GB1598233A

GB1598233A - Dentifrice abrasives and compositions

Info

Publication number: GB1598233A
Application number: GB9954/78A
Authority: GB
Original assignee: JM Huber Corp
Current assignee: JM Huber Corp
Priority date: 1977-12-20
Filing date: 1978-03-14
Publication date: 1981-09-16
Also published as: LU79230A1; ES467854A1; NO149031B; BR7801523A; FI780807A7; PH20181A; AT366907B; DE2811097A1; JPS60214725A; NO148358B; SE7802901L; CH640135A5; SE445293B; PH18150A; NL7802800A; DK158561C; FR2412307B1; CA1098830A; IE46578B1; AU3410078A

Abstract

An abrasive having a high fluoride compatibility for toothpaste contains a precipitated, amorphous silica. The silica contains 10 to 300 parts of alkaline earth metal ions per million parts of amorphous silica. It has a) a radioactive dentine abrasion value of at least 40, b) a packing density of 0.24 to 0.55 g/ml, c) an oil absorption of 70 to 95 ml/100 g, d) a BET surface area of 100 to 250 m<2>/g, e) a percentage loss on ignition of 4 to 6% and f) fluoride compatibility values of at least 90% when it is incorporated into fluoride-containing toothpastes.

Description

(54) DENTRIFRICE ABRASIVES AND COMPOSITIONS (71) We. J. M. HUBER CORPORATION, a CorPOration of the State of New Jersey, United States of America, of Navesink & River Road, Locust, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to improved dentifrice abrasives, and is particularly, but not necessarily exclusively concerned with novel, alkaline earth-treated, precipitated silica abrasives which are suitable for use in therapeutic toothpaste compositions containing both soluble fluoride salts as enamel solubility reducing agents and soluble phosphate salts as dental pellicle film penetration agents. The invention further relates to methods for preparing these improved precipitated silica abrasives and to toothpastes containing the improved abrasives including toothpaste embodiments which comprise both enamel solubility reducing agents (i.e. fluoride) and dental pellicle film penetration agents. Such toothpaste compositions exhibit both high fluoride compatibility and high cleaning performance.

The function of an abrasive substance in formulations intended for use in the oral cavity is to remove various deposits, including pellicle film, from the surface of the teeth. Pellicle film is tightly adherent and often contains brown or yellow pigments and thus imparts an unsightly appearance to the teeth. An advantageous toothpaste abrasive material should maximize film removal without causing undue abrasion to the hard tooth tissue. Dental researches are continually concerned with developing toothpaste abrasives which demonstrate satisfactory levels of cleaning and which are not unduly abrasive and damaging to the oral tissue.

In addition to abrasives, therapeutic toothpastes typically contain fluoride ion sources. The beneficial reduction in the incidence of dental caries resulting from the topical application to dental enamal surfaces of solutions containing fluoride ions is well known. Especially at solution pH's between about 4 and 8, fluoride ions are believed to interact with enamel to reduce the acid solubility of such enamel.

Enamel so treated with fluoride is more resistant to the formation of dental caries.

Accordingly, therapeutic toothpaste compositions are formulated to provide fluoride ion availability in brushing solutions formed in the oral cavity during use.

It has been postulated that the effectiveness of fluoride treatment in providing enamel antisolubility/anticariogenic benefits is dependent upon the amount of fluoride ion which is available for uptake by the enamel being treated. It is, of course, therefore desirable to formulate toothpaste compositions which provide maximum fluoride ion availability in brushing solutions formed therefrom.

However, efforts to utilize such ionic fluoride anticariogenic agents in toothpastes suitable for home use have been unable to provide the theoretical maximum soluble fluoride because of the tendency for ionic fluoride to be inactivated and thereby rendered unavailable for enamel uptake. That is, the toothpastes lose, upon storage (at rates which increase with temperature), the capability of providing the theoretical maximum amount of soluble fluoride. For purposes of this invention, the "soluble fluoride" content of any given toothpaste composition refers to the ppm concentration of fluoride ion which is found in the supernatant sample centrifuged from 1:3 by weight slurry of the toothpaste in water (1 :3=toothpaste:water).

Fluoride ion sources tend to interact with toothpaste impurities and with such toothpaste components as abrasives, buffers, etc. Such interaction diminishes the ability of the fluoride source to provide "soluble fluoride" upon use. The propensity of the toothpaste compositions herein to maintain their levels of soluble fluoride after storage is expressed hereinafter as "toothpaste fluoride compatibility". Thus, the toothpaste fluoride compatibility of a particular toothpaste composition is that percentage of the theoretical maximum amount of fluoride source that is actually measured as soluble fluoride after storage for a specified time and at a specified temperature (e.g. one week at 1200 F.). Similarly, the propensity of such a dentifrice component such as the abrasive to interact with the fluoride source to diminish the measured "soluble fluoride" level from the theoretical maximum amount of fluoride source (particularly in the presence of ellicle film penetration agents described in detail below) is expressed as "abrasive fluoride compatibility". The test procedures used herein to determine "toothpaste fluoride compatibility" values and "abrasive fluoride compatibility" values are described more fully hereinafter.

One toothpaste component which can Dose special difficulties in formulating fluoride toothpastes is a precipitated silica abrasive component. Precipitated silica abrasives are desirable for use in toothpastes since they have desiraly low dentin abrasion values. Certain prior art precipitated silica abrasives are generally compatible with soluble fluoride sources but have insufficiently high abrasivity to provide effective cleaning performance. Certain other prior art precipitated silica abrasives grovide acceptable cleaning performance but have low abrasive fluoride compatibility as measured by the method hereinafter. It is believed that no prior art precipitated silica abrasives give both high "abrasive fluoride compatibility" as well as acceptable cleaning performance, (as indicated by standard Radioactive Dentin Abrasion values). There is thus a clear need to formulate precipitated silica abrasives which exhibit high "abrasive fluoride compatibility" as well as acceptable cleaning performance. Accordingly, it is an object of the present invention to provide precipitated silica abrasives which exhibit high "abrasive fluoride compatibility" as well as acceptable cleaning performance.

Another dentifrice component which can be especially destructive of soluble fluoride content in certain toothpaste compositions is soluble phosphate. Soluble phosphate salts, upon toothpaste use, serve to enhance the ability of fluoride ions to penetrate dental pellicle film. For this reason, soluble phosphate salts are desirably included in fluoride toothpaste compositions. However, particularly in combination with silica dental abrasives, soluble phosphate pellicle penetration agents tend two promote loss of soluble fluoride in toothpastes containing these materials and, thus, the toothpastes exhibit low toothpaste fluoride compatibility values. There is thus a clear need to formulate precipitated silica abrasives which provide high toothpaste fluoride compatibility when utilized in fluoride toothpastes containing soluble phosphate salts as pellicle film penetration agents.

There is thus a further need to provide fluoride toothpastes which can contain precipitated silica abrasives in combination with soluble phosphate salts.

Accordingly, it is an object of the present invention to provide fluoride toothpaste compositions which contain soluble phosphate salts and precipitated silica abrasives and which nonetheless retain relatively high levels of soluble fluoride even after geriods of storage.

It has been surprisingly discovered that the above objectives can be realized by the present invention which provides a novel precipitated silica abrasive which has been treated with an alkline earth material, particularly calcium. By utilizing the instant dental abrasives, fluoride, toothpastes-;particularly those embodiments containing soluble phosphate salts--can be realized which have high toothpaste fluoride compatibility and excellent cleaning performance.

It is of course well known that therapeutic toothpaste compositions contain calcium phosphate materials as abrasives but these calcium materials are present in large amounts as described above and illustrated for example in U.S. Patents 3,624,199, issued November 30, 1971, Norfleet et al, and 3,864,471, issued February 4, 1975, Mills et al. Toothpaste compositions are also known in the art which contain small amounts of alkaline earth metal ions, such as calcium ions, and compositions of this type are illustrated by U.S. Patent 3,991,177, issued November 9, 1976, Vidra et al. This patent discloses toothpaste compositions which contain a stabilizer-activator for a dextranase enzyme agent with the stabilizer-activator being a salt such as calcium chloride present in an amount of .001 to 0.3 weight percent. This composition can also contain therapeutic fluoride and the abrasive agent is calcium carbonate.

Other prior art which discloses toothpaste compositions containing alkaline earth metal compounds or ions include U.S. Patents 3,095,356, issued June 25, 1963, to Moss; 3,122,483, issued February 25, 1964, to Rosenthal; 3,669,221, issued June 13, 1972 to Hase; 3,782,446, issued January 1, 1974, to Walter; 3,842,168, issued October 15, 1974, to Colodney; and 3,689,537, issued September 5, 1972, to Kuder. However, none of these prior art patents disclose therapeutic toothpaste compositions which contain as the abrasive agent a low structure precipitated silicon dioxide which contains about 10 to 300 parts per million of alkaline earth metal ion as described herein.

