NO174914B - mouthwash - Google Patents

Description

This invention relates to oral hygiene preparations. Such

preparations are defined in claim 1 and are used to prevent or inhibit bacterial growth on the tooth surfaces.

Preventing the adherent coating, dental plaque, on mammalian teeth (especially in humans) is a highly desired result. Dental plaque is the result when carcinogens and other types of bacteria gather in colonies on the surface of the teeth, forming a coating that adheres very well to the surface. It is believed that the formation of plaque on the tooth surface is one of the first steps in the development of dental caries and periodontal disease.

Many attempts have been made to prevent the formation of plaque on the tooth surface, and to remove plaque from such surfaces.

E.g. have you tried brushing, flossing and mouthwash and stimulators between the teeth. However, such treatments are not completely successful and must often be supplemented with periodic treatment by dentists. In our recently published European patent application, publ. No. 182.52 3 we learn that certain pharmaceutical preparations (as defined therein) are highly effective in preventing or significantly reducing (a) the colonization of tooth surfaces or simulated tooth surfaces by carcinogenic and other microorganisms commonly found in the oral environment, and (b) the adherent coating of dental plaque on the tooth surface which is the result of such microorganisms.

The preparation of polymers for use in the aforementioned specific pharmaceutical preparations is described in EP 182,523 and incorporated herein by reference.

Chlorhexidine is a cationic antiseptic that has been widely used in the medical profession as a topical antibacterial agent for more than 20 years; the preparation thereof is described in British patent document 705,838. It has been reported (Loe et al,

Journal of Periodontal Research, 1970, Vol 5, pp79-83) that chlorhexidine can be used as an antiseptic in the oral environment, and that under certain circumstances there is obviously a tendency for chlorhexidine to discolour the teeth. Such discoloration appears to be a feature common to cationic antiseptics. It has been shown

(Addy et al, Journal of Periodontal Research, vol. 9, pp 134-140)

that such discoloration is the result of a mutual influence between the cationic antiseptic and ingredients in the food, especially food rich in tannins, e.g. coffee, tea or red wine.

We have now found that when certain surfaces, e.g. tooth surfaces or hydroxyapatite, are treated with a combination of both (a) a polymer, as defined below, bearing specific polyalkylene oxide chains, and (b) a cationic antibacterial agent, the resulting treated tooth surfaces will surprisingly exhibit both increased antiplaque and antibacterial properties against certain oral microorganisms, e.g. can the combination lead to the control of so-called "bio-fouling" of the tooth surfaces.

In the presence of the aforementioned polymer, corresponding anti-bacterial effects can in fact be observed where the tooth surface has been treated with a lower concentration of a solution of the antibacterial agent. Moreover, we have now surprisingly found (i) that the aforementioned tendency to discoloration with chlorhexidine is in any case reduced, there is often no increase in discoloration even if more chlorhexidine is adsorbed on the tooth surface in the presence of the aforementioned polymer; (ii) the antibacterial properties of certain cationic antibacterial agents, e.g. chlorhexidine and alexidine, are increased on simulated tooth surfaces if the surface is treated successively with, or with a combination of, an acidic polymer, e.g. Polymer 93W (as defined below) and the aforementioned agent; and (iii) where composite fillings, e.g. Occlusion®, Opalux, Silux and Valux P50 etc. tend to be discolored by cationic antiseptics, such discolouration is in any case reduced in the presence of the aforementioned polymer. It will be understood that, in any case, reduction of such discolouration of the front teeth is particularly desirable.

According to the present invention, an oral hygiene preparation is provided which is characterized in that it comprises

(i) 0.001-10% by weight of at least one cationic antibacterial agent; and (ii) 0.05-30% by weight of at least one polymer, as defined in claim 1, having one or more polyalkylene oxide groups. Examples of cationic antibacterial agents that can be used in the present invention include benzalkonium chloride, bispyridinamines, e.g. octenidine, or preferably a polybiguanide, e.g. alexidine, or most preferably a bis-biguanide, e.g. chlorhexidine. By "polybiguanide" we mean a compound having several biguanide residues in the chain of the general formula I

or tautomers thereof. Often there are two, three or four such residues in the chain in the antibacterial agent used in the present invention. However, we do not rule out the possibility that it may be sufficient to provide at least a larger proportion of the repeating units in a higher molecular weight polymer, e.g. with molecular weight up to around 10,000.

