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A novel optical approach to achieving tooth whitening
journal of dentistry 36s (2008) s8–s14
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
A novel optical approach to achieving tooth whitening Andrew Joiner *, Carole J. Philpotts, Coralie Alonso, Alex T. Ashcroft, Naomi J. Sygrove Unilever Oral Care, Quarry Road East, Bebington, Wirral CH63 3JW, UK
article info
abstract
Keywords:
Objective: To investigate a new optical approach to tooth whitening by enhancing the
Tooth whitening
measurement and perception of tooth whiteness using blue coloured materials deposited
Tooth colour
onto the tooth surface.
Bleaching
Methods: Salivary pellicle coated human extracted teeth or polished enamel specimens
Perception
were used as substrates and their colour was measured using a colorimeter in the CIELAB
Aesthetics
mode. Whole teeth were treated with a range of blue dyes and pigments and the colour measured following rinsing with water. Whole teeth were treated with Blue Covarine for 30 s, rinsed with water and colour changes assessed via colorimetric and visual assessment with a Vita Shade guide under controlled lighting (D65). Deposition of Blue Covarine onto cut enamel specimens was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Tooth colour changes were also investigated following brushing for 1 min with toothpaste formulations containing Blue Covarine. Results: Blue Covarine gave a significantly greater Db* shift ( p < 0.0001) compared to water. Blue Covarine gave a mean Vita Shade change of 1.18 compared to the water control (0.03) ( p < 0.0001) and an increase in objectively measured whiteness index (WIO) ( p < 0.0001). Blue Covarine was chemically detected on enamel surfaces using TOF-SIMS. Toothpaste formulations containing Blue Covarine gave improvements in tooth whiteness. Conclusions: Blue Covarine has been identified as a new approach to tooth whitening. Its mode of action involves deposition and retention on tooth surfaces where it alters the optical properties of the tooth. This gives rise to an increase in the overall measurement and perception of tooth whiteness. # 2008 Elsevier Ltd. All rights reserved.
1.
Introduction
Tooth colour is important to a large proportion of patients and consumers. Indeed, a number of recent studies have shown that the personal dissatisfaction with tooth colour can range from 17 to 53% depending on the population of the study.1,2 Thus, manufacturers of oral care products continually strive to develop improved methods and new approaches for the whitening of teeth in order to meet this consumer and patient need. To this end, a vast choice of contemporary tooth whitening mass market products have been developed and these generally involve the improvement of tooth colour by
essentially two types of mechanisms, namely tooth bleaching or the removal and control of extrinsic stain. Tooth bleaching typically involves the application of hydrogen peroxide or carbamide peroxide containing gels to the teeth using painton, mouth guard or strip product formats. After several days or weeks treatment, the peroxide causes decolourisation or bleaching of the coloured materials found within the tooth structures giving rise to whiter teeth.3 The removal and control of extrinsic stain is possible via toothpaste and in particular tooth whitening formulations, which typically contain optimised abrasive and chemical ingredients to maximise cleaning.4
* Corresponding author. Tel.: +44 151 641 3000; fax: +44 151 641 1800. E-mail address: [email protected] (A. Joiner). 0300-5712/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2008.02.005
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The Commission International De l’Eclairage (CIE) in 1976 defined a three-dimensional colour space which provides a representation for the perception of colour stimuli. The three axes are L*, a* and b*, where L* represents a measure of the lightness of the object and a* and b* represent the colour on the red–green and yellow–blue axes respectively.5 Tooth whitening studies with peroxide based products have indicated that the yellow–blue shift (Db*) in tooth colour is important for perceptual tooth whitening. For example, Gerlach et al.6 investigated the subjective first-person response of two tooth bleaching hydrogen peroxide containing products after 2 weeks. The tooth colour was objectively measured before and after treatment and a subject questionnaire was completed after treatment. The data were fitted into a probability model and it was found that the subjective responses to whiteness improvement and satisfaction were significantly correlated with changes in b* values but not L* and a* values. Thus, the yellow–blue shift is of primary perceptual importance to the user of vital tooth bleaching products.7 In addition, an in vitro whitening study by Kleber et al.8 using a 1% hydrogen peroxide product demonstrated that the reduction of b* values occurred more rapidly and to a greater extent than changes in L* values. The study concluded that the b* component is a more important indicator of tooth whitening in bleaching. Similarly, the whitening clinical study by Goodson et al.9 reaffirms that whitening reduces yellowness (b* value) more consistently than it increases L* values. The hypothesis to be tested in the current paper is that the deposition of a blue agent to a tooth surface will give rise to changes in the optical properties of the tooth, particularly a yellow to blue colour shift, which can enhance the measurement and perception of tooth whitening. The aims of the current in vitro studies were: (1) to select possible blue agents that can give a yellow to blue colour shift; (2) to investigate visual perception and tooth whitening effects of the chosen active; (3) to investigate the delivery of this active to enamel surfaces in simple aqueous systems, and (4) investigate the instant tooth whitening effects of this active when delivered from a toothpaste.
2.
Materials and methods
Materials with the potential to deliver a yellow to blue shift on the surface of pellicle coated enamel were initially screened on human whole teeth in simple aqueous solution in order to identify a suitable candidate for further study. The selected blue agent was then applied to whole teeth from an aqueous solution in order to establish whether any resulting yellow to blue shift would be visually perceivable. A spectroscopic study was then undertaken in order to demonstrate that the observed colour change was, indeed, produced by the selected blue agent. Finally, the blue agent was incorporated into a toothpaste and an in vitro dose–response study performed in order to demonstrate that it could be delivered from such a product.
2.1.
Preliminary screening of potential blue agents
Human extracted anterior teeth, obtained for research purposes prior to the enactment of the Human Tissue Act and with
Table 1 – Blue agents tested Name
CI number
Patent Blue V FD&C Blue No. 1 Brilliant Black BN
CI 42051 CI 42090 CI 28440
Blue Covarine
CI 74160
Manufacturer Fiorio Colori, Italy Fiori Colori, Italy Sensient Cosmetic Technologies LCW, France Sensient Cosmetic Technologies LCW, France
informed consent, were mounted in acrylic resin blocks by embedding the roots into cold-cure acrylic resin (Simplex Rapid, Kemdent, Wiltshire, UK). Any remaining exposed dentine was sealed with two coats of nail varnish (No. 7, Colour LockTM Nail Enamel, Boots plc, Nottingham, UK). The enamel surfaces were then cleaned with a prophylaxis paste (Clean Chemical Sweden AB, Sweden) to remove any extrinsic stain. The teeth were then placed in sterile (gamma irradiated) pooled human whole saliva for 2 h to allow an in vitro salivary pellicle to form. The teeth were rinsed with water, and the baseline colour of the teeth measured with a chromameter (Minolta CR-321, Minolta Camera Co. Ltd., Japan) in the CIELAB mode by taking at least five separate measurements of the labial surface, and the mean b* value was calculated. A range of blue dyes and pigments (Table 1) commonly used in oral care products were prepared at a concentration of 0.2% (w/w) in deionised water (Milli-Q Plus, Millipore, USA). The teeth were randomly assigned to a test group or water control (n = 7 for each group). The teeth were dipped in the appropriate test solution for 30 s and then each treatment group of teeth was placed in a large beaker of water (300 ml). The teeth were removed after 5, 10, 20, 60 and 120 min total time and the colour of the teeth was remeasured. The teeth were returned to the beaker of water immediately after colour measurement. The mean change in b* value (Db*) was calculated for each time point from: Db ¼ b ðtÞ b ð0Þ where b*(t) is the b* value after t minutes and b*(0) is the b* value at baseline.