There is provided by the present invention a novel abrasive material for toothpaste compositions which comprises in its broadest embodiment, a precipitated silicon dioxide which is prepared from a solution consisting of water and an alkali metal silicate by acidulation. Such precipitated abrasives are treated to contain 10300 parts per million of alkaline earth metal ion, and are characterized by an RDA value of at least 40, an oil absorption value of 7W95 ccs/100 gram, a pack density of 0.24 to 0.55 grams per milliliter, a loss on ignition value of 4 to 6% and a BET surface area of 100 to 250 m2/g, with an average particle size of 5 to 15 microns, and said abrasive having a fluoride compatibility of at least 90%. Also provided is a method for the preparation of the novel abrasives of this invention which in eneral comprises formation of a low structure precipitated silicon dioxide by the acidulation of solutions consisting of water and sodium silicate (hereinafter called "fresh water solutions") with a mineral acid and subsequent treatment of the resulting wet cake with the required amount of alkaline earth metal ions.

The present invention further relates to fluoride-containing toothpaste compositions which exhibit minimal loss of soluble fluoride upon storage at normal temperatures and which provide excellent cleaning performance. Such toothpaste compositions comprise the amorphous, precipitated silica abrasives of the present invention, a source of fluoride ions, a binding agent, a humectant and water. Such toothpaste compositions provide a pH of from 4.0 to 8.0 when slurried with water in a 3:1 water/composition weight ratio.

The amorphous, precipitated silica abrasives of the present invention comprise from 6% to 35V by weight of the toothpaste compositions.

The fluoride ion source comprises from 0.01% to 3.0% by weight of the toothpaste compositions and can be any water-soluble material which yields fluoride ions in aqueous solution.

The binder comprises from 0.2% to 2% of the toothpaste compositions.

The humectant comprises~from about 5% to 55% by weight of the toothpaste composition. The water in the toothpastes herein comprises from 15% to 8( by weight of composition.

The present invention still further relates to novel, precipitated silicon dioxide dentifrice abrasives, methods for their preparation, and their incorporation into toothpastes to provide resulting compositions having excellent toothpaste fluoride compatibility values and excellent abrasivity values. The toothpaste compositions herein further essentially comriseawater-soluble fluoride ion source, a binding agent, and certain amounts of umectants and water. Each of these components as well as optional ingredients, composition use and composition preparation are described in detail as follows: The present invention also relates to low structure precipitated silicon dioxide materials which are suitable for use as dental abrasives. Such abrasives have ultimately associated therewith 10300 parts per million, preferably 10100 parts per million, of alkaline earth metal, preferably calcium, based on the amount of recoverable dry material. This dental abrasive material may be charaterized further by having a percent abrasive fluoride compatibility of at least 90%, a RDA of at least 40, preferably from about 70 to 120, a loss on ignition (hereinafter "LOI") in the range of 46%, a pack density in the range of 0.24 to 0.55 grams per milliliter, an oil absorption m tie range ofTO--95 ccJmO grams and a BET surface areain the range of 100--250 m2/g with an average particle size in the range of 5-15 microns. When incorporated into a toothpaste, the dental abrasives herein provide high fluoride compatibility and excellent cleaning performance. The definition of low structure silicon dioxide materials is given in United States Patent No.

3,893,840, mentioned above.

The dental abrasive materials of the present invention are precipitated silicon dioxides which are prepared by the general methods described, for example, in prior U.S. Patents 3,83,840, Issued July 8, 1975, to Wason; 3,988,162, issued October 26, 1976, to Wason; and Prior U.S. Patent 4,067,746 issued January 10 1978. Abrasives produced by such methods are subsequently treated with alkaline earth metal ions in the manner described herein. In general, the process for preparation of the silicon dioxides comprises the acidulation of an aqueous alkali metal silicate solution with a mineral acid to effect precipitation of silicon dioxide.

The acid addition is continued to an acid pH of 6 or less and the resulting precipitated silicon dioxide is then removed such as by filtration, and washed to remove any by-product materials such as alkali metal sulfate, to provide a wet cake. The resulting wet cake is then reslurried in its own water or with additional water and thereafter is treated with the required amount of alkaline earth metal ions in the form of a soluble salt, oxide or hydroxide to provide the abrasive materials of this invention.

The abrasive products of the present application are to be distinguished from the known precipitated silicon dioxide compositions which have been treated with alkaline earth metal ions. The known silicon dioxides treated with alkaline earth metals are abrasives which are useful for incorporation into toothpaste compositions so as to prevent corrosion of unlined aluminum toothpaste tubes.

Such corrosion-inhibiting precipitated silicon dioxides are silicon dioxides prepared by a so-called sulfate liquor method. In that method, an electrolyte such as alkali metal sulfate is admixed with the alkali metal silicate liquor during acidulation with mineral acid as disclosed for example in my U.S. Patents 3,960,586 and 3,928,541. While the known silicon dioxides treated with alkaline earth metals may be described as precipitated silicon dioxides having intimately admixed therewith an amount of alkaline earth metal ions which is within the range of that of the present invention, the abrasive products of the present invention have different characteristics from the silicon dioxides derived from the sulfate-liquor method. The sulfate liquor silica materials, when utilized in certain fluoridecontaining toothpaste compositions, do not provide the superior fluoride compatibility values of the present invention. The superior fluoride compatibility values of the dental abrasives of this invention are achieved only with the silicon dioxides prepared from so-called fresh-water alkali metal silicate process as described herein.

The silicon dioxide abrasives of the present invention, are alkaline earth metaltreated precipitated silicon dioxides which are prepared from fresh water silicate solutions. Such a process does not make use of any electrolyte such as sodium sulfate in preparation of the untreated precipitated silicon dioxide. Further, in the products of the present invention, it has been found that the presence of alkaline earth metal ions intimately associated with the resulting-silicon dioxide, must be present within a particular narrow range when fluoride compatibility is necessary.

Thus, the abrasive products of the present invention have fluoride compatibility values of at least 90 /O whereas those abrasives of the prior art generally give compatibility values of 89% or below as determined by the toothpaste fluoride compatibility tests described in t ion.

It is theorized that the improved fluoride compatibility of the instant dental abrasives is based on the manner in which the silanol groups therein are attached to the surface of the silicon dioxide product. Thus, in the fresh water silicate derived silicon dioxide of the present invention, the silanol groups on the surface of the material are believed to be more available than on the known sulfate liquor silicate derived silicon dioxide. Further, the surface acidity of the fresh water silicon dioxides, due to the silanol groups, is higher than the corresponding acidity of the silicon dioxides derived from the sulfate liquor process. Because the silanol groups are different in these two materials, the intrinsic surface acidity does not respond well to calcium treatment for fluoride compatibility in the sulfate liquor products.

Sulphate liquor silicate derived silicon dioxides treated with alkaline earth metals also have higher abrasive values than the silicon dioxides of this application.

The instant precipitated silicion dioxide abrasives are preferably prepared by charging an aqueous solution of an alkali metal silicate solution, preferably a sodium silicate solution, to a reactor for acidulation. The aqueous sodium silicate solution is a fresh water solution having an SiO2 to Na2O mole ratio of 2.0 to 2.7, a sodium silicate concentration range of 10--17 weight percent, and more preferably 12.5 to 15.5 weight percent, and a sodium silicate composition of nazi 2.6 SiO2 for best results. The fresh water sodium silicate solution is then raised to a temperature of 50 to 95"C. and with continuous agitation the solution is acidulated by the addition of an aqueous solution of a mineral acid having a concentration of 1020 weight percent at a substantially constant pH in the range of 8.5 to 10.5. The mineral acid is preferably sulfuric acid as sulfuric acid provides best results but as is known in the art (see U.S. Patents 3,988,162, 3,893,840 and 4,067,746), other acidulation agents such as nitric acid, phosphoric acid, hydrochloric acid, carbonic acid and the like can also be employed.

In the most preferred embodiment only a portion of the alkali metal silicate solution is charged to the reactor, brought to temperature under agitation, and the sulfuric acid and remainder of the alkali metal silicate solution simultaneously added to the initial silicate solution at the reaction temperature. Preferably 8 to 12 wt. % of the metal silicate is initially charged to the reactor. The remaining portion is then added with the sulfuric acid. The time period over which the alkali metal silicate and sulfuric acid are added to the alkali metal silicate in the reactor can be predetermined and is generally based on the volume of the reactor and the difficulties in control of the temperature and agitation. After completion of the addition of the alkali metal silicate solution, the acidulation agent is continually added until the pH of the reaction slurry falls below 6.0 and preferably to within the range of 4.6-5.0. The resulting slurry is the precipitated silicon dioxide contained in the reaction medium.

