AU707998B2

AU707998B2 - Dentifrice composition comprising an abrasive or additive based on silica and on calcium carbonate which is compatible with fluorine

Info

Publication number: AU707998B2
Application number: AU27045/97A
Authority: AU
Inventors: Frederic Amiche; Adrien Dromard
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1996-04-22
Filing date: 1997-04-22
Publication date: 1999-07-29
Anticipated expiration: 2017-04-22
Also published as: CN1216461A; FR2747569B1; KR20000005456A; ATE226060T1; WO1997039728A1; PL329563A1; DE69716423T2; TR199802113T2; FR2747569A1; ES2185011T3; BG102846A; DE69716423D1; BR9708796A; AU2704597A; CA2251640A1; EP0906084A1; EP0906084B1; JPH11511178A

Abstract

A toothpaste composition comprising at least one decay preventing agent, with a fluorine-containing compound base, and at least one silica, is characterized in that the silica is constituted of particles containing a dense active silica shell and a calcium carbonate core. Use, as an abrasive or additive agent in toothpaste compositions, of composite particles containing a calcium carbonate core and a dense active silica shell, the said shell containing optionally in an adsorbed state a Ca<2+> ion stabilising agent. Composite particles constituted of a calcium carbonate core and a dense active silica shell containing in adsorbed state at least one Ca<2+> ion stabilising agent.

Description

WO 97/39728 1 PCT/FR97/00721 DENTIFRICE COMPOSITION COMPRISING AN ABRASIVE OR ADDITIVE BASED ON SILICA AND ON CALCIUM CARBONATE

WHICH

IS COMPATIBLE WITH FLUORINE The subject-matter of the present invention is dentifrice compositions comprising, as additive or abrasive agent compatible with fluorine, particles comprising a calcium carbonate core and a dense active silica shell optionally comprising, in the adsorbed state, an agent for stabilizing Ca 2 ions. Another subject-matter of the invention is the use, as additive or abrasive agent for dentifrice compositions, of composite particles comprising a calcium carbonate core and a dense active silica shell optionally comprising, in the adsorbed state, an agent for stabilizing Ca 2 ions. An additional subject-matter of the invention is, as novel industrial product, composite particles composed of a calcium carbonate core and of a dense active silica shell comprising, in the adsorbed state, an agent for stabilizing Ca 2 ions.

Silica and calcium carbonate are commonly used in dentrifrice compositions as abrasive agents, aiding, by their mechanical action, in the removal of dental plaque. Silica can also act as thickener for conferring specific rheological properties on the dentifrice.

Dentifrice compositions contain various other additives, in particular additives for the prevention of caries, in particular fluorides.

The presence of fluorides poses the problem of their compatibility with abrasives based on calcium (for example, calcium carbonate) which, because of their surface properties, can limit the ability of fluorides to exert their therapeutic effect.

The Applicant Company has found that particles composed of a silica shell and of a calcium carbonate core are compatible with fluorine and are thus particularly advantageous in dentifrice compositions.

The subject-matter of the present invention is thus a dentifrice composition comprising at least one agent for the prevention of caries, which agent is based on a 10 fluorinated compound, and at least one silica, which composition is characterized in that Sg..

the silica is composed of particles comprising a dense active silica shell and a calcium carbonate core.

The said silica particles can exhibit an active (hydroxylated) silica shell with a •thickness of the order of 2 to 200 nm, preferably of 5 to 50 nm, for a calcium carbonate 15 core size of the order of 20 nm to 30 tm, preferably of the order of 50 nm to 20 gm.

o. 5.

i* Their BET specific surface is generally of the order of 1 to 100 m 2 preferably of the order of 1 to 40 m2/g. Their RDA abrasiveness can be of the order of 30 to 250, preferably of the order of 40 to 200.

o Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

The BET specific surface is determined R24'

S,

3 according to the Brunauer-Emet-Teller method described in "The Journal of the American Chemical Society", Vol.

page 309, February 1938, corresponding to NFT Standard 45007 (November 1987).