It will be understood that where a polybiguanide is used in the present invention, it may be present as a free base; preferably, however, it is present as a salt thereof, e.g. acetate or hydrochloride, or preferably, especially when the polybiguanide is a bis-biguanide having the structure shown in the general formula II, as the digluconate, i.e. the digluconate of 1,6-di(4-chlorophenyl-digluanido)hexane, which is known in the art as chlorhexidine.

We do not rule out the possibility that where a polybiguanide is used, e.g. chlorhexidine, in the form of a free base in the present invention, may be in admixture (eg as a salt) on the tooth surface, as a salt with an acidic polymer as defined below.

As possible explanations, without wishing to be bound thereby, for the increased antibacterial effect of the oral hygiene preparation according to the present invention, we suggest: (i) an increase in the amount of chlorhexidine adsorbed on the tooth surface; and or (ii) change in the adsorption strength of chlorhexidine on the tooth surface, so that it is more available to exert its antibacterial action on the surface; and/

or

(iii) change in the orientation on the tooth surface of adsorbed chlorhexidine, so that the antibacterial groups in it are more accessible to bacteria that come into the vicinity

of these; and or

(iv) ion-pairing between the cationic antibacterial agent and the acidic ions, where present, on the polymer.

In the preparation according to the present invention, several hydrogen bonds between the polymer and the biguanide cations can contribute to the aforementioned increase in quantity or change in strength of the adsorption or orientation.

Polymers of which the oral hygiene preparation according to the present invention is comprised are preferably acidic, by which we mean that there is at least one carboxylic acid group bound to the polymer backbone. However, we do not exclude the possibility that the polymer may be amphoteric, basic or neutral, although this is not preferred.

The one or more associated polyalkylene oxide groups which are bound to the polymers of which the oral hygiene preparations according to the invention are comprised are preferably ethylene oxide groups. However, we do not rule out the possibility that at least some of these may be alternative poly(lower) alkylene oxide groups, e.g. polypropylene.

Polymers that comprise the oral hygiene preparations according to the invention comprise one or more repeating units with general structure A

and one or more repeating units with general structure B

wherein X, which in the repeating units of structure A may be the same or different, and Y, which in the repeating units of structure B may be the same or different, are hydrocarbyl, or substituted hydrocarbyl residues, which form a backbone of the polymer;

Z is -CHR^CHR<2>-or (CH2)m-; in which

R<1>, which in the same repeating unit of structure B (when n or q is 2 or more) or in different repeating units of structure B may be the same or different, is hydrogen or a hydrocarbyl group; and

R<2>, which in the same repeating unit of structure B (when n or q is 2 or more) or in different repeating units of structure B may be the same or different, is hydrogen or a hydrocarbyl group;

except that R<1> and R<2> in a single unit -CHR<1->CHR<2->0- cannot both be hydrocarbyl;

R<3>, which in the same repeating unit of structure B (when q is 2 or more) or in different repeating units of structure B may be the same or different, is hydrogen or a hydrocarbyl group or an acyl group derived from an alkanoic acid having up to 5 carbon atoms;

m, when present, is a number from 3 to 10;

n is a number from 1 to 60;

p is a number from 1 to 4; and

q is a number from 1 to 4;

each (CO 2 H) group is connected via one or more intermediates L to the hydrocarbyl residue X, and in cases where p is 2 to 4 may be connected via L to the same or different carbon atoms in X;

L may be the same or different in the repeating units of structure A and selected from one or more direct linkages and one or more groups of atoms, each group providing a chain of one or more atoms to link a (CO 2 H) group with X, except that more than two (CO 2 H) groups cannot be directly bonded to the same carbon atom in X;

each ((ZO)nR 3 ) q group is connected via one or more intermediates

link M to the hydrocarbyl residue Y, and in cases where q is 2 to 4 may be linked via M to the same or different carbon atoms in Y;

M may be the same or different in the repeating units

with the structure B and is selected from one or more direct linkages and one or more groups of atoms where each group provides a chain of one or more atoms to link a (ZO)nR<3-> group with Y, except that more than two (ZO)nR3 groups cannot be directly bonded to the same carbon atom in Y;

the ratio of the number of -CO2H groups to the number of (ZO)nR<3->groups, especially where Z is -CH2CH2-, is within the range of 1:20 to 20:1.