After the pH of below 6.0 is reached, the slurry is then heated for a digestion period at a temperature of 10 to 300 C. above the reaction temperature and the reaction pH again adjusted as necessary. The resulting slurry is then filtered and washed with additional water to remove any reaction by-products such as sodium sulfate which may be contained in the silicon dioxide product. The wet cake moisture of the resulting filter cake is in the range of about 60-66% and is a low structure material. The above reaction to this point is generally the same as disclosed in prior Patents 3,893,840, 3,988,162 and 4,067,746 mentioned above, in the preparation of silicon dioxide prepared from fresh water alkali metal silicate.

In the process of the present invention, at the point of filtration and washing of the silicon dioxide wet cake, the material is then subjected to treatment with alkaline earth metal ions to produce the new abrasive products of the present invention. In accordance with the process of the present invention, the wet washed filter cake is then reslurried in its own water or with the addition of fresh water at ambient temperature with agitation. While under agitation, this slurry is then treated with sufficient alkaline earth metal ions, preferably calcium ions, in the form of a salt, oxide or hydroxide sufficiently soluble to provide an amount of alkaline earth metal ions corresponding to 10 to 300 parts per million, or .001 to .03 weight percent (based on the weight of the dry recoverable silicon dioxide), of alkaline earth metal ions intimately associated with the silicon dioxide.

The alkaline earth metal ion added at this point is preferably calcium ion because of its readily availability, low cost, and ease of incorporation into the silicion dioxide. The calcium ions can be incorporated into the silicon dioxide at this stage in any sufficiently water soluble form (i.e., soluble in water to the extent of at least .07 g/100 cc H2O at 200C.) such as with solutions of calcium nitrate, calcium oxide, calcium hydroxide, or calcium chloride. Lime or calcium hydroxide is preferred. Also, solutions of organic salts such as calcium acetate, calcium formate, and the like can also be used. The corresponding strontium and magnesium salt, oxide or hydroxide of the alkaline earth class can also be used.

Food grade salts, oxides or hydroxides should be used.

After treatment with the alkaline earth metal ion, the cake slurry is then agitated vigorously for 1020 minutes, preferably 15 minutes, to provide the effective level of alkaline earth metal for treatment onto the suface of the silicon dioxide abrasive. The resulting product is then dried. Preferably drying is conducted in a spray dryer at an inlet temperature of 483"C. and outlet temperature of 122"C. as known in the art, and subsequently milled to the desired degree of fineness.

Toothpastes Also provided by the present invention herein are therapeutic toothpastes containing the instant novel precipitated silica abrasives. In addition to the instant abrasives, the toothpaste compositions of the present invention further comprise certain amounts of a water-soluble fluoride ion source, a binding agent, a humectant and water. Each of these additional toothpaste components as well as optional toothpaste components are described in detail as follows: A. Abrasive As indicated above, the instant precipitated silica abrasives are particularly suitable for incorporation into fluoride-containing therapeutic toothpaste compositions. Therapeutic toothpastes employing such abrasives provide satisfactory tooth cleaning performance and also possess excellent abrasive fluoride compatibility characteristics. The instant toothpaste compositions essentially contain from 6% to 35%, preferably from 10% to 20%, by weight of the instant precipitated silica abrasives.

B. Fluoride Ion Source The instant therapeutic toothpaste compositions further contain from 0.01% to 3%, preferably from about 0.1% to 1.0%, by weight of a water-soluble, fluoride containing material which yields fluoride ions in aqueous solutions. Such fluoride ions combine with dental enamel and thereby reduce enamel solubility in acid.

Application of fluoride ions to dental enamel serves to protect teeth against decay.

A wide variety of fluoride ion-yielding materials can be employed as sources of soluble fluoride in the instant compositions. Examples of suitable fluoride ionyielding materials are found in Briner et al; U.S. Patent 3,535,421; issued October 20, 1970 and Widder et al; U.S. Patent 3,678,154; issued July 18, 1972. Preferred fluoride ion sources for use herein include sodium fluoride (NaF), stannous fluoride (SnF2), potassium fluoride (KF), potassium stannous fluoride (SnF2-KF), indium fluoride (InF3), zinc fluoride (Zn F2), ammonium fluoride (NH4F), and stannous chlorofluoride (SnCIF). Sodium fluoride and stannous fluoride are particularly preferred as well as mixtures thereof.

Preferably the instant toothpaste compositions provide from about 50 ppm to 500 ppm, more preferably from about 100 to 400 ppm, of fluoride ions in the aqueous solutions which contact dental surfaces when the toothpastes of the present invention are used in the mouth. As described more fully hereinafter, such solutions are simulated by preparing 3:1 water/toothpaste slurries (by weight) of the toothpaste compositions herein and by subsequently centrifuging such slurries to obtain an aqueous supernatant. The fluoride ion concentration in such a supernatant is taken as a measure of the "soluble fluoride" provided by any given fluoride toothpaste composition.

C. Binder A binder is essentially employed to prevent separation of the liquid and solid phases in the toothpaste compositions herein. Such binder materials are well shown in the toothpaste art. The most conventionally used binders are the seaweed colloids such as Carrageenan (Irish moss or Viscarin) and derivatives of cellulose, such as sodium carboxymethyl cellulose and hydroxyethyl cellulose. Another type of binder which is suitable for use herein is gums such as 1) vegetable gums, e.g., guar gums and 2) fermentation products e.g., xanthan gum. The binder component generally comprises from 0.2% to 2% by weight of the toothpaste compositions wherein. Since the natural and synthetic water dispersions of water binders are subject to microbial or mold attack, the toothpastes herein can optionally contain a relatively small amount of a preservative. Examples of preservatives typically employed are the esters of parahydroxyl benzoates.

Toothpaste binders are more fully described in Hager et al, U.S. Patent 2,839,448, issued June 17, 1958; and DiGiulio, 3,862,307, issued January 21, 1975.

D. Humectant Another essential component of the toothpaste compositions herein is a humectant. Suitable humectant materials are also well known in the toothpaste art.

The humectant serves to retain moisture and thereby to keep the toothpaste compositions from hardening upon exposure to air. Certain humectants can also impart desirable sweetness or flavor to toothpaste compositions. The humectant generally comprises from 5% to 55%, preferably from 20% to 36%, by weight of the toothpaste compositions herein.

Suitable humectants for use in this invention include edible polyhydric alcohols such as glycerine, sorbitol, xylitol and propylene glycol. Sorbitol is frequently employed as a 70% aqueous solution known as Sorbo. Mixtures of glycerine and sorbitol are especially preferred as the humectant component of the toothpaste compositions herein.

E. Water Water is another essential element of the toothpastes of this invention. Water employed in the preparation of commercially suitable toothpastes should be deionized and free of organic impurities. Water comprises from 15% to 80%, preferably from 15% to 40%, by weight of the toothpaste compositions herein.

F. Optional Ingredients In addition to the above described essential components, the toothpastes of this invention can contain a variety of optional conventional toothpaste ingredients. Such optional ingredients include (1) sudsing agents, (2) pellicle occurring salivary pellicle film formed on the teeth. Fluoride-containing toothpastes which utilize the levels of phosphate salts prescribed herein demonstrate enhanced fluoride pellicle diffusion and dental enamel fluoride uptake in comparison with fluoride toothpastes which contain no such phosphate pellicle penetration agents.

While relatively high levels of soluble phosphate salts can provide fluoride pellicle penetration benefits in fluoride toothpastes, the presence of such salts can also diminish the soluble fluoride stability of such toothpastes during storage. It has been surprisingly discovered, however, that such soluble phosphate salts can be included in the silica-containing, fluoride toothpastes herein with especially beneficial fluoride compatibility results if the particular alkaline earth metal treated precipitated silica abrasives herein are employed.

Phosphate salts optionally present in the toothpaste compositions herein are water-soluble. For purposes of this invention a "water-soluble" phosphate salt is one which is soluble in water to the extent of at least 3.0 g/100 cc H2O at 20"C.

The phosphates are those phosphorus compounds in the anions of which each atom of phosphorus is surrounded by four oxygen atoms arranged at the corners of a tetrahedron. By sharing oxygen atoms between tetrahedra, chains, rings and branched polymers of interconnected PO4 tetrahedra can be realized. Simple phosphates are orthophosphates. Polymeric phosphates include the polyphosphates such as the pyrophosphates and tripolyphosphates. Ring phosphates are the metaphosphates.

