NO168282B - dentifrice - Google Patents

Description

The invention relates to a dental care product which contains

a water-soluble zinc salt which provides an astringent effect on mucous membranes in the mouth and on periodontal tissue during tooth brushing, and optionally an alkali metal monofluorophosphate and/or a gelling agent. Each of the components is compatible and substantially unreactive with a hydrated silica gel polish.

The astringent action of zinc ions provided by water-soluble zinc salts to promote and improve oral hygiene has long been known. Nevertheless, there have been limitations to the practical use of zinc in dentifrices because zinc ions can easily react with typical dentifrice components, causing a significant loss of available zinc ions.

Likewise, the monofluorophosphate has long been known

to promote oral hygiene and reduce tooth decay by releasing fluoride, but its effectiveness has also been reduced due to the incompatibility with certain dentifrice components, such as water-soluble zinc compounds.

Nonionic gelling agents, such as hydroxyethylcellulose,

has preferably been used in dentifrices when a water-soluble zinc salt has been used. However, when alkali metal carboxymethylcellulose has been used in the presence of zinc ions, reactions take place which remove zinc ions, and this leads to a possible breakdown of the gel and phase separation. In US patent 3728446, the reaction in situ between zinc ions and alkali metal carboxymethylcellulose during the formation of visible particles is described.

Also, gel-type dentifrices which provide astringent action due to the presence of zinc ions have been subject to limitations due to the incompatibility of zinc ions with various silicon-containing polishes. Such silicon-containing polishing agents such as silica xerogel having an average particle size of 2-10 µm and generally a surface area of at least 300 m 2 /g, typically 300-370 m 2 /g or 600-800 m 2 /g, which are described in

US patent 3538230, is exposed to reaction in situ with zinc ions so that a large part of the theoretically available zinc ions is lost due to physico-chemical mechanisms, such as absorption.

Similar compatibility problems will occur if water-soluble zinc salts are present together with other salt polishing agents for dentifrices, especially calcium salts, e.g. dicalcium phosphate or calcium carbonate. In fact, it has been believed that it would be difficult to use water-soluble zinc salts and to maintain a strong availability of zinc ions in such common dentifrices.

Compatibility is also a problem when alkali metal monofluorophosphate is used together with such silicon-containing polishing agents in a dentifrice containing a water-soluble zinc salt.

It has therefore been difficult to produce dentifrices containing silicon-containing polishing agents and zinc ions with or without alkali metal monofluorophosphate and/or alkali metal carboxymethylcellulose so that the dentifrices remain effective by, at. it contributes with the astringent properties due to the presence of zinc ions and the anti-tooth decay properties due to the presence of fluoride. In particular, gel-type dentifrices which provide both astringent action due to zinc ions, with or without anti-tooth decay action due to: the presence of fluoride, have not been satisfactorily available due to the incompatibility between zinc ions and monofluorophosphate and alkali metal carboxymethylcellulose in the presence of various silicon-containing polishing agents .

According to the present invention, a precipitated, amorphous silica gel is used which has been described in British patent application 2038303A and in US patent 4528181. In the latter, a dental care agent containing the precipitated, amorphous silica gel is described and in which a fluoride double source containing sodium fluoride and sodium monofluorophosphate and a calcium source is stabilized with an alkali metal phytate to improve fluoride retention.

Such a precipitated, amorphous silica gel material is commercially available, for example, under the trademarks Syloblanc<®> 81, Syloblanc<®> 81C and Syloblanc<®>82. This material is clearly different from the types of xerogel that have been sold under the trademark Syloid<®> and which are specifically described in US patent 3538230. Although some products sold under the trademark Syloblanc(*r^ ) were previously or are still available under the trademark Syloi, none of the materials Syloblanc** 81, Syloblancw81C or Syloblanc® 82 have ever been available under the trademark Syloi <£>>. It should be particularly noted that the grades of silica gel used in accordance with the present invention are less abrasive wherever the surface area increases, while the grades of silica xerogel described in US patent 3538230 are generally more abrasive as their surface area increases.

