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Instant tooth whitening from a silica toothpastecontaining blue covarine

Luisa Z. Collins *, Mojgan Naeeni, Suzanne M. Platten

Unilever Oral Care, Quarry Road East, Bebington, Wirral CH63 3JW, UK

a r t i c l e i n f o

Keywords:

Tooth colour

Objective measurement

Digital imaging

a b s t r a c t

Objective: To measure the instant whitening effect delivered immediately after brushing

with a novel silica whitening toothpaste containing blue covarine.

Methods: A controlled, single blind, cross-over study was performed to compare the tooth

colour measured in a group of subjects at baseline and immediately after brushing with a

silica whitening toothpaste containing blue covarine versus a clear gel negative control

toothpaste. Measurements of tooth colour were made using a mobile non-contact camera-

based digital imaging system and expressed as CIELAB and WIO whiteness index.

Results: Analysis of covariance (ANCOVA) showed that the silica whitening toothpaste

containing blue covarine was significantly more effective than the negative control tooth-

paste ( p < 0.05), and made teeth measurably less yellow, less red and overall whiter

immediately after brushing.

Conclusion: A statistically significant reduction in tooth yellowness and improvement in

measured immediately after brushing with a novel whitening tooth-

covarine.

paste containing blue

tooth whiteness was

# 2008 Elsevier Ltd. All rights reserved.

1. Introduction

The desire for whiter teeth is responsible for the rapid growth

of the tooth whitening market segment over the last decade.

Many mass-market tooth whitening products are available

which claim to whiten teeth either by tooth bleaching or

through the removal/control of extrinsic stain.

Mass-market tooth bleaching products usually contain

peroxide at levels ranging from 3% to 6% and are supplied as

strips, paints-on gels or in trays. Products are applied either

once or twice daily for up to 14 days, depending on dose and

exposure time.1 In contrast, products that remove/control

extrinsic stain are more usually toothpastes with special

abrasive particles that through regular use (e.g. twice daily)

lead to whiter teeth after 2–4 weeks.2 Thus, the whitening

effects of mass-market bleaching products can be observed

quickly after 4–7 days. Whereas the changes in tooth white-

* Corresponding author. Tel.: +44 151 6413980; fax: +44 151 641 1833.E-mail address: luisa.z.collins@unilever.com (L.Z. Collins).

0300-5712/$ – see front matter # 2008 Elsevier Ltd. All rights reserveddoi:10.1016/j.jdent.2008.02.006

ness from toothpastes that remove/control stain are observed

over longer periods of time (2–4 weeks).

In order to observe an instant whitening effect from

toothpaste a silica whitening toothpaste has been developed

to deliver blue covarine to pellicle-coated tooth surfaces.

The delivery of the blue covarine to these surfaces causes a

shift in the yellow-blue colour axis (CIE b*) which has been

shown to aid whiteness perception.3 Joiner et al. have

demonstrated through a series of in vitro experiments that

blue covarine is deposited and retained on pellicle-coated

tooth surfaces causing a colour shift that ultimately gives

rise to an increase in the measurement and perception of

tooth whiteness.4

The aim of the in vivo study reported here was to measure

the instant whitening effect delivered immediately after

brushing with a novel silica whitening toothpaste containing

blue covarine.

.

j o u r n a l o f d e n t i s t r y 3 6 s ( 2 0 0 8 ) s 2 1 – s 2 5S22

2. Materials and methods

Eighty-three subjects were recruited to participate in this

controlled, single blind (with respect to the camera operator),

cross-over study. The objective of the study was to measure

the change in tooth colour and tooth whiteness, using a mobile

non-contact camera-based digital imaging system (DIS),

immediately after brushing with a novel silica whitening

toothpaste containing blue covarine versus a clear gel negative

control toothpaste. A full description of the mobile non-

contact camera-based DIS and validation of this system is

given by Smith et al.5

The protocol, information sheet and informed consent for

this study were reviewed and approved by Unilever Research

and Development Research Ethics Committee. All subjects

were aged 18 years or older, male or female and recruited from

the Wirral area, UK. (Subject selection was not balanced for

gender). Subjects were in good general health; without

significant pathologies of the oral soft/hard hard tissues and

had two normally aligned, natural upper central incisors, free

from restorations visible from the labial surface. Recruited

subjects who had extrinsic stain on their upper central

incisors had their upper central incisors professionally

cleaned by the study dentist prior to the first test session.

Women who were pregnant or nursing were not included.

