GB2412316A - Peroxide tooth whitening composition - Google Patents

Abstract

An oral care composition comprising a peroxide containing compound dispersed in an orally acceptable carrier, wherein the carrier comprises a humectant and a combination of bioadhesive agents consisting essentially of at least one natural gum and a carbomer. The Preferred peroxide sources include hydrogen peroxide, carbamide peroxide, calcium peroxide and percarbonates. Preferred humectants include glycerine, sorbitol, propylene glycol, glucose, sucrose and low molecular weight polyethylene glycols. Preferred gums include xanthan gum, carrageenan, alginates, gum karaya, guar gum, gum Arabic and pectins. Suitable carbomers homo- or copolymers are high molecular weight polymers of acrylic acid crosslinked with allylsucrose or allyl ethers of pentaerythritol. These carbomers may be partially or fully neutralised. Compositions comprising carabamide peroxide or hydrogen peroxide, glycerine, xanthan gum and a carbomer copolymer are exemplified. Such compositions show excellent substantivity to the teeth as a result of a synergistic interation between the gelling agents.

Description

ORAL COMPOSITION

The present invention relates to an oral care composition containing a peroxide containing compound. Specifically the present invention relates to a stable tooth whitening composition comprising synergistic gelling agents. Said composition shows excellent substantivity to the teeth.

White teeth have long been considered cosmetically desirable. Unfortunately, teeth almost invariably become discoloured in the absence of intervention. The tooth structure which is generally responsible for presenting a stained appearance is the enamel layer. Several factors contribute to enamel discoloration, but the three main factors are believed to be: (i) formation of plaque and tartar matrices on the tooth surface which then entraps stains; (ii) ingestion of certain drugs during gestational tooth formation; and (iii) discoloration due to oral cavity traumatization following which blood break-down products seep into the mineralized area of the teeth during enamel formation.

Over-the-counter teeth whitening preparations have been developed to address the cosmetic preference of many to restore luster to tooth enamel discolored by surface entrapped materials. There are various approaches to enamel whitening currently in general use. One approach is a physical abrading of the stain to effect stain removal, however this can be seen as potentially harmful to the teeth. This mechanical process may therefore be supplemented or even replaced by a chemical process which may involve an oxidative or enzymatic step to effect stain removal.

The chemical process generally utilizes a tooth whitening or bleaching formulation applied to a stained tooth surface for a specified period, after which the formulation is removed. Oxidizing agents represent one of the most widely distributed and utilized active agents in commercially available tooth whitening or bleaching products. Peroxide-containing agents such as carbamide peroxide, hydrogen peroxide and calcium peroxide are the most commonly used oxidizing agents, and are typically formulated into a liquid, solution, gel or paste. However it is known that products containing such agents may lose their whitening efficacy with time and retaining these types of formulations in the oral cavity, particularly in contact with the teeth has proved a problem. Moreover low viscosities of aqueous peroxide solutions do not allow the peroxide whitening agent to remain in contact with the teeth for the necessary time period to effect substantive whitening because of constant flushing effects of salivary secretions. The prior art indicates that viscous formulations show good substantivity when used in the oral cavity. EP-B 1 161 198 (Procter & Gamble Company) disloses a tacky or sticky aqueous tooth whitening substance suitable for application to the oral cavity via a thin film strip. However there remains a need for alternatives that do not suffer the drawbacks encountered with known formulations. It has therefore become desirable to provide simple formulations that do not require extensive stabilization, that are easy to manufacture and have excellent substantivity when applied directly to the oral cavity.

It has since been shown that viscosity is not directly related to substantivity and it is possible for a highly viscous formulation to show poor substantivity. The present invention therefore shows that substantivity effects can be increased synergistically by combining certain gelling agents.

It is an object of the present invention to provide a composition that meets these requirements. According to the invention there is provided an oral care composition comprising a peroxide containing compound dispersed in an orally acceptable carrier, wherein the carrier comprises a humectant and a bioadhesive agent consisting essentially of at least one natural gum and a carbomer.