Examples of suitable water-soluble polyphosphates for use herein include tetrapotassium pyrophosphate, tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate and potassium tripolyphosphate.

Examples of suitable water-soluble metaphosphates include monopotassium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate, and sodium he tametaphos hate. Many of these water-soluble polyphosphates and metaphosphates are utilized in the form of hydrated salts.

The most preferred phosphate salts for use in the present invention are the simple orthophosphate salts. Orthophosphate salts are derived from tribasic orthophosphoric acid of the formula H3PO4. Water soluble sodium, potassium and ammonium salts can be utilized.

There are about ten different crystalline sodium orthophosphate salts including the various hydrates. These include, for example NaH2PO4, NaH,PO 11,0, NaH7PO, 2H70, Na,H PO,. Na < HPOv 2H,O, Na7HPO4 7H2O, NaHPO4 . 12 H2O, Na3PO4 - 6H2O, Na3PO4. 8H2O, and mixtures thereof.

Preferred sodium orthophosphates include NaH2PO4 - H2O, Na2HPO4 - 2H2O and mixtures thereof. Especially preferred are mixtures of NaH2PO4. 1120 and Na2HPO4 21120 in a weight ratio of monosodium to disodium salt within the range of from 1:3 to 1:5.

Potassium and ammonium orthophosphates can also be utilized as pellicle penetration agents herein. Examples of such potassium and ammonium salts include KH2PO4, K2HPO4, K2HPO4- 2H2O, K2HPO4- 6H2O, K3PO4 - 3H2O, K3PO4 - 711 0 K3PO4 - 9H2O, (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4 and mixtures of these salts.

An especially preferred phosphate salt mixture for use in the toothpastes herein comprises a mixture of NaH2PO4 1120 and K2HPO4. 21120 in a weight ratio of sodium to potassium salt within the range of from 1:3 to 1:5.

The soluble phosphate salts of the present invention are commerically available materials. A more detailed description of such phosphate salts useful herein can be found in Kirk & Othmer, Encyclopedia of Chemical Technology, Second Edition, Volume 15, Interscience Publishers, Inc. (1968), pp. 232-276.

Preferably the instant toothpaste compositions provide from 0.5 mole/1000 g H2O to 2.0 moles/1000 g H2O concentrations of phosphate salts in the aqueous solutions which contact dental surfaces when the toothpastes of the present invention are used in the mouth. Again, the supernatant from 3:1 slurries of water and toothpaste are used to simulate such use solutions Additional pellicle film penetration agents can also optionally be added to the fluoride containing toothpastes of the present invention. Such optional ingredients further enhance the fluoride pellicle penetration benefits provided by the phosphate salts herein. Such agents include, for example, hydroxy acids and salts thereof such as citric acid, trisodium citrate, malic acid and tartaric acid. If present, such additional pellicle penetration agents comprise from about 0.2to to 5.0 by weight of the toothpaste composition.

3) Flavouring Agents Flavoring agents can also be added to the instant compositions. Suitable flavoring agents include oil of wintergreen, oil of peppermint, oil of spearmint, oil of sassafras, and oil of clove. Sweetening agents which can be used include saccharin, dextrose, levulose, aspartame, D-tryptophan, acetosulphan, dihydrochalcones and sodium cyclamate. Flavoring agents are generally used in toothpastes at levels of from 0.01% to 2% by weight and sweetening agents at levels of from 0.05% to 3% by weight.

4) Antiplaque/Anticalculus Agent Phosphorus-containing anticalculus agents and/or bis-biguanide antiplaque agents can also optionally be added to the toothpastes of this invention. Phosphoruscontaining anticalculus agents such as disodium ethane-l-hydroxy-l, 1diphosphonate and related materials are described more fully in McCune et al; U.S. Patent 3,488,419, issued January 6, 1970, Bis-biguanide antiplaque agents such as chlohexidine (1,6 - bis[N5 - p - chlorophenyl - M' - biguanido]hexane), the soluble and insoluble salts thereof and related materials such as 1,2 - bis(N5 - p trifluoromethylphenyl - N' - biguanido) ethane are described more fully in Haefele, U.S. Patent 3,934,002, issued January 20, 1976; Haefele, U.S. Patent 3,937,807, issued February 10, 1976; Procter & Gamble, Belgian Patent 843,244, published December 22, 1976 and Procter & Gamble, Belgian Patent 844,764, published January 31, 1977.

If present, the optional anticalculus and/or antiplaque agents generally comprise from 0.01% to 2.5% by weight of the toothphaste compositions herein.

5) Pigments and Coloring Agents, Misc.

A variety of other optional components well known in the art may be added to the toothpaste compositions herein to improve the aesthetic qualities of the toothpaste composition. These include pigments, dyes, speckles and the like. When present, these optional components generally comprise from 0.001 to 2% by weight of the toothpastes herein.

Composition Preparation Toothpaste compositions of the present invention are prepared simply by mixing together in any order and by any conventional means the essential an optional components herein. Once prepared, the compositions herein provide a pH of from 4.0 to 8.0, preferably 6.5 to 7.5, when said compositions are slurried with water in a 3:1 weight ratio of water to composition. Fluoride toothpastes providing pH values within the 4.0 to 8.0 range provide especially effective dental enamel antisolubility benefits compared to toothpastes with pH values outside this range.

Flavoring of toothpastes within this pH range is also comparatively easy.

Composition Use Toothpaste compositions of the present invention are used in conventional manner. The toothpaste compositions or slurries thereof are brushed onto dental surfaces and subsequently rinsed away.

During use of the toothpaste herein in conventional manner, pastes or slurries generally contact dental surfaces for at least about 30 seconds. More preferably such pastes or slurries contact dental surfaces for at least about 60 seconds.

The following examples are presented to illustrate the present invention but it is not to be considered as limited thereto. In the following examples, parts are by weight unless otherwise indicated.

EXAMPLE 1 Into a 30,000 liter stainless steel reactor jacketed for steam heating was added 1794 liters of sodium silicate solution (3.78 percent Na2O, 9.53 percent SiO2) of specific gravity 1.121 containing 42 grams of Na2O per liter. The reaction medium was heated to 880C. with continuous agitation. At this point sulfuric acid, 10% concentration (specific gravity 1.066) and sodium silicate solution were added simultaneously to the reaction medium at the rate of 151.4 llmin. acid and 351 I/min. sodium silicate while maintaining the reaction temperature at 880C.+10C.

These two solutions were added to the reaction medium for a predetermined length of time. The silicate addition was discontinued after 47 minutes but the acid addition was continued until the slurry pH was between 4.8-5.0. The reaction slurry was boiled at 1000C. for twenty minutes and the reaction pH was adjusted again to between 4.8-5.0. The resulting silica slurry was filtered, and washed to remove most of the reaction by-product (sodium sulfate) and the filter cake was dried and the dry product milled to the desired degree of fineness. The dry silica was subjected to various physical-chemical tests and the analysis of which are set forth hereinafter (See Table I). This example is preparation of a control product to which no alkaline earth metal is added.

EXAMPLE 2 Into a 30,000 liter stainless steel reactor jacketed for steam heating was added 1794 liters of sodium silicate solution (3.78 percent Na2O, 9.53 percent SiO2) of specific gravity 1.121 containing 42 grams of Na2O per liter. The reaction medium was heated to 880C. with continuous agitation. At this point sulfuric acid, 10% concentration (specific gravity 1.066) and sodium silicate solution were added simultaneously to the reaction medium at the rate of 151.4 l/min. acid and 351 Vmin. sodium silicate while maintaining the reaction temperature at 88 C.tl C.

These two solutions were added to the reaction medium for a predetermined length of time. The silicate addition was discontinued after 47 minutes but the acid addition was continued until the slurry pH was between 4.8-5.0. The reaction slurry was boiled at 1000C. for twenty minutes and the reaction pH was adjusted again to between 4.8-5.0. The resulting silica slurry was filtered and washed to remove most of the reaction by-product (sodium sulfate).

The washed filter cake was then reslurried without water addition at ambient temperature with agitation. While under agitation, the slurry was treated with 102 grams of Codex grade (U.S. purity food grade) hydrated lime (calcium hydroxide) to provide 2spmof calcium ion treatment based on the total weight of dry recoverable solid product in the slurry form. After treatment with the calcium ion, the cake slurry was agitated vigorously for 15 minutes to provide the effective level of calcium ion treatment onto the surface of the silicon dioxide abrasive. The resulting product is then spray dried at an inlet temperature of 483"C. and outlet temperature of 122"C., milled and characterized for abrasive and physical properties in the same manner as the abrasive in - Example 1.