2.2.
Perception study of the selected blue agent
Sixty-eight human extracted anterior and premolar teeth, mounted in acrylic as previously described above, were soaked in sterile (gamma irradiated) human whole saliva for 2 h and then rinsed with water. The baseline tooth colour was measured objectively with a chromameter (Minolta CR-321, Minolta Camera Co. Ltd., Japan) in the CIELAB mode. In addition, the tooth colour was visually assessed by three trained assessors using a Vita Shade Guide (VITA Zahnfabrik, Bad Sa¨ckingen, Germany) under controlled lighting conditions (D65) in a viewing cabinet (Verivide Ltd., UK). This cabinet has a neutral grey-coloured background and sides, and controlled simulated daylight (D65) conditions. These types of viewing cabinets are designed to provide ideal lighting conditions for the critical and consistent assessment of colour. The Vita Shade Guide was arranged from lightest to darkest according to the standard method10 and given a numerical value, where B1 = 1 (lightest shade) and C4 = 16 (darkest shade) (Table 2). The teeth
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Table 2 – Numerical assignment of Vita Shade tabs B1 1
A1
B2
D2
A2
C1
C2
D4
A3
D3
B3
A3.5
B4
C3
A4
C4
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
were randomly assigned to either a 30 s treatment with water (n = 34) or a 0.2% (w/w) Blue Covarine in water (n = 34). The teeth were rinsed with water and remeasured as before. Visual assessors were unaware of the treatment groups. The numerical change in Vita shade was calculated from: Vita Shade change ¼ Vita Score ðtreatmentÞ Vita Score ðbaselineÞ The overall mean Vita Shade change value was calculated from the scores of the three assessors. A positive score in the Vita Shade Change indicates the tooth colour is increasing in whiteness. In parallel, CIELAB colour differences were calculated from: DL ¼ L ðtÞ L ð0Þ Da ¼ a ðtÞ a ð0Þ where L*(t) is the L* value after t minutes and L*(0) is the L* value at baseline and a*(t) is the a* value after t minutes and a*(0) is the a* value at baseline. Db* was calculated as before. In addition, a whiteness index value (WIO) was calculated from the L*, a* and b* values and the change in WIO determined. This was accomplished by calculating the CIE tristimulus values X, Y and Z from the L*, a* and b* values, and then calculating the WIO whiteness index using previously described mathematical expressions.11
2.3. Spectroscopic determination of the deposition of Blue Covarine onto pellicle coated enamel Human enamel blocks (4 mm 4 mm 2 mm) were prepared as previously described.12 In outline, the roots of human extracted incisors and molars were removed and the lingual part of the tooth flattened to approximately 3 mm thick using a high abrasive disc (Tycet Ltd., Hemel Hempstead, Herts, UK), turned over and the facial surface polished with the abrasive disc to flatten the surface. The polished sections were cut on a diamond wire cutter (Two Well Model 3242 Wire Cutter, Ebner, Le Locle, Switzerland) into approximately 4 mm 4 mm 2 mm blocks. These blocks were then planar-polished to a final finish of 0.3 mm polishing agent (Micropolish II, Buehler, Illinois, USA). Specimens were stored in sterile (gamma irradiated) human whole saliva for 16 h and rinsed with deionised water. The baseline colour of the specimens was measured with a chromameter (Minolta CR241, Minolta Camera Co. Ltd., Japan). Specimens were then treated with either Blue Covarine at concentrations of 0.02% and 2% (w/w) in deionised water or deionised water control (n = 4 for each treatment) for 1 min. Following water rinsing, the colour of the specimens was remeasured and colour changes (Db*) calculated. Immediately, the specimens were mounted on a sample holder for analysis within a time-of-flight secondary ion mass spectrometer (TOFSIMS) IV-200 Instrument (Ion-Tof, GmbH, Munster, Germany) using a polyatomic primary source (Bismuth 3) in order to
chemically detect the presence of Blue Covarine on the enamel surface. As a reference, a thin film of Blue Covarine powder was prepared on a glass slide and held in place with double-sided tape. Spectra were recorded for the Blue Covarine reference material in order to ‘‘fingerprint’’ the material and to identify suitable characteristic peaks that could be used to subsequently identify the presence of Blue Covarine. The treated enamel specimens were then scanned (500 mm 500 mm) with the TOFSIMS in order to map the distribution of Blue Covarine material across the surface.
2.4.
Dose–response from a toothpaste
Human extracted anterior teeth, mounted in acrylic as previously described above, were soaked in sterile (gamma irradiated) human whole saliva for 2 h and then rinsed with water. The baseline tooth colour was measured with a chromameter (Minolta CR-321, Minolta Camera Co. Ltd., Japan) in the CIELAB mode. A series of identical silica based toothpaste formulations were prepared with the exception that part of the water content was replaced with either 0, 0.01, 0.05, 0.10 or 0.20% (w/ w) Blue Covarine. These were mixed with water and 0.5% (w/ w) sodium carboxymethyl cellulose (SCMC) aqueous solution in a paste:water:SCMC w/w ratio of 1:1:1 for 1 h prior to the treatment of tooth specimens. The tooth specimens were randomly allocated to one of the treatment groups (n = 5 per treatment). Each tooth was brushed for 1 min with the toothpaste slurry and a flat trim toothbrush and then rinsed with water (300 ml) for 15 s. The colour of the tooth was remeasured and colour changes from baseline calculated as before.
3.
Results
3.1.
Preliminary screening of potential blue agents
The mean Db* values for the extracted teeth after treatment with different test agents (0.2%, w/w in water) and immersion in water for different time periods are shown in Table 3. This clearly shows that teeth treated with Blue Covarine gave the largest reduction in b* value, indicating a yellow–blue shift in colour, whereas other tested agents gave only relatively small changes in b* value. Statistical analyses (ANOVA) showed an overall statistical significant difference between treatments at each time point. Further statistical comparisons (Dunnett’s method) showed that Blue Covarine was the only test agent that was significantly different to the water control ( p < 0.0001).
3.2.
Perception study of the selected blue agent
The mean change in Vita Shade and DL*, Da*, Db* and DWIO values are given in Table 4. This clearly shows that the 0.2% (w/
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Table 3 – Mean Db* values after treatment with different test agents (0.2% w/w in water) and immersion in water for different time periods (n = 7) Time (min)
Db* (S.E.) Water
5 10 20 60 120
0.14 0.34 0.34 0.04 0.29
(0.17) (0.24) (0.24) (0.16) (0.29)
Patent Blue V 0.85 0.47 0.33 0.38 0.19
(0.27) (0.29) (0.19) (0.21) (0.29)
FD&C Blue No. 1 0.06 0.40 0.19 0.36 0.11
Brilliant Black
(0.16) (0.29) (0.26) (0.16) (0.16)
0.06 0.06 0.57 0.32 0.10
(0.40) (0.37) (0.43) (0.29) (0.22)
Blue Covarine 2.71 2.41 2.47 2.49 2.30
(0.50) (0.38) (0.40) (0.50) (0.50)
Table 4 – Subjective and objective measurements of teeth (n = 34) treated with water or 0.2% (w/w) Blue Covarine Treatment Water 0.2% Blue Covarine
Mean Vita Shade change (S.E.)
