Field of the Invention

The present invention relates to dentifrice compositions, especially toothpastes.

Background of the Invention

The present invention relates to a dentifrice composition suitable for maintaining and enhancing oral health. Erosion of the enamel is one of the lifestyle disorders and is becoming more prevalent. Enamel, the hard, protective coating of the tooth, is susceptible to attack by acids, which makes it softer and ultimately to the exposure of the sensitive dentin underneath the enamel. The enamel is composed of hydroxyapatite crystals that create a porous surface. There is a need to stop or at least retard the erosion of enamel to maintain good oral health. Some oral care products seek to counter erosion of enamel by remineralisation using fluoride ions.

The resulting fluorapatite composition is harder than the original hydroxyapatite composition and more resistant to the acidic attack.

The present invention relates to a dentifrice that can cure or at least prevent lesions on the enamel caused by caries.

A variety of hardness tests are useful for evaluation of materials, quality control of manufacturing processes and research and development of new materials. Hardness, although empirical in nature, is an indicator of wear resistance. Microindentation tests extend hardness testing to materials too thin or too small for macro indentation tests. Microindentation tests permit the assessment of specific phases or constituents and regions or gradients.

EP3436155 B1 (Unilever) discloses toothpastes comprising chalk, zinc salt and smectite clay. Attempts to formulate toothpaste composition having calcium-based abrasive and a zinc salt usually lead to technical problems, especially the instability of zinc salts. In this publication, the antimicrobial benefits of zinc were retained and problems pertaining to stability are minimized by use of smectite clay and a buffering agent.

WO2017/108368 A1 (Unilever) discloses a fluoridated toothpaste that provides remineralization. The composition comprises abrasive, which could be silica or a calcium-based, and a combination of clays - 1 :1 layered silicate clay and a 2:1 layered silicate clay. The combination of ingredients not only results in higher bioavailability of fluoride but also significantly reduces the tendency of fluoride to degrade during storage.

W02021/165001 A1 (Unilever) discloses a new kind of thickening system to stabilise toothpaste compositions which contain calcium-based abrasives. The toothpaste comprises a hydrophilic inorganic thickener which swells by intercalating water and an aluminium silicate clay other than the hydrophilic inorganic thickener. The toothpaste composition comprises minimum humectant, not more than 5 wt% in total.

It is an object of the present invention to provide a dentifrice composition that can cure, prevent, or at least provide protection to the enamel against lesions caused by caries.

It is an object of the present invention to provide a dentifrice composition that can cure, prevent, or at least provide appreciable protection to the enamel against lesions caused by caries in a short span of from 8 to 21 days.

Summary of the Invention

It has been determined that the dentifrice in accordance with the present invention meets at least one of the objects. The present invention provides a dentifrice composition that can cure, prevent, or at least provide appreciable protection in a short span of 8 days of continued use to the enamel against lesions caused by caries. It has been observed that the extent of protection increases in proportion to the use, and it gets better from day 8 onwards which is evident in the form of results obtained from microindentation hardness tests.

In accordance with a first aspect, disclosed is a dentifrice composition comprising: a) 3 to 50 wt% abrasive; b) a zinc salt; c) 1 :1 layered silicate clay; and, d) 2:1 layered silicate clay. wherein said composition comprises from 0.1 wt.% to 3 wt.% zinc salt.

Without wishing to be bound by theory it is believed that the combination of two types of clays provides the unexpected technical benefits. Detailed Description of the Invention

These and other aspects, features and advantages will become apparent to those of ordinary skill in the art from a reading of the following detailed description and the appended claims. For the avoidance of doubt, any feature of one aspect of the present invention may be utilised in any other aspect of the invention. The word "comprising" is intended to mean "including" but not necessarily "consisting of" or "composed of." In other words, the listed steps or options need not be exhaustive. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se.

Similarly, all percentages are weight/weight percentages unless otherwise indicated. Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description and claims indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about". Numerical ranges expressed in the format "from x to y" are understood to include x and y.

When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated.

"Dentifrice composition" refers to a composition for which the intended use can include oral care, oral hygiene, or oral appearance, or for which, the intended method of use can comprise administration to the oral cavity. In some embodiments, an oral care composition is not intentionally swallowed, but is rather retained in the oral cavity for a time sufficient to affect the intended utility. The compositions as disclosed herein are for use by humans.

In the context of the invention, the "water activity" (a) of the composition is defined as a=p/p o where p is the measured partial pressure of the solution and po is the partial pressure of distilled deionised water. Unless stated otherwise, all water activities are quoted are at ambient temperature. Further references to water activity (or relative humidity, where relative humidity (RH) = 100 a) can be found in Morris, C. and Leech, R., "Natural and Physical Preservative Systems", Curry, J. "Water Activities and Preservatives", Cosmet. Toilet. 100, 53-55, and Christian, J.H.B., "Reduced Water Activity". ImSilliker, J.H. (ed) "Microbial ecology of Foods", vol. 1 , Academic Press, New York, pp170-192.

