IE43733B1 - Dentifrices - Google Patents

Description

This invention relates to dentifrices, particularly toothpastes.

When toothpaste formulations containing highly alkaline milled Bayer process alpha-alumina trihydrates are packed in unlacquered aluminium tubes they react with the aluminium walls of the tube to form gas on storage, even when· the pH of the toothpaste is substantially neutral, e.g. 7.1. It has been found that such reaction with the aluminium walls of the tube can be prevented by adjusting the pH of the toothpaste prior to storage to a value in the range from about .4 to θ·6 or 6.7, preferably from about 5.4 to 6.1 or 6.2. The pH may be adjusted by means of an organic carboxylic acid such as benzoic, citric, tartaric, i malic, acetic or propionic acid or other suitable (e.g. non-toxic) acidic material, such as sodium bisulphate, aluminium fluoride, aluminium sulphate or zinc sulphate The highly alkaline milled Bayer process alphaalumina trihydrate is one which in a 10$ slurry in • deionized water gives a pH of above about 8.5 (such as 8.8 or more). All percentages and other proportions herein are by weight unless otherwise indicated. When used in toothpaste formulation A, set forth below, it may yield a toothpaste having an initial pH (before storage) of at least 6.9. At such pH or higher (e.g. initial of pH 7.1 or 7.3) the resulting toothpaste, when packed in an unlined aluminium tube, gives, visible gas formation accompanied by bloating of the tube on storage at 100°H (38°C) for 3 months.

TOOTHPASTE FORMULATION A Milled alpha-alumina trihydrate 55$ 70?$ aqueous solution of sorbitol 27$ Sodium carboxymethyl cellulose (dentifrice grade) 0.8?$ Sodium lauryl sulphate 1.5$ Titanium dioxide (finely divided) 0.5$ Saccharin 0.2$ Benzoic acid 0.15$ Flavour 1.0$ Water Balance The foregoing formulation may be made in a conventional manner as by mixing the humectant (sorbitol), gelling agent (sodium carboxymethyl cellulose) and water, adding saccharin, benzoic acid and flavour, then adding the abrasive (alpha-alumina trihydrate) and the titanium dioxide whitener, deaerating, and mixing in the detergent (sodium lauryl sulphate). Alternatively, a pre-mix of the sodium carboxymethyl cellulose, benzoic acid, titanium dioxide and saccharin may he prepared, then added to the aqueous sorbitol with agitation, mixed thoroughly with high agitation for 15 minutes, after which the water is added and the mixing is continued for another 15 minutes or more until a smooth lump-free dispersion is obtained; the resulting blend is placed in a vacuum mixing vessel and the alumina trihydrate is drawn into the blend under vacuum while mixing slowly, then the degree of vacuum is increased and mixing at high speed is carried out under the high vacuum for _ 4 _ minutes, after which the vacuum is broken, the sodium lauryl sulphate (in solution in water) is added, the high vacuum is restored and the mixing is continued for another 10 minutes; the same procedure as used for the addition and blending of sodium lauryl sulphate is then used for the incorporation of the flavour.

Alkaline alpha-alumina trihydrates which cause corrosion at neutral pH are described, for instance, at page 1 of German OS 2509399 published 11 Sept. 1975.

One particular highly alkaline milled Bayer process material is the material made by Baco (British Aluminium Company) and sold under the designation AB 260. A typical sample of this material showed a pH of about 9.5 when dispersed in water at 20$ concentra5 tion. When a typical. sample of this material was incor porated into the previously mentioned toothpaste formulation A.but without the 0.15$ benzoic acid it was found that the initial pH of theformulation was about 8.1. When this same material was incorporated into that ) toothpaste formulation A containing the 0.15$ benzoic acid, the initial pH of the formulation was about 7.3; on storage for three months at 110°? (43°C) considerable gassing occurred. When the total amount of benzoic acid in the formulation was increased to 0.26$ j the initial pH of the formulation was about 6.3; on storage for 3 months at 110°P (43°C) no gassing was observed.

The highly alkaline milled alpha-alumina trihydrate generally has an average particle size in the range of about 2 to about 15 microns. Typically it has a relatively large proportion (such as 40)( or 50$ or more) of particles smaller than 7.5 microns and mayhave a low fines content, such as not more than 20$ byweight smaller than 3 microns. Thus, one sample of Baco AF 260 has the following typical approximate particle size distribution (measured by Coulter counter) 20$ finer than 5 microns, 40$ finer than 7.5 microns, 58$ finer than 10 microns, 82$ finer than 15 microns, 91$ finer than 20 microns, with a mean particle size of 8 microns, and at most 0.1$ retained on a BSS 350 (45 microns) sieve. A typical chemical analysis of the Baco AF 260 material is 65.5 ± 0.5$ AlgOj, 34.5 ± 0.5$ lost on ignition at 115O°C, 50 ppm maximum heavy metals calculated as Ph, 5 ppm maximum Pb, 1 ppm maximum arsenic, 0.55$ Na^O.

