This application relates to compositions for coating teeth, in particular to formulations that form a film on the teeth.

Compositions for coating teeth may have utility for a number of reasons, including acting as a barrier against damage (eg acid erosion), staining or decay, delivering active ingredients to the teeth, or to give the teeth an artificial colour. However, existing coatings have a number of disadvantages, including poor resistance to mechanical stress from mastication and staining from food and drink such as coffee and wine.

There has now been devised improved formulations for coating teeth that overcome or substantially mitigate the above mentioned and/or other problems associated with the prior art.

According to the first aspect of this invention, there is provided a composition for coating teeth, the composition comprising:

a film forming polymer; and

an orally acceptable solvent.

The most preferred film forming polymers are polyacrylate polymers and in particular polyacrylate copolymers. Suitable polyacrylate copolymers include those referred to by the brand name, Eudragit ^® . The film forming polymer most preferably comprises methyl methacrylate and in particular may be a copolymer comprising methyl methacrylate and either methacrylic acid or ethyl acrylate. The film forming polymer may comprise ammonium groups, which may be present as a salt, such as a methacrylic acid ester with quaternary ammonium groups, which may enhance the permeability of the coating to oral care actives or other substances.

The most preferred film forming polymers are anionic copolymers of methacrylic acid and methyl methacrylate, including those referred to by the brand name Eudragit ^® S100, or copolymers of ethyl acrylate, methyl methacrylate and a methacrylic acid ester with quaternary ammonium groups, in which the ammonium groups are present as a salt, including those referred to by the brand name Eudragit ^® RL or Eudragit ^® RS. These polymers have been found to form an effective tooth coating, in particular by bonding effectively to the surface of teeth and resisting erosion by water.

The incorporation of a suitable film forming polymer is necessary to obtain the barrier properties that will provide an effective tooth coating, for example to provide protection from acid erosion and appropriate sustained release of active ingredients and flavours. A particular challenge is to achieve a coherent application of this functional polymer coat whilst conforming to the surface of the tooth. The coat needs to be relatively inert to be able to resist the physical and environmental changes in the mouth such as changes in pH and mechanical stress from mastication.

The film forming polymer is preferably present in an amount of 10-25% by weight of the composition, more preferably 12-18% by weight of the composition, most preferably 15%. At higher levels (above 25%) the viscosity of the formulation increases and the product becomes more difficult to apply to the surface of the tooth. The drying time also increases.

The copolymer is preferably a copolymer of ethyl acrylate, methyl methacrylate and a methacrylic acid ester with quaternary ammonium groups, where the ammonium groups are present as a salt, which has been found to produce the most substantive film. By substantive is meant the resistance to removal by rubbing and to washing with water. This gives a good indication on the integrity of the film in the buccal cavity in the presence of saliva. In addition, this polymer gives a time controlled release of materials that is pH independent.

The composition may be for coating natural teeth (ie tooth enamel), artificial teeth, or both. Two main properties are important in evaluating the application and formation of the film barrier; forces of adhesion and cohesion.

It is believed that adhesion results from a "toothing" between polymer and substrate during the film formation from dispersion or solution. Therefore, irregularities on the surface of the substrate can facilitate adhesion. However, the polymer also sticks to very smooth surfaces such as glass. It is necessary for film formation to take place on the surface of the substrate. An isolated polymer layer, which was cast on, for example, Teflon or Silicone, will not adhere to another substrate after it has dried and set. In general, it can be said that the adhesion depends also on the substrate itself and also on the additional excipients that are present inside the polymer dispersion/solution (i.e. anti-tacking agents, pigments, plasticisers and emulsifiers).