Preferably, both R<1> and R<2>, when present, are both hydrogen.

Where R<1> or R2 is a hydrocarbyl group, it is preferably a lower alkyl group, more preferably methyl.

R<3> is preferably a lower alkyl group, more preferably methyl.

Where Z is -(CH2)m-, m is preferably 4; this allows a straightforward preparation of -(Z0)n from tetrahydrofuran.

It should be understood that the definition of the polymer contained in the preparation (as given above) is also intended to include a polymer in which at least some of the carboxyl groups in the repeating units of the general structure A have been converted into the corresponding salt anions CO2- ( as these are considered C02H groups in terms of the ratio between carboxyl and -Z0- groups), and the corresponding cations are e.g. ammonium (NH4+), or alkaline earth metals or preferably alkali metals (e.g. NA+, K+). We do not rule out the possibility that the cation may be derived from the cationic antibacterial agent per se; in fact, the discoloration tends to be further reduced when the cationic antibacterial agent is present as a salt of the acidic polymer, so that there is essentially no free chlorhexidine in the mouth.

In the general structure A, all the carboxyl groups are linked to the hydrocarbyl residue X by means of one or more intermediates (i.e. with a linking unit or units), which are denoted by L, and which are selected from one or more direct linkages (i.e. one or more direct linkages ) and one or more groups of atoms each providing a chain of one or more atoms to link carboxyl groups with X. In cases where p is 2-4, each carboxyl group may be linked via L to the same or, in cases where L represents more than one intermediate, to the same or different carbon atoms in X, although of course more than two carboxyl groups cannot be directly attached to the same carbon atom in X (and also provided that in such cases X has at least two carbon atoms, while it must it is understood that it is within the scope of the invention of X to have only one carbon atom). It should be noted that L can in principle represent up to 4 different intermediates in the structure A (in cases where p is 4). L can be the same or different in the repeating units of the structure A.

In cases where L represents one or more groups of atoms each providing a connecting chain of atoms, the chain will normally comprise one or more carbon atoms (which may for example comprise carbon atoms in an aryl ring) and or heteroatoms (especially N and or 0 ). Examples of possible connections that L can provide are:

where (except for the direct linkage) the upper term is to X and the lower term is to carboxyl. However, it is preferred in the present invention that L is one or more direct linkages, so that each carboxyl group is bound directly to a carbon atom in the polymer backbone.

In the structure A, p is preferably one or two, more preferably one (so that L can then represent one or at most two intermediate terms).

In the structure B, all the (ZO)nR<3-> groups are bound to the hydrocarbyl residue Y by means of one or more intermediates (i.e. with a connecting unit or units), this or these being denoted by M which is selected from one or more direct linkage (i.e. one or more direct bonds) and one or more groups of atoms, all of which provide a chain of one or more atoms to link (ZO)nR<3-> groups with Y. In cases where g is 2 to 4, all the (ZO)nR<3->groups can be linked by M to the same or, in cases where M represents more than one intermediate, to the same or different carbon atoms in Y, although more than (ZO)nR<3 -> groups cannot of course be directly bonded to the same carbon atom in Y (and also provided that in such cases Y has at least 2 carbon atoms, while it must be understood that it is within the scope of the invention that Y should have only one carbon atom. M may be the same or different in the repeating units of structure B.

While M may represent one or more direct bonds, it is preferred in the present invention that M is one or more groups of atoms which all provide a connecting chain of atoms; such a chain will usually comprise one or more carbon atoms (which could e.g. comprise carbon atoms in an aryl ring, e.g. benzyl ether) and/or heteroatoms (especially N and/or 0). Particularly preferred examples of chains represented by M are:

where the upper link is to Y and the lower link is to (Z0)nR<3>.

In the structure B, q is preferably one or two, more preferably one (so that M can then represent one, or at most two intermediate terms).