Peroxide containing compounds used as whitening agents in the present invention include the following compounds and mixtures thereof: hydrogen peroxide e.g. as a or 35%w/w aqueous solution, carbamide peroxide, calcium peroxide and percarbonates. - 2

Suitably the total amount of peroxide present in the liquid whitening composition of the invention is in the range of 1 to 40% w/w, preferably in the range 10 to 30%w/w, more preferably in the range 5 to 20%w/w.

A humectant is a key component of a composition of the invention. Suitable humectants include the following and mixtures thereof: glycerin, sorbitol, propylene glycol, sugars, such as glucose or sucrose, and low molecular weight polyethylene glycols (PEGs) i.e. in the range 200-600 e. g. PEG 200, 300, 400, and 600, available from Dow Chemicals USA, PO Box 1206, Midland MI48642. Glycerin is available from Albion Chemical Distributers, 215, Tunnel Ave., Greenwich, London SE10 OQW. Preferred humectants include glycerin and PEGs.

Suitably the humectant is present in an amount ranging from 30 to 95%w/w, preferably in the range 50 to 75%w/w, more preferably from 40% to 60%w/w.

A combination of bioadhesive agents are included in a composition of the invention.

In the present invention the bioadhesive agents will exhibit excellent adhesive properties i.e. have a strong affinity for biological surfaces such as teeth.

The combination of bioadhesive agents will include a natural gum and a carbomer material. Natural gums useful in the present invention include Xanthan Gum, Gum Karaya, Carragenan, Alginates, Guar Gum, Gum Arabic, Gum Ghatti, Locust Bean Gum, Tara Gum, Fenugreek Gum, Gum Tragacanth, Tamarind Gum, Gellan Gum, Succinoglucan Gum, Welan Gum, Rhamsan Gum, Aloe Polysaccharides, Chia Gum, Flaxseed Gum, Okra Gum, Psyllium Seed Gum, Quince Seed Gum, Curdlan, Pullulan, Pectins and mixtures thereof. Xanthan gum is also known by the tradename Keltrol and is available from Nutrasweet Kelco Co Ltd.,Penrhyn Road, Knowsley Industrial Estate, Prescot, Merseyside. L34 9HY, England. The preferred natural gum for use in the invention is either xanthan or karaya gum. The most preferred is xanthan. - 3

The term carbomer refers to both carbomer homopolymers and copolymers and their metal salts. Carbomers are synthetic high molecular weight polymers of acrylic acid that are crosslinked with either allylsucrose or allylethers of pentaerythritol. Carbomers can be either partially or fully neutralized. Suitable carbomers include the copolymers and homopolymers under the Carbopol(D name available from Noveon Inc., 2468 Industrial Parkway, Calvert City, Kentucky 42029, USA. Preferred polymers include Carbopol 974 and Carbopol 971.

Polymers such as Pemulen_ and Ultrez_ may also be used, examples of which include Pemulen TR1, Pemulen TR2 and Ultrez 10.

Most preferably the bioadhesive agents are a mixture of a natural gum ea. Xanthan gum and a carbomer copolymer e.g.Carbopol 974P.

Suitably the total amount of bioadhesive agents present are in an amount ranging from 0.1 to 20% w/w, preferably from 0.5 to 15%w/w, more preferably 1 to 10%w/w.

The composition may also comprise water, preferably deionised water. Water is an optional ingredient but if present it may be from 15 to 60%w/w, preferably 20 to 40% by weight of the composition (including the contribution from the aqueous peroxide ingredients, if used in this form).

Alcohol may also be present in the compositions disclosed herein. Alcohol may be used as an additional carrier, will increase the stability of the composition and will allow easy application of the composition to the teeth. Once the composition is applied to the teeth the alcohol will rapidly evaporate leaving the active ingredients firmly adhered to the teeth. Suitably 96% (pharmaceutical grade) ethanol is used.