The RDA ("Radioactive Dentine Abrasion") abrasiveness is measured according to the method described by J.J. Hefferren in "Journal of Dental Research", Vol. 55(4), page 563, 1976.

As regards the calcium carbonate core, it can be precipitated carbonate (aragonite, calcite), ground natural carbonates, and the like.

The core preferably exhibits a median diameter of the order of 50 nm to 20 Am.

The particles comprising a dense active silica shell and a calcium carbonate core can be prepared according to conventional processes by slow precipitation, on the calcium carbonate core, of active silica from an aqueous alkali metal silicate solution with adjustment of the pH using an acid (US-A-2,885,366).

A particularly outstanding process for the preparation of particles of this type consists in precipitating on calcium carbonate the dense active silica from an aqueous alkali metal M silicate solution, with an Si0 2 /Na 2 O ratio of at least 2, preferably of the order of 2.5 to 4, with adjustment of the pH using an acidifying agent, separation of the silica slurry formed and drying of the silica 4 suspension recovered, the operation of formation of silica slurry by precipitation being carried out according to the following stages: a first stage consisting in employing an initial vessel heel with a pH of the order of 8 to comprising water, calcium carbonate, an electrolyte salt from the group of alkali metals, the amount of electrolyte present being at least approximately 0.4 mol, preferably of the order of 0.4 to 1.5 mol, of alkali metal ion per litre of vessel heel, and optionally a buffer or basic agent, at a temperature of the order of 80 to 98 0

C;

a second stage consisting in introducing, into the said vessel heel, the alkali metal silicate in the form of an aqueous solution containing at least approximately 100 grams of SiO 2 /litre, preferably of the order of 100 to 330 grams of Si02/litre, and the acidifying agent, under conditions such that the kinetics K of formation of active silica, expressed in grams of silica/hour/gram of calcium carbonate, corresponds to a value K a 3 (A/200) 2', preferably K 4 (A/200) 2' and very particularly K a 6 (A/200) 2' n being equal to (T-90)/10 A representing the specific surface, expressed in m 2 of the carbonate to be coated and T the temperature in OC, the reaction mixture exhibiting a substantially constant pH of the order of 8 to 10 and being maintained at a temperature of the order of 80 to 98C, until the desired amount of silica has been formed.

The choice of the silicate and of the acidifying agent is made in a way well known per se.

The alkali metal silicate is advantageously a sodium or potassium silicate.

Use is generally made, as acidifying agent, of an inorganic acid, such as sulphuric acid, nitric acid or hydrochloric acid, or an organic acid, such as acetic acid, formic acid or carbonic acid. It is preferably sulphuric acid. This can be employed in the dilute or concentrated form, preferably in the form of an aqueous solution exhibiting a concentration of the order of 60 to 400 g/l. If it is carbonic acid, this can be introduced in the gaseous form.

The first stage consists in preparing the initial vessel heel.

The calcium carbonate is preferably introduced in the form of an aqueous dispersion.

The amount of calcium carbonate which can be employed is such that the vessel heel formed contains of the order of 10% to 50% of its weight of calcium carbonate.

Mention may in particular be made, among the electrolytes, of the salt of the starting silicate metal and of the acidifying agent. It is preferably (C

"RA

4

U

7VT sodium sulphate. However, sodium chloride, nitrate or hydrogencarbonate may be preferred if the presence of residual sulphate ions is not desired.

A buffer or basic agent can be employed in the initial vessel heel in order to ensure a pH of the said vessel heel of the order of 8 to This buffer or basic agent can be chosen from alkali metal hydroxides, such as sodium hydroxide, dissolved alkali metal silicates, alkali metal phosphates, alkali metal hydrogencarbonates, and the like.

The vessel heel obtained is brought to a temperature of the order [lacuna] 80 to 98 0

C.