It is believed that cohesion is a result of a "toothing" of the polymer-chains with each other. Due to the fact that these chains are relatively rigid/inflexible, the cohesion forces are normally much stronger than the adhesion forces. This can be demonstrated by the observation that a dried polymer-film can generally be completely peeled off from a substrate. This case is called an "adhesive fracture". Adhesion of dry films on a substrate can be made possible by "softening" the film with the inclusion of plasticiser or by melting. The addition of plasticisers however may permanently influence the cohesion. The melting method will have no effect on the cohesion inside the film. In this case an "adhesive fracture" will happen when peeling the film of the substrate. When high amounts of plasticiser are present it can lead to a "cohesive failure" when peeling the film off the substrate. This means parts of the film will still stick to the substrate and therefore the film falls apart.

The composition preferably further comprises one or more plasticisers. The use of a plasticiser may make the composition easier to apply to teeth, but has also been found to result in a coating that is less brittle and more resistant to damage. The use of a plasticiser may also improve the shape-forming properties of the composition, and in particular enable the composition to take the contours of the teeth, thus producing a coating with a more natural appearance. Preferably the plasticiser is present in an amount of between about 1 % and 3%, and preferably about 2%, by weight of the composition.

Preferably the plasticiser is triethyl citrate. Triethyl citrate is an ester of citric acid. It is a colourless, odourless liquid. In the formulations of the invention the triethyl citrate improves the flowability of the composition and the resistance of the resulting coating to mechanical stress.

The solvent evaporates following application of the composition to the teeth, leaving a coating on the surface of the tooth. The solvent is preferably volatile such that it evaporates, and hence produces a coating, more rapidly. In particular, the composition preferably produces a coating within 5 minutes, more preferably within 3 minutes, and most preferably within 60 seconds of being applied to the teeth.

A preferred solvent is ethanol, most preferably denatured ethanol, which may be present in an amount of between 60% and 80% by weight of the composition. Ethanol has established use in personal care and dental products and allows the composition to be sufficiently quick drying. Ethanol is generally regarded as nontoxic and non-irritant. Ethanol is a suitable solvent to solubilise the polymer and ensure it remains in solution until application. A further removal composition comprising the solvent may also be used to remove the coating from the teeth.

Preferably the composition further comprises a secondary polymer. The inclusion of a secondary polymer may produce a formulation that is easier to reapply and also more resistant to staining, particularly from materials such as coffee and wine. A secondary polymer may also prevent sedimentation (and further aids the redispersion) of any additional solid components present in the formulation on storage, such as pigments. Preferably the secondary polymer is an alkyl cellulose such as ethyl cellulose. Ethyl cellulose is a derivative of cellulose in which some of the hydroxyl groups on the repeating glucose units are converted into ethyl ether groups. The composition may further comprise one or more pigments. This is particularly desirable when the composition is for use as a cosmetic composition, for example to provide a pigmented coating to disguise stained or discoloured teeth. In particular, a composition comprising one or more pigments may give the teeth a more desirable appearance, and in particular a sparkly white appearance. The pigments are preferably selected from the group comprising titanium dioxide, mica and iron oxide based pigments, or any combination of the above.

Titanium dioxide is preferably present in the composition in an amount of between 3% and 7% by weight of the composition, and more preferably about 5% by weight of the composition. Titanium dioxide (purity 73) provides a matt finish but intensely white colour at levels above 5% by weight of the composition. Due to its high refractive index, titanium dioxide has light scattering properties that enable it to be used as white pigment and opacifier in film coating suspensions. According to the European Cosmetics Regulation (EC) No 1223/2009, Titanium Dioxide is permitted as a colourant in all cosmetic products (Annex IV, No. 143, CI 77891 ). Titanium Dioxide complies with the specification for E 171 (Titanium Dioxide) of Directive 95/45/EC laying down specific purity criteria concerning colours for use in foodstuffs.

Titanium dioxide and mica (Timiron ^® supersheen and Timiron ^® supersilk) in combination provide a shimmer as well as intense whiteness. Mica is a naturally occurring group of silicate minerals. It is widely used in the formulation of cosmetics and personal care products. Mica imparts a sparkly white appearance to cosmetics and personal care products and promotes a slight shimmer to the appearance of the teeth when applied.