Structure A preferably represents the repeating unit which can be derived by addition polymerization (usually initiated by free radicals) of a polymerizable olefinically unsaturated carboxylic acid. Examples of such acids are maleic acid (or fumaric acid), itaconic acid, the acids with the formulas

Preferably, the structure B represents the repeating unit derived from the polymerization (usually initiated by free radicals) of an addition-polymerizable olefinic unsaturated ester or amide, formed by the reaction of an unsaturated carboxylic acid (or an esterifiable or amidizable derivative thereof such as an acid chloride or anhydride) and a hydroxy compound of the formula HO(ZO)nR3 (to form the ester) or an amine of the formula H2N(ZO)nR3 (to form the amide).

The acid from which structure B can be derived is preferably acrylic acid or methacrylic acid, especially the latter, which, where an ester or amide derivative of methacrylic acid is used, gives rise to the following respective structures for B:

Acidic polymers, of which the oral hygiene preparations according to the present invention are comprised, preferably have a ratio between acid residues and associated polyalkylene oxide residues of approximately 6:1 (where each side chain is polyethylene glycol with a molecular weight of approximately 350, i.e. so-called PEG 350).

Polymers for use in the present invention are more fully described in our aforementioned European Patent Specification No. 182,523 which is hereby incorporated by reference.

In oral hygiene preparations according to the present invention, the at least one polymer present therein is typically in any case at a concentration of approximately 0.05 to 30% by weight of the mixture, the preferred concentration range being from approximately 0.1 to 5% by weight, and preferably 0.2 to 2% by weight.

The concentration of the at least one antibacterial agent in the oral hygiene preparations according to the invention is from 0.001 to 10% by weight of the mixture, the preferred concentration range being from 0.001 to 1.0% by weight, and most preferably 0.01 to 0.1% by weight.

Preferably, the mass of the polymer is greater than the mass of the antibacterial agent in oral hygiene preparations according to the present invention. However, we do not rule out the possibility that there may be larger amounts of antibacterial agents than polymer present.

The oral hygiene preparation according to the present invention typically comprises only one polymer as defined earlier herein, although we do not exclude the possibility that two or more such polymers may be present in the preparation.

The person skilled in the art will be able, by means of simple experiments, to formulate preparations according to the present invention, in which the ratio between antibacterial agents and polymer is such that an unwanted reaction is avoided.

The oral hygiene preparation according to the invention typically comprises a pharmaceutically acceptable carrier which is compatible with the antibacterial effectiveness of the cationic antibacterial agent, e.g. chlorhexidine. To maintain the effectiveness of chlorhexidine, it may be necessary to adjust its concentration in a particular carrier, and an appropriate concentration may

determined by the person skilled in the art by experiments.

Suitable conventional pharmaceutically acceptable carriers which can be used in the oral hygiene preparations according to the invention include water, ethanol (in which water or a water/ethanol mixture will often be a significant component of the carrier); such humectants as propylene glycol, isopropanol, glycerol and sorbitol; such gelling agents as cellulose derivatives, e.g. hydroxypropyl and hydroxyethyl cellulose, polyoxypropylene/polyoxyethylene block copolymers, (so-called "Poloxamers"), for example Synperonic PE 39/70 and PEF 87; certain gel stabilizers such as polyvinyl pyrrolidone; sweeteners such as sodium saccharin; preservatives such as cetylpyridinium chloride, and certain lower alkyl parahydroxybenzoates; surface-active agents such as polyoxy-ethylene isohexadecyl ether (Arlasolve 2 00) and certain colors and flavourings, on the approved EEC or FD&C lists. It will be understood that the aforementioned carrier is chosen so that it does not unreasonably inhibit the effectiveness of the oral hygiene preparation according to the present invention; in particular one does not prefer an anionic material, e.g. an anionic cellulose derivative or an anionic Synperionic.

The oral hygiene preparations of the present invention may be in the form of any conventional pharmaceutically acceptable oral hygiene formulation which contains (and is compatible with) an effective amount of a polymer and an antibacterial agent as previously defined herein. As examples of such formulations can be mentioned i.a. mouthwashes, rinses, rinsing solutions, abrasive and non-abrasive gel dentifrices, tooth cleaners, coated dental floss, coated or impregnated bristles for toothbrushes (natural or synthetic), interdental stimulating coatings, chewing gums, throat lozenges, anti-bad breath remedies, foams and spray.

The invention will now be illustrated by the following examples. The prefix "CT" to a sample no. means a comparative test.