The second stage consists in adding the silicate solution and the acidifying agent simultaneously to the vessel heel, which is kept stirred.

The respective amounts of alkali metal silicate and of acidifying agent are chosen so as to obtain the kinetics K of formation of active silica mentioned above and so as to maintain the pH of the reaction mixture at a substantially constant value of the order of 8 to 10 throughout the introduction of the two reactants.

These two solutions are introduced while maintaining the mixture at a temperature of the order of 80 to 98 0

C.

The introduction of the silicate solution is halted when the desired amount of silica has been formed. The minimum amount of silica desired is that corresponding to a deposition of the order of 1 to 150 parts by weight of SiO 2 per 100 parts by weight of calcium carbonate.

This second stage generally lasts of the order of 30 minutes to 2 hours.

The mixture obtained at the end of the second stage, after halting the introduction of the reactants, is optionally allowed to mature for approximately 10 to 30 minutes under the same temperature conditions.

On conclusion of the abovedescribed operations, a slurry of particles comprising active silica deposited on calcium carbonate is obtained, which slurry is subsequently separated (liquid/solid separation). This operation generally consists of a filtration (for example, separation by settling, use of a rotary vacuum filter, followed by washing with water.

The suspension thus recovered (filtration cake) is subsequently dried (oven, kiln, atomization).

The dentifrice composition forming the subject-matter of the invention contains of the order of 5 to 40%, preferably of the order of 5 to 35%, of its weight of silica composed of particles comprising a dense active silica shell and a calcium carbonate core and a fluorinated compound in an amount corresponding to a concentration of the order of 0.005 to 2%, preferably of the order of 0.1 to by weight of fluorine in the said composition.

8 The fluorinated compounds are in particular salts of monofluorophosphoric acid, in particular those of sodium, potassium, lithium, calcium, aluminium and ammonium, or alkali metal fluorides, in particular sodium fluoride.

An alternative form of the dentifrice composition forming the subject-matter of the invention consists in that the dense silica shell of the particles comprising a dense active silica shell and a calcium carbonate core contains, in the adsorbed state, at least one agent for stabilizing Ca 2 ions.

Mention may be made, among stabilizing agents, of water-soluble phosphorus derivatives, such as alkali metal phosphates (sodium, potassium or lithium pyrophosphates, orthophosphates, tripolyphosphates or hexametaphosphates).

The amount of the said stabilizing agent can represent up to 2% of the mass of the particles comprising a dense active silica shell and a calcium carbonate core, expressed on a dry basis.

The said particles can be obtained by treating the silica shell with an aqueous solution of the said stabilizing agent, which treatment is carried out by adding the said solution either to the silica slurry formed at the end of the precipitation stage, before filtration, or to the silica suspension (filtration cake) obtained after filtration, before drying.

Another embodiment consists in directly introducing the -kAK \cN O~zi said stabilizing agent into the dentifrice composition itself.

Dentifrice compositions containing particles comprising a calcium carbonate core and a dense active silica shell containing, in the adsorbed state, at least one agent for stabilizing Ca 2 ions can in particular contain, as fluorinated compound, an alkali metal fluoride, such as sodium fluoride.

The dentifrice composition forming the subject-matter of the invention can additionally contain: anionic, non-ionic, amphoteric or zwitterionic surface-active agents, in the proportion of approximately 0.1 to 10%, preferably of approximately 1 to of the weight of the said composition. Mention may be made, by way of example, of anionic surfactants, such as the sodium, magnesium, ammonium or ethanolamine salts of

C

8

-C

1 alkyl sulphates, which can optionally contain up to 10 oxyethylene and or oxypropylene units (sodium lauryl sulphate, in particular)

C

8

-C

1 alkyl sulphoacetates (sodium lauryl sulphoacetate, in particular)

C

8 -Cl 8 alkyl sulphosuccinates (sodium dioctyl sulphosuccinate, in particular)

