ORAL HYGIENE COMPOSITIONS

Abstract: An oral hygiene composition comprises from 0.01 to 2.0% by weight of the composition of a water soluble ionic fluoride, an ionic abrasive material containing metal cations capable of forming a water insoluble fluoride, and between 0.01% and 9% by weight of the composition of a water soluble ionic agent containing the anionic counter ions of the ionic abrasive together with metal cations capable of form­ ing a water soluble fluoride. The composition is useful in reducing or preventing the inactivation of a water soluble ionic fluoride by an ionic abrasive material.

Description: This invention relates to oral hygiene compositions having anti-cariogenic activity. Hitherto, it has been well known to incorporate a wide variety of fluoride compounds into oral hygiene compositions such as dentifrices in order to provide them with anti-cariogenic activity. This activity is believed to result from the effect of the fluoride compound in reducing the solubility of tooth enamel in weakly acidic media such as often occurs in the mouth owing to the action of bacteria on foods. The effect of reducing the solubility of dental enamel is believed to result from an interaction of hydroxyapatite, the mineral which constitutes the major part of dental enamel, with the fluoride to produce fluoroapatite. Fluorapatite has a lower solubility in a weakly acidic medium than hydroxyapatite. While sodium fluoride was one of the first fluorides advocated for addition to dentifrices, it has found relatively little use because it has long been believed that the calcium-containing abrasives often used in dentifrices, especially calcium carbonate, are incompatible with ionic fluorides such as sodium fluoride. Thus it was long ago reported that the anti-cariogenic effect of sodium fluoride was inhibited by the presence of calcium carbonate, no doubt because it was believed that these substances would primarily interact to produce the insoluble and inactive calcium fluoride. For this reason, sodium monofluorophosphate has often been used instead of sodium fluoride. DE-B-971 375 discloses the general principle that a source of soluble carbonate ions may be added to a calcium carbonate containing dentifrice, to suppress the formation of free calcium ions, according to the law of Mass Action, thereby preventing the loss of fluoride from solution as insoluble calcium fluoride. The preferred source of soluble carbonate ions is ammonium carbonate, the ammonium ions having a beneficial effect in their own right on fluoride availability. Sodium bicarbonate or sodium carbonate are disclosed as possible alternative sources of carbonate ions. There has not however been, as far as we are aware, any commerical application of this proposal, with dentifrice manufacturers preferring to use either a more insoluble calcium-containing abrasive such as calcium pyrophosphate or a non-calcium containing abrasive such as silica. We have now found a method of reducing or preventing the inactivation of water soluble ionic fluorides, such as sodium fluoride, by calcium carbonate. Accordingly, the present invention provides an oral hygiene composition comprising: from 0.01 to 2.0% by weight of the composition of a water soluble ionic fluoride; calcium carbonate; and between 0.5% and 6% by weight of the composition of a water soluble ionic agent comprising a mixture sodium carbonate and sodium bicarbonate, wherein the bicarbonate is in excess over the carbonate. The term ′water soluble ionic fluoride′ is used herein to include any ionic material which, in aqueous solution, provides fluoride or monofluorophosphate ions. The use of an alkali-metal fluoride is preferred, such as sodium, potassium or lithium fluoride; the use of sodium fluoride is especially preferred. Other suitable fluorides include ammonium, stannous and zinc fluorides. In addition to the ionic fluoride, an ionic monofluorophosphate may be used, preferably an alkali metal monofluorophosphate. Sodium monofluorophosphate, Na₂PO₃F, is especially preferred but the corresponding potassium and/or lithium salts can also be employed. The term 'monofluorophosphate' as used herein includes monofluoropolyphosphates, such as those of formulae Na₄P₃O₉F; K₄P₃O₉F; Na₃KP₃O₉F; (NH₄)₃NaP₃O₉F and Li₄P₃O₉F. The total amount of fluoride and monofluorophosphate used is dependent to some extent on the type of dentifrice composition, but it should be an effective, but non-toxic, amount. Typically the fluoride(s) is present in the oral hygiene composition in an amount to provide a total of from 0.025 to 0.25% of fluorine based on the weight of the oral hygiene composition. The preferred total fluoride level is from 0.05 to 0.15% by weight of the composition. The preferred amount of water soluble ionic agent present is from 5% to 6%. A preferred mixture consists of about 5% sodium bicarbonate and 0.5% sodium carbonate, by weight of the composition. The ionic agent is preferably present in the composition of the invention in the form of an aqueous solution so that it has no abrasive character of its own. Calcium carbonate can be in either of the geological forms known as Aragonite and Calcite or a mixture of the two. Other forms of calcium carbonate include powdered limestone and milled marble or mined powder products. Preferably the calcium carbonate should have a weight median diameter of less than 40 µm. Other dental abrasives may also be present in admixture with calcium carbonate. For instance there may be employed water-insoluble sodium or potasium metaphosphates, hydrated or anhydrous dicalcium phosphate, calcium pyrophosphate, aluminium trihydrate, tricalcium phosphate, calcium silicate, zirconium silicate or mixtures thereof. Particularly useful polishing agents are various forms of silica, especially silica xerogels as defined in U.S. Patent No. 3,538,230, though such xerogels may have an average particle size diameter up to 50 µm. The abrasive(s) may be employed in a total amount of from 10 to 99% by weight of the composition of the invention. Preferably such compositions are in the form of dentifrice pastes containing 20 to 75% of dental abrasive, though they can be in the form of powders containing 70 to 99% of the abrasive. If desired, the compositions of the invention can be formulated as striped dentifrice compositions, such as those described in U.K. Patent Specification No. 1271944. The oral hygiene compositions of the invention will also usually contain surfactants, gelling agents and other excipients such as flavouring and colouring agents. The surfactant is normally a water-soluble non-soap or synthetic organic detergent. Suitable surfactants include the water-soluble salts of: higher fatty acid monoglyceride monosulphates (for example sodium hydrogenated coconut fatty acid monoglyceride monosulphate); higher alkyl sulphates (for example sodium lauryl sulphate); alkylarylsulphonates (for example sodium dodecylbenzenesulphonates); and higher alkyl sulphoacetates (for example sodium lauryl sulphoacetate). There may also be used the saturated higher aliphatic acyl amides of lower aliphatic amino carboxylic acids having 12 to 16 carbon atoms in the acyl radical and in which the amino acid portion is derived from the lower aliphatic saturated monoaminocarboxylic acids having 2 to 6 carbon atoms, such as the fatty acid amides of glycine, sarcosine, alanine, 3-aminopropanoic acid and valine, particularly the N-lauroyl, myristoyl and palmitoyl sarcosinate compounds. Conventional non-ionic surfactants may also be included, if desired. The surface-active materials are generally present in an amount of 0.05 to 15%, preferably 0.5 to 5% by weight of the composition. The tooth powders and pastes are prepared in the usual manner. Thus, the ingredients can be mixed in the dry state or as slurries or solutions. In general the liquids in the dental cream or paste will comprise chiefly water, glycerine, sorbitol and/or a glycol, including suitable mixtures thereof. Suitably, the glycol is propylene glycol or a polyethylene glycol. It is preferred to use also a gelling agent in dental creams, such as natural or synthetic poms or gum-like materials, e.g. Irish Moss, gum tragacanth, sodium carboxymethylcellulose, polyvinylpyrrolidone or starch. Irish Moss and sodium carboxymethylcellulose are preferred gelling agents. The gum content is usually up to 10% and preferably 0.01 to 5% by weight of the preparation. The pH of the dental cream or an aqueous slurry of the tooth powder is 7 to 11, i.e. neutral to slightly basic. Typically the pH is pH 8.5 to 9.5. Other materials may be added, such as sweetening agents, for example soluble saccharin, flavouring oils (e.g. oils of spearmint, wintergreen peppermint), chloroform, colouring or whitening agents (e.g. titanium dioxide), preservative (e.g. sodium benzoate), emulsifying agents, silicones, alcohol, menthol, chlorophyll compounds (e.g. sodium copper chlorophyllin), antibacterial agents (e.g. chlorhexidine); anti-plaque agents, anti-calculus agents, agents for sensitive dentine (e.g. strontium salts, formaldehyde), and agents which enhance the anti-caries activity of fluorides (e.g. calcium glycerophosphate). The compositions of the invention may also be in a form of other oral hygiene compositions, for example, the ingredients may be incorporated in mouth washes of the suspension type, or in compositions which will be chewed by the user, for example, chewing gum, tablets, pastilles and lozenges. These compositions will contain the conventional base materials together with suitable flavours and sweetening agents and may be formulated in known manner. The compositions of the invention are illustrated by the following examples: The following Example 3 is a striped toothpaste composition made in accordance with U.K. Patent Specification No. 1271944. Example 3 Ratio of main body to secondary body is 62: 38

