Oral Hygiene Product for Tooth Whitening Based on the Natural Product Curcumin ^†

Abstract

Introduction: In everyday life, many people smoke, eat colored foods, and drink coffee, tea, and other beverages. The use of herbal products containing natural ingredients is better accepted by the public because of their safety. The aim of the present study was to develop two formulations of curcumin-based gels and investigate their anti-dyschromic qualities in teeth. Materials and Methods: This is an in vitro therapeutic clinical trial. A series of experiments was carried out on extracted teeth (n = 30). Samples were randomly divided into five subgroups. Readings were taken initially (T1), and then after immersion in a blackening process (T2). The brightening agent was applied for 5 min, three times a day. After 30 days of applications, new measurements were taken using a Vita Classical shade guide. Results: The curcumin and xanthan gum hydrogel that was used topically demonstrated superior efficacy in reducing dental dyschromia. These promising results suggest that this formulation could be an attractive option for the treatment of dental dyschromia. Conclusions: Curcumin-based gel presents itself as a promising candidate for the prevention and/or treatment of dental dyschromia. In addition, it has an excellent safety profile.

1. Introduction

Tooth discoloration, because of its impact on esthetic appearance, is frequently cited as a major esthetic concern, which can have significant psychological repercussions for some people.

A beautiful smile is considered a sign of youth, health and beauty, and a large number of patients seek a bright, white smile by trying various dental brightening techniques. The frequent and abusive use of lightening agents has led to an increase in the incidence of adverse effects associated with their use.

Herbal products are now a good alternative source because of their lower side effects and greater acceptance.

We have chosen to focus our attention on the botanical plant “Curcuma longa”, for which we propose a major contribution by exploring the plant’s innovative prospects as a natural product that could act as a next-generation solution for tooth whitening.

2. Materials and Methods

This is an in vitro study for a therapeutic trial. The work was carried out between March 2022 and July 2023 at the Conservative Odontology and Endodontics Department and the Galenical Pharmacy Laboratory of the Faculty of Medicine—Tlemcen.

The aim of this research is to develop a curcumin-based hydrogel and cream for the treatment of dental dyschromia, while evaluating the clinical efficacy of both formulations.

We will design a detailed experimental protocol. In addition, we will explore the various tools and techniques used in the development of our formulation. Throughout this study, we will draw on methods and procedures used in the field of dental product formulation to ensure reliable, reproducible results.

Thirty upper and lower human teeth were obtained from several dental practices in Tlemcen. Selected teeth were conditioned in a saline solution (0.9% sodium chloride), which was changed every 24 h and then cleaned, with any soft tissue residues removed.

A blackening process was prepared by combining equivalent quantities of coffee, tea, and soft drinks to obtain a dark mixture. The teeth were placed in glass vials containing the blackening process solution for 96 h at a temperature of 37 °C. After 96 h, the teeth were cleaned and dried.

A series of ethanoic solutions of curcumin at increasing concentrations were prepared to determine the amount of curcumin needed to obtain a lightening effect.

The solution was applied to the teeth three times a day, for 15 min, over a 30-day period. The brightening effect of the teeth contained in the preparation was assessed by eye with Vita Classical A1-D4 tinting.

The choice of dosage form for our curcumin-based tooth whitening product is a gel. This decision was motivated by its semi-solid form, which enables an easy and precise application to the teeth, thus ensuring prolonged contact with the tooth surface, and its pleasant texture, which enables curcumin to be incorporated effectively, ensuring better bioavailability and optimal penetration into dental tissue. Two gel products have been prepared: a xanthan gum gel and a curcumin-based Carbopol gel.

3. Results

A Vita Classical A1-D4 colorimeter was used to measure color (

Table 1. CIELAB coordinates [1].

CIELAB Coordinates for Vita Classical Shades
Vita Classical
Shades	L*	a*	b*
C4	34.92	7.23	12.87
A4	43.05	8.34	14.94
C3	46.29	6.78	12.88
B4	50.02	8.17	18.33
A3.5	48.94	8.49	15.70
B3	49.28	7.97	16.83
A3	56.16	7.96	14.58
D3	55.65	7.19	11.69
D4	55.57	6.18	14.40
C2	54.83	6.87	13.40
C1	55.87	5.15	8.81
A2	60.55	6.99	12.46
D2	59.41	5.59	8.59
B2	61.90	6.09	12.55
A1	63.46	5.05	9.11
B1	9.85	4.24	7.34

). The samples were measured initially, after immersion in the darkening process, and also after the lightening procedure. Additional artificial saliva was added as required to keep the teeth moist.

The color change (∆E*ab) was calculated using this equation:

∆E* ab = [(∆L*) 2 + (∆a*) 2 + (∆b*) 2] 1/2

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-Vertical parameter L*: Reference to luminosity;

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-Color coordinates a*: Chromatic axes in the red–green direction;

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-Color coordinates b*: Chromatic axes in the yellow–blue direction;

The CIELAB-based whiteness index was calculated as follows:

WI D = 0.511 L* − 2.324 a* − 1.100 b*

When the ΔE was above the threshold of acceptability (ΔE* > 3.48), it was considered as a clinically visible change, while a value of 1.74 was accepted as the threshold of perceptibility. Theorem-type environments (including propositions, lemmas, corollaries, etc.) can be formatted as follows.

For samples immersed in the liquid from the blackening process, the teeth underwent a color change perceptible to the naked eye, exceeding the acceptability threshold for some samples.

In terms of color change after tooth lightening using dental cream and curcumin hydrogel, both products produced positive changes. However, the group using xanthan gum showed a more significant difference than the group using Carbopol.