In most of the following examples, the oral bacterium Streptococcus mutans NCTC 10449 was used as the standard bacterium. It was grown in Brain Heart Infusion (BHI) (ex Oxoid) in a Bioflo Model C30 Fermenter. A 750 ml container containing 350 ml of bacterial suspension was used. The bacteria were grown at 37°C with a dilution rate of 0.1 per hour, an air flow of 0.24 litres/min. and a stirring speed of 300 rpm. A sample (approximately 20 ml) of the bacterial suspension was taken out of the fermenter for each experiment. The bacteria were centrifuged for 10 min. at 4,000 rpm, they were resuspended in modified Ringer's salt solution (0.54 g/l NaCl; 0.02 g/l KCl; 0.03 g/l ClCa2; and 0.75 g/l sodium mercapto-acetate), centrifuged again, resuspended and diluted (10-fold) in modified Ringer's salt solutions. The approximate bacterial concentration in the diluted salt solutions was 10<8> per ml.

Streptococcus mitior

NCTC 7864 was grown in 100 ml Brain Heart Infusion broth in batch culture for 24 hours. The culture was then centrifuged for 30 min. at 3,500 rpm and washed twice by resuspending the pellet in saline and centrifugation. The bacterial suspension was then adjusted to approximately 10<7> to 10<8> cells per ml.

Whole saliva was used in additional examples.

Adsorption surfaces

Discs of hydroxyapatite were made by compressing hydroxyapatite powder (tribasic calcium phosphate (Ca10(OH)2(PO4)6(ex. Aldrich)) and sintering at 1,100°C. The discs were reused after heating in an oven at 900°C for 2 hours between experiments.

Application of polymers

Slices of hydroxyapatite were treated for 2 min. at room temperature with a solution (1 wt/vol.%) of a polymer, e.g. Polymer 93W, in a 1:1 (by volume) mixture of industrial methylated spirit/water. The slices were then washed by dipping and shaking them 5 times in a container of running water at about 15°C.

Application of antibacterial agent

Aqueous solutions of chlorhexidine and IMS solutions of alexidine were separately adsorbed for specific time periods on the surfaces of polymer-treated hydroxyapatite discs where appropriate (untreated discs were used in comparative tests). The discs were then washed by dipping and shaking them 5 times in a container of running water.

Pol<y>mers

The polymer referred to herein as "Polymer 93W" is an acidic polymer as described and prepared in Example 5 of our aforementioned EP 182,523. (Other "acidic" polymers described hereafter were prepared by a similar process. Polymer 93W comprises methacrylic acid and PEG350Mat residues in a target ratio of 6:1.

By "PEG350Mat" we mean a polyethylene oxide with a molecular weight of around 350 which has been terminally substituted with methoxy and methacryloyl groups, i.e.

CH2=C(CH3)COO(CH2CH2O)nCH3

where n is about 8.

PEG 150 Mat, PEG1000 Mat and PEG 2000 Mat indicate similar polyethylene oxides with molecular weights of 150, 1000 and 2000 respectively.

The polymer Mil was prepared under the conditions described in example 15 in EP 182,523, except that a hydroxy-end-substituted PEG was used instead of an amino-end-substituted PEG.

Loeffler's methylene blue

95% ethyl alcohol (30 ml), methylene blue (0.3 g) and water (100 ml).

Example 1-2

These examples show that Polymer 93W retains its anti-adhesive properties in the presence of adsorbed chlorhexidine.

Slices of hydroxyapatite were treated with a 1% by weight solution of Polymer 93W and then with certain antibacterial agents for specific periods of time. The discs thus treated were immersed in a bacterial suspension (30 ml) in a Petri dish for 2 hours. The discs were removed from bacterial suspension and were washed by dipping and shaking 5 times in a container of running water. Bacteria adhering to the slides were stained using Loeffler's methylene blue. The reduction in bacterial adhesion was determined by microscopic examination.

The results are shown in table 1.

From Table 1 it can be seen that chlorhexidine and alexidine do not reduce the anti-adhesive properties of Polymer 93W applied to slices of hydroxyapatite.