Yield stress is a useful rheological indicator of consumer perception if the toothpaste appears to be too runny and may be perceived to be less effective with inappropriate sensory. On application of a stress the toothpaste sample behaves as an elastic solid at lower values resisting the flow. Further on reaching a critical value defined as yield stress, the sample starts to flow and the viscosity falls rapidly. Yield stress wherever referred to, has been measured by stress sweep measurements using an Anton Paar rheometer with a cone and plate geometry. All measurements were made at 25°C.

The term aqueous implies that the compositions in accordance with the invention comprises water, preferably 10 to 60 wt%, more preferably 15 to 50 wt% and most preferably 20 to 40 wt% water. The water includes any that may come along with some other ingredients such as humectants, in particular, sorbitol.

Alcohol-free means that the compositions in accordance with the invention comprise not more than 1 wt%, preferably more than 0.5 wt% ethyl alcohol.

The term gel indicates physical appearance of the compositions of the invention. The gel compositions are transparent to light, i.e. , they allow visible light to pass through. Clear gel toothpastes are popular with consumers. Undoubtedly, this is due, at least in part, to their appearance. On the other hand, there are some other types of dentifrice compositions that are not gels but are opaque. That is because such compositions usually contain opacifying ingredients such as chalk or other calcium-based abrasives.

The method for assessing transparency involves use of a standard chart consisting of black symbols varying in size on a white background. This is the RIT Alphanumeric Resolution Test Object, RT 4-74, produced by Graphic Arts Research Center, Rochester Institute of Technology. Any other equivalent may also be used so long as the results do not differ drastically. The ability to discern the symbols clearly through a sample of product of standard thickness is measured. The symbols are assigned numbers from -12 to +13. The higher, more positive the number, the greater the clarity. The method can be applied to measurement of transparency of the dentifrice. If even the most prominent symbol cannot be readily defined through the layer of toothpaste, the gel dentifrice is considered cloudy and not transparent enough. In the practice of this invention, products with a numerical rating of about -12 or higher are considered transparent.

Gel dentifrice compositions of the invention preferably comprises a liquid or aqueous phase. The liquid phase of the composition is preferably formulated such, that its refractive index closely matches the refractive index of the abrasive, when silica is used as the abrasive. The liquid phase usually comprises water and a humectant, the latter usually being sorbitol or glycerol or a combination of the two. Water has Rl of 1 .333, sorbitol (70% aqueous solution) has an Rl of 1.457 and glycerine an Rl of 1.473.

Refractive index of the liquid phase can be calculated from the respective refractive indices of the constituting ingredients.

Viscosity of a toothpaste is measured at room temperature (25°C) with a Brookfield Viscometer, Spindle No.4 and at a speed of 5 rpm. Values are quoted in centipoises (cP=mPa.s) unless otherwise specified.

The present invention relates to a dentifrice composition comprising: a) 3 to 50 wt% abrasive; b) a zinc salt; c) 1 :1 layered silicate clay; and, d) 2:1 layered silicate clay.

In one aspect of the invention, the dentifrice composition is preferably a toothpaste.

The dentifrice composition of the invention comprises 3 to 50 wt% abrasive. A primary function of cleaning agents or abrasives is to provide the properties of cleaning and stain removal. Typically, cleaning is directly correlated to the abrasivity of the abrasive on tooth dentin and is measured by RDA. In other words, the higher the RDA, the higher the abrasivity. Even though this is typically true, some cleaning grades can provide high cleaning efficiency at reduced level of abrasion when compared with other cleaning grades.

It is preferred that the abrasive is silica-based or calcium-based.

In one aspect of the invention the abrasive is silica. When the dentifrice composition of the invention is a gel toothpaste, it preferably comprises the 3 to 20 wt% silica, more preferably 4 to 15 wt% and most preferably 4 to 10 wt%.

Such toothpastes are usually transparent or translucent gels. The term gel indicates physical appearance of the compositions. The gel compositions are transparent to light, i.e., they allow visible light to pass through. Clear gel toothpastes are popular with consumers. When the oral care composition of the invention is a toothpaste in the form of a gel, it is preferred that the compositions do not comprise more than 5 wt%, preferably more than 2 wt% and more preferably more than 1 wt% calcium-based abrasive. It could affect the transparent nature of the compositions.

Further preferably the abrasive silica comprises medium- and high-abrasive silica, where medium-abrasive silica is preferably in majority. Their relative proportions may vary. Preferably the abrasive silica is low refractive index silica with an apparent refractive index in the range of 1.41 to 1.47, preferably 1.435 to 1.445, preferably having a weight mean particle size of between 5 and 15 pm, a BET (nitrogen) surface area of between 10 and 100 m ² /g and an oil absorption of about 70 to 150 cm ³ /100 g. Examples of suitable low refractive index abrasive silicas having an R.l. of between 1.435 and 1.445 are Tixosil 63 and 73 ex Rhone Poulenc; Sident 10 ex Degussa; Zeodent 113 ex Zeofinn; Sorbosil AC 77 ex Ineos having an R.l. of approximately 1.440. Other examples include the Sylodent® and Syloblanc® range of abrasive silicas from Grace.