Timiron ^® supersheen may be present in the composition in an amount of about 2% by weight in order to give a brightening effect. Timiron ^® supersheen may also be present in the composition in an amount of about 10-15% by weight of the composition in order to produce a colour that, in combination with other iron oxide based pigments, can produce colours similar to the VITA shade guide, a common teeth colour measurement system.

Iron oxide is widely used in cosmetic and personal care products. The grade included in this formulation is specifically used for dental and oral applications. It is included to provide a subtle off-white colour that is characteristic of a natural shade.

The composition may further comprise a flavouring component. The flavouring component is preferably selected from the group comprising mint based flavourings and sweeteners. These components provide the best organoleptic properties on tasting the product. The sweetener is preferably sucralose as this provides a particularly pleasant taste profile and, in addition, as sucralose has a high surface area, any solid particles are easily dispersed in the formulation. Sucralose is a non-nutritive sweetener. The majority of ingested sucralose is not broken down by the body. As a result, it is non-calorific. A level of 0.1 -0.2% by weight of the composition has been shown to produce the best taste profile in combination with the preferred mint flavour.

Peppermint flavour is particularly preferred in order to compensate for the bitterness of preferred solvents, and is preferably present in the composition at an amount of 0.2% by weight.

The composition may further comprise additional beneficial ingredients, such as an oral care active. The composition preferably further comprises calcium hydroxyapatite. Nanoparticles of calcium hydroxyapatite may be included to enhance the natural salivary remineralisation of dental enamel. Demineralisation of dental enamel is exacerbated by poor oral hygiene and dietary habits. The normal dynamic balance between demineralisation and remineralisation is supported by regular use of calcium hydroxyapatite. When included in the formulation this material assists the restorative action of saliva by providing a constant source of calcium and phosphate ions for remineralisation. Regular exposure to calcium hydroxyapatite helps prevent caries and stabilise rampant caries by counteracting the consequences of poor oral hygiene, acidic foods and carbonated drinks.

The coating produced by the composition may be for any one or more of delivering an oral care active to the teeth, giving the teeth an artificial colour, being a barrier against damage (eg acid erosion), staining or decay, or functioning as a dental sealant or dental bonding composition.

According to a second aspect of the invention, there is provided an oral care kit comprising the composition according to the first aspect of this invention, and a remover composition for removing the tooth coating.

The kit may further comprise an applicator for the composition, such as a brush, and a device to aid removal of the composition from the teeth, such as an abrasive or absorbent pad onto which the remover composition may be applied.

The remover composition preferably comprises the solvent, in particular ethanol, in an amount of between 30% and 50%, and in particular about 40%, by weight of the remover composition. The solvent dissolves the coating and removes it from the surface of the tooth and enables it to be removed.

Preferably the remover also comprises purified water in an amount of between 20% and 30%, and in particular about 25%, by weight of the remover composition. Purified water is a vehicle solvent in the manufacture of pharmaceutical and personal care preparations and is used in this formulation to aid the infusion of the remover composition into pads which can be used to apply the remover.

The remover may further comprise a flavouring. Sorbitol may be included in the remover to enhance the overall flavour profile giving a pleasant mouth feel when used. It is also a humectant for the mouth and gums. Sorbitol is used as an excipient in pharmaceutical, cosmetics and food products. It is often used as a substitute for sucrose and meets organoleptic and dietetic requirements. It is sugar-free, low calorie and does not induce dental caries.

The remover may also comprise glycerol. Glycerol is widely used as a solvent and sweetening agent in oral preparations. It is also a viscosity-increasing agent and humectant for the mouth and gums.

Peppermint flavour may be added to give the desired organoleptic characteristics of the product on application. Novamint mentholyptus may be included as a suitable fragrance for the remover based on its sensory profile and suitability to be incorporated into systems that contain ethanol.

Examples

The invention is exemplified by the following compositions. Each of the

compositions is formulated in the following way:

Due to the volatile nature of preferred solvents used in the composition, a cold process is required. Each of the materials is added and mixed by weight. The high portions of ethanol solvent content provide assurance that the microbiological quality of the product will be satisfactory at the time of manufacture.