"%Antiadhesion" ("%AA") is defined by the equation:

It will be understood that (a) where the polymer does not reduce the area of the surface covered with bacteria is: and (b) where the polymer prevents the bacteria from adhering to the surface is:

Similar results were obtained when a sample of a material commonly used for the manufacture of dental prostheses, as described below, was treated with Polymer 93W and chlorhexidine, then exposed to Streptococcus mitior NCTC 7864.

Example 3-5

These examples show that the antibacterial action of chlorhexidine on hydroxyapatite is increased at certain concentrations when used in the presence of Polymer 93W.

Solutions of chlorhexidine were adsorbed onto sterile hydroxyapatite discs that had been treated with Polymer 93W. Cells of S. mutans were taken from a fermenter and diluted 100-fold in BHI agar at 40°C. The inoculated agar was layered on HAP discs.

Agar-coated discs were incubated at 27°C overnight. Bacterial growth throughout the agar was determined on a scale from 0 (no growth) to 10 (control).

Since the surface of all hydroxyapatite discs was brought into contact with the same number of bacteria in each case, the anti-adhesion could not contribute to the observed result, i.e. that only the antibacterial effect was measured. The results in Table 2 reveal that the combination of Polymer 93W and chlorhexidine gave an increased antibacterial effect compared to chlorhexidine per se at the same concentration of chlorhexidine used.

In the comparative tests CT 2, 3, 4 and 5, the discs were not treated with Polymer 93W. Comparative test 2 is a blind test; in comparative test 2A, the disc was exclusively treated with Polymer 93W.

Example 6-9

These examples show the combination of anti-adhesive and anti-bacterial results that can be achieved using a combination of a polymer and chlorhexidine, and that such a combination provides an improvement over the individual components per se.

Sterile slices of hydroxyapatite were treated with a 1 wt/vol.% solution of Polymer 93W, and then with solutions of specific concentrations of chlorhexidine. The slices were incubated in freshly collected whole saliva for 1 hour at 37°C, and washed by dipping and shaking them 5 times in a container of running water. Excess water was removed from the surface of all discs by touching the edge of these with filter paper.

BHI agar containing 0.04 wt/vol.% bromocresol green (to visualize bacterial growth on the white hydroxyapatite disks) was pipetted at 40°C onto the disks, so that a thin film of agar formed on the surface.

The slices were incubated at 37°C overnight. The results are shown in table 3. In the comparative tests 6-10, the treatment with Polymer 93W was omitted. In the comparative test 11, Polymer 93W was used, without chlorhexidine.

From table 3 it can be seen that for certain concentrations of chlorhexidine, e.g. 0.01 and 0.001%, the presence of Polymer 93W will increase the bactericidal and/or bacteriostatic effect thereof. CT11 shows the reduction in bacterial growth resulting from the anti-adhesion properties of the polymer per se.

Example 10- 2 0

These examples show that treatment of the hydroxyapatite discs with certain polymers

a) increases the amount of chlorhexidine adsorbed on these, and

b) improves the retention of the adsorbed chlorhexidine by

subsequent washing treatment.

Preparation of the polymers B3 and B18

Methacryloyl chloride (0.58 mol) was added over 2 h to a mixture of toluene (600 mL), Jeff "360" or "2070" (0.5 mol) and 2,6-lutidine (0.56 mol) cooled in a ice bath. A rich white precipitate formed. The reaction mixture was allowed to stand for 3 hours, and the white precipitate was filtered off and washed with toluene. The filtrate was evaporated under reduced pressure and the residue was kept under vacuum to remove volatiles. The products (80-90% yield) were characterized by infrared and proton magnetic resonance spectroscopy.

The amino-terminated products from both reactions (with terminal butoxy or methoxy groups from "360" and "2070" respectively) were converted separately to the N-methacrylaloyl derivatives thereof and copolymerized with methacrylic acid under the conditions described in Example 11 of the EP patent application , publ. No. 182,523.

Slices of hydroxyapatite were pre-equilibrated in double distilled water for 1 hour. The discs were removed from the water, blotted dry and kept at room temperature for approximately 30 min. A UV reflectance scan was performed on them. The optical density at 266 nm was typically about 0.9. All washers that had an O.D. which was significantly different from this number, was discarded.

