Field of the Invention

The present invention relates to an oral care composition for providing whitening benefits to teeth.

Background of the Invention

Long-lasting whitening of teeth is of considerable interest to consumers. Foods and drinks such as tea, coffee and wine may form dental stains by directly depositing chromogens on the tooth surface. Attraction of materials to the tooth surface plays a critical role in the deposition of extrinsic dental stain. The chromogens in these beverages that are responsible for causing dental stain are known as tannins and are composed of polyphenols such as catechins. These materials generate color due to the presence of conjugated double bonds and are thought to interact with the tooth surface via an ion exchange mechanism.

Traditional tooth whitening methods involve either peroxide bleaching from kit formats or abrasive stain removal from toothpaste formats. Additionally, highly white particles like titanium dioxide are included in oral care compositions, that are expected to deposit on the surface of the tooth thereby ensuring a more white appearance of the tooth. Recently there has been a move to get away from traditional whitening agents like those based on titanium due to expected regulatory pressures in certain countries I regions. In light of this, the present inventors with their extensive knowledge and research in the area of tailored crystal structures of inorganic materials, have developed a specific (sheet like) morphology of calcium citrate that provides enhanced whitening as compared to titanium hydroxide.

WO2012/143220 (Unilever) discloses an oral care composition for whitening and remineralizing teeth comprising a phosphate source and re-generation source calcium salt having a particle size of five microns or less so that in-situ hydroxyapatite may be generated upon use. The calcium salt therein are calcium carbonate, calcium silicate, calcium sulfate, calcium phosphate, calcium gluconate, calcium oxide, calcium lactate, calcium hydroxide, calcium carboxymethyl cellulose, calcium alginate, calcium salts of citric acid.

EP3222326 (2017, Unilever) discloses a calcium source having a water solubility less than 0.1 moles per litre at room temperature in combination with a phosphate source for use in preventing calculus. The calcium source discloses therein are calcium gluconate, calcium oxide, calcium lactate, calcium carbonate, calcium hydroxide, calcium sulphate, calcium carboxymethyl cellulose, calcium alginate, calcium salts of citric acid, calcium silicate or a mixture thereof.

US 5219602 A (Saleeb, 1993) discloses aqueous dispersion of calcium citrate salt compositions adaptable for use in food compositions, particularly as opacifiers, whitening agents, texture modifiers and partial fat substitutes.

US 5275806 A (Gbogi, 1994) discloses topical sun-protection composition which comprise effective amounts of the reaction product of a calcium compound such as calcium hydroxide, calcium oxide, or calcium carbonate, with citric acid, the reaction product exhibiting a calcium :citrate molar ratio of 2.5:2 to 2.95:2.

The above-mentioned art known to the present inventors indicate incorporation of various calcium salts/ sources including calcium salts of citric acid. Calcium salts of citric acid known in the art and commercially available have a rod like structure. The cited prior art does not disclose the specific sheet like morphology developed by the present inventors to ensure whitening of teeth.

It is thus an object of the present invention to provide for a composition for whitening teeth.

It is another object of the present invention to provide for such a composition that does not include titanium based whitening particles.

Summary of the Invention

The present invention relates a tooth whitening composition comprising:

(a) sheet like crystals of calcium citrate having an average length in the range of 0.5 to 4 micrometer; average width in the range of 0.5 to 4 micrometer and average thickness in the range of 30 to 100 nanometers; and

(b) an orally acceptable vehicle, wherein said composition is an oral care composition..

Another aspect of the present invention relates to a composition of the invention wherein the sheet like crystals of calcium citrate are prepared using a process comprising the steps of:

(a) mixing a calcium salt with a water-soluble ionic citrate in an aqueous solution of a polyhydric alcohol for extended period of time to generate a precipitate;

(b) filtering the precipitate and drying it to prepare the sheet like crystals of calcium citrate. Yet another aspect of the present invention relates to a non-therapeutic method of whitening teeth comprising the steps of:

(i) applying the composition of the invention on to a tooth surface for at least one minute; and

(ii) rinsing said surface to be substantially free of the composition.

Detailed Description of the Invention

Except in the examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use may optionally be understood as modified by the word “about”.

All amounts are by weight of the final composition, unless otherwise specified.