In measuring the pH of a slurry of the milled alpha-alumina trihydrate the mixture of the solid and deionized water is stirred for 5 minutes and then a conventional pH meter is introduced while stirring is continued to maintain a substantially uniform slurry. The measuring instrument may be, for instance, an BIB model 1150 combination pH electrode connected to an Orion model 801 digital pH/mV meter; this may also be employed for measuring the pH values of the toothpastes.

It has been found that when toothpaste formulations contain the highly alkaline milled alphaalumina trihydrate in admixture with alkali metal fluoride, e.g. sodium fluoride, the inclusion of the fluoride in the toothpaste results in a chemical -,6reaction which raises the pH. For instance, when 0.24% by weight of sodium fluoride was incorporated into a toothpaste containing 0.2% benzoic acid (ordinarily sufficient to give a toothpaste pH of less than . 7, as indicated above) the pH of the toothpaste was found to be about 8.2. The addition of more benzoic acid (e.g. to raise the benzoic acid content to 0,50% giving a pH of 6.20) did not overcome the tendency to react with the tube walls; considerable gassing 0. occurred on storage as described above. It has been found, however, that when the fluoride content is supplied by a mixture of - alkali metal monofluorophos- : phate, e.g. sodium monofluorophosphate (MFP”), and alkali metal fluoride, in a monofluorophosphate: . fluoride mol ratio in the range from 1.5:1 to 5:1, preferably 1.5:1 to 3:1, the reactive tendency is inhibited., The total proportion of soluble fluoride (e.g. MFP calculated as F plus NaF calculated as F). added to the. toothpaste should be no more than 1500 3. ppm, and at least 500 ppm, most preferably at least 800 ppm, e.g. about 1000 ppm.

It has also been found that in these formulations the presence of the highly alkaline milled alphaalumina trihydrate results in greater retention of i. soluble fluoride than when less alkaline milled alphaalumina trihydrate is employed, at the same initial pH of the toothpaste.

One example of such a less alkaline alphaalumina trihydrate is Alcoa C-333, a product of Alcoa . (Aluminum Company of America), Its specifications state that its average particle size is about 6.5-8.5 microns and, by hydrometer analysis, 94-99% is below 30 microns, 85-93% is below 20 microns, 56-67% is below 10 microns and 28-40% is below 5 microns. Other .' typical properties as given by the manufacturer are 65.0% (64.5% minimum), Si02 0.01% (0.02% maximum), Fe203 0.005% (0.005% maximum), Na20-0.15% (0.25% maximum), soluble Na2Q (by standard Alcoa test methods) 0.02% (0.04% maximum), moisture (110°C) 0.4% (0.70% . maximum), bulk density (loose)44 lb/ft^, bulk density (packed) 77 Ib/ft^, specific gravity 2.42, screen analysis 99% through 325 mesh sieve (98% minimum).

Its pH, measured in a 20% slurry in deionized water is usually about 8.5 or less. When this material is . employed in toothpaste formulation A, given above, it typically yields a toothpaste having an initial pH well below 6.7, such as about 6.2.

Thus, according to the present invention a toothpaste containing abrasive particles of milled . alpha-alumina trihydrate reactive with alkali metal fluorides also contains alkali metal fluoride and alkali metal monofluorophosphate the mol ratio of the monofluorophosphate to the fluoride being in the range from 1.5:1 to 5:1 and the total amount of the mono25. fluorophosphate and the fluoride (calculated as F) being in the range from 500 to 1500 ppm.

Use of toothpastes according to the invention may reduce substantially the solubility of dental enamel particularly as compared to a formulation con30. taining complex fluoride (e.g. MFP) as the only source of fluoride. Thus, enamel solubility is reduced compared with the situation in which MBP is the sole fluoride source; while avoiding gassing normally occurring in formulations containing alkali metal fluoride as the sole fluoride source. The following Examples illustrate the invention.

All the Examples herein are conducted at room temperature unless otherwise indicated.