DL* (S.E.)
Da* (S.E.)
Db* (S.E.)
0.03 (0.51) 1.18 (0.18)
0.69 (0.16) 1.44 (0.31)
0.16 (0.06) 0.38 (0.04)
0.07 (0.09) 1.33 (0.12)
DWIO (S.E.) 0.82 (0.31) 3.64 (0.76)
w) Blue Covarine treatment gave a larger increase in mean Vita Shade change compared to water, and the difference between treatments was of high statistical significance ( p < 0.0001, Student’s t-test). The differences between treatments for the other colour parameters were also of statistical significance as follows; DL* ( p < 0.05); Da* ( p < 0.0001); Db* ( p < 0.0001), and DWIO ( p < 0.0001).
3.3. Spectroscopic determination of the deposition of Blue Covarine onto pellicle coated enamel Blue Covarine consists of a phthalocyanine ring structure with a tightly bound central copper ion as shown in Fig. 1. The TOFSIMS spectra obtained from the Blue Covarine reference clearly showed peaks due to the molecular species [M H] at m/z of +575, 576, 577, 578 and 579. These were found to be relatively intense and gave rise to a characteristic intensity pattern due to ions with additional H atoms overlapping with the copper isotope peaks (Fig. 2). The mean colour change (Db*) (S.E.) for the 2.0% and 0.02% Blue Covarine treated specimens were 2.33 (0.74) and 1.34 (0.39), respectively. For the control pellicle coated enamel
Fig. 2 – Typical TOF-SIMS spectrometry results for (a) Blue Covarine powder, (b) enamel–water, (c) enamel–0.02% Blue Covarine and (d) enamel–2.0% Blue Covarine.
specimens treated with water, the TOF-SIMS spectra did not show any of the characteristic peaks for Blue Covarine. Checks were made on the data for the presence of salivary pellicle and there were found to be several low mass nitrogen-containing fragment ions that would be consistent with the presence of peptide-like or similar materials. All specimens treated with Blue Covarine did show the presence of intense characteristic peaks for the Blue Covarine fingerprint in the 500–600 Da range (Fig. 2). When the enamel surfaces were mapped with the TOFSIMS for specific ions, it was found that Blue Covarine was relatively evenly distributed on the 0.02% (w/w) Blue Covarine treated surfaces (Fig. 3). Similar distributions were observed for the 2.0% (w/w) Blue Covarine surfaces. No Blue Covarine was detected on the water treated control surfaces.
3.4.
Fig. 1 – Chemical structure of Blue Covarine.
Dose–response from a toothpaste
The mean Db* and DWIO values versus Blue Covarine concentration in a silica based toothpaste are shown in Figs. 4 and 5, respectively. Figs. 4 and 5 clearly show a decrease
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Fig. 3 – TOF-SIMS positive ion images of an enamel surface treated with 0.02% (w/w) Blue Covarine; total ions (left) and Blue Covarine (right).
Fig. 4 – A plot of mean Db* values (S.E.) versus Blue Covarine concentration.
Fig. 5 – A plot of mean DWIO values (S.E.) versus Blue Covarine concentration.
in tooth yellowness and an increase in tooth whiteness with increasing Blue Covarine concentration, with linear correlation coefficients of 0.9681 and 0.8671, respectively.
4.
Discussion
The use of in vitro models is an important step for the initial identification of new oral care actives and the preliminary evaluation and optimisation of product prototypes. There have
been a large number of in vitro models described in the literature which have been successfully used to evaluate the efficacy and safety of tooth whitening actives and products.3,4,13 In general, these models use whole or cut human or bovine tooth specimens and utilise their pre-existing natural colour, although a few models have increased the level of intrinsic stain of the tooth by pre-staining with black tea or blood components.3 The colour measurement of teeth is possible using a number of techniques, including visual comparison with a shade guide, spectrophotometers, colorimeters or digital image analysis.5 In general, colorimeters have shown good repeatability of natural tooth colour measurements in vitro and in vivo14–16 and have been used successfully in measuring colour changes of teeth following tooth bleaching treatments.3 In the current study, the use of a colorimeter for objectively measuring changes in tooth colour has again been demonstrated as a suitable method. When tooth specimens are treated with Blue Covarine the colorimeter is sensitive enough to measure the changes in colour from baseline. In the first study, it was demonstrated that Blue Covarine was the only material tested to give a significant reduction in b* value compared to the water control. This reduction in b* value is most likely due to the deposition of the Blue Covarine onto the tooth surface, which imparts a change to the optical properties of the tooth surface. The reduction in b* value was also maintained for the duration of the experiment of 120 min water rinsing, which indicates that the Blue Covarine has a relatively high affinity for pellicle coated tooth surfaces. In contrast, all other materials tested had a relatively poor affinity for the surface and/or were readily removed upon rinsing with water, since no significant changes in b* values were observed compared to the water control. Thus, further in vitro studies were conducted on the Blue Covarine material. In the second study, the effects of Blue Covarine on tooth colour and whiteness were assessed objectively with a colorimeter and subjectively via visual assessment by colour matching of the tooth specimen with a shade guide. A number of factors can affect shade guide usage in clinical dentistry, for example lighting conditions, room de´cor, experience of the assessor and fatigue of the human eye.3,5 Therefore, care must be taken to standardise and control these factors. In the
journal of dentistry 36s (2008) s8–s14
current study, the tooth specimens were visually assessed in a viewing cabinet. The use of viewing cabinets has been described and used in a number of in vitro dental studies where visual colour assessment of the specimens was critical, for example the matching and colour acceptance of dental materials17,18 and assessing shade differences between acrylic resin dentures and natural teeth.19 Using this set-up, a mean Vita Shade change from baseline of 1.18 was observed for the Blue Covarine treated tooth specimens compared to 0.03 for the water control. The increase in mean Vita Shade demonstrates that the Blue Covarine is able to impart a visual perceptual increase in tooth whiteness. This is in sharp contrast to the water-treated tooth specimens where no significant change from baseline was observed. It has been argued that even though a change in b* value is an important indicator of tooth whitening, none of the component vectors of CIELAB should be considered in isolation to measure tooth whiteness.20 Although CIELAB is one of the recommended colour systems for application in dentistry,21 it was not designed to measure whiteness.20 Currently, different whiteness indices exist,11 but in order for a whiteness index to be valid it must be used on the types of materials for which it is intended. For example, WIC (CIE recommended whiteness index) is widely used in the textile, paint and