C

8

-C,

1 alkyl sarcosinates (sodium lauryl sarcosinate, in particular)

SC

8

-C

18 alkyl phosphates, which can optionally contain up to 10 oxyethylene and or oxypropylene units

C

8

-C

18 alkyl ether carboxylates, containing up to oxyethylene and or oxypropylene units sulphated monoglycerides, and the like non-ionic surface-active agents, such as optionally polyethoxylated fatty esters of sorbitan, ethoxylated fatty acids, polyethylene glycol esters, and the like amphoteric surface-active agents, such as betaines or sulphobetaines water, in the proportion of approximately 5 to preferably approximately 10 to 40%, of the weight of the said composition humectants, in the proportion of approximately 10 to preferably of 10 to 70%, of the weight of the said composition, humectants such as glycerol, sorbitol, polyethylene glycols, lactilol, xylitol, and the like thickening agents, such as certain silica used for this purpose (Tixosil 43®, sold by Rh8ne-Poulenc, and the like) in the proportion of 5 to 15% by weight and/or polymers used alone or in combination, such as xanthan gum, guar gum, cellulose derivatives (carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and the like), crosslinked polyacrylates, such as Carbopol® products distributed by Goodrich, alginates or carrageenans, Viscarin®, and the like, in the proportion of 0.1 to 5% by weight agents for stabilizing Ca 2 ions, such as water- 11 soluble phosphorus derivatives, such as alkali metal phosphates (sodium, potassium or lithium pyrophosphates, orthophosphates, tripolyphosphates or hexametaphosphates) other ingredients, such as other polishing abrasives, such as silica, precipitated calcium carbonate, magnesium carbonate, calcium phosphates, titanium oxide, zinc oxide, tin oxide, talc, kaolin, and the like bactericidal, antimicrobial or anti-plaque therapeutic agents, such as zinc citrate, polyphosphates, guanidines, bisbiguanides or another therapeutic cationic organic compound flavourings (essence of aniseed, of Chinese anise, of mint, of juniper, cinnamon, clove or rose), sweeteners, colorings (chlorophyll), preservatives, and the like.

The dentifrice composition forming the subject-matter of the invention can be provided in various forms (pastes, gels, creams), which are prepared using conventional processes.

The compatibility of the particles comprising a silica shell and a calcium carbonate core (particles known as "abrasive" in the tests) with sodium monofluorophosphate (MFP), on the one hand, and with sodium fluoride (NaF), on the other hand, was measured using the following tests: Measurement of the MFP compatibility A suspension containing 20% by weight of abrasive is 12 prepared by bringing 10 g of abrasive into contact at 600C in 40 g of a mother solution containing 625 ppm of MFP in a solvent chosen from water, a 50/50 sorbitol/water mixture or a 35/65 glycerol/water mixture.

The suspension and a control sample comprising the mother solution without abrasive are kept stirred magnetically in an oven [lacuna] 37C for 4 weeks.

The control sample and the suspension are brought back to room temperature and centrifuged.

The supernatant is removed and then filtered, as is the control solution.

Quantitative determination by ionometry of the total soluble fluorine in the supernatant requires a prior hydrolysis treatment in acidic medium, which releases the fluorine ions present in the complex form in the

MFP.

The hydrolysis is carried out by bringing together ml of supernatant with 5 ml of 5N sulphuric acid and 20 ml of deionized water and placing in an oven at for at least 5 hours.

The compatibility of the abrasive, expressed in is defined by the ratio [C/Co] x 100, C representing the concentration of fluorine in the supernatant tested (after hydrolysis) and C O the concentration of fluorine in the control (after hydrolysis).

In addition, the concentration of fluorine ion in the 13 supernatant was measured before acid hydrolysis, in order to have access to the concentrations of fluorine resulting from hydrolysis of the MFP.