Because of the poor compatibility between most polishing agents and zinc, including the polishing agents described in US patent 3,538,230, it was completely unexpected that a particular silicon-containing polishing material would not present such a problem and, moreover, that the reaction between zinc ions and alkali metal carboxymethylcellulose in the presence of such polishing agent is significantly reduced. It was also unexpected that zinc ions and alkali metal monofluorophosphate remain stable and compatible during the release of fluorine in the presence of such a special siliceous polishing material. It has nevertheless been found according to the invention that retention of a strong astringent effect due to zinc ions is achieved when such a special silicon-containing polishing material is used, regardless of whether alkali metal carboxymethylcellulose is also used or not, or when monofluorophosphate is used to provide high concentrations of fluoride ions which also be retained.

It is an advantage of the present invention that it provides an astringent dentifrice which contains zinc ions and which can effectively contain monofluorophosphate and/or an alkali metal carboxymethylcellulose gelling agent.

It is a further advantage of the present invention that it provides an astringent dental paste which contains zinc ions and which may optionally contain monofluorophosphate and/or an alkali metal carboxy-methylcellulose gelling agent.

The invention thus relates to an astringent dental care agent which is characterized in that it comprises 20-90% by weight of a liquid carrier comprising water in an amount of at least 3% by weight of the dental care agent, 0.5-5% by weight of a gel agent and 10-50% by weight % of a polishing agent comprising a synthetic, precipitated, amorphous silica gel with an average particle size of 1-30.um and

a) a surface area of 1-600 m 2/g,

b) a pore volume of 0.05-0.5 cm 3/g,

c) a product of surface area (in m 2/g) and pore volume (in cm 3/g) less than or equal to 240,

d) a calculated pore diameter of 1.5-2.5 nm and

e) a water content below 25% by weight,

and with up to 5% by weight of a water-soluble zinc salt which gives

at least 50 ppm zinc ions in the dental care product, and possibly an alkali metal monofluorophosphate in an amount that will give 0.01-1% by weight of fluoride ions.

As indicated above, the synthetic, precipitated silicon dioxide is of the type described in British patent application 2038303A and in US patent 4528181. Special qualities of the silicon dioxide material described in these publications are suitable for use in the dentifrice according to the invention. Also, particular grades which are particularly preferred are described in a publication of Grace G.m.b.H., Norderstadt, West Germany, October 1980, as Syloblanc® 81 and Syloblan<® 82 with the following typical physical and chemical characteristics:

(s)

According to a variant of Syloblanc<*>^ 81 available as Syloblanc^ 81C, the pH (5% suspension in water) is 6-8.

Syloblanc<®> 81 and Syloblanc^ 81C are especially very effective for polishing tooth surfaces. Syloblanc® 82 has a lower polishing effect, but can be used by consumers who want such a reduced effect. Likewise, qualities of the silicon dioxide material can be used in suitable amounts in admixture with each other to give the desired polishing properties. It should be noted that the dentifrices are compatible in unlined aluminum dentifrice tubes even in the absence of phytate salt, which is indicated as necessary in US patent 4528181. The precipitated amorphous silica gel is used

in an amount of 10-50, typically 10-40, wt% in a dentifrice gel.

Aqueous slurries of the silicon dioxide materials (eg 5-20% slurries) typically have a pH of 2-9. As the dental care agent according to the invention preferably has a pH (measured in a 10% aqueous slurry) of at least 5.5, e.g. 5.5-7.5, the toothpaste's pH can be adjusted with a suitable material, such as sodium hydroxide etc.