EXAMPLE 1 A toothpaste formulation is prepared in a conventional manner by mixing the following ingredients: glycerol-20.2$; sodium carboxymethyl cellulose 1.1$, saccharin 0.2$, benzoic acid 0.29$, Baco AB 260 51.5$, titanium dioxide 0.5$, sodium monofluorophosphate (a technical grade containing about 94$ sodium monofluorophosphate, together with hydrolysis products thereof such as HaP, phosphates, etc.) 0.82$ (about 1000 ppm B); sodium fluoride 0.12$ (about 500 ppm J?); sodium lauryl sulphate 1.5$, flavour 0.8$; balance water.

) The initial pH of the toothpaste is 6.7. On storage in unlined aluminium tubes for 3 months at 110°B (43°C) it shows a very good fluoride retention and the tubes· are not swollen.

EWiPIES 2- 5 j Example 1 is repeated except that the proportions of MBP, HaB and benzoic acid, and the initial pH, are as follows: ME? ppm E liaE ppm E Mol Ratio Initial pH 5» Benzoic Acid Example 2 800 200 4:1 6.3 0.313 Example 3 700 300 2.33:1 6.5 0.317 Example 4 600 400 1.5:1 6.5 0.380 Example 5 0 1000 0 6.2 0.50 In each of Example 3 2 to 4 the storas ;e (as in Example 1) does not result in gassing and the soluble fluoride content after such storage is measured at over 700 ppm. In the comparison Example 5, the tubes gas severely on such storage and the measured soluble fluoride content is markedly lower.

From the foregoing it will be observed that the use of sodium fluoride in the toothpaste containing alpha-alumina trihydrate of high alkalinity tends to cause attack of unlined aluminium tubes even when the initial pH of the toothpaste is such that attack would be inhibited in the absence of the sodium fluoride.

When the proportion of sodium fluoride is such as to provide about 500 ppm E (as in Example 1) but the proportion- of MEE is lower than that in Example 1 (i.e. a proportion such as to provide about 500 ppm E, rather than the 1000 ppm E of Example 1) the results have been borderline; thus in two experiments (using the same formulation, except as noted below) in which the molar ratio was 1:1, specifically using amounts of ME? and HaE which each provided 500 ppm E (for a total of 1000 ppm E as in Examples 2 to 5), no gassing was observed when the amount of benzoic acid was 0.40$ and the 3 7 3 3 -10initial pH was 6.6 while severe gassing was observed, (under the same 43°C 3-month storage conditions) when the amount of benzoic acid was 0.33$ and the initial pH was 6.4. ΕΣΑΜΡΕΕ 6 Example 1 is repeated except that the 1.5$ sodium lauryl sulphate is replaced by 2$ sodium Nlauroyl sarcosinate and the proportions of MFP, NaF and benzoic acid are as follows: .0 MFP NaF $ Benzoic ppm F ppm F Acid 1000 500 0.33 In this Example the storage (as in Example 1) does not result in gassing, and measurements of soluble fluoride after such storage indicate good fluoride retention.

• In these Examples the fluoride compounds are included as.dry powders in the pre-mix (with benzoic acid) as mentioned above. They may be added in other ways, as in the aqueous solution of the detergent which is incorporated after the alumina trihydrate has been added.

It.will be noted that the Baco trihydrate, which appears to be somewhat less reactive with the j fluoride, has a lower fines content than the Alcoa trihydrate and thus may have a smaller surface area for reaction. The manufacturer of Baco AF 260 has advised that its surface area (as measured by light π extinction) is well below 1.5 m /g, specifically about ο o ) 1 m /g, e.g. 1.1 m /g. The manufacturer of Alcoa - 11 C-333 has advised, that its surface area (as measured by BET nitrogen adsorption) is about 2 to 2.5 m /g.

The light extinction method for measuring specific surface is described at pages 10-12 of the publication The (Physical Examination of Alumina published by B.A. Chemical ltd., London, which teaches that the method correlates well with other procedures.

The milled alpha-alumina trihydrate may be modified during its manufacture.

A conventional way of manufacturing alphaalumina trihydrate (hereinafter referred to simply as trihydrate) is by the Bayer process. In that process trihydrate is precipitated from a solution of sodium aluminate. See Encyclopedia of Chemical Technology, Kirk-Othmer, 2nd Edition, Vol. 1. p. 937 - 941 and Vol. 2. p. 41-45, 50-51. The trihydrate is precipitated in the form of granules or agglomerates which are too large for general use as a dentifrice abrasive, e.g. about 40 - 100 microns diameter. Therefore, the granules or agglomerates after drying (sometimes after water-washing and drying) are ground to a suitable particle size, e.g. to an average particle diameter in the range of about 2 to about 20 microns, such as 5 to 10 microns diameter.