On the other hand, there are some other types of dentifrice compositions of the toothpaste type that are not gels but are opaque. That is because such compositions usually contain opacifying ingredients such as chalk or other calcium-based abrasives.

Alternatively, and more preferably the dentifrice compositions of the invention comprise calcium -based abrasive. When the dentifrice composition of the invention comprises a calcium-based abrasive, it preferably comprises 10 to 50 wt% abrasive, more preferably 10 to 45 wt%, further preferably 20 to 40 wt% calcium-based abrasive.

It is particularly preferred that this abrasive is fine ground natural chalk (FGNC). It is obtained from limestone or marble. FGNC may also be modified chemically or physically by coating during or after milling by heat treatment. Typical coating materials include magnesium stearate and oleate. The morphology of FGNC may also be modified during the milling process by using different milling techniques, for example, ball milling, air-classifier milling or spiral jet milling. FGNC can be used as the sole calcium containing abrasive. However, FGNC can also be used with other calcium containing abrasives to balance the abrasion.

Other preferred calcium-based abrasives include dicalcium phosphate (DCP), calcium pyrophosphate and precipitated calcium carbonate (PCC). When a combination of Calciumbased abrasives is used, it is preferred that FGNC is 35 to 100 %, more preferably 75 to 100 % and especially from 95 to 100 % of the total abrasive. In such cases, the balance, most preferably, is PCC.

Other abrasives can also be used depending upon the intended degree of abrasion and the composition of the paste. These include synthetic abrasive polishing agents such as amorphous precipitated silica and silica gels. Other abrasives include magnesium carbonate, sodium metaphosphate, potassium metaphosphate, zirconium silicate, potassium metaphosphate, magnesium orthophosphate, tricalcium phosphate, magnesium orthophosphate, trimagnesium phosphate, aluminum silicate, zirconium silicate and perlite.

Alternatively the composition of the invention comprises a first and a second dentifrice composition, where the first composition comprises a silica-based abrasive and the second composition comprises a calcium-based abrasive.

The two types of compositions may preferably be presented in the form of a multiphase composition, such as core-&-sheath type or a side-by-side form. Alternatively, the compositions may be provided in the aforesaid forms by way of packaging solutions, such as core-&-sheath type.

Further preferably the dentifrice compositions comprise 2 to 15 wt% thickening silica. The primary function of thickening silica is to build viscosity, without increasing the level of abrasion (RDA) in the overall formulation. Also, they can be used as texturing agents in formulations that use alternative abrasives other than silica. These physical characteristics have effect on the rheological properties of the formulation. For example, and perhaps more relevantly, the higher the oil absorption of the thickener, the higher the viscosity imparted to the formulation. In addition to having a substantial impact on the viscosity of the toothpaste system, the thickening silica also plays a role in the mouthfeel of the paste. If the level of the cleaning agent in the system is low, than the formulator may wish to use a less efficient thickener to achieve an overall solids level consistent with the desired mouthfeel.

This is especially the case when the compositions comprise silica as the abrasive. A variety of thickening silicas are commercially available. When present, preferred thickening silicas include AEROSIL®T series from Degussa or the CAB-O-SIL® series from Cabot Corporation, silica gels such as the SYLODENT® or SYLOX® series from W. R. Grace & Co or precipitated silica such as ZEOTHIX® 265 from J. M. Huber Corporation. Useful silica thickeners also include ZEODENT® 165, ZEODENT® 163 and/or 167 and ZEOFREE® 153, 177, and/or 265 silicas, all available from J. M. Huber Corporation. Other preferred thickening silicas include MFIL®, MFIL®-P (From Madhu Silica), SIDENT® 22 S and AEROSIL® 200 (Ex. Evonik Industries), SYLODENT® and PERKASIL® thickening silicas from WR Grace & Company and Tixosil® 43 and 331 from Rhodia, synthetic finely divided pyrogenic silica such as those sold under the trademarks SYLOID® 244, SYLOID® 266 and AEROSIL® D-200.

Zinc salt

The dentifrice composition of the invention comprises a zinc salt. Preferably the composition comprises 0.1 to 3 wt% of said zinc salt, more preferably 0.1 to 2 wt% and most preferably 0.1 to 1 wt%.

It is preferred that solubility of the compound of zinc at 20°C is 0.001 to 80 g/100 g water.

It is preferred that the compound of zinc is at least one of zinc sulphate, zinc chloride, zinc nitrate, zinc citrate, zinc oxide, zinc lactate, zinc gluconate, zinc glycinate, zinc oleate, zinc hydroxide or zinc peroxide, zinc oxide, zinc lactate, zinc chloride, zinc citrate, zinc acetate, zinc borate, zinc butyrate, zinc carbonate, zinc formate, zinc gluconate, zinc glycerate, zinc glycolate, zinc phosphate, zinc picolinate, zinc proprionate, zinc salicylate, zinc silicate, zinc stearate, zinc tartrate, zinc undecylenate, zinc phosphate, zinc ricinoleate or mixtures thereof. It is preferred that the zinc salt is selected from the group consisting of zinc chloride, zinc sulphate, zinc nitrate, zinc citrate, zinc gluconate, zinc acetate, zinc lactate, zinc salicylate, zinc gluconate and zinc ascorbate.