It should be noted that in specifying any ranges of values, any particular upper value can be associated with any particular lower value.

For the avoidance of doubt, 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.

The disclosure of the invention as found herein is to be considered to cover all embodiments as found in the claims as being multiply dependent upon each other irrespective of the fact that claims may be found without multiple dependency or redundancy.

Where a feature is disclosed with respect to a particular aspect of the invention (for example a composition of the invention), such disclosure is also to be considered to apply to any other aspect of the invention (for example a method of the invention) mutatis mutandis.

“Oral care composition” for the purposes of the present invention means a paste, powder, liquid, gum, serum or other preparation for cleaning the teeth or other surfaces in the oral cavity.

“Toothpaste” for the purpose of the present invention means a paste or gel dentifrice for use with a toothbrush. Especially preferred are tooth pastes suitable for cleaning teeth by brushing for about one minutes, preferably two minutes. “Mouth wash” for the purpose of the present invention means liquid dentifrice for use in rinsing the mouth. Especially preferred are mouth washes suitable for rinsing the mouth by swishing and/or gargling for about half a minute before expectorating.

The present invention relates to a tooth whitening composition comprising calcium salt of citric acid which has a specific plate I sheet like morphology; and an orally acceptable base. Calcium salt of citric acid has the molecular formula Ca ₃ (cit) ₂ . xH ₂ O where (cit) is a citrate group; and x has a value from 0 to 4

Sheet like crystals of calcium citrate for use in the oral care composition of the invention has an average length in the range of 0.5 to 4 micrometer; average width in the range of 0.5 to 4 micrometer and average thickness in the range of 30 to 100 nanometers. The average length of the sheet like crystals of calcium citrate is preferably in the range of 2 to 3 micrometer. The average width of the sheet like crystals of calcium citrate is preferably in the range of 2 to 3 micrometer. The average thickness of the sheet like crystals of calcium citrate is preferably in the range of 60 to 80 nanometers.

The sheet like crystals may be preferably configured during the process of its preparations such that they comprise two to five layers of the sheet like crystals stacked upon each other.

Without wishing to be bound by theory, the present inventors believe that when sheet-like crystals of calcium citrate are included in a toothpaste used for brushing teeth, the material deposited due to its unique morphology delivers enhanced whitening while minimizing abrasion of the tooth surface.

The composition of the invention comprises an orally acceptable base. The orally acceptable base preferably comprises an abrasive, a surfactant, a volatile alcohol, a humectant or combinations thereof. More preferred orally acceptable bases include an abrasive, a humectant or mixtures thereof. The orally acceptable base preferably is included in as much as 99.8%, more preferably at as much as 96% by weight of the composition. The orally acceptable base is included in at least 80% more preferably at least 90%, by weight of the composition.

The oral care composition of the present invention may be delivered in the form of an ointment, a gel, a dentifrice or a mouthwash. Dentifrices include forms like toothpaste and toothpowder. A composition is most preferably presented in the form of a toothpaste, a toothpowder or a mouthwash.

Oral care composition of the present invention preferably comprises an abrasive. The abrasive may preferably be calcium carbonate or silica. Gels usually contain silica, whereas opaque creams generally contain calcium-based abrasives, especially chalk (calcium carbonate). In opaque toothpastes, the compositions have 5 to 60 wt% calcium-based abrasive. In more preferred compositions it is 30 to 60 wt% and furthermore preferably from 35 to 55 wt%.

Optimal compositions have 40 to 55 wt% calcium-based abrasive.

A preferred abrasive is fine ground natural chalk (FGNC), which is a form of chalk. It is obtained from limestone or marble. FGNC may also be modified chemically or physically by coating during milling or after milling by heat treatment. Typical coating materials include magnesium stearate or 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 may be used as the sole calcium-based abrasive. However, FGNC may also be used with the other calcium-based abrasives for some balance of abrasion. Usually, the particle size of chalk is from 1 to 60 pm, and preferred sizes range from 1 to 15 pm.

Other preferred calcium-based abrasives include dicalcium phosphate (DCP), calcium pyrophosphate and precipitated calcium carbonate (PCC), which preferably are included at 25 to 55 wt%, more preferably 35 to 50 wt%.