With regard to the whiteness index (WI D), the highest values were observed in samples treated with xanthan gum. Comparing the whiteness index with the acceptability and perceptibility thresholds, it was found that after 30 days, the xanthan gum group had values above both thresholds for the following samples: 01, 02, 03, 04, and 05; sample 06 had a decrease in L* and a* and an increase in the b* parameter, but significantly eliminated the tooth stain.

With regard to the whiteness index (WI D), the Carbopol group showed a negative value for sample 01, while samples 02 and 03 showed no significant result in terms of tooth lightening. Sample 04, on the other hand, did show a result.

4. Discussion

The aim of this study was to evaluate the effect of brushing with a natural agent, curcumin. Curcumin, a popular but unspecified agent used to brighten teeth, is widely available on the Internet without any scientific basis or proof [2].

The result was a yellowing of the first and second test samples. The increase in the yellow chroma of the samples can be justified by the essential oils. The literature results indicate that after 30 days samples containing curcumin showed a decrease in yellow saturation, and that the decrease in yellow chroma after 30 days can be explained by the fact that curcumin is a non-polar polyphenol. Pigmented solutions such as coffee and tea with high polarity leach out, causing a color change through the pigmentation of enamel chromophores. As curcumin is non-polar, there is no leaching, which reduces its penetration capacity. Thus, during longer brushing, equivalent to 30 days [3], the abrasiveness of curcumin could suppress the initial coloration (after 14 days), where they evaluated the color of a curcuma extract-based toothpaste.

The results of the literature report offer contradictory conclusions regarding the persistence of yellow saturation, even after 30 days. We concluded that the concentrations of curcumin used in the first and second tests were above a certain threshold, and based on this conclusion, we decided to significantly reduce the concentration of curcumin used.

In addition, curcumin has low water solubility, chemical stability, and oral bioavailability [3], so although positive results have been reported for various techniques used for dental brightening, some significant drawbacks remain with current systems. From the above, it can be understood that what is needed are stable, pre-mixed viscous/gelled brightening compositions that do not cause the premature decomposition of the active dental brightening agent.

Various formulations of curcumin in powder, paste, gel, and poultice form have been widely used, proving its various pleiotropic effects. It is known for its formidable anti-inflammatory, antioxidant and antimicrobial properties, as well as for its hepatoprotective, immunostimulant and antiseptic properties [4].

We decided to formulate two products specifically for their tooth-lightening effect, those being aqueous gels containing curcumin. We chose to apply curcumin locally as a gel rather than as a mouthwash or buccal irrigant. This is because a gel has the advantage of longer retention in the mouth than a mouthwash or buccal irrigant.

Thickening agents or gelling agents help to increase viscosity, facilitate placement, and ensure that the composition remains in place during treatment. Thickening agents preferably have the quality of being substantially inert in the presence of the brightening agent and are not easily broken down by it. Thickening agents that are substantially hydrophilic have been found to be preferred in the present invention.

The null hypothesis was that there would be no difference in the surface color of the tooth enamel brushed with these two products. The null hypothesis was rejected because the two formulations resulted in a color change, even above the perceptibility threshold for some samples. Nevertheless, the color change was below the threshold of acceptability after 30 days of brushing for some samples tested with the second formulation and in sample 06 of the first formulation.

The application of color science to dentistry has made it possible to measure tooth color objectively, with the most commonly used color space today being CIELAB [5] (Commission Internationale de l’Eclairage). In fact, many researchers in different countries have reported L*, a*, and b* values for teeth measured in vivo using instrumental techniques such as spectrophotometers, colorimeters, and digital image analysis. In general, these studies show a wide range of L*, a*, and b* values [6,7], but consistently show that there is a significant contribution from b* or yellowing to natural tooth color. Further developments in color science have led to the description of tooth whiteness and changes in tooth whiteness on the basis of whiteness indices.

The WI D index [7] is used in dentistry to assess lightening perceptibility, by correlating visual assessments with CIE L*a*b* coordinates. The application of this index reduces the subjectivity of visual analysis and quantifies the lightening effect. High positive WI D values indicate higher whitening perceptibility, while low values are associated with lower whitening perceptibility, discolored, or less white teeth.

A comparison of the mean values of L*, a*, and b*, after T2 and T3, enables us to analyze these variations, with curcumin causing an increase in the L* parameter of 9/12 samples.

Although xanthan gum showed a more pronounced lightening effect than Carbopol in these preliminary studies, it is important to note that these results do not lead to the conclusion that Carbopol has no lightening effect.

The technique of keeping the teeth soaked in artificial saliva may lead to dilution or rubbing effects. However, it is more likely that this method approximates an ideal scenario rather than the real oral environment, where dilution and friction effects would be more pronounced [8].

To draw definitive conclusions on the brightening effect of Carbopol, further research is essential to fully assess its effect in terms of tooth brightening. Further studies, involving larger samples, rigorous experimental protocols, and in-depth analysis, will be required to obtain more comprehensive and reliable results.

5. Conclusions

In conclusion, the management of dental dyschromia is an essential part of modern esthetic dentistry.

In our study, we explored the use of innovative curcumin–xanthan and curcumin–Carbopol products for the treatment of dental dyschromia. The results showed that curcumin–xanthan had a more pronounced effect, representing a promising advance in the field of esthetic dentistry. We can conclude that, although curcumin was an effective lightening agent, it was not the only one.

6. Patents

A patent has been registered with the Algerian National Institute of Industrial Property.