The water-soluble zinc salt is present in the dentifrice in an amount of up to 5% by weight, preferably 0.01-3, and most preferably 0.1-2.0% by weight. Water-soluble zinc salts for the dentifrices according to the invention are at least 10% by weight, preferably at least 20% by weight, soluble in water. At least 50 ppm zinc ions are provided in the dental care agent, preferably at least 750 ppm and most preferably at least 1000 ppm, zinc ions. Suitable zinc salts include zinc sulfate, zinc chloride, zinc bromide, zinc iodide, zinc nitrate and zinc acetate. Zinc chloride in an amount of 0.01% by weight will give approx. 50 ppm zinc ions, and 0.2% by weight will give approx. 1000 ppm zinc ions. 0.48% by weight zinc sulfate heptahydrate will give approx. 1000 ppm zinc ions. In addition, zinc oxide, which is a slightly soluble (less than 0.0005%) zinc compound, can also be added to prevent the product's pH from being lowered. The zinc oxide acts as a buffer system and improves the pH stability and compatibility in unlined aluminum tubes. It may be present in an amount of 0.005-0.5% by weight.

The dentifrice comprises a liquid carrier containing 3-60% by weight of water, typically mixed with at least one humectant. The liquid phase makes up 20-90% by weight of the dental care agent and is generally made up of 25-80

wt% liquid, typically with 3-50, preferably 3-10, wt% water in a substantially clear dentifrice gel or in a dentifrice gel which would have remained substantially clear but for the presence of an opacifier , such as titanium dioxide, and 11-50% water in a cloudy to opaque dentifrice gel with 10-90, preferably 15-80, wt% humectant. Typical humectants include glycerol, sorbitol (eg 70% solution), maltitol, polyethylene glycol with a molecular weight of 400-600, propylene glycol and mixtures thereof.

The dentifrice also contains a gelling agent or binder as a solid carrier although this may be present in small amounts because the synthetic, precipitated silicon dioxide can cause thickening or gel formation in the dentifrice so that it acquires a cream-like or paste-like consistency. Alkali metal carboxymethyl cellulose is preferred as the gelling agent in the present dental care products, but other gelling agents or binders that may be present include hydroxyethyl cellulose, hydroxypropyl cellulose, xanthan, Irish moss, iotacarrageenan, gum tragacanth, polyvinyl pyrrolidone, starch or mixtures thereof. Such gel agents can be used in an amount of 0-05-5, typically 0.05-2,

and preferably 0.1-1.5% by weight. It is particularly preferred to

use sodium carboxymethyl cellulose.

Alkali metal phosphates, such as sodium monofluorophosphate or potassium monofluorophosphate, are compatible in the dentifrice. Sodium monofluorophosphate is particularly preferred. When it was previously attempted to prepare a dentifrice with a liquid carrier, gelling agent, polishing agent, zinc salt and sodium monofluorophosphate, significant amounts of zinc ions and fluoride ions were lost due to insolubilization. It is surprising that when the polishing agent is the defined synthetic, precipitated, amorous silica gel, high concentrations of fluoride ions and a substantial retention of zinc ions are obtained. Such a high level of fluoride retention is not obtained when a single fluoride, e.g. sodium fluoride, is used.

Sodium monofluorophosphate, Na2P0jF, can have a widely varying purity in commerce. It can be used with any suitable purity, provided that any impurities do not adversely affect the desired properties to a significant extent. In general, it is desired that the purity is at least 80% by weight, preferably at least 90% by weight, calculated as sodium monofluorophosphate, the rest being mainly made up of impurities or by-products from production, such as e.g. sodium fluoride or water-soluble sodium phosphate salt. Expressed in another way, the sodium monofluorophosphate used should have a total fluoride content of more than 12%, preferably 12.7%, a content of not more than 1.5%, preferably not more than 1.2%, of free sodium fluoride, and a content of sodium monofluorophosphate of at least 12%, preferably at least 12.1%, all calculated as fluoride. Alkali metal monofluorophosphate is present in such an amount that it will provide fluoride in an amount of 0.01-1, preferably about 0.1, wt%. Sodium monofluorophosphate can thus be present in an amount of 0.076-7.6%, preferably 0.76%, which corresponds to 100-10000 ppm, preferably approx. 1000 ppm, fluoride.