Other abrasives may also be used depending upon the intended degree of abrasion. These include synthetic abrasive polishing agents such as amorphous precipitated silica and silica gels. It is preferred that gel compositions of the invention comprises silica as the abrasive. Abrasive silica for incorporation in the composition of the invention is preferably one with a low refractive index. The low refractive index silicas, used as abrasives in the present invention are preferably silicas with an apparent refractive index (Rl) 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 mm, a BET (nitrogen) surface area of between 10 and 100 m ² /g and an oil absorption of about 70 - 150 cm ³ /100 g, but abrasive silicas with a lower apparent refractive index may also be used . Typical examples of suitable low refractive index abrasive silicas (e.g. having an Rl of between 1.435 and 1.445. The amount of these silicas in the composition of the present invention generally ranges from 5-60% by weight, usually 5-20% by weight of the composition.

Other abrasive agents 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.

Suitable humectants are preferably used in the oral care composition of the present invention.

Preferred humectant for inclusion in the present invention is a polyhydric alcohol (also referred to as polyol). Preferred ones include, for example, glycerin, sorbitol, propylene glycol, dipropylene glycol, diglycerol, triacetin, mineral oil, polyethylene glycol (preferably, PEG-400), alkane diols like butane diol and hexanediol, ethanol, pentylene glycol, or a mixture thereof. Glycerin, polyethylene glycol, sorbitol or mixtures thereof, are the preferred humectants, most preferred ones being glycerol (also known as glycerine) and sorbitol.

The humectant may be present in the range of from 10 to 90% by weight of oral care compositions. More preferably, the humectant makes up from 25 to 80%, and most preferably, from 45 to 70% by weight of the composition, based on total weight of the composition and including all ranges subsumed therein.

Preferably, an oral care composition comprises a surfactant. Preferably the composition comprises at least 0.01% surfactant by weight of the composition, more preferably at least 0.1% and most preferably from 0.5 to 7%. Suitable surfactants include anionic surfactants, such as the sodium, magnesium, ammonium or ethanolamine salts of C8 to C18 alkyl sulphates (for example sodium lauryl sulphate), C8 to C18 alkyl sulphosuccinates (for example dioctyl sodium sulphosuccinate), C8 to C18 alkyl sulphoacetates (such as sodium lauryl sulphoacetate), C8 to C18 alkyl sarcosinates (such as sodium lauryl sarcosinate), C8 to C18 alkyl phosphates (which can optionally comprise up to 10 ethylene oxide and/or propylene oxide units) and sulphated monoglycerides. More preferably the surfactant comprises or is an anionic surfactant. The preferred surfactants are sodium lauryl sulphate and/or sodium dodecylbenzene sulfonate. Most preferably the surfactant is sodium lauryl sulphate. Other suitable surfactants include nonionic surfactants, such as optionally polyethoxylated fatty acid sorbitan esters, ethoxylated fatty acids, esters of polyethylene glycol, ethoxylates of fatty acid monoglycerides and diglycerides, and ethylene oxide/propylene oxide block polymers. Other suitable surfactants include amphoteric surfactants, such as betaines or sulphobetaines. Mixtures of any of the above described materials may also be used. Most preferred surfactants are an alkali metal alkyl sulphate or a betaine.

In a preferred embodiment, the composition comprises a thickener. Thickeners that may be used in this invention include, sodium carboxymethyl cellulose (SCMC), hydroxyl ethyl cellulose, methyl cellulose, ethyl cellulose, gum tragacanth, gum arabic, gum karaya, xanthan gum, sodium alginate, carrageenan gum, guar gum, Irish moss, starch, modified starch, silica based thickeners including silica aerogels, magnesium aluminum silicate (e.g., Veegum), Carbomers (cross-linked acrylates) and mixtures thereof.

Typically, thickening silica, sodium carboxymethyl cellulose and/or a Carbomer is/are preferred thickeners for use in the composition of the invention.

Thickening silica is especially preferred to be used in gel toothpastes.

Gel toothpastes generally contain upto 8.5 wt% thickening silica whereas opaque toothpastes typically contain 3 to 4 wt% thickening silica.