The washed, unground granules usually show an alkaline reaction when slurried in water. For instance, depending on the degree of washing before drying, the pH of a 10$ or 20$ by weight of trihydrate slurry at room temperature may be in the range from about 7.5 to 8.5, 9 or 9.5. 3 733 -12The pH can be measured with an Orion model 801 Digital pH/mv meter which is fitted with an EID model 1150 Combination pH and reference electrode. The instrument is first calibrated at room temperature by placing the electrode into 50 ml of pH buffer solution in a 100 ml beaker and adjusting the calibration control until the instrument reading corresponds to the buffer pH. The electrode is then, removed, washed with deionized water and placed into 125 g of a preLO pared 20% slurry on the trihydrate sample in deionized water, in a 250 ml beaker, and its pH reading taken.

On grinding, the alkalinity, thus measured, increases and the pH measured (as above) of the ground, unwashed, material is generally above 8. For instance, •5 the pH on grinding may change as follows: 7.5 (before grinding) to 8.8 (after grinding); 8.8 (before) to 9.2 (after).

It Is believed that by grinding the trihydrate in the presence of a surface-modifying agent, inclu-0 sions of alkali exposed by fracture of the trihydrate granules during the grinding, or highly active sites produced by fracturing during grinding, may be brought into intimate contact with the surface-modifying agent and thereby neutralized or inactivated. This reduces the risk of localized corrosion in the dentifrice during storage.

The amount of surface-modifying agent required will generally be within the range from 0.01 to 2% such as about 0.1% to 0.5%, by weight based on the ) weight of trihydrate. - 13 Surface-modifying agents may act by deactivating reactive sites on the trihydrate and/or forming a coating of at least monomolecular thickness on the trihydrate, at least during the beginning of grinding. Surface-modifying agents which may be employed are nontoxic and include organic acids, which contain a polar and non-polar group, and salts thereof, such a3 benzoic acid, lauric acid, stearic acid, oleic acid, naphthenic acid, fatty acyl amides of amino acids, such as Ulauroyl (or li-oleoyl or N-stearoyl) sarcosine and phenol which have low water solubility, and salts thereof, as well as solid or liquid organic acids of greater water-solubility such as acetic acid, propionic acid or other lower alkyl carboxylic acids, citric acid, tartaric acid, malic acid and salts thereof, such as alkali metal salts, e.g. sodium salts. Polar-nonpolar carboxylic acids and salts are described in U.S. Patent 2,274,521. Inorganic acid forming salts such as sodium bisulphate and aluminium chloride, aluminium sulphate and zinc sulphate also may be employed.

Additional non-toxic surface-modifying agents which may be employed include mono- and polyhydric alcohols; dentally acceptable polishing and thickening agents; and polyelectrolytes. The most preferred materials are those which are more acidic than the trihydrate.

Mono- and polyhydric alcohols include methanol, ethanol, n-propanol, isopropanol, n-octanol, ethylene glycol, tri-ethylene glycol, ethylene glycol monomethyl ether, l-amino-2-propanol, monoethanolamine and ^3733 -14triethanolamine.' Dentally acceptable polishing materials vbich can modify the surface of the trihydrate include insoluble sodium metaphosphate, dicalcium phosphate, calcium carbonate and other alkali earth metal phosphates and carbonates, sodium aluminosilicate and crystalline and colloidal silica. The surface-modifying agent may be a material of very fine particle size, e.g. less thanl micron diameter; acidic silica particles such as pyrogenic silica, e.g. Cabosil, may be used (CABOSII is a trade mark).

Polyelectrolytes, particularly those ionic polymeric polyelectrolytes available under the name Tamol,' such as Tamol 731 and Tamol 850, also can modify the surface of the trihydrate. Polymeric carboxylic acids, such as the vinyl methyl ether - maleic anhydride copolymer, can be used for this purpose.

In addition to the surface-modifying agents mentioned above, suitable materials include detergents ) such as anionic sulphates and phosphates, nonionic, condensates including an ethylene oxide moiety and ampholytics such as imidazole derivatives. Typical detergents are-described below. Mon-polar materials Including waxes, and hydroi carbon oils and grease, e.g. mineral oils such as liquid paraffin, e.g. light or heavy petrolatum, petroleum jelly and petroleum wax can also modify the surface of the trihydrate.

Vegetable oils such as palm oil and hydrogenated palm oil may also be used. - 15 It is preferred that the amount of surfacemodifying agent present he at least that needed to form a coating of monomolecular thickness on the trihydrate particles, and/or to enter into reaction with and deactivate sites in the trihydrate, at least during the beginning of the grinding; preferably an excess, such' as 5$ (or more) excess, is used, particularly when ball milling. The surface area of the trihydrate p granules before grinding is generally well below 1 m /g p and it may increase during grinding to about 1 m /g or p above, such as to 3 or 5 m /g or higher.