Any suitable surfactant or cleansing material may be incorporated into the dentifrices. Such compatible materials are desired to provide additional cleansing, foaming and antibacterial properties depending on the particular type of surfactant, and are selected accordingly. These cleaning agents are usually water-soluble compounds and can have an anionic, non-ionic, amphoteric or cationic structure. It is generally preferred to use the water-soluble, synthetic, organic surfactants which are not soaps. Suitable cleaning materials are known and include, for example, the water-soluble salts of higher fatty acid and monoglyceride monosulfate surfactants (eg, sodium coconut fatty acid monoglyceride monosulfate), higher alkyl sulfate (eg, sodium lauryl sulfate), alkylaryl sulfonate (eg, sodium dodecylbenzene sulfonate or higher fatty acid esters of 1,2-dihydroxypropanesulfonate) etc.

Additional surfactants include those

substantially saturated higher aliphatic acylamides of lower aliphatic aminocarboxylic acid compounds, such as those having 12-16 carbon atoms in the acyl radical. The amino acid moiety is generally derived from the lower aliphatic saturated monoaminocarboxylic acid compounds. Suitable compounds are the fatty acid amides of glycine, sarcosine, alanine, 3-aminopropanoic acid or valine with 12-16 carbon atoms in the acyl group. However, it is preferred to use the N-lauroyl, N-myristoyl or N-palmitoylsarcoside compounds to achieve optimal effects.

The amide compounds can be used in the form of the free acid or preferably as water-soluble salts thereof, such as the alkali metal, ammonium, amine or alkylolamine salts. Specific examples of these are sodium and potassium N-lauroyl, myristoyl or palmitoyl sarcosides, ammonium or ethanolamine N-lauroyl glycide or alanine. For the sake of simplicity, here "aminocarboxylic acid compound" or "sarcoside" or similar designations shall indicate such compounds which have a free carboxyl group or the water-soluble carboxylate salts.

Such materials are used in a pure or practically pure state. They should be as free as practicable from soap or similar higher fatty acid material which tends to reduce the activity of these compounds. In normal practice, the amount of such a higher fatty acid material is below 15% by weight of the amide and insufficient to adversely affect it, and the amount is preferably less than 10% by weight of the amide material.

Other particularly suitable surface-active materials include non-ionic agents, such as condensates of sorbitan monostearate with approx. 20 moles of ethylene oxide, condensates of ethylene oxide with propylene oxide, condensates of propylene glycol (Pluronic*^ materials) or amphoteric agents, such as long-chain (alkyl)-amide alkylene alkalized amine derivatives available under the trademark Mirano]<®> C2M> Cationic surfactant germicides or antibacterial compounds, such as diisobutylphenoxyethoxyethyldimethylbenzylammonium chloride, benzyldimethylstearylammonium chloride, tertiary amines with one fatty alkyl group (with 12-18 carbon atoms) and two (poly)oxyethylene groups attached to the nitrogen atom

(typically containing a total of 2-50 ethenoxy groups per molecule)

and salts thereof with acids, or compounds of the formula

in which R denotes eh fatty alkyl group with 12-18 carbon atoms and x, y and z together are 3 or higher, as well as salts thereof with mineral acids or organic acids, can also be used. It is preferred to use 0.05-5% by weight of the above-mentioned surface-active materials in the oral care products according to the invention.

Various other materials can be incorporated into the tooth creams according to the invention. Examples of these are opacifying agents, preservatives, stabilizers, silicones, chlorophyll compounds and ammoniacal materials, such as urea, diammonium phosphate or mixtures thereof. These auxiliary additives are incorporated into the existing dental care products in quantities that will not adversely affect the desired properties and characteristics to a significant extent, and they are selected in a suitable way and used in normal quantities.