It is preferred that the zinc salt is water-soluble. By that it means having water solubility greater than 0.01 g/100g water). For example, solubility (g/100 g water) of some preferred sparingly water-soluble compounds of zinc is as follows: zinc citrate 6.11 and zinc lactate 1.4. Watersoluble compound of zinc whose solubility at 20°C is greater than 10 g/100 g water include zinc sulphate, zinc chloride and zinc nitrate.

Alternatively, the zinc salt includes a combination of insoluble and soluble zinc salts. However it is preferred that the zinc salt is water soluble.

Clays

The composition of the invention comprises a 1 :1 layered silicate clay. Preferably the 1 :1 layered silicate is a kaolinite. It is preferred that the kaolinite is selected from the group consisting of kaolin, halloysite, nacrite and dickite. More preferably it is kaolin. Kaolinites have a dioctahedral sheet and the species included within the kaolinites subgroup are kaolinite, dickite, nacrite and halloysite clay minerals, but not limited thereto. Serpentines are trioctahedral sheet minerals which has a tetrahedral sheet and an octahedral sheet having magnesium with minor amounts of aluminium and the species within this subgroup are preferably chrysotile, lizardite and antigorite.

Kaolin (also known as kaolinite) is a naturally occurring mineral. Preferred kaolin is a hydrous aluminium silicate and represented as AbC ^SiCb^FW. Preferred kaolinites have particle size distribution such that at least 98 wt% of the particles have a particle size of 2 pm or less. It is preferred that the 1 :1 layered silicate clay is of the non-swelling type.

Kaolinites have a dioctahedral sheet and the species included within the kaolinites subgroup are kaolinite, dickite, nacrite and halloysite clay minerals, but not limited thereto. Kaolinite is particularly preferred in the disclosed invention. Kaolinite, commonly known as kaolin clay, is a naturally occurring mineral. Kaolinite may be a calcined kaolin, highly purified calcined kaolin, colloidal kaolin, or hydrated kaolin, but not limited thereto. Preferred kaolinite is a hydrous aluminium silicate and represented as AhC ^SiCb^FW. Preferred kaolinite have particle size distribution such that at least 98 wt% of the particles have a particle size of 2 pm or less. Preferably the kaolinite is a refined kaolin and further preferably the refined kaolin includes 38 wt% AI2O3 and 45wt% SiCb and a maximum of 0.5 wt% of Fe2Os.

It is preferred that the dentifrice composition comprises 0.01 to 5 wt% of said 1 :1 layered silicate clay, more preferably 0.1 to 3wt% and still more preferably 0.1 to 2 wt% and most preferably 0.1 to 1 wt%.

The dentifrice composition of the invention comprises a 2:1 layered silicate clay. It is preferred that the 2:1 layered silicate is a smectite clay. Preferably the 2:1 layered silicate clay is selected from the group consisting of phyllosilicates, montmorillonites, bentonites, hectorites, sodium magnesium silicates, aluminium magnesium silicate, organically modified smectites and organically modified montmorillonite clay. The pyrophillite-talc group preferably includes talc which is a hydrous magnesium silicate; pyrophyllite which is a hydrous aluminium silicate; or minnesotaite which is a hydrous iron silicate. The vermiculite group of clay preferably includes the dioctahedral vermiculite or the trioctahedral vermiculite. The trioctahedral vermiculites preferably has a layer charge of 0.6 to 0.7. It is highly preferred that the 2:1 layered silicate clay is of the smectite group of clay which includes but not limited to montmorillonite, smectite, beidellite, nontronite saponite, hectorite, sauconite or laponite. The smectite group of clay is preferably dioctahedral smectites or trioctahedral smectites.

Examples of suitable dioctahedral smectites include, but are not limited to, montmorillonite (often referred to as bentonite), smectite, beidellite, nontronite.

Typically montmorillonite and smectite have a low total charge content of from 0.3 to 0.6 and most of the charge originates in the octahedral sheet. Beidellite is an expandable dioctahedral smectite having a total charge content of 0.7 or higher and a tetrahedral charge content of 0.4. When the dioctahedral smectites is a montmorillonite, it is typically carbonate free and preferably water-washed.

Examples of suitable trioctahedral smectites include, but are not limited to, saponite, hectorite, sauconite, and laponite. Trioctahedral smectites having a total charge content of 0.3 to 0.5 includes hectorite which has magnesium and lithium in the octahedral sheet and saponite which has considerable magnesium in the octahedral sheet and some aluminium substitution in the tetrahedral sheet.

A particularly preferred 2:1 layered clay is a smectite group of clay which may be from a natural source, processed or purified from a natural source or prepared synthetically. More preferably the 2:1 layered silicate clay is a magnesium aluminium silicate (various grades are commercially available as VEEGLIM® from R. T. Vanderbilt Company); purified sodium magnesium silicates (commercially available as LAPONITE® in various grades); organically modified smectites including tetra alkyl and/or trialkyl ammonium smectites (organically modified montmorillonite clays) such as quaternium-18 bentonite, quaternium-18 hectorite, stearalkonium bentonite and stearalkonium hectorite/ and mixtures thereof. Magnesium aluminium silicates clays are particularly preferred. An example is VEEGLIM® HV.