Quantitative determination of the total soluble fluorine in toothpastes containing

MFP

g of toothpaste with the following composition: Composition by weight carboxymethylcellulose 0.8 sorbitol 18 sodium monofluorophosphate 0.8 sodium saccharinate (sweetener) 0.2 sodium benzoate (preservative) 0.3 abrasive tested Tixosil 43 (thickening silica) sodium lauryl sulphate (30% aqueous solution) 4 flavouring 0.8 deionized water 30.1 are suspended in 90 g of water at room temperature for months.

The suspension is subsequently centrifuged and the supernatant filtered.

Quantitative determination by ionometry of the total soluble fluorine in the supernatant requires a prior hydrolysis treatment in acidic medium, which releases the fluorinated ions present in the complex form in the

MFP.

IN Tc P Yj The hydrolysis is carried out by bringing together ml of supernatant with 5 ml of 5N sulphuric acid and ml of deionized water and placing in an oven at 60 0

C

for at least 5 hours.

The concentration of fluorine in the supernatant tested is measured after hydrolysis, as well as before hydrolysis.

Measurement of the compatibility with respect to sodium fluoride NaF The principle of the measurement consists in leaving the test abrasive in contact with a sodium fluoride solution of known concentration for 10 days at 37 0

C.

The amount of fluoride present in the liquid medium obtained by centrifuging is measured by ionometry.

Procedure The test silica is suspended at 20% in an aqueous NaF solution containing 625 ppm expressed as fluoride F-.

Contact is maintained [lacuna] 10 days at 37 0 C with stirring. The suspension is centrifuged. The supernatant is diluted 20-fold with water. The concentration of F- is measured by ionometry and compared with the concentration in the initial solution, which has had no contact with the abrasive.

The amount of unreacted F- is thus determined. The result of the NaF compatibility is expressed by (unreacted F-/starting x 100 A second subject-matter of the invention consists of the use, as additive or abrasive agent in dentifrice compositions, of composite particles comprising a calcium carbonate core and a dense active silica shell optionally containing, in the adsorbed state, an agent for stabilizing Ca 2 ions.

The characteristics of the said particles, as well as one of their possible method of preparation, have already been mentioned above.

They can be used in the proportion of approximately to 40%, preferably approximately 5 to 35%, of the weight of the said compositions.

A final subject-matter of the invention consists, as novel industrial product, of composite particles composed of a calcium carbonate core and of a dense active silica shell containing, in the adsorbed state, at least one agent for stabilizing Ca2+ ions.

A method for preparing the said composite particles has already been mentioned above.

The following examples are given by way of illustration Example 1 A vessel heel is prepared by introduction, into a litre reactor, of 3.5 litres of water, of 0.68 mol/litre of vessel heel of sodium in the sodium chloride form, of 1150 g of precipitated calcium carbonate (Sturcal H, sold by Rh8ne-Poulenc, exhibiting a particle size of 11 Am and a BET specific surface of 4 m 2 and of sodium silicate, with an SiO 2 /NaO2 ratio of 3.5 (aqueous solution containing 130 g of SiO 2 per litre), in an amount corresponding to a concentration of 4 g of SiO 2 per litre of vessel heel. The vessel heel, with a pH of 9, is brought to 90°C and kept stirred.

The following are subsequently introduced simultaneously: an aqueous sodium silicate solution, with an SiO 2 /Na2O ratio of 3.5, the concentration of which is 130 g of SiO, per litre of solution, and an aqueous sulphuric acid solution containing 80 g of acid per litre, so as to form 230 g of silica in 90 minutes.

After maturing for 30 minutes, the slurry obtained is filtered. The filtration cake is washed with water and then dried in an oven at 80 0

C.

Analysis of the product by electron microscopy

(TEM)

shows that the thickness of the silica layer deposited is of the order of 20 nm.

The BET [lacuna] surface of the final particles is 2.9 m 2 /g.