For certain purposes it may be desirable to include

antibacterial agents in the dentifrices according to the invention. Typical antibacterial agents that can be used in an amount of 0.01-5, preferably 0.05-1, wt% of the dentifrice include cetylpyridinium chloride and benzethonium chloride as well as N 1 -4(chlorobenzyl)-N 5-(2,4- dichlorobenzyl)-biguanide, p-chlorophenylbiguanide, 4-chloro-benzhydrylbiguanide, 4-chlorobenzhydrylguanylurea, N-3-lauroxy-propyl-N^-p-chlorobenzylbiguanide, 1,6-di-p-chlorophenylbiguanide-hexane, 1-(lauryldimethylammonium )-8-(p-chlorobenzyldimethyl-ammonium)-5,6-dichloro-2-guanidinobenzimidazole, N<1->p-chloro-phenyl-N 5-laurylbiguanide, 5-amino-1,3-bis (2- ethylhexyl)-5-methylhexahydropyrimidine and their non-toxic addition salts.

Any flavoring or sweetening agents can be used to flavor the dental care agents according to the invention. Examples of suitable flavoring ingredients include the flavoring oils, e.g. oils of spearmint, peppermint, wintergreen, sassafras, clove, sage, eucalyptus, marjoram, cinnamon, lemon or orange, as well as methyl salicylate. Suitable sweeteners include sucrose, lactose, maltose, sorbitol, sodium cyclamate, sodium saccharin, dipetides according to US patent 3939261 or oxathiazine salts according to US patent 3932606. Suitable flavoring and sweetening agents can collectively amount to 0.01-5% by weight or more of the toothpaste.

The dentifrice is packaged in a container from which it can be easily extruded, such as e.g. in a toothpaste dispensing container which is operated using a pressure difference or mechanically, or a lined or unlined aluminum tube or a wax-lined lead tube or plastic tube which may be laminated with aluminium. The rheological properties are highly desirable when a mechanically operated discharge container of the type described in British patent application 2070695A is used. This dispensing container includes a dispensing nozzle, a pull member, a central rod, a piston and a dispensing control device - which is operated by hand.

A pressure differential operated discharge vessel can be

of the aerosol or vacuum type. Suitable differential pressure discharge vessels include those comprising a coincident

bare, product-containing bag which is arranged in a rigid container containing a propellant fluid. In such dispensing containers, operation of the valve will mean that only the product will be dispensed as the drive fluid is separated from the product by means of the bag which is impervious to fluid. Dispensing devices of this type are described in US patents 3828977 and 3838796. These are the so-called "Sepro" dispensing devices. So-called "Exxel" and "Enviro Spray" containers are also operated by means of pressure.

A further different type of dispensing device is the barrier piston container described in US patent 4171757. Such a container includes a valve, a product-containing compartment and a substantially fluid-tight barrier piston that separates the driving fluid from the contained product (the so-called "Diamond" container) .

The dental care agent is typically produced by forming a premix of the gel agent and the liquid carrier components, e.g. water and humectant, which may also contain additional ingredients, such as the monofluorophosphate and/or sweetener, and with this the synthetic, precipitated silica gel and the zinc salt are mixed. Additional used ingredients can then be added.

The invention will be described in more detail below with the help of a number of design examples. In these, all quantities are based on weight unless otherwise stated.

Example 1

The following opaque gel toothpastes are manufactured and filled in lined aluminum tubes:

The theoretical amount of soluble zinc ions in each dentifrice gel is 1000 ppm or 0.1%.

For the dental care agent A, it is not necessary for a thickening material to be present for the desired gel type to be achieved. The consistency of the toothpaste is approximately the same as the consistency of the toothpaste B.

Each toothpaste is aged at room temperature and at 43°c. Both retain largely the same desired consistencies. The percentage amounts of available soluble zinc ions in each dentifrice are determined and are as follows:

The dentifrice A containing Syloblan 81 retains superior concentrations of soluble zinc ions compared to the otherwise generally equivalent dentifrice

agent B containing Syloblanc<®> ALI.

