z vs Y* .16
b X 150.35 ± 4.27 147.95 ± 3.48 < .001 Y 149.49 ± 3.16 146.96 ± 2.79 < .0001 Z 149.64 ± 4.40 150.33 ± 4.01 .113 P value (ANOVA) .82 .03
X vs Y* .99 X vs Z* .20 Z vs Y* .03
SH as evaluated by X-Rite X 6.13 ± 3.73 9.93 ± 4.43 < .001 Y 6.27 ± 4.87 9.67 ± 4.08 .004 Z 5.67 ± 4.10 6.47 ± 3.87 .31 P value (ANOVA) .92 < .05
X vs Y* .98 X vs Z* .08 Z vs Y* .12
(L) Lightness, (b) yellowness, (SH) shade, (Z) placebo gel, (Y) test gel, and (X) positive control gel. *Post hoc group comparison in case of significant P values in ANOVA was performed taking Bonferroni correction into account.
Table 2 Treatment outcome regimen A (prophylaxis prebleaching) (mean ± SD)
Statistical analysis Means and standard deviations were calcu-
lated for each parameter. To detect differ-
ences between the treatment groups, an
analysis of variance (ANOVA) was performed
at baseline and at the end of each treatment
regime. Within-treatment group differences
analyzed by paired t tests. In cases of skewed
distribution parameters, the Wilcoxon test
was used. A .05 error level was set before the
statistical test procedures.
RESULTS
Bleaching regimen A (prophylaxis prebleaching) Table 1 presents the L, b, and SH values
measured at baseline and after prophylaxis.
The differences between the baseline L and
b values and the corresponding prophylaxis
values were statistically significant (P < .05,
Wilcoxon test). The improvement in SH val-
ues did not reach the significance level (Figs
2a, 2b, 2d, and 2e).
Fig 3 Example of treatment result in the nonprophylaxis group (for control gel). (a, b) Measured with digital imaging analysis; (c, d) measured with X-Rite Shade Vision. (a, c) Baseline; (b, d) after whitening.
a b
c d
C4 D3
Table 2 presents a summary of the meas-
urement results after prophylaxis and after
2-week whitening treatment in regimen A
separately for teeth in the X, Y, and Z study
groups. No statistically significant differences
were indicated among the groups with
respect to prophylaxis scores. The overall dif-
ference among the study groups X, Y, and Z
in all parameter means was statistically sig-
nificant (ANOVA, P < .05). The mean values
of both positive control group (X) and test
group (Y) were comparable, with non–statis-
tically significant differences in post hoc
group comparison. However, all values were
improved when compared to placebo, at
least in trend. The significance level was
reached when comparing group X with
placebo regarding L, and group Y with place-
bo regarding b (Figs 2c and 2f).
The within-group comparison of the mean
prophylaxis values with the mean 2-week
whitening values of L, b, and SH showed the
differences for groups X and Y to be signifi-
cant. This was not true for the placebo group
(see Table 2).
Bleaching regimen B (bleaching with no prophylaxis) Table 3 presents a summary of the measure-
ment results at baseline and after 2-week
whitening treatment in regimen B separately
for teeth in the X, Y, and Z study groups. No
statistically significant differences were found
among the groups with respect to baseline
scores. The overall difference in all parameter
means among the three treatment subgroups
after whitening was statistically significant for
only L [PM] (ANOVA, P = .01), but not for b
and SH (ANOVA, P = .16 and P = .28, respec-
tively). In post hoc testing, the means of L
[PM] in group X and group Y were compara-
ble, with non–statistically significant differ-
ences. However, L was significantly higher in
both of these groups compared to placebo.
The comparison within the group of mean
baseline values with the 2-week whitening
values of L, b, and SH showed the differ-
ences for groups X and Y in regimen B to be
significant (paired t test) (Fig 3). The param-
eters improved as a result of whitening treat-
ment. Again, this was not true for the
placebo group (see Table 3, Fig 4).
P value* After bleaching BL vs bleaching
Group (n = 15) After prophylaxis (2-week data) (paired t test)
L X 155.64 ± 13.26 165.97 ± 7.79 < .001 Y 157.79 ± 9.82 165.17 ± 7.29 < .001 Z 158.90 ± 7.02 158.32 ± 6.53 .39 P value (ANOVA) .68 .01
X vs Y* .98 X vs Z* .02 Z vs Y* .04
b X 150.77 ± 3.53 148.17 ± 3.23 < .001 Y 150.94 ± 4.12 148.72 ± 3.84 < .001 Z 150.65 ± 4.10 150.61 ± 3.53 .84 P value (ANOVA) .98 .16
SH as evaluated by X-Rite X 5.80 ± 4.50 9.13 ± 3.73 < .001 Y 5.33 ± 3.49 8.60 ± 4.01 .001 Z 6.47 ± 3.75 6.93 ± 3.84 .45 P value (ANOVA) .73 .28
(L) Lightness, (b) yellowness, (SH) shade, (Z) placebo gel, (Y) test gel, and (X) positive control gel. * Post hoc group comparison in case of significant P values in ANOVA was performed taking Bonferroni correction into account.
Table 3 Treatment outcome group B (bleaching with no prophylaxis) (mean ± SD)
Al Machot et a l
Comparison of bleaching regimens A and B The 2-week whitening results were com-
pared between whitening regimen with
prophylaxis (A) and without prophylaxis (B)
separately for the two whitening gels X and Y
to examine whether prophylaxis before the
home use of paint-on gels is beneficial in
terms of the efficacy of the whitening prod-
uct (Tables 4 and 5). The mean changes in
tooth lightness, yellowness, and shade over
baseline (L, b, SH) were similar in both
whitening groups, with no statistically signifi-
cant differences between the two whitening
regimens, except L in group Y (test gel),
which reached a borderline level of signifi-
cance (P = .04). The mean improvement in
lightness in regimen A was –11.9, compared
to –7.4 in regimen B.
Fig 4 Example of treatment result in the nonprophylaxis group (for placebo gel). (a, b) Measured with digital imaging…