The kinetics of addition of the sodium silicate was 0.134 g (SiO 2 (CaCO 3 Example 2 The abrasive prepared in Example 1 is tested for compatibility with MFP in solution in water and in sorbitol/water and glycerol/water mixtures.

The results obtained are given in Table 1 and compared with those obtained with the same amount of Sturcal H (precipitated calcium carbonate, sold by Rh6ne-Poulenc, exhibiting a particle size of 11 m and a BET specific surface of 4 m 2 as abrasive agent.

Example 3 The abrasive prepared in Example 1 is tested for compatibility with MFP in the dentifrice composition described above.

The results obtained are given in Table 1 and compared with those obtained with Sturcal H.

Example 4 A vessel heel is prepared by introduction, into a litre reactor, of 3.5 litres of water, of 0.68 mol/litre of vessel heel of sodium in the sodium chloride form, of 1150 g of precipitated calcium carbonate (Sturcal H, sold by Rh6ne-Poulenc, exhibiting a particle size of 11 pm and a BET specific surface of 4 m 2 and of sodium silicate, with an SiO 2 /NaO2 ratio of 3.5 (aqueous solution containing 130 g of SiO, per litre), in an amount corresponding to a concentration of 4 g of SiO 2 per litre of vessel heel. The vessel heel, with a pH of 9, is brought to 90C and kept stirred.

The following are subsequently introduced simultaneously: an aqueous sodium silicate solution, with an Si02/Na 2

O

ratio of 3.5, the concentration of which is 130 g of SiO 2 per litre of solution, and an aqueous sulphuric acid solution containing 80 g of acid per litre, so as to form 460 g of silica in 180 minutes.

C.

Analysis of the product by electron microscopy

(TEM)

shows that the thickness of the silica layer deposited is of the order of 40 nm.

The BET [lacuna] surface of the final particles is 2.4 m 2 /g.

The kinetics of addition of the sodium silicate was 0.134 g (Si0 2 (CaC03).

Example The abrasive prepared in Example 4 is tested for compatibility with NaF.

The results obtained are given in Table 2 and compared with those obtained with the same amount of Sturcal H (precipitated calcium carbonate, sold by Rh8ne-Poulenc, exhibiting a particle size of 11 pm and a BET specific surface of 4 m 2 as abrasive agent.

Table 1 Medium MFP compatibility ppm of F- before water in hydrolysis Abrasive of Example 1 83 165 Sturcal H 76 142 Medium MFP compatibility ppm of F- before 50/50 sorbitol/water in hydrolysis Abrasive of Example 1 69 113 Sturcal H 57 96 Medium MFP compatibility ppm of F- before 35/65 glycero/water in hydrolysis Abrasive of Example 1 83 126 Sturcal H 65 118 Medium MFP compatibility ppm of F- before dentifrice in hydrolysis Abrasive of Example 1 61 92 Sturcal H 40 165 Table 2 Medium, water NaF compatibility in Abrasive of Example 4 88 Sturcal H

Claims

1. Dentifrice composition comprising at least one agent for the prevention of caries, which agent is based on a fluorinated compound, and at least one silica, wherein the silica is composed of particles comprising a dense active silica shell and a calcium carbonate core.

2. Dentifrice composition according to claim 1, wherein the silica particles exhibit a dense active silica shell with a thickness of about 2 to 200 nm, for a calcium carbonate core size of about 20 nm to 30 tm.

3. Dentifrice composition according to claim 2, wherein the silica shell has a see: oooo thickness of about 5 to 50 nm and the calcium carbonate core size is about 50 nm to 0000 tm.

4. Dentifrice composition according to claim 1, wherein the silica particles exhibit a BET specific surface of about 1 to 100 m2/g.

5. Dentifrice composition according to claim 4 wherein the BET specific surface is °15 about 1 to 40 m 2 /g.

Dentifrice composition according to any one of the preceding claims, wherein the silica particles exhibit an RDA abrasiveness of the order of 30 to 250.