Thickener, when present, preferably makes up from 0.01 to about 10%, more preferably from 0.1 to 9%, and most preferably, from 1.5 to 8% by weight of the composition.

Water may preferably be included in 5 to 95%, in particular 10 to 75%, and especially at from 10 to 60%, further-more preferably 10 to 45% by total weight of the composition.

When the oral care composition of this invention is a toothpaste or gel, the same typically has a viscosity from about 30,000 to 180,000 centipoise, and preferably, from 60,000 to 170,000 centipoise, and most preferably, from 65,000 to 165,000 centipoise.

The oral care composition of the present invention may contain a variety of other ingredients which are common in the art to enhance physical properties and performance. These ingredients include antimicrobial, anti-caries agents, plaque buffers, fluoride sources, vitamins, plant extracts, desensitizing agents, anti-calculus agents, biomolecules, flavors, proteinaceous materials, preservatives, opacifying agents, coloring agents, pH-adjusting agents, sweetening agents, particulate abrasive materials, polymeric compounds, buffers and salts to buffer the pH and ionic strength of the compositions, and mixtures thereof. Such ingredients typically and collectively make-up less than 20% by weight of the composition, and preferably, from 0.0 to 15% by weight, and most preferably, from 0.01 to 12% by weight of the composition, including all ranges subsumed therein.

The reaction to prepare the sheet like crystals of calcium citrate for inclusion in the composition of the invention comprises the steps of (a) mixing a calcium salt with a water-soluble ionic citrate in an aqueous solution of a polyhydric alcohol for extended period of time to generate a precipitate; (b) filtering the precipitate and drying it to prepare the sheet like crystals of calcium citrate.

The preferred calcium salt for use in the above reaction are calcium chloride, calcium nitrate, or calcium acetate. The preferred water-soluble ionic citrates for use in the above reaction are sodium citrate, potassium citrate, or ammonium citrate; most preferred being alkali metal citrates like sodium citrate or potassium citrate. The preferred polyhydric alcohol for use in the reaction to prepare the calcium citrate of the invention are ethylene glycol, propylene glycol, glycerol, polyethylene glycol or polypropylene glycol, more preferably propylene glycol, glycerol, or polyethylene glycol.

The reaction to prepare the precipitate is generally carried out for 1 to 24 hours preferablylO to 16 hours.

The calcium citrate which is used in the present invention is therefore most preferably prepared using a process comprising the following steps: a) first mixing a water-soluble calcium salt with a water-soluble ionic citrate. The preferred mole ratio of calcium ion to citrate ion is in the range of 2:1 to 1 :1 most preferably in a 3:2 molar ratio in an aqueous solution of polyhydric alcohol. The polyhydric alcohol in the reaction mixture is preferably in the range of 5 to 20 wt% most preferably about 10 wt%, with respect to total reaction batch size. The reaction is carried out for an extended period of time preferably at room temperature (about 25 °C), to generate a precipitate; b) the filtering the precipitate and c) drying it to prepare the calcium citrate.

According to another aspect of the present invention there is provided a non-therapeutic method of whitening teeth comprising the steps of (i) applying the composition of the present invention on to a tooth surface for at least one minute; and (ii) rinsing the surface to be substantially free of the composition. The method is preferably non-therapeutic i.e., for achieving cosmetic benefits.

The invention will now be illustrated with the help of the following non-limiting examples. Examples

Examples A-D, 1-3: Whitening provided by various samples within and outside the invention: The following samples were analyzed for whitening benefits using various samples.

Example - A: Tea-stained hydroxyapatite (HAP) disk.

The following procedure was used to prepare the tea -stained disk:

HAP Tea Staining Protocol

Step 1 :Take 2 gm of tea leaves in a beaker.

Step 2: Add 100 ml boiling distilled water to the beaker and wait for two minutes.

Step 3: Filter the solution using a filter paper after two minutes, into a petri dish.

Step 4: Immerse pristine HAP disks into the solution (-100 ml volume, while the tea was still warm) for 5 minutes and then reverse the sides and let it sit for another 5 minutes.

Step 5: Dip rinse each disk in Milli Q water twice.

Step 6: Leave it in air for drying for 20-30 minutes, with the circular disk standing on its edge and both sides exposed to air.