The surface-modifying agent may be in liquid form at the ambient grinding temperature. This may be, for instance, a solution, a solid surface-modifying agent in a solvent therefor, or a liquid mixture of solid and liquid surface-modifying agents, such as a 50-50 mixture of ethylene glycol and benzoic acid, mineral oil and stearic acid or mineral oil and benzoic acid. The grinding temperature is generally well below 100°C such as about 20, 30 or 40°C. The material being ground is preferably substantially dry, e.g. its water content is preferably below 20$ of the weight of trihydrate, such as 1$ or 2$.

The grinding of the trihydrate in the presence of the surface-modifying agent may be practised using techniques and apparatus recognised in the art. Bor instance, ball milling is described in Surface Activity in Bine Dry Grinding Berry & Kamack, pages 1S6-202, in Solid/liquid Interface; Cell/Water Interface (Biological) Vol. 4. Edited by J.H. Schulman (Proceedings of the Second International Congress on Surface Activity, London, 1957.) Academic Press, New York, 1958, Grinding low-Soda Alumina by Hart and Hudson, Ceramic Bulletin, Vol. 43, No. 1 (1964); and. Η.S. Patent 3,358,937.

VIbrative-Energy Milling is described in the article by Hart and Hudson and Pin-type Milling is described in Perry, Chemical Engineers' Handbook, 5th Edition, 1973, paged 8-57 to 8-71.

The surface-modifying agent may be added to the .0 material being fed to the mill, may be metered into the mill itself during operation or may be added to the wet slurry before grinding. It is also permissible to add the surface-modifying agent to the size classification zone associated with the mill. Thus it is common to5 pass the product of the mill to a size classification zone (e.g. a cyclone) from which the oversize, insufficiently ground, particles are returned to the mill for further grinding.

Pulverisation and reduction of particle size of granules of washed Bayer process alumina trihydrate may be effected, for example, by charging a procelain ball mill pot containing a 50$ ball charge of procelain balls ranging in diameter, from 1 cm to 2.5 cm with the alumina trihydrate granules together with 0.5$ benzoic acid based on the weight of the trihydrate such that the ratio of ball volume to powder volume is 2:1« Pot sizes range from 0.5 litre to 30 litres depending on charge size, 1 litre is used.

The pot is sealed, and placed on a No. 2 ' Motorised Pascall laboratory Ball Mill such that it -17rotates horizontally about its axis on a pair of rubbercovered rollers, one driven and one idler, each 15i long. Drive is by a j H.P. electric motor with a variable speed control. The motor is started and the speed adjusted such that the halls tumble in the mill pot to reduce the particle size of the trihydrate. The motor is then stopped, the pot removed and the charge separated from the halls by sieving and then suitably classified to remove large particles, such as those larger than 20 microns, which large particles are returned to the hall mill.

EXAMPLE 7 A washed unground Bayer process trihydrate of the more alkaline (Baco) type is ground in the presence of 0.5$ benzoic acid and the resulting milled trihydrate is used in a formulation as set forth in Example 1 above. The pH of the toothpaste is about 6.3. On aging at 43°0 for 3 months in unlined aluminium tubes only very slight gassing is observed.

The surface-modifying agents mentioned above may also be incorporated into the toothpaste formulation without first contacting them with the abrasive. One particularly suitable agent for this purpose is pyrogenic silica such as that sold as Aerosil 200 or Cabosil.

The Aerosil 200 is a hydrophilic pyrogenic silica having an acidic reaction. Typically the grade 200 has a BET surface area of 200 ± 25 m2/g and a pH (in 4$ slurry in water) of about 3.6 to 4·3. Detailed descriptions of this material are found in publications 37 3 3 - 18 of the manufacturer, Degussa; see for instance, Kautschuk und Gummi, Kunststoffe 20 (1967) p. 578-586.

The Aerosil 200 particles have silanol groups at their surfaces and, in aqueous dispersion, the particles move, under the influence of an electric field, to the positive pole, i.e. they carry a negative charge.

As illustrated above, the toothpastes generally contain an aqueous vehicle including a gelling agent and a detergent or surface-active agent, together with LO flavour and sweetener, besides the alpha-alumina trihydrate, monofluorophosphate and fluoride. Other ingredients may be present as well.

Organic surface-active agents may be used in the dentifrice to achieve increased prophylactic action .5 and to assist in achieving thorough and complete dispersion of the compositions throughout the oral cavity.