Preferably a 10% aqueous solution of the 2:1 layered silicate clay has a pH of 8 to 10.

It is preferred that the dentifrice composition comprises 0.01 to 5 wt% of said 2:1 layered silicate clay, more preferably 0.1 to 3 wt% and still more preferably 0.1 to 2 wt% and most preferably 0.1 to 1 wt%. Humectant

Dentifrice composition of the invention preferably comprises 5 to 50 wt% of one or more humectants. Alternatively, it is preferred that the dentifrice composition of the invention comprises 5 to 40 wt% humectant. Further preferably the composition comprises 10 to 40 wt% humectant, more particularly 10 to 20 wt% humectant in the aggregate. A particularly preferred humectant is sorbitol, generally available as 70% aqueous solution.

Humectants are generally included in toothpastes for a soft a supple mouth feel. Humectants also reduce the tendency of toothpastes to lose moisture. It is preferred that the humectant is at least one of glycerine, sorbitol, maltitol and xylitol. Sorbitol is available as a 70% aqueous solution. Preferably the compositions comprise glycerine and sorbitol for a lubricated mouth feel, but their cumulative levels do not exceed the disclosed upper limit. Lower humectant content provides an effective way to reduce the cost of the product.

In one aspect of the invention, alternatively, the composition comprises less than 5 wt% humectant. It is preferred that the composition comprises upto 3 wt%, more preferably upto 2 wt% humectant. In this case it is also preferred that the dentifrice composition is humectant- free. By humectant-free is meant that the composition comprises not more than 1 wt% humectant in the aggregate.

It is particularly preferred that when the dentifrice composition of the invention comprises less than 5 wt% humectant, the abrasive is a calcium-based abrasive.

It is particularly preferred that when the dentifrice composition of the invention comprises 5 to 40 wt% humectant, the abrasive is a silica-based abrasive.

Preferably the composition of the invention composition comprises a buffering agent selected from the group consisting of alkali metal silicates, alkali metal hydroxides, alkali metal bicarbonates, alkali metal carbonates, alkali metal pyrophosphates and arginine.

The pH

Preferably the pH of the dentifrice composition of the invention at 1 wt.% of the oral care composition in water as measured at 25°C is from 6.0 to 10.0, preferably from 6.5 to 9.5, more preferably 6.5 to 9.0, even more preferably from 7.0 to 8.0. Further ingredients

The dentifrice composition of the invention preferably comprises one or more of the ingredients discussed hereinafter.

The exact ingredients and the dosage (wt%) would depend on the nature and type of the oral care composition. For example, while a toothpaste invariably comprises an abrasive, a serum may not need any abrasive.

Surfactants

Dentifrice compositions, especially toothpastes generally contain a surfactant, also commonly referred to as sudsing agent. Suitable surfactants are those which are reasonably stable and provide foam throughout a wider pH range. It is preferred that compositions comprise an anionic surfactant.

Anionic surfactants useful herein include the water-soluble salts of alkyl sulfates having from 8 to 20 carbon atoms in the alkyl radical (e.g., sodium alkyl sulfate) and the water-soluble salts of sulfonated monoglycerides of fatty acids having from 8 to 20 carbon atoms. Sodium lauryl sulfate and sodium coconut monoglyceride sulfonates are examples of anionic surfactants of this type.

Preferably the dentifrice compositions comprise 0.25 to 12 wt%, more preferably from 0.5 to 8 wt%, and most preferably from 1 to about 6 wt% anionic surfactant.

Some anionic surfactants, in particular, sodium lauryl sulphate itself have antibacterial effect. Such action provides some degree of instant antibacterial effect. However, this effect is generally very short-lived. Other surfactants like nonionic, amphoteric or zwitterionic surfactants may also be included.

Nonionic surfactants can be broadly defined as compounds produced by the condensation of alkylene oxide groups (hydrophilic in nature) with an organic hydrophobic compound which may be aliphatic or alkyl- aromatic in nature.

Examples of suitable nonionic surfactants include poloxamers (sold under trade name PLURONIC®), polyoxyethylene, polyoxyethylene sorbitan esters (sold under trade name TWEENS®), POLYOXYL® 40 hydrogenated castor oil, fatty alcohol ethoxylates, polyethylene oxide condensates of alkyl phenols, products derived from the condensation of ethylene oxide with the reaction product of propylene oxide and ethylene diamine, ethylene oxide condensates of aliphatic alcohols, long chain tertiary amine oxides, long chain tertiary phosphine oxides, long chain dialkyl sulfoxides, and mixtures of such materials.

Further preferably the dentifrice compositions of the invention comprises a thickening system which comprises thickening silica and at least one of carboxymethyl cellulose, xanthan gum or guar gum. Other binders and thickeners such as sodium carboxymethylcellulose, xanthan gum, gum arabic may also be included, as well as synthetic polymers such as polyacrylates and carboxyvinyl polymers such as Carbopol®. It is preferred that dentifrice compositions of the invention comprise a thickening system which comprises thickening silica and at least one of carboxymethyl cellulose, xanthan gum or guar gum.