A specially selected applicator will be used to apply the composition directly to the surface of the tooth. Table 1 : A composition according to this invention for producing a clear coating

This formulation leaves a clear coating on the teeth following application, which will have the following effects:

Protects from acid enamel erosion

Helps prevent tooth stain formation

Is capable of gradually releasing active ingredients and flavours

Example 2. White Coatings

Table 2: A composition according to this invention for producing a white coating

Name of Ingredient Quantity % ^w / _w Function

Calcium Hydroxyapatite 3.00 Remineralisation Active

Denatured Ethanol 67.09 Solvent

Ammonio Methacrylate Copolymer Type A 15.00 Polymer

Pigments (Titanium Dioxide) 10.00 Pigment

Ethyl Cellulose 2.50 Polymer

Triethyl Citrate 2.00 Plasticiser

Peppermint Flavour 0.20 Flavour

Sucralose 0.20 Sweetener

Iron Oxide Yellow 0.01 Pigment

Total Weight 100.0 Table 3: A further composition according to this invention for producing a white coating

These formulations leave a white coating on the teeth following application, which changes the appearance of the teeth such that is appears instantly brighter and/or whiter, and furthermore will have the following effects:

Protects from acid enamel erosion

Helps prevent tooth stain formation

Is capable of gradually releasing active ingredients and flavours Example 3. Coating Removal Composition

The composition of the formulation is summarised in the table below:

Table 4: A composition according to this invention for removing coatings from the teeth

Name of Ingredient Quantity % ^w / _w Function

Denatured Ethanol 40.0 Solvent

Purified Water 25.0 Solvent

Sorbitol Liquid 20.0 Humectant/Sweetener

Glycerol 10.0 Humectant

Novamint Metholyptus 2.5 Fragrance

Peppermint Flavour 2.5 Flavour

Total Weight 100.0 A specially selected pad will be infused with the coating removal composition and applied to remove all varieties of coating from the surface of the teeth. The pad infusion provides a mechanical aid for the removal of the varnish from the teeth.

Example 4. The inclusion of a secondary polymer in the composition improves the stain resistance of the resulting tooth coating

40g of each of Formulations A and B set out in Table 5 were prepared using a magnetic stirrer process. Whilst stirring the ethanol 96%, each ingredient was added, starting with the polymers, Eudragit ^® RL PO (the brand name for a copolymer of methyl methacrylate and a low content of methacrylic acid ester with quaternary ammonium groups) and ethyl cellulose, ensuring full homogenisation before adding the next ingredient.

Table 5

20g of a 5%w/w coffee solution was prepared by adding 1 g of Instant Coffee Granules - Douwe Egberts Classic Rich Roast Continental to 19g of purified water.

Bovine enamel blocks sectioned to 5x5mm (approximately shade 1 M2 according to the Vita 3D tooth guide) were dried and placed on the stainless steel tray.

Formulations A and B were then applied to all exposed surfaces of separate enamel blocks, ensuring that they were completely coated. The coffee solution was then added drop wise (using a dropper pipette) ensuring the enamel blocks were completely immersed. The enamel blocks were then incubated for 20 minutes at 60°C. Saliveze Artificial Saliva (Lot 1362A) was then used to rinse the residual coffee solution from the enamel blocks, which were then allowed to dry before observation.

Figure 1 depicts the enamel blocks following drying, in which Block A (left) was coated with Formulation A, and Block B (right) was coated with Formulation B.

According to the Vita 3D tooth guide, Block A was approximately shade 2L and Block B was approximately shade 2M. Accordingly, Block A exhibited less evidence of staining than Block B, indicating that Formulation A produces a coating that is more resistant to staining than the equivalent Formulation that excluded a secondary polymer in the form of ethyl cellulose (Formulation B).

The combination of the film forming polymer, Eudragit ^® RL PO, with the secondary polymer, ethyl cellulose, therefore improves the resistance of compositions to coffee staining.