Suitably alcohol may be used in the range 1 to 70%w/w, prefereably 5 to 40%w/w and more preferably 7.5 to 20%w/w.

Additionally, compositions of the present invention will suitably contain acceptable additives or excipients conventional in the field of oral care products including for example chelating agents such as ethylenediaminetetraacetic acid and/or citric acid, antisensitivity agents such as potassium and strontium salts, colouring agents, a fluoride source such as sodium fluoride or sodium monoflurophosphate, flavouring agents and sweetening agents. The additives or excipients used in any given composition will be compatible both with each other and with the essential ingredients of the composition such that there is no interaction which would impair the performance of the active ingredients. All additives or excipients must of course be non-toxic and of sufficient purity to render them suitable for human use.

A pH adjusting agent may also be added to aid stability and to make the composition sate for oral use. The pH of the whitening compositions prior to use is approximately 4.5-6. During use the formulation rapidly takes up moisture from the teeth surface, allowing for the wetting and swelling of the gum. This is turn may solubilise the carbomer raising the pH to above this value, e.g approximately 6.5.

This in itself thickens the gel by increasing its bioadhesive properties. The rise in pH observed is beneficial to the breakdown reaction of the peroxide and so increasing the bleaching efficiency of the formulation.

The oral care composition of the invention is a highly viscous liquid or gel that may be presented in any form that is suitable for application to the oral cavity. It may conveniently be applied to one or all of the teeth. On application to teeth, the composition forms a protective barrier which adheres firmly to the teeth and retains the components of the formulation in a matrix-type environment.

The composition adheres sufficiently to remain on the teeth for a period of time e.g. up to a few hours. Suitably the composition is applied at night time, allowing peroxide activity to take place during sleep periods. During use, the peroxide is released slowly from the gel, in an amount and at such a rate as required to effect stain removal. The gel may be removed from the user's teeth by any convenient means e.g. brushing and/or by rinsing with a mouthwash.

The term "painted onto the teeth" above is intended to encompass all manner of applying the whitening composition to the teeth and includes sponging, coating, daubing, spraying, wiping and rubbing. Preferably the composition is applied to the teeth with a soft applicator brush. Suitably the composition is housed in a container such as a bottle or tube, and the composition is applied with a soft applicator brush.

If the composition is to be supplied in a bottle and brush this may be provided in a kit form e.g. as may be used with a conventional nail varnish kit. Alternatively the composition may be housed in a dispensing device such as a pen with an applicator brush attached thereto e.g. generally of the type used with the Brite Smile To Go_ Whitening pen.

The whitening compositions of the present invention are prepared by adding and mixing the ingredients of the composition in a suitable vessel such as a stainless steel tank provided with a mixer. In the preparation of the composition the carbomer was slowly added to the humectant to allow dispersion and was then neutralized with NaOH to obtain the appropriate pH. The natural gum was then dispersed separately in a further carrier (if necessary) and added to the mixture in the vessel. The mixture was mixed until homogeneity was achieved. The final whitening product prepared is then suitably packaged and stored as required.

Advantageously the composition of the invention is suitably prepared as a single or one component system i.e. it does not require segregation and then mixing of ingredients just prior to use. In a second aspect of the invention there is provided a kit of parts comprising an anhydrous liquid tooth whitening composition as hereinbefore described, a container for housing the composition and an applicator for applying the composition to teeth to be whitened.

In an alternative aspect there is provided a method of whitening teeth comprising: a. preparing a tooth whitening composition as hereinbefore described; b. painting the composition onto teeth to be whitened, suitably at night-time c. maintaining the composition in contact with the teeth for a plurality of hours per day. - 6

d. repeating steps b and c for multiple days e.g. up to fourteen days, to thereby whiten the teeth.

The present invention is illustrated by the following examples but is not limited thereby.