plastic industries. The WIC has been investigated for its suitability in determining the visual perception of whiteness of teeth by Luo et al.22 In their psychophysical experiments, 26 teeth samples were ordered in terms of perceived whiteness under controlled conditions by nine observers and compared with instrumental measurements of the same samples. It was found that, although the correlation coefficient (r2) was good (0.87), the WIC was inadequate in that it would generate about 13.5% wrong decisions (compared with the average visual performance of 5.7%). Luo et al.22 then proposed a modified version of the whiteness index (WIO) which was shown to be more suitable for the visual assessment of tooth whiteness. In addition, the WIO was shown to be the most appropriate index to measure changes in tooth whiteness following a tooth bleaching regime.20 For the objective colour measurements in the perception study, the tooth specimens treated with Blue Covarine showed significant changes in all CIELAB colour components compared to the water control. Despite the slight reduction in L* value for Blue Covarine treated specimens, which on its own might imply the lightness of the tooth has been slightly reduced, there is also a reduction in a* and b* values, and as discussed above, none of the component vectors of CIELAB should be considered in isolation to measure overall tooth whiteness. Therefore, the L*, a* and b* values were converted to the WIO whiteness index and shown to give an overall increase in whiteness for the Blue Covarine treated teeth. Thus, Blue Covarine changes the optical properties of teeth by shifting their colour from one area of the colour space to another, where the new tooth colour can be measured objectively and perceived subjectively as whiter. Using the current methods it is now possible to measure increases in tooth whiteness both subjectively and objectively on the same tooth specimens following tooth whitening treatments, including Blue Covarine optical effects technology and hydrogen peroxide bleaching.20 In addition, this approach
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may prove valuable in determining and comparing tooth whitening effects of other technologies and techniques in the future. The retention of Blue Covarine on the tooth surface in vitro was evaluated only up to 120 min in an aqueous environment. Considering that the Db* values did not change significantly between 60 and 120 min of water rinsing, it is speculated that the optical effect could last for many hours longer. The longevity of the effect under in vivo conditions may be different and needs further investigation. However, the potential of the Blue Covarine optical route to give an instant and perceivable tooth whitening effect following brushing has been demonstrated in vitro. TOF-SIMS is a powerful surface characterisation technique that is able to determine the composition, structure, orientation and spatial distribution of molecular and chemical structures on a biomaterial surface.23 Indeed, it is a technique that has been applied to the chemical characterisation of a wide range of different types of surfaces, including those relevant in the dental field. For examples, determining fluoride uptake on enamel,24 chemical characterisation of peritubular dentine25 and various calcium phosphates including hydroxyapatite.26 In the current study, we have shown the applicability of TOF-SIMS to the chemical detection of Blue Covarine deposition onto pellicle coated enamel surfaces. In addition, Blue Covarine is deposited relatively uniform across the surface in a non-specific way. This confirms that the yellow–blue colour shift of the enamel specimens occurs due to the direct deposition of Blue Covarine onto the enamel surface. Tooth whitening products are marketed in many different formats including gels, paint-on products, strips, mouth guards and toothpaste.3 However, one of the most accessible products for many patients and consumers is toothpaste and the growth in the tooth whitening market is reflected by the growth in the whitening toothpaste sector.27 In the final experiment, Blue Covarine was formulated into a silica based toothpaste formulation in order to investigate whether Blue Covarine optical effects can be delivered from this format. From Figs. 4 and 5 it can clearly be seen that Blue Covarine containing toothpastes can reduce tooth yellowness and increase tooth whiteness, respectively, after a 1 min brushing protocol. In addition, there is a clear dose–response effect with higher concentrations of Blue Covarine giving rise to reduced levels of yellowness and increased levels of whiteness. Traditional tooth whitening methods typically involve either peroxide-based bleaching to effect intrinsic tooth colour changes or abrasive cleaning to effect extrinsic stain removal.3,4 From the experiments described in the current work, Blue Covarine has been identified as a new approach to tooth whitening. The mode of action of Blue Covarine involves its deposition and retention on tooth surfaces where it can alter the optical properties of the tooth by primarily giving a yellow to blue colour shift. However, the overall colour shift ultimately gives rise to an increase in the measurement and perception of tooth whiteness. What is most unexpected is that these effects can be demonstrated after only one treatment of a relatively short exposure time (e.g. 30 s) and can be effectively delivered from a toothpaste formulation after brushing for only 60 s. Thus, this technology has great
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potential for developing the next generation of tooth whitening toothpastes whereby an instant whitening effect may be achieved after just one brushing. In addition, this potential new whitening toothpaste would have the recognised health benefits of an efficacious source of fluoride to prevent and reverse caries processes together with an effective abrasive and surfactant system for tooth cleaning. Future work will focus on the further development of such toothpaste formulations with optimised Blue Covarine delivery, together with measurement of the relevant optical effects in vivo and overall consumer acceptability in terms of other sensory and in-use attributes (e.g. flavour and foam quality). In conclusion, within the limitations of the studies Blue Covarine has been identified as a new approach to tooth whitening. Its mode of action involves deposition and retention on tooth surfaces where it can alter the optical properties of the tooth which ultimately gives rise to an increase in the measurement and perception of tooth whiteness.
[14]
Role of funding source
[15]
This supplement was supported by Unilever Oral Care. The authors retained full editorial control and responsibilities throughout the preparation of the manuscripts.
[8]
[9]
[10]
[11] [12]
[13]
[16]
[17]
Conflict of interest All authors are employees of Unilever.
Acknowledgements The authors would like to thank Ian Hopkinson (Unilever Oral Care) for his help in the colour calculations and Ian Fletcher (Intertek MSG, Cleveland) for his help with the TOF-SIMS analyses.