EXAMPLE 3 The method of this example was the same as in Example 2 except the rate of addition of sulfuric acid was at the rate of 162.7 liters per minute and the calcium addition was 204 grams of calcium hydroxide which provides 50 parts per million of calcium ion. The product was then characterized.

EXAMPLE 4 This example was the same as Example 2 except that the rate of addition of sulfuric acid was 166.5 liters per minute and the calcium addition comprised 408 grams of calcium hydroxide to provide 100 parts per million of calcium ion in the silicon dioxide. The product was then characterized.

EXAMPLE 5 In this example, a dentifrice silica abrasive was prepared by initially adding 1420 liters of sodium silicate solution (4.09 percent Na2O, 10.31 percent SiO2) of specific gravity 1.131 containing 46.3 grams of Na2O per liter to the reactor as reaction medium. The reactor was heated to 910C. with continuous agitation. At this point sulfuric acid, 12% concentration (specific gravity 1.08) and sodium silicate solution were added simultaneously to the reaction medium at the rate of 162.7 Vmin acid and 315.7 Vmin sodium silicate while maintaining the reaction temperature at 91+10C. The silicate addition was discontinued after 47 minutes but the acid addition was continued until the slurry pH was between 4.6--4.8. The reaction slurry was boiled at 1000C. for twenty minutes and the reaction pH was adjusted again between 4.6--4.8. The resulting silica slurry was filtered and washed to remove sodium sulfate by-product.

The washed filter cake was then reslurried without water addition at ambient temperature with agitation. While under agitation the slurry was treated with 510 grams of Codex grade (U.S. purity food grade) hydrated lime (calcium hydroxide) to provide 125 ppm of calcium ion treatment based on the total weight of the dry recoverable silicon dioxide abrasive present in the slurry form. After treatment with the calcium ion, the cake slurry was agitated vigorously for 15 minutes to provide the effective level of calcium ion treatment onto the surface of the silicon dioxide abrasive. The resulting product was then spray dried at an inlet temperature of 483"C. and an outlet temperature of 1220C., milled and then characterized.

EXAMPLE 6 This example was the same as Example 5 except that 1608 liters of sodium silicate solution was initially charged to the reactor as reaction medium and the acid rate was increased to 170.3 I/min but the silicate rate was maintained at 315.7 Vmin.

The washed filter cake was treated with 816 grams of calcium hydroxide to provide 200 parts per million of calcium ion treatment onto the surface of silica abrasive. The product was then characterized.

EXAMPLE 7 This example was the same as Example 2 except that the calcium ion addition was 2,040 grams of calcium hydroxide to provide 500 parts per million of calcium ions. The product was then characterized.

After preparation of the products of Examples 1 to 7 they were characterized for physical properties and the results are set forth in the following Table I.

TABLE I Pack Oil Average Ex. Density Absorption** BET Surface*** Particle Size No. O/,LOI* (g/ml.) (cc/100 g.) Area (M2/g) (microns)**** 5.0 0.35 94 151 7.7 2 4.4 0.43 89 234 8.6 3 5.5 0.40 90 227 7.8 4 4.9 0.41 91 192 7.9 5 6.0 0.47 85 215 11.0 6 5.4 0.50 78 201 14.5 7 5.1 0.32 95 172 7.6 *Water loss when a predried silicon dioxide abrasive is heated from 105"C.

to 9000C., inclusive.

**Determination of Oil Absorption, ASTM, D281-31 ***J. Am. Chem. Soc. 60, 309-319 (1938) ****As measured by Coulter Counter Model TA II Several representative toothpastes of the present invention are set forth in the following examples that utilize the instant precipitated silica abrasives.

EXAMPLE 8 A toothpaste is formulated utilizing the precipitated silica abrasive of Example 2 which has the following composition: Amount Component (Wt. %) Precipitated Silica Abrasive (Example 2) 16.0 Sodium Fluoride (NaF) 0.28 Sorbitol Solution (70 /O) 32.0 Glycerin 13.0 Sodium Carrageenan 0.75 Monosodium Orthophosphate Monohydrate (NaH2PO4 H2O) 2.15 Disodium Orthophosphate Dihydrate (Na2HPO4. 2H2O) 8.34 Sodium Alkyl Sulfate Solution (28.8%) 6.0 Coconut Monoglyceride Sodium Sulfonate 0.9 Flavor 1.22 Sodium Saccharin 0.3 Color (FD & G Blue #1 Solution 1%) 0.35 Titanium Dioxide (TiO2) Trisodium Citrate Dihydrate (CH5Na3O, . 2H2O) 0.25 Distilled Water q.s.

Total 100.0 The above toothpaste composition is prepared by admixing the components thereof in the normal manner of toothpaste preparation. Preferably, the water component is first added to a suitable container to which thereafter is added with moderate agitation, in order, the pellicle film penetration agents, the flavor, the humectant and, thereafter, the remaining components.

A 3:1 weight slurry of the above freshly prepared composition with water (3:1 is water to composition) produces a pH of about 7.1.

Such a toothpaste composition provides beneficial fluoride treatment for dental tissue brushed therewith due to the high toothpaste fluoride compatability.

The toothpaste also provides good cleaning and an RDA of 100. When stored for prolonged periods of time at 800 F, such a toothpaste exhibits minimal loss of soluble fluoride.

Toothpastes providing substantially similar fluoride treatment benefits, toothpaste fluoride compatibility, and cleaning performance are realized when in the Example 8 composition, the sodium fluoride is replaced with an equivalent amount of stannous fluoride, sodium chlorofluoride, potassium fluoride, potassium stannous fluoride, indium fluoride, zinc fluoride or ammonium fluoride.

Toothpastes providing substantially similar fluoride treatment benefits and substantially similar cleaning performance are realized when, in the Example 8 composition, the phosphate salt mixture is replaced with an equivalent amount of NaH2PO4, NaH2P04. 1120, NaH2PO4 21120, Na2HPO4, Na2HPO4. 2H20, Na2HPO4 # 7H20, Na3PO4 # 6H70, NawPO4 # 8H2O, KH2PO4, K < HPO..

K2HPO4 - 2H2O, K2HPO4 # 6H2O, K3PO4 # 3H2O, K3PO4 - 7H2O, K3PO4 # 9H2O, (NH4) H2PO4, (NH4)2HPO4, (NH4)3PO4, other mixtures of NaH2PO4. H2O and Na2HPO4-2H2O in monosodium to disodium weight ratios of froin 1:3 to 1:5, mixtures of NaH2PO4 1120 and K2HPO4 - 21120 in sodium to potassium salt weight ratios of from 1:3 to 1:5, tetrapotassium pyrophosphate, tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, monopotassium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate or sodium heptametaphosphate; provided such compositions provide a 3:1 slurry pH of from 4.0 to 8.0.

EXAMPLE 9 A high abrasive level toothpaste is formulated utilizing the precipitated silica abrasive of Example 3 which has the following composition: Amount Component (Wt. %) Precipitated Silica Abrasive (Example 3) 35.0 Sodium Fluoride (NaF) 0.22 Glycerin 5.0 Sorbitol Solution (70%) 20.0 Carboxymethyl Cellulose (0.7 D.S.) 0.5 Magnesium Aluminum Silicate (Veegum (Registered Trade Mark) Flakes) 0.3 Monosodium Orthophosphate Monohydrate (NaH2PO4 - H2O) 0.3 Disodium Orthophosphate Dihydrate (Na2HPO4 2H20) 0.3 Sodium Alkyl Sulfate Solution (28.8%) 2.3 Coconut Monoglyceride Sodium Sulfonate 0.7 Flavor 0.9 Sodium Saccharin 0.2 Titanium Dioxide (TiO2) 0.5 Speckles 0.5 Distilled Water q.s.

Total 100.0 Toothpastes providing substantially similar fluoride treatment benefits, toothpaste fluoride compatibility, and cleaning performance are realized when in the Example 9 composition, the precipitated silica abrasive component prepared as in Example 3 is replaced with an equivalent amount of abrasives prepared by Examples 2, 4, 5 and 6.