Claims: 1. An oral hygiene composition of pH from 7 to 11, comprising: from 0.01 to 2.0% by weight of the composition of a water soluble fluoride source consisting of an ionic fluoride optionally admixed with an ionic monofluorophosphate; calcium carbonate; and between 0.5% and 6% by weight of the composition of an ionic agent comprising a mixture of sodium carbonate and sodium bicarbonate, wherein the bicarbonate is in excess over the carbonate. 2. A composition according to claim 1 in which the water soluble fluoride source is a mixture of an ionic fluoride and an ionic monofluorophosphate. 3. A composition according to claim 1 or 2 in which the ionic fluoride comprises an alkali metal fluoride and the ionic monofluorophosphate comprises an alkali metal monofluorophosphate. 4. A composition according to any one of claims 1 to 3, in the form of a dentifrice. 5. A dentifrice dispenser containing a composition according to claim 4. 6.A method of reducing or preventing the inactivation of a water soluble fluoride source by calcium carbonate in an oral hygiene composition, which comprises adding to a composition comprising the water soluble fluoride source and calcium carbonate an ionic agent which is obtained by the incorporation into the composition of an alkali metal carbonate and an alkali metal bicarbonate, to produce a composition as defined in claim 1.

Inventors: JACKSON, ROBERT JOHN
Applicants: BEECHAM GROUP PLC
Application year: 1983
Main classification: A61K7
IPC codes: A61K8, A61Q11