Similar superior retained concentrations of soluble zinc ions are obtained when Syloblanc** 81 in dentifrice A is replaced by Syloblanc 82 and by a 1:1 mixture of Syloblanc® 81 and 82, in each case with the concentration

of sodium hydroxide reduced or by omitting sodium hydroxide, with their amounts added to sorbitol (70%).

Likewise, superior retained concentrations of soluble zinc ions are obtained when Syloblanc^ 81 is replaced by Syloblanc® 81C, with sodium hydroxide looped and its amount added to sorbitol (70%).

0.25 part zinc oxide is incorporated into each of the dentifrices A and B instead of corresponding amounts of sorbitol, whereby the pH is stabilized during aging and improved compatibility with unlined aluminum tubes is achieved over longer periods.

Example 2

The following opaque toothpaste gels are manufactured and filled in lined aluminum tubes:

The theoretical amount of soluble zinc ions i

each dentifrice gel is 1000 ppm or 0.1%.

For the dentifrice A, it is not necessary for a thickening material to be present to initially obtain the desired gel character.

Each toothpaste is aged at room temperature and at 43°C. Both generally retain equally desirable consistencies. The percentage of available soluble zinc ions in each dentifrice is determined as follows:

(3)

The dentifrice A containing Syloblancr^ 81 retains its gel character and superior concentrations of soluble zinc ions compared to the otherwise largely equivalent dentifrice B containing Syloblanc^ 63. When the usual 7 MXF grade of sodium carboxymethylcellulose is used, phase separation and degradation occur. ning in the presence of Syloict^ 63 as a polishing agent, which does not

(s)

occurs to an equally strong degree when Syloblanc^ 81 is used.

It should be noted that the assessment concentrations after two weeks and 1 month for the dental care agent B at 43°C indicate variations in routine tests.

Similar superior concentrations of retained soluble zinc ions are obtained when Syloblanc 81 in the dentifrice

(s)

A is replaced with Syloblanc<**> 82 and with a 1:1 mixture of

few)

Syloblanc"^ 81 and 82, in each, with reduced concentrations of sodium hydroxide, or omitted with their amounts added to sorbitol (70%).

Likewise, superior retained concentrations of soluble zinc ions are obtained when Syloblanc^ 81 is replaced by Syloblanc^ 81C, with sodium hydroxide omitted and its amount added to sorbitol (70%).

0.25 part zinc oxide is incorporated into each of the toothpastes A and B instead of corresponding amounts of sorbitol, whereby the pH is stabilized during aging and the compatibility with unlined aluminum tubes is improved over longer periods.

Example 3

The following opaque dentifrice gels are manufactured and filled in lined aluminum tubes

The theoretical amounts of soluble zinc ions and fluoride in each toothpaste gel are 1000 ppm or 0.1% for both the zinc ions and the fluoride.

Each toothpaste is aged at room temperature and at 43°C. The percentage amounts of available soluble zinc ions and of fluoride in each dentifrice are determined and are as follows at room temperature:

The dental care agent A, which contains sodium monofluorophosphate, provides a substantial retention of both zinc ions and fluoride compared to the dental care agent B, which contains sodium fluoride. At 43°C, gas develops in the lined aluminum tube containing the dentifrice B, but the unlined aluminum tube containing the dentifrice A remains stable.

The retention of zinc ions and fluoride is low when the xero-gel Syloia<*>^ 63 replaces Syloblanc^ 81.

Similar results to those found for dentifrice A are obtained when potassium monofluorophosphate is substituted?

sodium monofluorophosphate.

Similar superior concentrations of retained soluble zinc ions and fluoride are obtained when Syloblanc<®> 81 in dentifrice A is replaced with Syloblanc® 82 and with a 1:1 mixture of Syloblanc^ 81 and 82, in each, with concentrations of sodium hydroxide reduced or omitted with their amounts added to sorbitol (70%).

Likewise, superior retained concentrations are achieved

(s)

of soluble zinc ions and fluoride when Syloblanc<**> 81 is-

d)

replaced with Syloblanc 81C, with sodium hydroxide omitted and

the amount of this added to sorbitol (70%).