Toothpastes providing substantially similar fluoride treatment benefits and substantially similar cleaning performance are realized when, in the Example 9 composition, the phosphate salt mixture is replaced with an equivalent amount of NaH,PO,, NaH2PQ. H2O, NaH2PQ. 2H2O, Na2HPO4, Na2HPO4 2H20 Na2HPO4. 7H,O, Na3PO4 # 6H2O, Na3PO4 # 8H2O, KH2PO4, K2HPO4, K2HPO4- 2H2O, K2HPO4 - 6H2O, K3PO4- 3H2O, K3PO4 - 7H2O, K3PO4. 91120, (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, other mixtures of NaH2PO4-H2O and Na,HPO,ZH,O in monosodium to disodium weight ratios of from 1:3 to 1:5, mixtures of NaH2PO4 1120 and K2HPO4.2112O in 2H,O in sodium to potassium salt weight ratios of from 1:3 to 1:5, tetrapotassium pyrophosphate, tetrasodium pyrophosphate, disodium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, monopotassium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate or sodium heptametaphosphate; provided such compositions provide a 3:1 slurry pH of from 4.0 to 8.0.

EXAMPLE 10 A clear toothpaste is formulated utilizing the precipitated silica abrasive of Example 4 which has the following composition: Amount Component (Wt. %) Precipitated Silica Abrasive (Example 4) 20.0 Sodium Fluoride (NaF) 0.24 Sorbitol Solution (70%) 57.0 Glycerin 15.0 Sodium Carrageenan 0.5 Phosphoric Acid (85%) 0.10 Sodium Alkyl Sulfate Solution (28.8%) 4.0 Flavor 1.0 Sodium Saccharin 0.2 Color (FD & C Blue &num;1 Solution 1%) 0.05 Distilled Water q.s.

Total 100.0 Toothpastes providing substantially similar fluoride treatment benefits, toothpaste fluoride compatibility and cleaning performance are realized when in the Example 10 composition, the precipitated silica abrasive component prepared as in Example 4 is replaced with an equivalent amount of abrasives prepared by Examples 2, 3, 5 and 6.

A toothpaste providing substantially similar fluoride treatment benefits and an improved anticalculus benefit is realized when the Example 10 composition additionally contains about 1.0% by weight of disodium ethane-l-hydroxy-l, 1diphosphonate.

Testing and Evaluation The precipitated silica abrasives herein can be used to prepare especially desirable therapeutic toothpaste compositions containing soluble phosphate pellicle film penetration agents. Such compositions provide both high abrasive fluoride compatability and yet have good tooth cleaning performance. The following tests and evaluation serves to demonstrate the excellent fluoride compatibility provided by the precipitated silica dental abrasives herein in the toothpaste composition of the present invention. It is also shown hereinbelow that abrasives of the present invention provide higher abrasive fluoride compatibility than similarly prepared abrasives which have not been treated so as to contain the essential amounts of alkaline earth material. The excellent cleaning performance of the toothpaste compositions herein is additionally demonstrated. Finally, it is shown herein that abrasives made from a sulfate liquor acidulation process-even though containing an alkaline earth material-fail to provide the high fluoride compatibility values of the "fresh water" precipitated silica abrasives provided herein.

Abrasive Fluoride Compatibility Precipitated silica dental abrasives can be screened for their relative compatibility with fluoride materials by means of a 24 hr. abrasive slurry test. Such a test can be used to generate data which can predict the availability of soluble fluoride in certain types of fluoride toothpastes after storage over approximately a four-week period at 80"F.

The 24 hour abrasive slurry test is used to generate fluoride compatibility values which are defined as that percentage of theoretical maximum available fluoride which is actually measured after 24 hours as soluble fluoride by the following test method. In this method (Orion (Registered Trade Mark) Specific Ion Electrode Method) a standard sodium fluoride stock solution containing 1624 ppm of fluoride is prepared by dissolving 2.80 grams of sodium fluoride, 21.5 grams of NaH2PO4 and 83.4 grams of NazHPO4 21120 in 672.5 grams of deionized distilled water and stored in a eolyethylene bottle. Thirty (30) grams of this solution is then weighed out. Seven (7) grams of the silica abrasive being tested is then dispsered into the solution and contacted for 24 hours at a temperature of about 1000 F.

(37.80C.). After 24 hours, the precipitated silica abrasive/fluoride solution is centrifuged for 20 minutes at 15000 rpm or until the supernatant is clear. Then 10 ml. of the supernatant is pipetted into a plastic vial. Thereafter, 10 ml. of ETA/THAM solution is likewise pipetted into the plastic vial. (The EDTA/THAM solution is a 0.2 molar in EDTA (ethylene diaminetetraacetic acid, disodium salt) and 0.2 molar in THAM (2 - Amino - 2 - hydroxymethyl - 1,2 - propanediol) and adjusted to pH 8.0 with sodium hydroxide). A magnetic stirring bar is added and gentle stirring is initiated. The fluoride ion concentration is determined by direct potentiometry with the Orion fluoride electrode (Model 95-09). Emf is converted to parts per million (ppm) fluoride in the supernatant by means of a logarithmic equation. The fluoride compatibility value is then calculated by expressing the measured ppm soluble fluoride as a percentage of the theoretically available soluble fluoride.

Using this method, the relative abrasive fluoride compatibility values are determined for the several abrasives prepared according to Examples I through 7.

The results of such evaluation are set forth in the following Table II.

TABLE II Abrasive Fluoride Compatibility Calcium Abrasive Treatment Fluoride Example No. (ppm) Compatibility 1 (Control) 0 76% 2 25 93% 3 50 94% 4 100 93% 5 125 91% 6 200 90% 7 500 88% The Table II data demonstrate that the precipitated silica abrasives herein containing particular amounts of an alkaline earth material provide markedly superior abrasive fluoride compatibility in comparison with that provided by an alkaline earth-free abrasive material which is otherwise similarly prepared. Thus, precipitated silica abrasives prepared as in Examples 2 through 6 should be suitable for realizing toothpastes containing fluoride and pellicle film penetration agents that demonstrate high abrasive fluoride compatibility.

Abrasive Fluoride Compatibility in Toothpastes Preferred toothpastes herein containing precipitated silica abrasives and pellicle film penetration agents are evaluated for abrasive fluoride compatibility.

The toothpastes which are prepared for evaluation have the composition of the toothpaste of Example 8 and differ only in the variation of the abrasive component.

To determine fluoride compatibility values for the toothpastes tested, a soluble fluoride determination method is used which is similar to the method described above for the determination of abrasive fluoride compatibility values. In this method, the toothpaste compositions are stored for a specified length of time in a laminate tube. Thereafter, 15.0 grams of the composition is placed in a 100 ml.

DB

The supernatant is then treated as in the abrasive fluoride compatibility determination method described above. Soluble fluoride concentration is similarly measured and an abrasive fluoride compatibility value for each toothpaste is similarly calculated. The toothpaste fluoride compatibility values of the respective toothpastes evaluated are shown in Table III. The abrasives evaluated are those prepared as described in Examples 1 through 7 above and characterized in Table I above.

TABLE III Toothpaste Fluoride Compatibility Toothpaste Calcium Fluoride Abrasive Treatment Compatibility (Example No.) (ppm) (1 wk. 80"F.) 1 (Control) 0 76% 2 25 99% 3 50 98% 4 100 99% 5 125 97% 6 200 94% 7 500 90% The Table III data demonstrate that the preferred toothpastes herein which utilize the instant precipitated silica abrasives provide superior abrasive fluoride compatibility values in comparison with that provided by a similar toothpaste composition containing the non-alkaline earth treated precipitated silica abrasive prepared by the method of Example 1. The data of Table III further demonstrate that the soluble fluoride availability from the fluoride ion source material is not significantly diminished upon storage when the silica abrasives of the present invention are employed in the preferred toothpastes herein.

Of course, it is to be recognized that the amount of available soluble fluoride in even the toothpaste compositions herein will decrease to some extent as a function of increasing time and temperature of storage. Thus, toothpaste fluoride compatibility values for toothpastes stored for longer periods or at more severe temperatures are generally lower than those exemplified above.

Additional abrasive fluoride compatibility data for several toothpastes demonstrating storage for longer periods and higher temperatures are shown in Table IV.

TABLE IV Toothpaste Fluoride Compatibility (High Temperature/Prolonged Storage) Toothpaste Fluoride Compatibility Abrasive Calcium Treatment I week 1 week 4 month 5 month (Example No.) (ppm) 80"F. 120"F. 80"F. 80"F.

0 0 76% 64"/, 64% 2 25 99% 97% 91% - 3 50 98%- 96% 91% - 4 100 99% 95% 91% - 5 125 97% 92% - - 6 200 94% 900/, 7 500 90% 86% - 89% The Table IV data demonstrate that the preferred toothpastes herein maintain their relatively high fluoride abrasive compatibility levels even under prolonged storage or under severe storage conditions.