It is preferred to employ as the surface-active agent a detersive material which imparts to the dentifrice detersive and foaming properties. The proportion of surface-active agent is generally within the range from 0.05 to 5%, more usually within the range from 0.5 to 3%, such as 1 to 2%. As indicated above, a particularly preferred surface-active agent is an H-acyl sarcosine having at least about 10 carbon atoms (e.g. 12-18 carbon atoms) in the acyl group, such as sodium IT-lauroyl sarcosinate. It is also permissible to use other amide-linked carboxylic surface-active agents, such as higher aliphatic acyl amides of lower aliphatic amino carboxylic acid compounds (e.g. those having, say, 12 ) to 16 or 18 carbon atoms In the higher acyl radical 3 7 3 3 - 19 which is preferably of the saturated, type, and up to 4 carbon atoms in the carboxylic portion) and including those disclosed at pages 37 to 39 of Schwartz and Perry Surface Active Agents and Detergents Volume II published 1958 by Interscience Publishers, U.S.A. The amide-linked carboxylic surface-active agent may be substantially the sole surface-active agent. There may also be present other anionic, amphoteric or non-ionic surface-active agents, preferably in minor amounts in relation to the amide-linked surface-active agent (such as less than 1$ of the total toothpaste formulation, e.g. 0.7$ or 0.5$).

The anionic detergents include water-soluble salts of higher (i.e. having at least 12 carbon atoms) fatty acid monoglyceride monosulphates, such as the sodium salt of the monosulphated monoglyeeride of hydrogenated coconut oil fatty acids, higher alkyl sulphates, such as sodium lauryl sulphate, alkyl aryl sulphonates, such as sodium dodecyl benzene sulphonate, olefin sulphonates, such as sodium olefin sulphonate in which the olefin group contains 12-21 carbon atoms, higher alkyl sulphoacetates and higher fatty acid esters of 1,2dihydroxy propane sulphonates.

The nonionic detergents include such materials as condensates of sorbitan monostearate with approximately 60 moles of ethylene oxide with propylene oxide condensates of propylene glycol (Pluronics - PIURONIC is a trade mark), other examples of suitable nonionic detergents are condensation products of alkyl phenols with ethylene oxide, e.g. the reaction product of 3 7 3 3 iso-octyl phenol with 6 to 30 ethylene oxide units; condensation products of alkyl thiophenols with 10 to 15 ethylene oxide units; condensation products of higher fatty alcohols and monoesters of hexahydric alcohols and inner ethers thereof such as sorhitan monolaurate, sorbital mono-oleate and mannitan monopalmitate Examples of amphoteric detergents are H-alkylheta-aminopropionic acid; and E-alkyl-tieta iminodipropionic acid; and E-alkyl, E,E-dimethyl glycine. .0 The alkyl group may he, for example, that derived from coco fatty alcohol, lauryl alcohol, myristyl alcohol (or a lauryl-myristyl mixture), hydrogenated tallow alcohol, cetyl alcohol, stearyl alcohol or blends of such alcohols. The substituted amino-propionic and imino.5 dipropionic acids are often supplied as the sodium or other salt forms, which may likewise be used in the practice of this invention. Examples of other amphoteric detergents are betaines containing a sulphonic group instead of the carboxylic group; betaines in which the long chain substituent is joined to the carboxylic group without an-intervening nitrogen atom, e.g. inner salts of 2-trimethylamiho fatty acids such as 2-trimethylaminolauric acid, and compounds of any of the previously mentioned types in which the nitrogen atom is replaced by phosphorus.

It is also permissible to employ a cationic surface-active agent or detergent. Examples of these are diamines, such as those of the type rhec2h4mh2 wherein R is an alkyl group of 12 to 22 carbon atoms 3 7 3 3 - 21 such as H-2-aminoethyl stearyl amine and U-2-aminoethyl myristyl amine; amido-linked amines such as those of the type R^COMHCgH^KH^ wherein R1 is an alkyl group of 9 to 20 carbon atoms, such as N-2-amino ethyl-stearyl and M-amino ethyl myristyl amide; quaternary ammonium compounds wherein typically one of the groups linked to the nitrogen atom is an alkyl group which contains an alkyl group of 10 to 18 carbon atoms and each of the other alkyl groups typically contains 1 to 3 carbon atoms and which may bear inert substituents such as phenyl groups, and there is present an anion such as halogen, acetate or methosulphate. Typical quaternary ammonium detergents are ethyl-dimethyl-stearyl ammonium chloride, benzyl-dimethyl myristyl ammonium chloride, benzyl-dimethyl-stearyl ammonium bromide, trimethyl stearyl ammonium chloride, trimethylcetyl ammonium bromide, dimethyl-ethyl dilauryl ammonium chloride, dimethyl-propyl-myristyl ammonium chloride and the corresponding methosulphates and acetates. Other cationic surface active germicides and antibacterial compounds such as diisobutylphenoxyethoxyethyl dimethyl benzyl ammonium chloride, benzyl dimethyl stearyl ammonium chloride, tertiary amines having one fatty alkyl group (of from 12 - 18 carbon atoms) and two (poly) oxyethylene groups attached to the nitrogen (typically containing a total of from 20 to 50 ethanoxy groups per molecule) and salts thereof with acids, and compounds of the structure: (CHgCHgO)^ 'QySJil \ Vilrj wHgU J R2-H-CHoCHo0HoB· (oh9ch9o)_h (CH2CH2O)yH wherein R is a fatty alkyl group typically containing from 12 to 18 carbon atoms, and X, y, and z total 3 or higher, as well as salts thereof with mineral or organic acids, may also be used.