It is preferred that that dentifrice compositions comprises a binder, which lends a good structure, especially to a dentifrice in the form of toothpaste. Cellulosic binders are especially preferred. Preferred cellulosic binders include cellulose ethers, which include hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethylhydroxyethyl cellulose (EHEC), carboxymethyl cellulose (CMC), carboxymethylhydroxyethyl cellulose (CMHEC), hydroxypropylhydroxyethyl cellulose (HPHEC), methyl cellulose (MC), methyl hydroxypropyl cellulose (MHPC), methylhydroxyethyl cellulose (MHEC), carboxymethylmethyl cellulose (CMMC), hydrophobically modified carboxymethyl cellulose (HMCMC), hydrophobically modified hydroxyethyl cellulose (HMHEC), hydrophobically modified hydroxypropyl cellulose (HMHPC), hydrophobically modified ethylhydroxyethyl cellulose (HMEHEC), hydrophobically modified carboxymethylhydroxyethyl cellulose (HMCMHEC), hydrophobically modified hydroxypropylhydroxyethyl cellulose (H MH PH EC), hydrophobically modified methyl cellulose (HMMC), hydrophobically modified methylhydroxypropyl cellulose (HMMHPC), hydrophobically modified methylhydroxyethyl cellulose (HMMHEC), and hydrophobically modified carboxymethylmethyl cellulose (HMCMMC).

Other cellulosic binders include cationic hydroxyethyl cellulose (cationic HEC), cationic hydrophobically modified hydroxyethyl cellulose (cationic HMHEC) and microcrystalline cellulose.

A highly preferred binder is Sodium carboxymethyl cellulose (SCMC). Particularly preferred sodium carboxymethyl celluloses include those with degree of substitution of from 0.6 to 0.99, preferably from 0.7 to 0.95. Preferred toothpaste compositions may also include one or more other thickening agents such as carboxyvinyl polymers which include carbomers which are commercially available from B. F. Goodrich as the CARBOPOL® series, including CARBOPOL® 934, 940, 941 and 956.

Other preferred grades include acrylates/Cio-30 alkyl acrylate cross polymers which are commercially available as ULTREZ® 21 , PEMULEN® TR-1 , and PEMULEN®TR-2, from Noveon Corporation. Preferred compositions can include 0.05 to 10 wt%, more preferably 0.1 to 5 wt%, and even more preferably 0.25 to about 4 wt% of other thickening agents.

The dentifrice compositions of the invention may contain optional further ingredients such as cosmetically acceptable carriers like starch and sucrose.

The dentifrice compositions preferably include alkali metal silicate. The alkali metal is sodium or potassium, preferably sodium. Sodium silicate is generally available as 10 to 40 % aqueous solution, most common being 30 % solution. Sodium silicate is available as neutral sodium silicate or alkaline sodium silicate. Preferred toothpastes have neutral sodium silicate. Sodium silicate is available with varying ratios of Na2<D: SiC>2.

Sodium silicate with Na2<D: SiC>2 ratio in the range of 3.0 to 3.8 is preferred, more highly preferred range being 3.25 to 3.5. Preferred toothpastes include 0.1 to 5 wt% silicate (on dry weight basis). Thus, a 30 % solution of sodium silicate is added to the composition in an amount in the range of 0.3 to 16 wt%.

Flavours such as peppermint and spearmint oils may also be included, as well as preservatives, colouring agents, pH adjusting agents, sweetening agents and so on. Suitable flavoring components include oil of Wintergreen, oil of peppermint, oil of spearmint, clove bud oil, menthol, anethole, methyl salicylate, eucalyptol, cassia, 1 -menthyl acetate, sage, eugenol, parsley oil, oxanone, alpha-irisone, marjoram, lemon, orange, propenyl guaethol, cinnamon, vanillin, ethyl vanillin, heliotropine, 4-cis-heptenal, diacetyl, methyl-para-tert-butyl phenyl acetate, and mixtures thereof. Coolants may also be part of the flavor system. Preferred coolants are the paramenthane carboxyamide agents such as N-ethyl-p-menthan-3- carboxamide (known commercially as "WS-3®") and mixtures thereof. The flavour is generally from 0.001 to 5 wt%.

Anti-caries agents such as sodium- and stannous fluoride, aminefluorides, monosodiumfluorophosphate, casein, plaque buffers such as urea, pyruvates, arginine, small peptides, calcium lactate, calcium glycerophosphate, strontium polyacrylates may also be included. A preferred anti-caries agent is sodium monofluorophosphate. Other optional ingredients include vitamins such as Vitamin C, and plant extracts. Desensitising agents such as potassium bicarbonate, potassium oxalate, potassium nitrate as well as strontium salts may also be included.

Buffers and salts to buffer the pH and ionic strength of the compositions may also be included. Liposomes and other encapsulates may also be used to improve delivery or stability of active ingredients.

Furthermore, the oral care compositions may comprise anti-calculus agents such a alkali metal pyrophosphates, hypophosphite-containing polymers, organic phosphonates and phosphorcitrates.