Cleaning Performance The dental cleaning ability of the silica abrasives herein can be estimated by means of Radioactive Dentin Abrasion (RDA) testing. RDA values can be used to estimate the relative cleaning performance of various abrasives for any given type of dentifrice abrasive. Thus, for precipitated silica abrasives, an RDA value (measured by the method provided below) of at least 40, preferably between 70 and 120, is needed to insure that the abrasive has sufficient abrasivity to be an effective dentifrice cleaner. Prior art precipitated silica abrasives which do exhibit high toothpaste fluoride compatibility generally are poor cleaners for oral hygiene purposes as evidenced by low RDA values. The alkaline earth treated abrasives, however, provide both effective tooth cleaning and high fluoride compatibility.

Several commerical precipitated silica abrasives which demonstrate relatively high toothpaste fluoride compatibility as measured herein are selected for evaluation for RDA values. Testing is conducted within a standard toothpaste matrix having the composition of the toothpaste of Example 8, which differs only in the variation of the abrasive component.

The method which is employed for determining the RDA values for toothpastes that are tabulated in Table V is described below. This test method is described more fully in the Journal of Dental Research, July-August, 1976, by Hefferren, pp. 563-573. The specific steps for determining RDA values are set forth as follows: A. Selection and preparation of teeth Sound, single-rooted permanent teeth that are caries-free and vital at extraction are selected. Teeth are then scraped clean with a scalpel. The crown and root tip of each tooth are removed using an abrasive disc so as to prepare a dentin sample 14 mm long and at least 2 mm wide at the narrower end. Cut pieces of root (dentin chips) or, alternatively, an additional tooth, are also prepared to be later used in determining a correction factor for self-absorption of radiation.

B. Irradiation of dentin The prepared roots and dentin chips described in Step A are exposed to a neutron flux of 2x 1012 neutrons/cm2 for three hours.

C. Mounting of roots After irradiation, the irradiated roots are embedded in a mount of cold-curing dental methacrylate resin and mounted onto a cross-brushing machine.

Toothbrushes used throughout the test are 50-Tuft, medium, flat, "Pepsodent" (Registered Trade Mark) toothbrushes.

D. Preconditioning the dentin surfaces Prior to initial test run, the freshly mounted, irradiated roots are brushed with a reference slurry (10 g calcium pyrophosphate+50 ml of a 0.5% CMC-10% glycerine solution) for 6,000 brush strokes. At the beginning of each subsequent day's test run, the roots are brushed for 1,000 strokes.

E. Test run After preconditioning, the dentin samples are then conditioned with the referencesurry (same slurry as in Step D) for 1,500 brush strokes at the beginning, during and end of each test run. The test run consists of brushing dentin samples for 1,500 brush strokes with a slurry of test product (25 g dentifrice+40 ml deionized of distilled water).

F. Preparation of correction factors The correction factors are prepared by dissolving the dentin chips or, alternatively, an additional tooth, from Step B in 5 ml. conc. HCI brought to a volume of 250 ml. with distilled water. One ml. of this solution is added to test pastes and reference slurries which are prepared similarly to those in Step E, and then neutralized with 0.1 N NaOH.

Radioactive Tracer Counting The radioactivity of the slurry samples (1.0 ml.) is determined with an Intertechnique SL-30 liquid scintilation counter. Alternate counting procedure: 3 ml. aliquots of each slurry are transferred to stainless steel, flat-bottom 1 inchx5/16 inch planchets and counted using Nuclear Chicago Geiger Counting System.

Calculations The radioactive dentin abrasion value (RDA) for a particular paste will be the ratio of the average corrected counts for that paste to the average count for the reference multiplied by 100. The reference abrasive is given an arbitrary dentin abrasion value of 100 units.

The results of such RDA value determination are set forth in the following Table V.

TABLE V Radioactive Dentin Abrasion Values Toothpaste Fluoride Compatibility Abrasive RDA One Week (800 F.) A. (Example No.) 1. Control 75+7 76% 2. 80+21 99% 3. 67+8 98% 4. 80+1 99% 5. 103+5 97% 6. 111+5 94% 7. 56+4 90% B. Commercial Precipitated Silica Products 8.Sident*31 14+2 92% 9. Neosyl*2 25+2 78% 10. QUSO* G-303, 22+2 87% 11. Neosyl*ET4 26+4 84% *Registered Trade Marks '-A precipitated silica marketed by Degussa, Inc. (N.Y.C.).

2A precipitated silica marketed by Joseph Crosfield & Sons, Ltd. (London, England).

3A precipitated silica marketed by Philadelphia Quartz Co. (Valley Forge, Pa.).

4A precipitated silica marketed by Joseph Crosfield & Sons, Ltd.

The Table V data demonstrate that commerical precipitated silica abrasives may well demonstrate high abrasive fluoride compatibility but are not sufficiently abrasive so as to be useful as dentifrice abrasives. Surprisingly, the instant novel precipitated silica abrasives provide outstanding abrasive fluoride compatibility yet simultaneously provide excellent RDA abrasivity values, which values can be used as an indicator of relative dental cleaning performance.

"Fresh Water" versus "Sulfate Liquor" Abrasives As indicated hereinabove the abrasive products of the present invention are related to but distinctly different from the known calcium treated silicas. To demonstrate such a difference, the following evaluation is made to compare the fluoride compatability of the known calcium treated silicas with that of the abrasive products of this invention. The "sulfate liquor" silicon dioxide materials tested are prepared in accordance with the process disclosed in U.S. Patent 3,960,586, issued June 1, 1976, by the following procedure: Dry sodium sulfate was added to 10.0 gallons of water in a 200 gallon reactor so that the sodium sulfate concentration in the reaction medium was 10%. The pH of the reaction medium was then adjusted to 9.0 by the addition of sodium silicate.

The reaction temperature was 65"C. (150"F.). The sodium silicate solution had an SiOJNa2O mole ratio of 2.5 and a concentration of 2.0 pounds per gallon. Sodium silicate was added to the reaction medium for 4 minutes. At this point the sodium silicate addition was stopped and sulfuric acid of 11.4% of concentration was added to the reaction medium until the pH of 9.0 was reached. At this point the sodium silicate solution and the sulfuric acid solution were added simultaneously for a period of 35 minutes. At the end of the 35 minute period of silicate addition, the silicate was discontinued and the acid addition was continued until a slurry pH of 5.5 was obtained. The batch was digested at 770 C. for 20 minutes and the resulting wet cake recovered and washed.

The wet cake was then treated in the manner described for Example 2 of this application, divided into six separate portions and treated respectively with 50, 100, 200, 400 and 800 parts per million of calcium from aqueous solutions of calcium hydroxide. Each wet cake was then dried and processed as described for Example 2 and characterized in the following Table VI where the first abrasive is a control in which no calcium was added. Table VI sets forth the results of such evaluation.

TABLE VI Abrasive "Sulfate Liquor" Ca Addition Fluoride Abrasive (ppm) Compatibility* A 0(control) 88 B 50 89 C 100 88 D 200 88 E 400 86 F 800 82 *Determined by test described for Table II.

As can be seen from the Table VI data, the known calcium treated "sulfate liquor" abrasives provide abrasive fluoride compatibility values which are generally lower than those provided by the "fresh water" silica abrasives of the present invention (See Table II). Furthermore, the addition of an alkaline earth metal to abrasives made by the "sulfate liquor" method does not result in a dramatic improvement in abrasive fluoride compatibility. Conversely, as can be seen from a comparison of Table II, the addition of equivalent amounts of alkaline earth metal to the silica abrasives herein made by the "fresh water" method does result in dramatic improvements in abrasive fluoride compatibility.

WHAT WE CLAIM IS: 1. An abrasive composition comprising a precipitated amorphous silicon dioxide prepared from a solution consisting of water and an alkali metal silicate by acidulation, which silicon dioxide has been intimately reacted with a salt oxide, or hydroxide of an alkaline earth metal so as to have present therein 10300 parts per million of alkaline earth metal ions in said amorphous silicon dioxide exhibiting a Radioactive Dentin Abrasion value of at least 40, a pack density of 0.24 to 0.55 grams per milliliter, an oil absorption of 7095 ccs/100 grams, a BET surface area of 100--250m2/g, 1 Dercent loss on ignition of 46%, and an average particle size of 5 to 15 microns, the abrasive having a fluoride compatibility of at least 90%.

2. A composition according to Claim 1 wherein said alkaline earth metal ions are selected from the group consisting of calcium, strontium and magnesium.