The whitening toothpaste containing blue covarine was

formulated with a silica abrasive system. The clear gel

negative control toothpaste was of the same formulation

without the addition of blue covarine. Both pastes were

manufactured by Unilever Oral Care, Italy, and contained

1450 ppm fluoride. The toothpastes were supplied to the study

site in identical white 75 ml tubes labelled with different

product codes. The identity of the product codes was only

revealed after the statistical analysis had been completed.

All subjects attended two test sessions, which were

scheduled on separate days within the same week; the

minimum washout period was 24 h. From recruitment until

the end of the study, all subjects were requested to continue

using their own toothpaste and toothbrush at home. They

were asked not to renew their toothbrush until after the test

had completed and not to change the brand or type of

toothpaste they were using. Subjects were requested to refrain

from eating, drinking or brushing their teeth for 1 h prior to

each test session.

At each test session, a set of ‘baseline’ images were

collected using the DIS. Subjects wore sterile plastic cheek

retractors and protective eye goggles during the imaging

procedure. Subjects positioned themselves with their chin on

the DIS chin rest and forehead against the forehead rest. The

DIS operator collected an image of the subject’s teeth after the

lights had been switched on for a fixed time. The image was

checked for quality, and saved. If the image was out of focus,

Table 1 – Subject demographics

Groups n Mean age (S.E.)

All subjects 78 43.1 (1.36)

Male 7 44.1 (4.08)

Female 71 43.0 (1.45)

additional images were collected until an in-focus image had

been captured. After collecting the baseline image, subjects

brushed with one of the study toothpastes using their normal

brushing technique for 90 s followed by a 5 s 5 ml water rinse.

Immediately after brushing, subjects had their teeth re-

imaged (‘post’ image).

The study toothpastes were tested in a randomised order.

The randomisation was computer generated and comprised of

a list, which varied between the two product codes. Subjects

were assigned their randomisation codes based on the order in

which they attended their first test session. The operator of the

DIS was blinded with respect to the toothpaste randomisation.

All images were analysed in Adobe Photoshop CS2 version 9

(Adobe System Inc., Seattle, WA, USA). The upper central

incisors were highlighted using the magnetic lasso tool to

obtain values for red, green and blue (RGB) from within the

highlighted region. These values were transcribed into an

Excel spreadsheet algorithm which calculated the CIELAB

colour space values and WIO whiteness index.6 All measure-

ments collected within a test session were standardised

against the whiteness values taken from imaging a ceramic

white tile colour standard (Ceram, Staffordshire, UK) at the

start of each test session. The calculated CIELAB values and

WIO whiteness index were submitted for statistical analysis.

Using the CIELAB definition, colour is defined through three

axes: L* represents a measure of the lightness of the object (a

positive L* value indicates lightness, whereas a negative L*

value is darker); a* is a measure of the colour on the red to

green axis (positive a* is nearer red and negative a* is closer to

green); b* represents the colour on the yellow-blue axis

(positive b* is closer to yellow and negative b* value is nearer

blue).7

Paired t-tests were used to test for significant differences

between the baseline and post images for each of the

toothpastes tested. The post values for the test and negative

control groups were compared by analysis of covariance

(ANCOVA) using the baseline values as covariate. For all

analyses, the level of statistical significance was p < 0.05.

3. Results

Seventy-eight subjects completed the two product cross-over

study to measure the optical effect of blue covarine delivered

from a novel silica whitening toothpaste. One subject was

excluded for medical reasons unrelated to the study test

toothpastes and four subjects failed to complete the study for

personal reasons. Subject demographics are shown in

Table 1.

The DWIO whiteness index for the test toothpaste showed

that teeth became significantly whiter ( p < 0.05) immediately

after brushing with the silica whitening toothpaste containing

Minimum age Maximum age

20 69

28 57

20 69

Table 2 – Mean CIELAB and WIO whiteness index baseline and post brushing (standard error)

Treatment Colour index Baseline Post Difference(post-base)

Significance (pairedcomparisons)