The aqueCus vehicle of the dentifrice preferably .0 forms, with the abrasive particles, a mass of a consistency which can be extruded from a collapsible aluminium tube. The vehicle will generally contain liquids and solids. In general, the liquid portion comprises water, I glycerine or aqueous sorbitol, including suitable .5 mixtures thereof, It is usually advantageous to use a mixture of both water and a humectant such as glycerine or sorbitol. The total liquid content is generally 20 to 90$ by weight of the dentifrice and typically includes up to 30$ by weight of water, 0 to 80$ by weight of glycerine and 0 to 80$ by weight of sorbitol. Preferably up to 20$ by weight of water, 15 to 40$ by weight of glycerine and 0 to 50$ by weight of sorbitol are present in the dentifrice. .

The solid portion of the vehicle may be a gelling agent, such as the natural and synthetic gums and gumlike materials, such as Irish Moss, gum tragacanth, alkali metal carboxymethyl cellulose and hydroxyethyl carboxyethyl carboxyl-methyl cellulose, polyvinyl pyrrolidone, starch water soluble, hydrophilic colloidal carboxyvinyl polymers, such as those sold under the trade 4-3?23 mark CARBOPOL as Carbopol 934 and Carbopol 940 and synthetic inorganic silicate clays such as those sold under the trade mark LAPONITE as laponite CP and laponite SP. These grades of laponite have the formula (SisMg5>1Li0>6H7i6024 0.6’ The solid portion of the vehicle is typically present in amounts up to 10$ by weight of the dentifrice and preferably 0.5 to 5$ by weight. When employed, grades of laponite are preferably used in amount of 1 to 5$ by weight.

Any suitable flavouring or sweetening materials may be employed in formulating a flavour for the dentifrice. Examples of suitable flavour constituents include flavouring oils, e.g. oils of spearmint, peppermint, Wintergreen, sassafras, clove, sage, eucalyptus, majoram, cinnamon, lemon and orange, as well as methylsalicylate. Suitable sweetening agents include sucrose, lactose, maltose, sorbitol, perillartine and saccharine. Suitably, flavour and sweetening agents may together constitute from 0.01 to 5$ or more of the dentifrice. Chloroform may also be used.

As already indicated, it is also permissible to employ a less alkaline milled alpha-alumina trihydrate in place of part (e.g. £, | or f) or all of the highly alkaline material.

The alpha-alumina trihydrate need not be the sole abrasive in the dentifrice, particularly where the surface-modified material is employed. Other dental abrasives which may also be present include calcium 3 7 3 3 -2 4carbonate, magnesium carbonate, tricalcium phosphate, dicalcium phosphate dihvdrate, insoluble sodium metaphosphate, calcium pyrophosphate, synthetic amorphous complex aluminosilicates and silica (including dehydrated silica gel.)’ The total amount of abrasive including milled alpha-alumina trihydrate will usually be in the range from 10 to 60S, preferably 20 to 60S by weight of the dentifrice.

Tha alkali metal monoflurophosphates which may be employed include sodium monoflurophosphate, lithium monoflurophosphate, potassium monofluorophosphate and ammonium monofluofophosphate. The preferred salt is sodium monof luo rop'nosph ate (Na^P.O^P) which, as commercially available, may vary considerably in purity. It may be used in any suitable purity provided that any impurities do not substantially adversely affect the desired properties. In general, the purity is desirably at least 80%. For. best results, it should be at least 85%, and preferably at least 90% by weight as sodium monofluorophosphate with, the balance being primarily impurities or by-products of manufacture such as sodium fluoride and water-soluble sodium phosphate salt. Expressed in another way, the sodium monofluorcphosphate typically has a total fluoride content of about 12%, preferably about 12.7%, a content of up to 1.5%, typically up to 1.2% of free sodium fluoride; and a sodium monofluorophosphate content of at least 12%, preferably at least 12.1% all calculated as fluorine.