[18]
[19]
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[21]
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bleaching systems. Compendium of Continuing Education in Dentistry 2000;21:S22–S28. Kleber CJ, Putt MS, Nelson BJ. In vitro tooth whitening by a sodium bicarbonate/peroxide dentifrice. Journal of Clinical Dentistry 1998;9:16–21. Goodson JM, Tavares M, Sweeney M, Stultz J, Newman M, Smith V, et al. Tooth whitening: tooth color changes following treatment by peroxide and light. Journal of Clinical Dentistry 2005;16:78–82. Collins LZ, Maggio B, Liebman J, Blanck M, Lefort S, Waterfield P, et al. Clinical evaluation of a novel whitening gel, containing 6% hydrogen peroxide and a standard fluoride toothpaste. Journal of Dentistry 2004;32:13–7. Joiner A, Hopkinson I, Deng Y, Westland S. Tooth colour and whiteness. Journal of Dentistry 2008;36:S2–7. Joiner A, Weader E, Cox TF. The measurement of enamel wear of two toothpastes. Oral Health and Preventative Dentistry 2004;2:383–8. Joiner A. Review of the effects of peroxide on enamel and dentine properties. Journal of Dentistry 2007;35:889–96. Tung FF, Goldstein GR, Jang S, Hittelman E. The repeatability of an intraoral dental colorimeter. Journal of Prosthetic Dentistry 2002;88:585–90. Douglas RD. Precision of in vivo colorimetric assessments of teeth. Journal of Prosthetic Dentistry 1997;77:464–70. Macpherson LMD, Stephen KW, Joiner A, Scha¨fer F, Huntington E. Comparison of a conventional and modified tooth stain index. Journal of Clinical Periodontology 2000;27:854–9. Barrett AA, Grimaudo NJ, Anusavice KJ, Yang MCK. Influence of tab and disk design on shade matching of dental porcelain. Journal of Prosthetic Dentistry 2002;88: 591–7. Regain JC, Johnston WM. Color acceptance of direct dental restoratives materials by human observers. Color Research and Application 2000;25:278–85. Young L, Glaros AG, Moore DJ, Collins JF. Assessing shade differences in acrylic resin denture and natural teeth. Journal of Prosthetic Dentistry 1994;71:575–80. Luo W, Westland S, Brunton P, Ellwood R, Pretty IA, Mohan N. Comparison of the ability of different colour indices to assess changes in tooth whiteness. Journal of Dentistry 2007;35:109–16. Seghi RR, Johnston WM, O’Brien WJ. Performance assessment of colorimetric devices on dental porcelains. Journal of Dental Research 1989;68:1755–9. Luo W, Westland S, Ellwood R, Pretty I. Evaluation of whiteness formulae for teeth. In: Nieves J.L., HernandezAndres J. (Eds.), Proceedings of the 10th Congress of the International Colour Association. 2005; p. 839–42. Belu AM, Graham DJ, Castner DG. Time-of-flight secondary ion mass spectrometry: techniques and applications for the characterization of biomaterial surfaces. Biomaterials 2003;24:3635–53. Chin-Ying SH, Xiaoli G, Jisheng P, Wefel JS. Effects of CO2 laser on fluoride uptake in enamel. Journal of Dentistry 2004;32:161–7. Gotliv BA, Robach JS, Veis A. The composition and structure of bovine peritubular dentin: mapping by time of flight secondary ion mass spectrometry. Journal of Structural Biology 2006;156:320–33. Lu HB, Campbell CT, Graham DJ, Ratner BD. Surface characterization of hydroxyapatite and related calcium phosphates by XPS and TOF-SIMS. Analytical Chemistry 2000;72:2886–94. Pickles MJ, Evans M, Philpotts CJ, Joiner A, Lynch RJM, Noel N, et al. In vitro efficacy of a whitening toothpaste containing calcium carbonate and perlite. International Dental Journal 2005;55:197–202.
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
A novel optical approach to achieving tooth whitening Andrew Joiner *, Carole J. Philpotts, Coralie Alonso, Alex T. Ashcroft, Naomi J. Sygrove Unilever Oral Care, Quarry Road East, Bebington, Wirral CH63 3JW, UK
article info
abstract
Keywords:
Objective: To investigate a new optical approach to tooth whitening by enhancing the
Tooth whitening
measurement and perception of tooth whiteness using blue coloured materials deposited
Tooth colour
onto the tooth surface.
Bleaching
Methods: Salivary pellicle coated human extracted teeth or polished enamel specimens
Perception
were used as substrates and their colour was measured using a colorimeter in the CIELAB
Aesthetics
mode. Whole teeth were treated with a range of blue dyes and pigments and the colour measured following rinsing with water. Whole teeth were treated with Blue Covarine for 30 s, rinsed with water and colour changes assessed via colorimetric and visual assessment with a Vita Shade guide under controlled lighting (D65). Deposition of Blue Covarine onto cut enamel specimens was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Tooth colour changes were also investigated following brushing for 1 min with toothpaste formulations containing Blue Covarine. Results: Blue Covarine gave a significantly greater Db* shift ( p < 0.0001) compared to water. Blue Covarine gave a mean Vita Shade change of 1.18 compared to the water control (0.03) ( p < 0.0001) and an increase in objectively measured whiteness index (WIO) ( p < 0.0001). Blue Covarine was chemically detected on enamel surfaces using TOF-SIMS. Toothpaste formulations containing Blue Covarine gave improvements in tooth whiteness. Conclusions: Blue Covarine has been identified as a new approach to tooth whitening. Its mode of action involves deposition and retention on tooth surfaces where it alters the optical properties of the tooth. This gives rise to an increase in the overall measurement and perception of tooth whiteness. # 2008 Elsevier Ltd. All rights reserved.
1.
Introduction
Tooth colour is important to a large proportion of patients and consumers. Indeed, a number of recent studies have shown that the personal dissatisfaction with tooth colour can range from 17 to 53% depending on the population of the study.1,2 Thus, manufacturers of oral care products continually strive to develop improved methods and new approaches for the whitening of teeth in order to meet this consumer and patient need. To this end, a vast choice of contemporary tooth whitening mass market products have been developed and these generally involve the improvement of tooth colour by
essentially two types of mechanisms, namely tooth bleaching or the removal and control of extrinsic stain. Tooth bleaching typically involves the application of hydrogen peroxide or carbamide peroxide containing gels to the teeth using painton, mouth guard or strip product formats. After several days or weeks treatment, the peroxide causes decolourisation or bleaching of the coloured materials found within the tooth structures giving rise to whiter teeth.3 The removal and control of extrinsic stain is possible via toothpaste and in particular tooth whitening formulations, which typically contain optimised abrasive and chemical ingredients to maximise cleaning.4
* Corresponding author. Tel.: +44 151 641 3000; fax: +44 151 641 1800. E-mail address: [email protected] (A. Joiner). 0300-5712/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jdent.2008.02.005
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The Commission International De l’Eclairage (CIE) in 1976 defined a three-dimensional colour space which provides a representation for the perception of colour stimuli. The three axes are L*, a* and b*, where L* represents a measure of the lightness of the object and a* and b* represent the colour on the red–green and yellow–blue axes respectively.5 Tooth whitening studies with peroxide based products have indicated that the yellow–blue shift (Db*) in tooth colour is important for perceptual tooth whitening. For example, Gerlach et al.6 investigated the subjective first-person response of two tooth bleaching hydrogen peroxide containing products after 2 weeks. The tooth colour was objectively measured before and after treatment and a subject questionnaire was completed after treatment. The data were fitted into a probability model and it was found that the subjective responses to whiteness improvement and satisfaction were significantly correlated with changes in b* values but not L* and a* values. Thus, the yellow–blue shift is of primary perceptual importance to the user of vital tooth bleaching products.7 In addition, an in vitro whitening study by Kleber et al.8 using a 1% hydrogen peroxide product demonstrated that the reduction of b* values occurred more rapidly and to a greater extent than changes in L* values. The study concluded that the b* component is a more important indicator of tooth whitening in bleaching. Similarly, the whitening clinical study by Goodson et al.9 reaffirms that whitening reduces yellowness (b* value) more consistently than it increases L* values. The hypothesis to be tested in the current paper is that the deposition of a blue agent to a tooth surface will give rise to changes in the optical properties of the tooth, particularly a yellow to blue colour shift, which can enhance the measurement and perception of tooth whitening. The aims of the current in vitro studies were: (1) to select possible blue agents that can give a yellow to blue colour shift; (2) to investigate visual perception and tooth whitening effects of the chosen active; (3) to investigate the delivery of this active to enamel surfaces in simple aqueous systems, and (4) investigate the instant tooth whitening effects of this active when delivered from a toothpaste.
2.
Materials and methods
Materials with the potential to deliver a yellow to blue shift on the surface of pellicle coated enamel were initially screened on human whole teeth in simple aqueous solution in order to identify a suitable candidate for further study. The selected blue agent was then applied to whole teeth from an aqueous solution in order to establish whether any resulting yellow to blue shift would be visually perceivable. A spectroscopic study was then undertaken in order to demonstrate that the observed colour change was, indeed, produced by the selected blue agent. Finally, the blue agent was incorporated into a toothpaste and an in vitro dose–response study performed in order to demonstrate that it could be delivered from such a product.