3. A composition according to Claim 1 wherein the amount of alkaline earth metal ion present ranges from IO--100 ppm.

4. A composition according to Claim 1 wherein the alkaline earth metal is calcium ion.

5. A composition according to Claim 1 wherein said abrasive is prepared by preparation of an amorphous silicon dioxide by precipitation through acidulation of a solution consisting of water and an alkali metal silicate with a mineral acid, isolating a wet cake of said precipitated product, and reacting said wet cake with a solution of a salt, oxide or hydroxide of said alkaline earth metal.

6. A composition according to Claim 5 wherein the mineral acid is selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and carbonic acid.

7. A composition according to Claim 6 wherein only a portion of the alkali metal silicate is initially charged to the reaction vesse:, the remaining portion of the alkali metal silicate solution is simultaneously added with the mineral acid, and the silicate solution addition discontinued after a predetermined period of time, and wherein mineral acid is added to a pH of less than 6.0, and wherein the wet cake is isolated by filtration and washing.

8. A composition according to Claim 7 wherein the alkaline earth metal ion is calcium and is added in the form of a solution of a salt, oxide or hydroxide selected from the group consisting of calcium hydroxide, calcium oxide, calcium nitrate and calcium chloride.

9. A method for the production of a composition of Claim 1, which method comprises forming a solution consisting of water and an alkali metal silicate having an SiO2 to X2O mole ratio of 2.0 to 2.7, wherein X is alkali metal, at a reaction temperature in the range of 50 to 950 C., acidulating with a mineral acid until precipitation of silicon dioxide is substantially complete, then continuing the mineral acid addition until the pH is 6.0 or less, digesting at a temperature 10- 30"C. higher than the reaction temperature for a period of 1030 minutes, filtering the resulting slurry and washing the solid product with fresh water, reslurrying the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. TABLE VI Abrasive "Sulfate Liquor" Ca Addition Fluoride Abrasive (ppm) Compatibility* A 0(control) 88 B 50 89 C 100 88 D 200 88 E 400 86 F 800 82 *Determined by test described for Table II. As can be seen from the Table VI data, the known calcium treated "sulfate liquor" abrasives provide abrasive fluoride compatibility values which are generally lower than those provided by the "fresh water" silica abrasives of the present invention (See Table II). Furthermore, the addition of an alkaline earth metal to abrasives made by the "sulfate liquor" method does not result in a dramatic improvement in abrasive fluoride compatibility. Conversely, as can be seen from a comparison of Table II, the addition of equivalent amounts of alkaline earth metal to the silica abrasives herein made by the "fresh water" method does result in dramatic improvements in abrasive fluoride compatibility. WHAT WE CLAIM IS:

1. An abrasive composition comprising a precipitated amorphous silicon dioxide prepared from a solution consisting of water and an alkali metal silicate by acidulation, which silicon dioxide has been intimately reacted with a salt oxide, or hydroxide of an alkaline earth metal so as to have present therein 10300 parts per million of alkaline earth metal ions in said amorphous silicon dioxide exhibiting a Radioactive Dentin Abrasion value of at least 40, a pack density of 0.24 to 0.55 grams per milliliter, an oil absorption of 7095 ccs/100 grams, a BET surface area of 100--250m2/g, 1 Dercent loss on ignition of 46%, and an average particle size of 5 to 15 microns, the abrasive having a fluoride compatibility of at least 90%.

resulting wet cake in water and under agitation conditions, adding sufficient alkaline earth metal ion in the form of a sufficiently soluble alkaline earth metal salt, oxide or hydroxide in sufficient amount to add to said wet cake alkaline earth metal ions in the range of 10300 parts per million based on the dry recoverable product in said slurry, agitating the resulting mixture to provide adherence of the effective level of said alkaline earth metal treatment on the surface of said silicon dioxide, drying and recovering the solid product.

10. A method according to Claim 9 wherein the mineral acid is selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and carbonic acid.

11. A method according to Claim 10 wherein only a portion of the alkali metal silicate is initially acidulated by the mineral acid and the remaining portion is added to the alkali metal silicate solution simultaneously with the mineral acid.

12. A method according to Claim 10 wherein the alkaline earth metal ion is selected from the group consisting of calcium, strontium and magnesium.

13. A method according to Claim 10 wherein the alkaline earth metal ion is calcium and is added as a salt, oxide or hydroxide selected from the group consisting of calcium hydroxide, calcium oxide, calcium nitrate and calcium fluoride.

14. A method according to Claim 10 wherein the alkaline earth metal salt, oxide or hydroxide is reacted with the wet cake slurry at ambient temperature.

15. A method according to Claim 14 wherein the alkaline earth metal treated silicon dioxide is dried by spray drying.

16. A method according to Claim 10 wherein the alkali metal silicate is sodium silicate, the acidulating acid is sulfuric acid, the alkaline earth metal ion is added in the form of calcium hydroxide to provide a 10100 parts per million of calcium ion intimately reacted with said silicon dioxide product.

17. A toothpaste composition, comprising: A. from 6% to 35% by weight of a precipitated silica abrasive material which is a precipitated amorphous silicon dioxide prepared from a solution consisting of water and an alkali silicate by acidulation, which has been intimately reacted with a solution of a salt oxide or hydroxide of an alkaline earth metal so as to have present 1 300 parts per million of alkaline earth metal ions in said amorphous silicon dioxide, said amorphous silicon dioxide exhibiting a Radio-active Dentin Abrasion value of at least 40, an average particle size of from 5 to 15 microns in diameter, a pack density of 0.24 to 0.55 grams per milliliter, an oil absorption of 7095 ccs/100 grams, a BET surface area of 100250 m2/g, and a percent loss on ignition of 4- 6%, said abrasive having a fluoride compatibility of at least 90%; B. from 0.01% to 3.0% by weight of a water-soluble, fluorine containing material which yields fluoride ions in aqueous solution; C. from 5% to 55% by weight of a humectant; D. from 0.2% to 2.0% by weight of a binding agent; and E. from 15% to 80% by weight of water; said composition providing a pH of from 4 to 8 when slurried with water in a 3:1 water/composition weight ratio.

18. A toothpaste composition in accordance with Claim 17, which composition additionally contains from 5% to 12% by weight of a water-soluble phosphate pellicle film penetration agent selected from the group consisting of orthophosphate salts, pyrophosphate salts, tripolyphosphate salts and metaphosphate salts.

19. A toothpaste composition in accordance with Claim 18 wherein: A. the precipitated silica abrasive comprises from 10% to 20% by weight of the composition; B. the fluorine-containing material comprises from 0.1% to 1.0% by weight of the composition; C. the humectant comprises from 20% to 35% by weight of the composition; D. the water component comprises from 15% to 40% and E. the pH provided by a 3:1 water/composition slurry flanges from 6.5 to 7.5.

20. A composition in accordance with Claim 19 which composition additionally contains from .1% to 6% by weight of the composition of a sudsing agent; and wherein A. the fluorine-containing material is selected from the group consisting of sodium fluoride and stannous fluoride; B. the phosphate pellicle film penetration agent is an orthophosphate salt; and C. the humectant is selected from the group consisting of glycerin, sorbitol xylitol and mixtures thereof.

21. A composition in accordance with Claim 20 wherein A. the fluorine-containing material is sodium fluoride; and B. the sudsing agent is selected from the group consisting of:

1. The water-soluble salts of alkyl sulfates having from 8 to 18 carbon atoms in the alkyl radical,

2. the water-soluble salts of sulfonated monoglycerides of fatty acids having from 8 to 18 carbon atoms in the fatty acid moiety; and

3. mixtures thereof.

22. A composition in accordance with Claim 19 wherein the binding agent is carrageenan.

23. A composition in accordance with Claim 20 which composition additionally contains from 0.2% to 5% by weight of the tootpaste composition of a second pellicle film penetration agent selected from the group consisting of critric acid, trisodium citrate, malic acid and tartaric acid; and wherein A. the fluorine-containing material is sodium fluoride; and B. the phosphate pellicle film penetration agent is a mixture of sodium dihydrogen phosphate monohydrate and disodium hydrogen phosphate dihydrate in monosodium to disodium weight ratio of 1:3 to 1:5.

24. A toothpaste composition in accordance with Claim 19 which contains an additional component selected from the group consisting of A. from 0.010/, to 20/ bv weight of a flavouring agent: B. from 0.05% to 3% by weight of a sweetening agent: C. from 0.0loo to 2.5% by weight of an anticalculus agent which is disodium ethane-l hydroxy-l, 10-diphosphonate; D. from 0.01% to 2.5% by weight of a bis-biguanide antiplaque agent; and E. mixtures of these additional toothpaste composition components.

25. Abrasive compositions according to Claim 1 and substantially as hereinbefore described.

26. Methods of production of abrasive compositions as in Claim 1 and substantially as hereinbefore described.