0.25 part zinc oxide is incorporated into each of the toothpastes A and B instead of corresponding amounts of sorbitol, whereby the pH is stabilized during aging and the compatibility with unlined aluminum tubes is improved over longer periods.

Example 4

The following stable, visually clear dentifrice gels are manufactured and filled in unlined aluminum tubes:

Example 5

The following stable, visually clear dentifrices-A

gels are produced and filled in lined aluminum tubes:

Similar stability is achieved when potassium carboxymethyl cellulose replaces sodium carboxymethyl cellulose

Example 6

The following stable, visually clear dentifrice gels are manufactured and filled in unlined aluminum tubes:

Example 7

The following cloudy and opaque dentifrice gels are manufactured and packaged in mechanically operated dispensing containers:

In the examples, sodium cyclamate can replace sodium saccharin.

Example 8

The following stable, cloudy and opaque dentifrice gels are manufactured and filled in unlined aluminum tubes:

In the examples, sodium cyclamate can replace sodium saccharin.

Example 9

The following stable, cloudy and opaque dentifrice gels are manufactured and packaged in mechanical dispensing containers:

In the examples, sodium cyclamate can replace sodium saccharin.

Claims (13)

1. Tooth care agent with astringent effect, characterized in that it comprises 20-90% by weight of a liquid carrier comprising water in an amount of at least 3% by weight of the tooth care agent, 0.5-5% by weight of a gel agent and 10-50% by weight of a polishing agent comprising a synthetic, precipitated, amorphous silica gel with an average particle size of 1-30.um and a) a surface area of 1-600 m 2 /g, b) a pore volume of 0.05-0.5 cm < 3>/g, c) a product of surface area (in m 2/g) and pore volume (in cm 3/g) below or equal to 240, d) a calculated pore diameter of 1.5-2.5 nm and e) a water content of less than 25% by weight, and with up to 5% by weight of a water-insoluble zinc salt which means that the tooth care agent is provided with at least 50 ppm zinc ions, and optionally an alkali metal monofluorophosphate in an amount which gives 0.01 - 1% by weight of fluoride ions. 2. Tooth care agent according to claim 1, characterized in that the zinc salt is present in an amount of 0.01-3% by weight. 3. Tooth care agent according to claim 1 or 2, characterized in that the zinc salt consists of zinc sulphate, zinc chloride, zinc bromide, zinc iodide, zinc nitrate or zinc acetate. 4. Tooth care product according to claims 1-3, characterized in that the zinc salt is zinc sulfate heptahydrate. 5. Tooth care agent according to claims 1-3, characterized in that the zinc salt is zinc chloride. 6. Tooth care product according to claims 1-5, characterized in that the water in the liquid carrier constitutes 3-10% by weight of the dental care agent and that the synthetic, amorphous silica gel constitutes 10-40% by weight of the dental care agent. 7. Tooth care product according to claims 1-5, characterized in that the water in the liquid carrier constitutes 11-50% by weight of the tooth care product. 8. Tooth care agent according to claims 1-7, characterized in that the synthetic, amorphous silica gel is at least one of the following synthetic, amorphous silica gels with the additional characteristics: 9. Tooth care agent according to claims 1-8, characterized in that an alkali metal mono- . fluorophosphate is present and that it is sodium monofluorophosphate. 10. Tooth care product according to claims 1-9, characterized in that the water-soluble zinc salt is present in an amount which gives approx. 1000 ppm zinc ions, and that the alkali metal monofluorophosphate is present in an amount that gives approx. 1000 ppm fluoride. 11. Tooth care agent according to claim 10, characterized in that the zinc salt is zinc sulfate heptahydrate and that the alkali metal monofluorophosphate is sodium monofluorophosphate. 12. Tooth care product according to claims 1-11, characterized by the fact that it is packaged in an unlined aluminum tube. 13. Tooth care agent according to claims 1-12, characterized in that it also contains 0.005-0.5% by weight zinc oxide.