2.1.
Preliminary screening of potential blue agents
Human extracted anterior teeth, obtained for research purposes prior to the enactment of the Human Tissue Act and with
Table 1 – Blue agents tested Name
CI number
Patent Blue V FD&C Blue No. 1 Brilliant Black BN
CI 42051 CI 42090 CI 28440
Blue Covarine
CI 74160
Manufacturer Fiorio Colori, Italy Fiori Colori, Italy Sensient Cosmetic Technologies LCW, France Sensient Cosmetic Technologies LCW, France
informed consent, were mounted in acrylic resin blocks by embedding the roots into cold-cure acrylic resin (Simplex Rapid, Kemdent, Wiltshire, UK). Any remaining exposed dentine was sealed with two coats of nail varnish (No. 7, Colour LockTM Nail Enamel, Boots plc, Nottingham, UK). The enamel surfaces were then cleaned with a prophylaxis paste (Clean Chemical Sweden AB, Sweden) to remove any extrinsic stain. The teeth were then placed in sterile (gamma irradiated) pooled human whole saliva for 2 h to allow an in vitro salivary pellicle to form. The teeth were rinsed with water, and the baseline colour of the teeth measured with a chromameter (Minolta CR-321, Minolta Camera Co. Ltd., Japan) in the CIELAB mode by taking at least five separate measurements of the labial surface, and the mean b* value was calculated. A range of blue dyes and pigments (Table 1) commonly used in oral care products were prepared at a concentration of 0.2% (w/w) in deionised water (Milli-Q Plus, Millipore, USA). The teeth were randomly assigned to a test group or water control (n = 7 for each group). The teeth were dipped in the appropriate test solution for 30 s and then each treatment group of teeth was placed in a large beaker of water (300 ml). The teeth were removed after 5, 10, 20, 60 and 120 min total time and the colour of the teeth was remeasured. The teeth were returned to the beaker of water immediately after colour measurement. The mean change in b* value (Db*) was calculated for each time point from: Db ¼ b ðtÞ b ð0Þ where b*(t) is the b* value after t minutes and b*(0) is the b* value at baseline.
2.2.
Perception study of the selected blue agent
Sixty-eight human extracted anterior and premolar teeth, mounted in acrylic as previously described above, were soaked in sterile (gamma irradiated) human whole saliva for 2 h and then rinsed with water. The baseline tooth colour was measured objectively with a chromameter (Minolta CR-321, Minolta Camera Co. Ltd., Japan) in the CIELAB mode. In addition, the tooth colour was visually assessed by three trained assessors using a Vita Shade Guide (VITA Zahnfabrik, Bad Sa¨ckingen, Germany) under controlled lighting conditions (D65) in a viewing cabinet (Verivide Ltd., UK). This cabinet has a neutral grey-coloured background and sides, and controlled simulated daylight (D65) conditions. These types of viewing cabinets are designed to provide ideal lighting conditions for the critical and consistent assessment of colour. The Vita Shade Guide was arranged from lightest to darkest according to the standard method10 and given a numerical value, where B1 = 1 (lightest shade) and C4 = 16 (darkest shade) (Table 2). The teeth
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Table 2 – Numerical assignment of Vita Shade tabs B1 1
A1
B2
D2
A2
C1
C2
D4
A3
D3
B3
A3.5
B4
C3
A4
C4
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
were randomly assigned to either a 30 s treatment with water (n = 34) or a 0.2% (w/w) Blue Covarine in water (n = 34). The teeth were rinsed with water and remeasured as before. Visual assessors were unaware of the treatment groups. The numerical change in Vita shade was calculated from: Vita Shade change ¼ Vita Score ðtreatmentÞ Vita Score ðbaselineÞ The overall mean Vita Shade change value was calculated from the scores of the three assessors. A positive score in the Vita Shade Change indicates the tooth colour is increasing in whiteness. In parallel, CIELAB colour differences were calculated from: DL ¼ L ðtÞ L ð0Þ Da ¼ a ðtÞ a ð0Þ where L*(t) is the L* value after t minutes and L*(0) is the L* value at baseline and a*(t) is the a* value after t minutes and a*(0) is the a* value at baseline. Db* was calculated as before. In addition, a whiteness index value (WIO) was calculated from the L*, a* and b* values and the change in WIO determined. This was accomplished by calculating the CIE tristimulus values X, Y and Z from the L*, a* and b* values, and then calculating the WIO whiteness index using previously described mathematical expressions.11
2.3. Spectroscopic determination of the deposition of Blue Covarine onto pellicle coated enamel Human enamel blocks (4 mm 4 mm 2 mm) were prepared as previously described.12 In outline, the roots of human extracted incisors and molars were removed and the lingual part of the tooth flattened to approximately 3 mm thick using a high abrasive disc (Tycet Ltd., Hemel Hempstead, Herts, UK), turned over and the facial surface polished with the abrasive disc to flatten the surface. The polished sections were cut on a diamond wire cutter (Two Well Model 3242 Wire Cutter, Ebner, Le Locle, Switzerland) into approximately 4 mm 4 mm 2 mm blocks. These blocks were then planar-polished to a final finish of 0.3 mm polishing agent (Micropolish II, Buehler, Illinois, USA). Specimens were stored in sterile (gamma irradiated) human whole saliva for 16 h and rinsed with deionised water. The baseline colour of the specimens was measured with a chromameter (Minolta CR241, Minolta Camera Co. Ltd., Japan). Specimens were then treated with either Blue Covarine at concentrations of 0.02% and 2% (w/w) in deionised water or deionised water control (n = 4 for each treatment) for 1 min. Following water rinsing, the colour of the specimens was remeasured and colour changes (Db*) calculated. Immediately, the specimens were mounted on a sample holder for analysis within a time-of-flight secondary ion mass spectrometer (TOFSIMS) IV-200 Instrument (Ion-Tof, GmbH, Munster, Germany) using a polyatomic primary source (Bismuth 3) in order to
chemically detect the presence of Blue Covarine on the enamel surface. As a reference, a thin film of Blue Covarine powder was prepared on a glass slide and held in place with double-sided tape. Spectra were recorded for the Blue Covarine reference material in order to ‘‘fingerprint’’ the material and to identify suitable characteristic peaks that could be used to subsequently identify the presence of Blue Covarine. The treated enamel specimens were then scanned (500 mm 500 mm) with the TOFSIMS in order to map the distribution of Blue Covarine material across the surface.
2.4.
Dose–response from a toothpaste
Human extracted anterior teeth, mounted in acrylic as previously described above, were soaked in sterile (gamma irradiated) human whole saliva for 2 h and then rinsed with water. The baseline tooth colour was measured with a chromameter (Minolta CR-321, Minolta Camera Co. Ltd., Japan) in the CIELAB mode. A series of identical silica based toothpaste formulations were prepared with the exception that part of the water content was replaced with either 0, 0.01, 0.05, 0.10 or 0.20% (w/ w) Blue Covarine. These were mixed with water and 0.5% (w/ w) sodium carboxymethyl cellulose (SCMC) aqueous solution in a paste:water:SCMC w/w ratio of 1:1:1 for 1 h prior to the treatment of tooth specimens. The tooth specimens were randomly allocated to one of the treatment groups (n = 5 per treatment). Each tooth was brushed for 1 min with the toothpaste slurry and a flat trim toothbrush and then rinsed with water (300 ml) for 15 s. The colour of the tooth was remeasured and colour changes from baseline calculated as before.