Examples

I. A composition was prepared having the following ingredients: Ingredient | %w/w l Glycerin 44.50 Keltrol 2.00 Carbopol 974 1.00 Deionised water 23.00 Hydrogen peroxide (35%w/w) 16.00 Ethanol 13.00 Stabilisers 0.50 Total 100.00 * Keltrol is a tradename for Xanthan gum II. A composition was prepared having the following ingredients: Ingredient gowlw PEG 6 25.00 Keltrol 2. 00 Carbopol 974 1.00 Deioinsed water 50.00 Hydrogen peroxide (30 % wlwj 20.00 Stabilisers 2.00 Total 100.00 *Keltrol is a tradename for Xanthan gum A composition was prepared having the following ingredients: Ingredient | %w/w l Propylene Glycol 75.00 Keltrol 2.00 Carbopol 980 2.00 Ethanol 9.50 Carbamide peroxide 11.00 Stabilisers 0.50 Total 100.00 *Keltrol is a tradename for Xanthan gum Determination of Gel SubstantivitY Method Hydrated bovine teeth were treated with gel that was labelled with a dye e.g. erythrosin. The treated teeth were then placed in a shaker bath containing Phosphate Buffer Saline. The treated bovine teeth were then assessed for the percentage of gel remaining every 5 minutes for 30 minutes. The Substantivity Score was then measured as the sum of percentage of gel remaining through the course of the experiment.

Results The results are shown in Fig 1 below that shows the synergy in the substantivity property with the combination of xanthan gum and Carbopol 974.

Conclusion

Synergy was shown to exist when xanthan gum was mixed with Carbopol 974. 8

Determination of bleaching effects using Bovine Enamel Whitening Model.

The bleaching effects of the composition disclosed in Example l above was determined and compared to the bleaching effects observed with a commercially available preparation.

Method Bovine teeth were used and L* (from CIE 1976 L*a*b* colour space scale) was measured at the start of the experiment using a spectrocolorimeter. Example l was applied to the teeth and these were placed into a container such that a liquid substantivity challenge was applied to the treated teeth. At the end of the treatment time the teeth were rinsed and dried and L* was remeasured using a spectrocolorimeter. This method was repeated for a number of days to mimic in-vivo night time use of the product. At the end of the experiment the overall change in L* (i.e AL) was calculated.

Results The results are shown in Figure 2 below.

Conclusion

The results indicate that the change in L (AL)after 14 hours treatment was higher than a commercially available night time product.

Claims (6)

1. Claims 1. An oral care composition comprising a peroxide contaning

   compound dispersed in an orally acceptable carrier, wherein the carrier comprises a humectant and a combination of bioadhesive agents consisting essentially of at least one natural gum and a carbomer.
2. 2. An oral care composition according to claim 1 wherein the peroxide containing compound is selected from hydrogen peroxide, carbamide peroxide, calcium peroxide, percarbonates, and mixtures thereof.
3. 3. An oral care composition according to claim 1 or claim 2 wherein the humectant is glycerin.
4. 4. An oral care composition according to any one of claims 1 to 3 wherein the bioadhesive agents are selected from Xanthan Gum, Gum Karaya, Carragenan, Alginates, Guar Gum, Gum Arabic, Gum Ghatti, Locust Bean Gum, Tara Gum, Fenugreek Gum, Gum Tragacanth, Tamarind Gum, Gellan Gum, Succinoglucan Gum, Welan Gum, Rhamsan Gum, Aloe Polysaccharides, Chia Gum, Flaxseed Gum, Okra Gum, Psyllium Seed Gum, Quince Seed Gum, Curdlan, Pullulan, Pectins and mixtures thereof plus a carbomer homopolymer or copolymer.
5. 5. A kit of parts comprising a tooth whitening composition according to any one of claims 1 to 4, a container for housing the composition and an applicator for applying the composition to teeth to be whitened.
6. 6. A method of whitening teeth comprising: a. preparing a tooth whitening composition according to any one of claims 1 to - 10 4; b. painting the composition onto teeth to be whitened; c. maintaining the composition in contact with the teeth for a plurality of hours per day; and then d. repeating steps b and c for multiple days to thereby whiten the teeth. 11