Other optional ingredients that may be included are e.g. bleaching agents such as peroxy compounds e.g. potassium peroxy diphosphate, effervescing systems such as sodium bicarbonate/citric acid systems and colour change systems.

The compositions of the invention may also contain coloured particles suspended therein, e.g. coloured silica agglomerates or other coloured particles to impart a "speckled" appearance to the dentifrices. The oral care compositions may also contain stripes of a coloured paste, to provide for a visually clear gel-type dentifrice with coloured stripes or a separate coloured phase.

Toothpastes with calcium containing abrasives especially chalk are prone to bacterial growth. Certain preservatives, e.g., methyl, ethyl, butyl, propyl and isopropyl esters of parahydroxybenzoic acid may be particularly useful against bacterial growth. A mixture of methyl, ethyl, butyl and propyl esters of parahydroxybenzoic acid is particularly preferred.

The activity of this mixture can be enhanced by adding phenoxyethanol. Formaldehyde and dimethyl hydantoin are other preferred preservatives. Preservatives are generally included at 0.005 to 0.8 wt%.

Dentifrice compositions of the invention may comprise an organic polyphosphate or a water- soluble salt thereof, said polyphosphate or said salt having average chain length of at least 4. It is preferred that the composition comprises 0.01 to 5 wt% organic polyphosphate, more preferably 0.05 to 4 wt%, further preferably 0.15 to 3 wt% and most preferably 0.15 to 2 wt%. It is preferred that the organic polyphosphate is phytic acid. In this case, it is in the acid form. Phytic acid, also known as myo-inositol hexaphosphate, or inositol hexaphosphoric acid, is a biodegradable chelating agent in liquid form with chelating performance comparable to that of EDTA. Herein, the term "phytate" includes phytic acid and its salts as well as the other polyphosphorylated inositol compounds.

When the organic polyphosphate is in the form of water-soluble salt, it preferably is an alkali metal salt or an alkaline earth metal salt. Preferably the salt is at least one of sodium phytate, potassium phytate, magnesium phytate, calcium phytate, stannous phytate, zinc phytate, copper phytate or ferrum phytate.

Dentifrice compositions of the invention may also comprise an inorganic polyphosphate or a water- soluble salt thereof, having average chain length of at least 4. It is preferred that the composition comprises 0.1 to 5 wt% inorganic polyphosphate, more preferably 0.5 to 4 wt%, further preferably 0.5 to 3 wt% and most preferably 0.5 to 2 wt%.

Inorganic polyphosphates useful in embodiments of the oral care formulations disclosed herein may consist of multiple phosphate molecules arranged in a linear and/or cyclic configuration. A polyphosphate is generally understood to consist of two or more phosphate molecules arranged primarily in a linear configuration, although some cyclic derivatives may be present. Although pyrophosphates (n=2) are technically polyphosphates, the polyphosphates desired are those having at least 4 phosphate groups. In one embodiment, such polyphosphates are made by blending linear and cyclic polyphosphates with sufficient concentration to yield a specific average chain length of at least 4. The inorganic polyphosphates may also be of branched form.

It is preferred that the inorganic polyphosphate is pyrophosphate, trimetaphosphate, tripolyphosphate or ultrametaphosphate. The inorganic polyphosphate may be present in the form of a blend of linear and cyclic polyphosphates, comprising predominantly cyclic combinations of polyphosphate compounds, or “cyclic/cyclic combination polyphosphate blends”, or predominantly linear combinations of polyphosphate compounds, or “cyclic/linear combination polyphosphate blends,” for example tetrapolyphosphate 4 and hexametaphosphate 6. Polyphosphates larger than tetrapolyphosphate usually occur as amorphous glassy materials. Preferred in this invention are the linear polyphosphates having the formula: XO(XPOs)nX wherein X is sodium, potassium or ammonium and n averages from 4 to 125. Preferred polyphosphates are those having n averaging from about 6 to about 21 , such as those commercially known as Sodaphos (n=6), Hexaphos (n=13), and Glass H (n=21).

It is particularly preferred that the inorganic phosphate is hexametaphosphate. More particularly it is sodium hexametaphosphate. It has the structure:

The inorganic polyphosphate or a water-soluble salt thereof is other than a monofluorophosphate or a tripolyphosphate.

The weight ratio of the organic phosphate to inorganic phosphate is 1 :10 to 1 :0.05, more preferably 1 :7 to 1 :0.1.

The dentifrice composition of the present invention, especially toothpastes, is prepared by conventional methods of making oral care compositions. Such methods include mixing the ingredients under moderate shear and atmospheric pressure.

Anti-bacterial agents may also be included such as Triclosan, chlorhexidine, sanguinarine extract, metronidazole. Further examples of anti-bacterial agents are quaternary ammonium compounds such as cetylpyridinium chloride; bis-guanides such as chlorhexidine digluconate, hexetidine, octenidine, alexidine; halogenated bisphenolic compounds such as 2,2' methylenebis-4(4-chloro-6-bromophenol).

Polymeric compounds which can enhance the delivery of active ingredients such as antibacterial agents can also be included.