7. Dentifrice composition according to claim 6 wherein the RDA abrasiveness is about 40 to 200.

8. Dentifrice composition according to any one of the preceding claims, wherein the said particles comprising a dense active silica shell and a calcium carbonate core can be obtained by precipitation on calcium carbonate of active silica from an aqueous alkali metal M silicate solution, with an Si0 2 /Na 2 O ratio of at least 2, with adjustment of the -21- pH using an acidifying agent, separation of the silica slurry formed and drying of the silica suspension recovered.

9. Dentifrice composition according to claim 8 wherein the SiO 2 /Na 2 O ratio is about to 4.

10. Dentifrice composition according to claim 8, wherein the formation of silica slurry by precipitation is carried out according to the following stages: Ia first stage consisting in employing an initial vessel heel with a pH of the order of 8 to 10 comprising water, calcium carbonate, an electrolyte salt from the group of alkali metals, the amount of electrolyte present being at least approximately 0.4 mol, of alkali metal ion per litre of vessel hell, and optionally a buffer or basic agent, at a temperature of the order of 80 to 98 0 C; a second stage consisting in introducing, into the said vessel heel, the alkali metal silicate in the form of an aqueous solution containing at least approximately 100 grams of SiO 2 /litre, and the acidifying agent, under conditions such that the kinetics 15 K of formation of active silica, expressed in grams of silica/hour/gram of calcium carbonate, corresponds to a value 0 K 3 (A/200) 2", ;preferably K 4 (A/200) 2" and very particularly K 6 (A/200) 2" n being equal to (T-90)/10 A representing the specific surface, expressed in m 2 of the carbonate to be coated and T the temperature in °C, -22- the reaction mixture exhibiting a substantially constant pH of the order of 8 to 10 and being maintained at a temperature of the order of 80 to 98C, until the desired amount of silica has been formed.

11. Dentifrice composition according to claim 10, wherein in the first stage the electrolyte is present in an amount of 0.4 to 1.5 mol of alkali metal ion per litre of vessel heel, and in the second stage the aqueous solution contains about 100 to 330 grams of SiO 2 /litre.

12. Dentifrice composition according to any one of claims 8 to 10, wherein the alkali metal silicate is a sodium or potassium silicate. o* o10

13. Dentifrice composition according to any one of claims 8 to 12, wherein the S• oacidifying agent is chosen from sulphuric acid, nitric acid, hydrochloric acid, acetic acid, S formic acid or carbonic acid.

14. Dentifrice composition according to claim 13, wherein the acidifying agent is sulphuric acid.

15 15. Dentifrice composition according to any one of claims 8 to 14, wherein the amount [lacuna] calcium carbonate employed is such that the vessel heel formed contains of the order of 10% to 50% of its weight of calcium carbonate.

16. Dentifrice composition according to any one of claims 8 to 15, wherein the calcium carbonate employed exhibits a size of the order of 20 nm to 30 rm.

17. Dentifrice composition according to claim 16 wherein the calcium carbonate size is between about 50 nm to 20 atm. N T \,7x 0 0 @000 e g. S 00 C.. 0 *0 0S@0 9 0 23

18. Dentifrice composition according to any one of claims 8 to 16, wherein the electrolyte is chosen from sodium sulphate, sodium chloride, sodium nitrate or sodium hydrogencarbonate.

19. Dentifrice composition according to any one of claims 1 to 18, wherein it contains of the order of 5 to 40% of its weight of silica composed of particles comprising a dense active silica shell and a calcium carbonate core and a fluorinated compound in an amount corresponding to a concentration of 0.005 to by weight of fluorine in the said composition.

20. Dentifrice composition according to claim 19 containing about 5 to 35% silica 10 and/or about 0.005 to 2% of a fluorinated compound.

21. Dentifrice composition according to any one of claims 1 to 20, wherein the fluorinated compound is a salt of monofluorophosphoric acid or an alkali metal fluoride.