3.
Results
3.1.
Preliminary screening of potential blue agents
The mean Db* values for the extracted teeth after treatment with different test agents (0.2%, w/w in water) and immersion in water for different time periods are shown in Table 3. This clearly shows that teeth treated with Blue Covarine gave the largest reduction in b* value, indicating a yellow–blue shift in colour, whereas other tested agents gave only relatively small changes in b* value. Statistical analyses (ANOVA) showed an overall statistical significant difference between treatments at each time point. Further statistical comparisons (Dunnett’s method) showed that Blue Covarine was the only test agent that was significantly different to the water control ( p < 0.0001).
3.2.
Perception study of the selected blue agent
The mean change in Vita Shade and DL*, Da*, Db* and DWIO values are given in Table 4. This clearly shows that the 0.2% (w/
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Table 3 – Mean Db* values after treatment with different test agents (0.2% w/w in water) and immersion in water for different time periods (n = 7) Time (min)
Db* (S.E.) Water
5 10 20 60 120
0.14 0.34 0.34 0.04 0.29
(0.17) (0.24) (0.24) (0.16) (0.29)
Patent Blue V 0.85 0.47 0.33 0.38 0.19
(0.27) (0.29) (0.19) (0.21) (0.29)
FD&C Blue No. 1 0.06 0.40 0.19 0.36 0.11
Brilliant Black
(0.16) (0.29) (0.26) (0.16) (0.16)
0.06 0.06 0.57 0.32 0.10
(0.40) (0.37) (0.43) (0.29) (0.22)
Blue Covarine 2.71 2.41 2.47 2.49 2.30
(0.50) (0.38) (0.40) (0.50) (0.50)
Table 4 – Subjective and objective measurements of teeth (n = 34) treated with water or 0.2% (w/w) Blue Covarine Treatment Water 0.2% Blue Covarine
Mean Vita Shade change (S.E.)
DL* (S.E.)
Da* (S.E.)
Db* (S.E.)
0.03 (0.51) 1.18 (0.18)
0.69 (0.16) 1.44 (0.31)
0.16 (0.06) 0.38 (0.04)
0.07 (0.09) 1.33 (0.12)
DWIO (S.E.) 0.82 (0.31) 3.64 (0.76)
w) Blue Covarine treatment gave a larger increase in mean Vita Shade change compared to water, and the difference between treatments was of high statistical significance ( p < 0.0001, Student’s t-test). The differences between treatments for the other colour parameters were also of statistical significance as follows; DL* ( p < 0.05); Da* ( p < 0.0001); Db* ( p < 0.0001), and DWIO ( p < 0.0001).
3.3. Spectroscopic determination of the deposition of Blue Covarine onto pellicle coated enamel Blue Covarine consists of a phthalocyanine ring structure with a tightly bound central copper ion as shown in Fig. 1. The TOFSIMS spectra obtained from the Blue Covarine reference clearly showed peaks due to the molecular species [M H] at m/z of +575, 576, 577, 578 and 579. These were found to be relatively intense and gave rise to a characteristic intensity pattern due to ions with additional H atoms overlapping with the copper isotope peaks (Fig. 2). The mean colour change (Db*) (S.E.) for the 2.0% and 0.02% Blue Covarine treated specimens were 2.33 (0.74) and 1.34 (0.39), respectively. For the control pellicle coated enamel
Fig. 2 – Typical TOF-SIMS spectrometry results for (a) Blue Covarine powder, (b) enamel–water, (c) enamel–0.02% Blue Covarine and (d) enamel–2.0% Blue Covarine.
specimens treated with water, the TOF-SIMS spectra did not show any of the characteristic peaks for Blue Covarine. Checks were made on the data for the presence of salivary pellicle and there were found to be several low mass nitrogen-containing fragment ions that would be consistent with the presence of peptide-like or similar materials. All specimens treated with Blue Covarine did show the presence of intense characteristic peaks for the Blue Covarine fingerprint in the 500–600 Da range (Fig. 2). When the enamel surfaces were mapped with the TOFSIMS for specific ions, it was found that Blue Covarine was relatively evenly distributed on the 0.02% (w/w) Blue Covarine treated surfaces (Fig. 3). Similar distributions were observed for the 2.0% (w/w) Blue Covarine surfaces. No Blue Covarine was detected on the water treated control surfaces.
3.4.
Fig. 1 – Chemical structure of Blue Covarine.
Dose–response from a toothpaste
The mean Db* and DWIO values versus Blue Covarine concentration in a silica based toothpaste are shown in Figs. 4 and 5, respectively. Figs. 4 and 5 clearly show a decrease
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Fig. 3 – TOF-SIMS positive ion images of an enamel surface treated with 0.02% (w/w) Blue Covarine; total ions (left) and Blue Covarine (right).
Fig. 4 – A plot of mean Db* values (S.E.) versus Blue Covarine concentration.
Fig. 5 – A plot of mean DWIO values (S.E.) versus Blue Covarine concentration.
in tooth yellowness and an increase in tooth whiteness with increasing Blue Covarine concentration, with linear correlation coefficients of 0.9681 and 0.8671, respectively.
4.