Negative control L* 68.39 (0.40) 68.60 (0.42) 0.20 (0.11) Not significant

a* 6.99 (0.11) 7.21 (0.12) 0.21 (0.03) p < 0.05

b* 28.85 (0.30) 28.86 (0.31) 0.01 (0.05) Not significant

WIO index �55.03 (1.71) �54.95 (1.79) 0.08 (0.31) Not significant

Whitening toothpaste

containing blue covarine

L* 68.51 (0.40) 68.51 (0.42) �0.001 (0.12) Not significant

a* 7.06 (0.12) 6.97 (0.12) �0.09 (0.03) p < 0.05

b* 29.01 (0.30) 28.65 (0.30) �0.36 (0.06) p < 0.05

WIO index �55.28 (1.70) �54.14 (1.70) 1.14 (0.30) p < 0.05

j o u r n a l o f d e n t i s t r y 3 6 s ( 2 0 0 8 ) s 2 1 – s 2 5 S23

blue covarine. A statistically significant shift in WIO whiteness

index was not observed for the negative control toothpaste

(Table 2). Paired comparisons between the baseline and post

values showed that the test toothpaste containing blue

covarine caused a statistically significant reduction in tooth

yellowness (p < 0.05), whereas the negative control did not

significantly effect the measurement of b* (Fig. 1).

ANCOVA analysis showed that the whitening toothpaste

containing blue covarine was significantly more effective than

the negative control toothpaste ( p < 0.05), and made teeth

appear less yellow, less red and overall whiter immediately

after brushing.

4. Discussion

The mobile non-contact camera-based DIS used in this study

has been shown to be a reproducible and reliable means of

measuring tooth colour and tooth whiteness.5 This type of

instrumental analysis of tooth colour provides an objective

measure that helps to eliminate the introduction of bias

within studies.8 The sensitivity of this method of colour

analysis can be exploited to measure small colour differences9

which may otherwise be lost in the noise when using less

discriminatory methods such as subjective assessment using

the Vita shade guide.

The baseline L*, a* and b* values recorded during this study

ranged from 52.98 to 75.50, 5.14 to 10.58, and 21.58 to 35.23,

respectively. Although direct comparison of the results

obtained using this system with those published by other

authors is not recommended as each system is designed

differently; these values are similar to those recorded within

the literature for other non-contact camera-based digital

imaging systems.10–12

Fig. 1 – Effect of test toothpastes on Db* (S.E.).

A statistically significant reduction in tooth yellowness was

measured immediately after brushing with the silica whiten-

ing toothpaste containing blue covarine. The mean difference

in Db* was �0.36 (standard error [S.E.] = 0.06). A similar shift in

Db* of �0.24 (S.E. = 0.11) was observed by Farrell et al.13 after

two, 30 min applications of an 18% carbamide peroxide gel,

covered by a polythene strip barrier. This change in b* was a

statistically significant reduction in tooth yellowness com-

pared to the baseline value (p < 0.05). In three separate

studies, where the same 18% carbamide peroxide gel was

used twice daily, over a greater number of days, the shift in b*

was �0.34 (S.E. = 0.06) after 7 days,14 �0.27 (S.E. = 0.23) after 14

days15 and �0.21 (S.E. = 0.11) after 21 days.16 In each of these

studies, the positive controls (which were 19% sodium

percarbonate film, 6% hydrogen peroxide bleaching strips or

5% carbamide peroxide gel trays, respectively) produced

changes in b* ranging from �0.84 to �2.53 units.

A number of studies have been published using non-contact

camera-based digital imaging methods to measure changes in

tooth colour resulting from regular brushing with a variety of

toothpastes. The Db* values are displayed in Table 3. As

summarised, Yudhira et al.11 observed that a whitening

toothpaste with an alumina abrasive system delivered a

significant shift in b* after 2 weeks of twice daily brushing,

but this was not maintained when measured again after 12

weeks of use. The magnitude of shift in b* after 2 weeks of twice

daily brushing was the same as observed for the blue covarine

toothpaste after just one brushing event. Luo et al.12 observed a

much larger shift in b* after 1 and 2 weeks of brushing with a

regular non-whitening toothpaste; however, they also recorded

a much larger Db* for their positive control group using 6%

hydrogen peroxide whitening strips, �3.53 (S.E. = 0.29) and

�4.49 (S.E. = 0.36) after 1 and 2 weeks, respectively. This

difference in measurement is most likely due to different

instrument design. The non-contact camera-based DIS used in

the study reported here generates data with similar values to

the imaging system used by Gerlach et al.3,8,10,11,13–17

The age of subjects who completed the study ranged from

20 to 69 years. The magnitude of Db* measured immediately

after brushing with the blue covarine toothpaste was found to

be independent of b* value recorded at baseline (correlation

coefficient = 0.020) and subjects age (correlation coeffi-

cient = 0.022). Although subjects were not selected to speci-

fically represent a range of ages or baseline b* values the

absence of correlations suggests that the significant reduction

in tooth yellowness measured immediately after brushing was

not dependant on subject age or starting tooth colour.