22. Dentifrice composition according to claim 21, wherein the fluorinated compound is a sodium, potassium, lithium, calcium, aluminium or ammonium salt of 15 monofluorophosphoric acid or sodium fluoride.

23. Dentifrice composition according to any one of claims 1 to 22, wherein the dense silica shell of the particles contains, in the adsorbed state, at least one agent for stabilizing Ca 2 ions.

24. Dentifrice composition according to claim 23, wherein the agent for stabilizing Ca ions is an alkali metal phosphate, preferably a sodium, potassium or lithium pyrophosphate, orthophosphate, tripolyphosphate or hexametaphosphate.

Dentifrice composition according to claim 23 or 24, wherein the said agent for stabilizing Ca 2 ions is adsorbed at the surface of the silica shell by treating the silica -24- shell with an aqueous solution of the said stabilizing agent, which treatment is carried out by adding of the said solution either to the silica slurry formed at the end of the precipitation stage, before filtration, or to the silica suspension obtained after filtration, before drying.

26. Dentifrice composition according to any one of claims 1 to 25, wherein it additionally contains anionic, non-ionic, amphoteric or zwitterionic surface-active agents in the proportion of approximately 0.1 to 10%, of the weight of the said composition, water in the proportion of approximately 5 to 50%, of the weight of the said S" composition, humectants in the proportion of approximately 10 to 85%, of the weight of •oo• the said composition, thickening agents in the proportion of 0.1 to 15% by weight, 2+ optionally at least one agent for stabilizing Ca 2 ions and other ingredients chosen from o *so other polishing abrasives, bactericidal, antimicrobial or anti-plaque therapeutic agents, flavourings, sweeteners, colorings or preservatives.

27. Dentifrice composition according to claim 26 containing about 1 to 5% of said too: 15 surface active agents, about 10 to 40% water, and about 10 to 70% of humectants.

S•28. Dentifrice composition according to any one of claims 1 to 27, wherein it is provided in the paste, gel or cream form.

29. Use, as additive or abrasive agent in dentifrice compositions, of composite particles comprising a calcium carbonate core and a dense active silica shell optionally containing, in the adsorbed state, an agent for stabilizing Ca 2 ions.

Use according to claim 29, wherein the said composite particles are as defined in any one of claims 2 to 6, 23 or 24 or can be obtained according to any one of claims 8 to 18 or

31. Use according to claim 29 or 30, wherein the said composite particles are employed in the proportion of approximately 5 to 40%, of the weight of the said dentifrice compositions.

32. Use according to claim 31 wherein the composite particles are employed in a proportion of approximately 5 to

33. Composite particles composed of a calcium carbonate core and of a dense active silica shell containing, in the adsorbed state, at least one agent for stabilizing Ca 2 ions.

34. Composite particles according to claim 33, wherein the said stabilizer is an alkali .e metal phosphate, preferably a sodium, potassium or lithium pyrophosphate, 0@4. 4P 6:06 1 0 orthophosphate, tripolyphosphate or hexametaphosphate. *00*

35. Composite particles according to claim 33 or 34, wherein the said stabilizer can represent up to 2% of the mass of the said composite particles.

36. Composite particles according to any one of claims 33 to 35, wherein they can be .:obtained according to claim 15

37. A dentifrice composition substantially as herein described with reference to any 00 one of the examples but excluding comparatives.

38. Use of composite particles as an additive or abrasive agent in dentifrice "compositions substantially as herein described with reference to any one of the examples but excluding comparatives. 2o

39. Composite particles substantially as herein described with reference to any one of the examples but excluding comparatives. DATED this 9th Day of March, 1999 RHODIA CHIMIE Attorney: PAUL G. HARRISON 2o i 2 5 Fellow Institute of Patent Attorneys of Australia r of BALDWIN SHELSTON WATERS