Discussion
The use of in vitro models is an important step for the initial identification of new oral care actives and the preliminary evaluation and optimisation of product prototypes. There have
been a large number of in vitro models described in the literature which have been successfully used to evaluate the efficacy and safety of tooth whitening actives and products.3,4,13 In general, these models use whole or cut human or bovine tooth specimens and utilise their pre-existing natural colour, although a few models have increased the level of intrinsic stain of the tooth by pre-staining with black tea or blood components.3 The colour measurement of teeth is possible using a number of techniques, including visual comparison with a shade guide, spectrophotometers, colorimeters or digital image analysis.5 In general, colorimeters have shown good repeatability of natural tooth colour measurements in vitro and in vivo14–16 and have been used successfully in measuring colour changes of teeth following tooth bleaching treatments.3 In the current study, the use of a colorimeter for objectively measuring changes in tooth colour has again been demonstrated as a suitable method. When tooth specimens are treated with Blue Covarine the colorimeter is sensitive enough to measure the changes in colour from baseline. In the first study, it was demonstrated that Blue Covarine was the only material tested to give a significant reduction in b* value compared to the water control. This reduction in b* value is most likely due to the deposition of the Blue Covarine onto the tooth surface, which imparts a change to the optical properties of the tooth surface. The reduction in b* value was also maintained for the duration of the experiment of 120 min water rinsing, which indicates that the Blue Covarine has a relatively high affinity for pellicle coated tooth surfaces. In contrast, all other materials tested had a relatively poor affinity for the surface and/or were readily removed upon rinsing with water, since no significant changes in b* values were observed compared to the water control. Thus, further in vitro studies were conducted on the Blue Covarine material. In the second study, the effects of Blue Covarine on tooth colour and whiteness were assessed objectively with a colorimeter and subjectively via visual assessment by colour matching of the tooth specimen with a shade guide. A number of factors can affect shade guide usage in clinical dentistry, for example lighting conditions, room de´cor, experience of the assessor and fatigue of the human eye.3,5 Therefore, care must be taken to standardise and control these factors. In the
journal of dentistry 36s (2008) s8–s14
current study, the tooth specimens were visually assessed in a viewing cabinet. The use of viewing cabinets has been described and used in a number of in vitro dental studies where visual colour assessment of the specimens was critical, for example the matching and colour acceptance of dental materials17,18 and assessing shade differences between acrylic resin dentures and natural teeth.19 Using this set-up, a mean Vita Shade change from baseline of 1.18 was observed for the Blue Covarine treated tooth specimens compared to 0.03 for the water control. The increase in mean Vita Shade demonstrates that the Blue Covarine is able to impart a visual perceptual increase in tooth whiteness. This is in sharp contrast to the water-treated tooth specimens where no significant change from baseline was observed. It has been argued that even though a change in b* value is an important indicator of tooth whitening, none of the component vectors of CIELAB should be considered in isolation to measure tooth whiteness.20 Although CIELAB is one of the recommended colour systems for application in dentistry,21 it was not designed to measure whiteness.20 Currently, different whiteness indices exist,11 but in order for a whiteness index to be valid it must be used on the types of materials for which it is intended. For example, WIC (CIE recommended whiteness index) is widely used in the textile, paint and plastic industries. The WIC has been investigated for its suitability in determining the visual perception of whiteness of teeth by Luo et al.22 In their psychophysical experiments, 26 teeth samples were ordered in terms of perceived whiteness under controlled conditions by nine observers and compared with instrumental measurements of the same samples. It was found that, although the correlation coefficient (r2) was good (0.87), the WIC was inadequate in that it would generate about 13.5% wrong decisions (compared with the average visual performance of 5.7%). Luo et al.22 then proposed a modified version of the whiteness index (WIO) which was shown to be more suitable for the visual assessment of tooth whiteness. In addition, the WIO was shown to be the most appropriate index to measure changes in tooth whiteness following a tooth bleaching regime.20 For the objective colour measurements in the perception study, the tooth specimens treated with Blue Covarine showed significant changes in all CIELAB colour components compared to the water control. Despite the slight reduction in L* value for Blue Covarine treated specimens, which on its own might imply the lightness of the tooth has been slightly reduced, there is also a reduction in a* and b* values, and as discussed above, none of the component vectors of CIELAB should be considered in isolation to measure overall tooth whiteness. Therefore, the L*, a* and b* values were converted to the WIO whiteness index and shown to give an overall increase in whiteness for the Blue Covarine treated teeth. Thus, Blue Covarine changes the optical properties of teeth by shifting their colour from one area of the colour space to another, where the new tooth colour can be measured objectively and perceived subjectively as whiter. Using the current methods it is now possible to measure increases in tooth whiteness both subjectively and objectively on the same tooth specimens following tooth whitening treatments, including Blue Covarine optical effects technology and hydrogen peroxide bleaching.20 In addition, this approach
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may prove valuable in determining and comparing tooth whitening effects of other technologies and techniques in the future. The retention of Blue Covarine on the tooth surface in vitro was evaluated only up to 120 min in an aqueous environment. Considering that the Db* values did not change significantly between 60 and 120 min of water rinsing, it is speculated that the optical effect could last for many hours longer. The longevity of the effect under in vivo conditions may be different and needs further investigation. However, the potential of the Blue Covarine optical route to give an instant and perceivable tooth whitening effect following brushing has been demonstrated in vitro. TOF-SIMS is a powerful surface characterisation technique that is able to determine the composition, structure, orientation and spatial distribution of molecular and chemical structures on a biomaterial surface.23 Indeed, it is a technique that has been applied to the chemical characterisation of a wide range of different types of surfaces, including those relevant in the dental field. For examples, determining fluoride uptake on enamel,24 chemical characterisation of peritubular dentine25 and various calcium phosphates including hydroxyapatite.26 In the current study, we have shown the applicability of TOF-SIMS to the chemical detection of Blue Covarine deposition onto pellicle coated enamel surfaces. In addition, Blue Covarine is deposited relatively uniform across the surface in a non-specific way. This confirms that the yellow–blue colour shift of the enamel specimens occurs due to the direct deposition of Blue Covarine onto the enamel surface. Tooth whitening products are marketed in many different formats including gels, paint-on products, strips, mouth guards and toothpaste.3 However, one of the most accessible products for many patients and consumers is toothpaste and the growth in the tooth whitening market is reflected by the growth in the whitening toothpaste sector.27 In the final experiment, Blue Covarine was formulated into a silica based toothpaste formulation in order to investigate whether Blue Covarine optical effects can be delivered from this format. From Figs. 4 and 5 it can clearly be seen that Blue Covarine containing toothpastes can reduce tooth yellowness and increase tooth whiteness, respectively, after a 1 min brushing protocol. In addition, there is a clear dose–response effect with higher concentrations of Blue Covarine giving rise to reduced levels of yellowness and increased levels of whiteness. Traditional tooth whitening methods typically involve either peroxide-based bleaching to effect intrinsic tooth colour changes or abrasive cleaning to effect extrinsic stain removal.3,4 From the experiments described in the current work, Blue Covarine has been identified as a new approach to tooth whitening. The mode of action of Blue Covarine involves its deposition and retention on tooth surfaces where it can alter the optical properties of the tooth by primarily giving a yellow to blue colour shift. However, the overall colour shift ultimately gives rise to an increase in the measurement and perception of tooth whiteness. What is most unexpected is that these effects can be demonstrated after only one treatment of a relatively short exposure time (e.g. 30 s) and can be effectively delivered from a toothpaste formulation after brushing for only 60 s. Thus, this technology has great
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potential for developing the next generation of tooth whitening toothpastes whereby an instant whitening effect may be achieved after just one brushing. In addition, this potential new whitening toothpaste would have the recognised health benefits of an efficacious source of fluoride to prevent and reverse caries processes together with an effective abrasive and surfactant system for tooth cleaning. Future work will focus on the further development of such toothpaste formulations with optimised Blue Covarine delivery, together with measurement of the relevant optical effects in vivo and overall consumer acceptability in terms of other sensory and in-use attributes (e.g. flavour and foam quality). In conclusion, within the limitations of the studies Blue Covarine has been identified as a new approach to tooth whitening. Its mode of action involves deposition and retention on tooth surfaces where it can alter the optical properties of the tooth which ultimately gives rise to an increase in the measurement and perception of tooth whiteness.
[14]
Role of funding source
[15]
This supplement was supported by Unilever Oral Care. The authors retained full editorial control and responsibilities throughout the preparation of the manuscripts.
[8]
[9]
[10]
[11] [12]
[13]
[16]
[17]
Conflict of interest All authors are employees of Unilever.
Acknowledgements The authors would like to thank Ian Hopkinson (Unilever Oral Care) for his help in the colour calculations and Ian Fletcher (Intertek MSG, Cleveland) for his help with the TOF-SIMS analyses.
[18]
[19]
[20]
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