Anti-caries agents such as sodium- and stannous fluoride, aminefluorides, monosodiumfluorophosphate, casein, plaque buffers such as urea, pyruvates, arginine, small peptides, calcium lactate, calcium glycerophosphate, strontium polyacrylates may also be included. A preferred anti-caries agent is sodium monofluorophosphate. Other optional ingredients include vitamins such as Vitamin C, and plant extracts. Desensitising agents such as potassium bicarbonate, potassium oxalate, potassium nitrate as well as strontium salts may also be included.

Typically, the composition is packaged.

In toothpaste or gel form, the composition may be packaged in a conventional plastic laminate, metal tube or a single compartment dispenser. The same may be applied to dental surfaces by any physical means, such as a toothbrush, fingertip or by an applicator directly to the sensitive area.

The composition can be effective even when used in an individual’s daily oral hygiene routine. For example, the composition may be brushed onto the teeth. The composition may be used daily, for example for use by an individual once, twice or three times per day.

Therapeutic treatments can be summarized as being measures directed to the maintenance (prophlyaxis) or restoration (therapy) of health. ‘Therapy’ is concerned with bringing a body from a pathological state back to its normal, healthy state and with preventing a pathological state. Treatment by therapy is defined as any treatment which is designed to cure, alleviate, remove or lessen the symptoms of, or prevent or reduce the possibility of contracting any disorder or malfunction of the human or animal body.

The

In accordance with another aspect disclosed is a packaged product comprising dentifrice composition of the invention. The gel composition is preferably packaged in a collapsible tube such that it becomes easy to dispense a small amount without much dexterity. Alternatively, the composition is packaged in another type of container, such as a bottle or a jar, preferably with suitable means for dispensing a known quantity of the composition. The pack may be further packed in a suitable secondary package like a carton or a box, preferably with useful information about the contents and instructions for use.

The composition can be effective even when used in an individual’s daily oral hygiene routine.

For example, the composition may be brushed onto the teeth. The composition may, for example, be contacted with the teeth for 1 one second to 20 hours. More preferably from 1 s to 10 hours, more preferably still from 10 s to 1 hour and most preferably from 30 s to 5 minutes. The composition may be used daily, for example for use by an individual once, twice or three times per day. When the oral care composition is a dual-phase composition, the two phases of the composition are mixed during application. The mixed phases are typically left on the teeth for from 3 minutes to 10 hours, more preferably from 3 minutes to 8 hours. The application may be carried out one to five times monthly.

The invention will now be explained in detail with help of non-limiting examples.

Examples

Example 1

A series of toothpaste composition as per Table 1 were formulated. For the sake of uniformity, all the compositions contained a calcium-based abrasive, and the compositions were formulated in such a way that there were minimal differences between the formulations and the differences were designed such that reasonably accurate inferences could be drawn from the information contained in table 1, read-with the observations noted in Table 2.

The composition named positive-control and comparative-example 1 were outside the scope of the invention. Example-A was within the invention.

TABLE 1 This experiment concerns the dynamic variation in mineral saturation and pH associated with natural caries processes. Lesions of caries were formed on dentine enamel discs using a methyl cellulose gel- lactic acid system. After the lesions were formed, they were subjected to a cycling procedure where they were treated with a test sample then placed into an acidic buffer, followed by neutral buffer. This cycle was repeated six times a day for up to 22 days Overnight and on non-treatment days, the enamel specimens were kept in neutral buffer. The extent of remineralization was determined by measuring microhardness using microindentation. The microhardness of the enamel was measured for the initial sound enamel, after the formation of the caries lesions, then after 8, 15 and 22 days of treatment.

Microindentation hardness testing (or microhardness testing) is a method for measuring the hardness of a material on a microscopic scale. A precision diamond indenter is impressed into the material at loads from a few grams to 1 kg. The impression length, measured microscopically, and the test load are used to calculate a hardness value. The hardness values obtained are useful indicators of a material’s properties and expected service behavior. Conversions from microindentation hardness values to tensile strength and other hardness scales (e.g., Rockwell) are available for many metals and alloys.

ASTM Standard E 384 fully describes the two most common microindentation tests - the Vickers and the Knoop tests.

The indentations are typically made using either a square-based pyramid indenter (Vickers hardness scale) or an elongated, rhombohedral-shaped indenter (Knoop hardness scale). The tester applies the selected test load using dead weights. The length of the hardness impressions is precisely measured with a light microscope using either a filar eyepiece or a video image and computer software. A hardness number is then calculated using the test load, the impression length, and a shape factor for the indenter type used for the test.

Vickers microindentation hardness observations.

The observations are summarised in Table 2. TABLE 2 On day-8 and 15 the hardness value obtained by use of Example A was better than comparative example 1. By day-22 Example A proved to be significantly better than Example 1.

The illustrated examples indicate that dentifrice compositions of the invention can cure, prevent, or at least provide appreciable protection in a short span of 8 days of continued use to the enamel against lesions caused by caries. The examples illustrate that the extent of protection increases in proportion to the use, and it gets better from day 8 onwards which is evident in the form of results obtained from microindentation hardness tests.