Examples B-D, 1-3:

The disks so obtained as mentioned above were now ready for further experiments where whitening samples were coated on to the disks using the following drop casting protocol.

HAP drop casting protocol

Step 1 : Drop 10OpI of test sample on the stained full disk.

Step 2: Spread the sample as evenly as possible across the disk.

Step 3: Let it dry in the air for 20 minutes.

Step 4: Keep it in the oven at 40°C for 10 minutes to dry and measure the L*a*b* values.

The whitening samples dropped on to the disks above were as follows:

Example B: Titania STV 455 at 1 wt%.

Example C: Calcium citrate synthesized using conventional process (used at 1 wt%).

Example D: Commercially available calcium citrate (used at 1 wt%).

Example 1 : Calcium citrate synthesized using process of the invention with glycerol as the crystal habit modifier (used at 1 wt%).

Example 2: Calcium citrate synthesized using process of the invention with propylene glycol as the crystal habit modifier (used at 1 wt%). Example 3: Calcium citrate synthesized using process of the invention with polyethylene glycol (68k) as the crystal habit modifier (used at 1 wt%).

The calcium citrate for Example C (using conventional process) was prepared using the following procedure:

50 ml aqueous solutions of calcium chloride dihydrate [CaCl2.2H2O], 1.2 M and of sodium citrate dihydrate [Na ₃ C6H5Oy.2H ₂ O], 0.8 M. [Stoichiometric ratio of 3:2] were prepared. In a pool of 100 ml water, calcium chloride and sodium citrate was added dropwise under continuous stirring (300 rpm) over magnetic stirrer at 25°C, simultaneously. The stirring was continued for another 5 hours and then the mixture was left overnight for ~ 15 hours. The precipitate which settled at the bottom was vacuum filtered, washed and dried in the oven at 100°C, followed by drying in a vacuum desiccator.

The calcium citrate for Examples 1-3 (using the process of the invention) was prepared using the following procedure:

50 ml aqueous solutions of calcium chloride dihydrate [CaCl2.2H2O], 1.2 M and of sodium citrate dihydrate [Na ₃ C6H5Oy.2H ₂ O], 0.8 M. [Stoichiometric ratio of 3:2] were prepared. In a pool of 100 ml water containing 10% (w/w of the batch size) either of propylene glycol, glycerol or polyethylene glycol, calcium chloride and sodium citrate was added dropwise under continuous stirring (300 rpm) over magnetic stirrer at 25 °C, simultaneously. The stirring was continued for another 5 hours and then the mixture was left overnight for ~ 15 hours. The precipitate which settled at the bottom was vacuum filter, washed and dried in the oven at 100 °C, followed by drying in a vacuum desiccator.

The morphology of the various samples of calcium citrate prepared above was measured using SEM as follows:

Powder sample was taken on a conducting carbon tape and then gold coated for 60 s under vacuum, SEM was analysed using Hitachi S4700 SEM machine at 10kV external voltage and 100 torr vacuum and different magnifications at 12 mm working distance.

The whiteness of the samples of HAP disks prepared above (Examples A - B, 1-3) were then measured using the following procedure: Procedure used for L*a*b* measurement Stain measurement on surface was measured using a Konica Minolta Spectrophotometer (CM2600D) with the following attributes:

Wavelengths 360 nm -740 nm, L*, a* and b* values, instrument calibrated using standard black and white surfaces as provided by instrument maker.

L* presented here is the average of at least five measurements taken on the circular surface of 0.5 cm diameter in the SCI and SCE modes with small aperture.

The data on the L* along with the morphology of the samples of calcium citrate is summarised in Table -1 below:

TABLE 1

The data in the table above indicates that calcium citrate as per the invention. (Examples 1-3) gives enhanced whitening on HAP discs as compared to conventional calcium citrate as well as conventional material like titanium dioxide (Examples A -D). Examples E-G and 4-6: Whitening obtained with different concentration of calcium citrate Experiments similar that in Table 1 were conducted except that a different concentration was used (0.5 wt%) instead of 1.0 wt%. The whiteness obtained is summarized in Table 2 below:

TABLE 2

The data in Table 2 indicates that calcium citrate as per the invention (Examples 4 to 6) is also equally effective at a lower concentration (0.5 wt%).