Thus, in a monofluorophosphate-containing dentifrice where the sole source of sodium fluoride is as an -25impurity of the monofluorophosphate, the lowest ratio of monofluorophosphate to fluoride would be about 8:1, well above the maximum ratio of 5:1 of the present invention. Other monofluorophosphate salts which . - may be used included monofluorophesphates such as Na4P3OgF, K4P3OgF, (NH4)4P3O9F, (ΝΗ^ΝηΡ-^Γ, and Li4P3O9F.

Various other materials may be incorporated in the dentifrices, Examples thereof are colouring or . whitening agents or dyestuffs, preservatives, silicones, chlorophyll compounds, ammoniated materials such as urea, diammonium-phosphate and mixtures thereof, antibacterials and other constituents. The adjuvants‘are incorporated in the compositions in amounts which, do . not substantially adversely affect the properties and characteristics desired. When antibacterials are present, typically the amount is 0.01 to 5% by weight. Typical antibacterial agents include Ν'- (,4-chlorobenzyl) 5 N -(2,4-dichloroben2yl] biguanide; p-cholorophenyl biguan20. ide; 4-cholorbenzyhydryl biguanide; 4-chiorobenzhydryl5 guanylurea; N-3-lauroxypropyl-N -p-chlorobenzylbiguanide; 1,6-di-p-chloropheynylbiguanidoxhexane; 1,6-bis(2-ethylhexylbiguanido) hexane; 1-(lauryldimethylammonium)-8-(g-chlorobenzyl-dimethylaramonium) octane dichlor25. ide; 5,6-dichloro-2-guanideinobenzimidazole; N^-o-.chlorophenyl-N -laurylbiguanide; 5-amino-l,3-bis (,2-ethylhexyl)-5-methylhexahydro pyrimidine; and their nontoxic acid addition salts.

The pH of the toothpaste may be adjusted as . desired, as by inclusion of appropriate amounts of acidic -26materials,(e.g. benzoic acid, citric acid or aluminium sulphate). Generally the toothpaste pH will be in the range of about 5 to 9, determined directly on the paste, preferably 6 to 8, such as about 6.0, 6.5 or 7.0.

. Other dentifrice ingredients may also be present if desired, in appropriate conventional proportions. For disclosures of such ingredients and of proportions of ingredients employed in toothpastes, see Patent Specifications Nos. 34,431 and 31776 and British Patent Specification No. 1,260,332. .0.

Additionally dentally acceptable polishing materials may Be ground with a . surface-modifying agent as described in order to increase their stability characteristics in toothpastes and containers therefor.

Claims (10)

1. A toothpaste containing abrasive particles of milled alpha-alumina trihydrate reactive with alkali metal fluorides and also containing alkali metal fluor5 ide and alkali metal monofluorophosphate, the mol ratio of the monofluorophosphate to the fluoride being in the range from 1.5:1 to 5:1 and the total amount of the monofluorophosphate and the fluoride (calculated as F) being in the range from 500 to 1500 ppm. lo

2. A toothpaste as claimed in Claim 1 in which the mol ratio of the monofluorophosphate to the fluoride is in the range from 1.5:1 to 3:1.

3. A toothpaste as claimed in Claim 1 or Claim 2 in which the total amount of the monofluorophosphate 15 and the fluoride (calculated as F) is at least 800 ppm.

4. A toothpaste as claimed in any of the preceding Claims in which the monofluorophosphate is sodium monofluorophosphate and the fluoride is sodium fluoride.

5. A toothpaste as claimed in any of the preceding !0 Claims the milled alpha-alumina trihydrate abrasive particles of which have been produced by milling Bayer process alkaline alpha-alumina trihydrate in the presence of a surface-modifying agent.

6. A toothpaste as claimed in Claim 5 in which the 25 surface-modifying agent is acidic.

7. · A toothpaste as claimed in Claim 6 In which the surface-modifying agent is a carboxylic acid.

8. A toothpaste as claimed in Claim 5 in which the surface-modifying agent comprises hydrophilic pyrogenic silica.

9. A toothpaste as claimed in any of the preceding Claims which contains a minor proportion of particles of hydrophilic pyrogenic silica.

10. A toothpaste substantially as described in any of Examples 1 to 4, 6 and 7.