Table 3 – Mean Db* reported after brushing with toothpaste

Authors Product n Treatmenttime (twice daily)

Adjusted meanDb* (S.E.)

Change frombaseline

Gerlach et al.17 Anti-cavity toothpaste

and placebo gel strip

29 14 days �0.05 (0.11) Not significant

Gerlach and Barker16 Dual-phase whitening toothpaste 14 21 days �0.06 (0.13) Not significant

Gerlach et al.15 1% hydrogen peroxide toothpaste 14 14 days �0.05 (0.22) Not significant

Gerlach et al.10 Anti-cavity toothpaste and

placebo gel strip

18 7 days �0.26 (0.20) Not significant

Yudhira et al.11 Silica whitening toothpaste

and placebo gel strip

16 14 days 0.03 (0.21) Not significant

12 weeks 0.14 (0.18) Not significant

Alumina whitening toothpaste

and placebo gel strip

15 14 days �0.37 (0.21) Not significant

12 weeks �0.20 (0.19) Not significant

Luo et al.12 Non-whitening toothpaste 21 7 days �1.11 (0.11) p < 0.05

14 days �0.85 (0.07) p < 0.05

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The WIO whiteness index was used by Luo et al.,11 who

measured baseline WIO values of �77.88 (S.E. = 1.97) and

�76.43 (S.E. = 2.85) for their test and control groups, respec-

tively. These values are approximately 20 units more negative

(less white) than the values reported here. This could be due to

different populations of subjects or instrument differences.

A statistically significant shift in WIO of 1.14 units

(S.E. = 0.30) was measured immediately after brushing with

the whitening toothpaste containing blue covarine. This shift

was larger than that observed for the negative control, 0.08

(S.E. = 0.31) and larger than that previously reported within the

literature for a non-whitening toothpaste.12

The changes in b* and WIO in the current study clearly

indicate an objectively measured improvement in tooth

whiteness immediately after brushing with a novel silica

whitening toothpaste containing blue covarine. Since the b*

value is the most important parameter for perceptual changes

for users of vital tooth bleaching products,3 the measured

changes in b* and WIO in the current study can potentially help

drive the perception of whiter teeth immediately after

brushing and every time this toothpaste is used. Indeed, in

vitro studies have demonstrated that blue covarine deposited

on teeth can give both an objective and subjective measure of

increase in tooth whiteness.4

The magnitude of the changes in b* and WIO in the current

study suggest modest changes in overall tooth colour have been

measured, but nonetheless are significantly greater than the

changes recorded for the control product. In terms of consumer

relevance, the perception of the colour of objects is known to be

a complex phenomenon, with many factors affecting the final

perception of their colour, including lighting conditions, the

reflection and absorption of light by the object, the adaptation

state of the observer and the context in which the object is

viewed.18 The perception of tooth colour following tooth-

brushing is also likely to be equally complex, with many

attributes of the product (e.g. flavour, foam quality, abrasivity)

together with the context of the teeth, gums and lips all

potentially influencing the overall perception. The contribution

of these various factors on perception of tooth colour is clearly

worthy of further systematic scientific study. Regardless of how

it is generated, the subjectiveperception of the end user is one of

the most important measures of consumer relevance.

Current whitening toothpastes improve tooth whiteness by

the removal and control of extrinsic stain gradually over a

period of weeks.19–21 However, in the current study, the tooth

whitening effects were demonstrated immediately after a

single brushing with the silica whitening toothpaste contain-

ing blue covarine. The optical effect from the blue covarine

helps the user of the product to get an immediate and

perceivable whitening benefit from the toothpaste4 every time

it is used, in addition to the gradual, longer term whitening

benefit from the effective silica abrasive system within the

toothpaste.22 Thus, the user of the silica whitening toothpaste

containing blue covarine will obtain both immediate and long

term tooth whitening benefits.

5. Conclusion

A statistically significant reduction in tooth yellowness and

improvement in tooth whiteness was measured immediately

after brushing with a novel whitening toothpaste containing

blue covarine.

Role of funding source

This supplement was supported by Unilever Oral Care. The

authors retained full editorial control and responsibilities

throughout the preparation of the manuscripts.

Conflict of interest

Luisa Z. Collins, Mojgan Naeeni and Suzanne Platten are

employees of Unilever Plc.

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