The acceptable slices were immersed in a 1% by weight solution of polymer (1:1/IMS: water) for 5 min. The discs were removed from the polymer solution; was washed by immersion and shaking 5 times in a container of running water; were patted dry; allowed to stand for 30 min. and was then scanned.

All the polymer-coated discs were immersed in aqueous (15 ml) chlorhexidine solution (0.02 w/v%) for 1 hour. They were washed as described above, allowed to stand for 30 minutes and then scanned. Then they were placed in a flow-through (250 ml/min) wash tank (1200 ml) for 1 hour; patted dry, allowed to stand for 30 min., and then scanned.

DMAEM:N N-dimethyl-2-aminoethyl methacrylate.

MAA: Methacrylic acid

MA: Maleic acid;

PEG: Polyethylene glycol.

PPG: Polypropylene glycol;

wherein n is such that "2070" has an MV of about 2000 and R = H or CH3 in a ratio of about 7:3; Allyl-PEG 350: Ethoxylated allyl alcohol; except for B10, the methacrylate or methacrylamido derivatives of the side chains shown were present as general structure B;

B10: contains terminal hydroxy groups.

The aforementioned UV scanning was carried out using a Unikam SP1750 Ultraviolet Spectrophotometer.

The "difference in optical density" results shown in Table 4 were determined therefrom.

From tables 4 and 5 it can be seen that the acidic polymers gave a significant increase in the amount of chlorhexidine adsorbed. Many of the hydroxyapatite surfaces coated with an acidic polymer adsorbed more chlorhexidine from a 0.02 w/v% solution than the pure hydroxyapatite surface from a 2 w/v% solution of chlorhexidine, i.e. that an improvement greater than 100 times was observed. The basic (Polymer 73) and amphoteric (Polymer B12) polymers gave no improvement in the amount of chlorhexidine adsorbed. Similarly, polymethacrylic acid produced no increase in adsorbed chlorhexidine, showing that it was the PEG-(or PPG) chains, and not the carboxyl groups, that were responsible for the observed effect.

The results of the washing experiments showed that after 1 hour about 23% of the originally adsorbed chlorhexidine was still adsorbed on hydroxyapatite discs alone, while the amount for polymer-treated discs was about 80%. After overnight washing, the amount of adsorbed chlorhexidine, if any, that remained on the clean HAP discs was below the detection limit; and about 50-60% of the amount of chlorhexidine originally adsorbed on polymer-treated discs was still adsorbed. Polymer-treated discs thus adsorbed more chlorhexidine than bare discs, and it was also less easily washed away from the surface thereof.

Examples 21-29

These examples, in combination with examples 10-20 and 6-9, show an increase in antibacterial properties (at a given chlorhexidine concentration) without the expected increase in staining.

General procedure

Slices of hydroxyapatite were pre-equilibrated in double distilled water for 1 hour. The pre-equilibrated disks were immersed in 1 wt/vol.% aqueous or IMS:water (1:1) solution of polymer for 5 min. They were removed from the polymer solution and washed by dipping and shaking 5 times in a container of running water. The washed slices were then immersed in 15 ml of an aqueous chlorhexidine solution (with a concentration shown in Table 6) for 5 min. The discs were removed from the chlorhexidine solution and immersed in 15 ml of a tea solution for 1 hour at room temperature. The discs were removed from the tea solution and washed as described above. The steps consisting of immersion in chlorhexidine and tea solution and washing were repeated 3 times, using fresh chlorhexidine and tea solution each time. After these 3 rounds, the discs were immersed in tea solution overnight; then they were washed as described above, allowed to dry for 1 hour at room temperature, and the amount of staining produced on them was determined.

The tea solution was prepared by adding 500 ml of boiling water to 2 tea bags. The tea bags were removed after 5 min. and the tea was allowed to cool to room temperature. The tea was filtered with standard filter paper, and stored at 4°C before use.

The colored disks prepared according to the general procedure were scanned using UV/visible reflectance spectrophotometry as described in Examples 10-20, and compared to tea blanks (i.e., no chlorhexidine adsorbed). Figure 1 shows typical UV curves that were obtained. In Figure 1, a = bare slice of hydroxyapatite; b = blank sample of tea; and c, d, e = tea/chlorhexidine treatments at 0.002%, 0.02% and 0.2% concentrations of chlorhexidine, respectively.

The polymers listed in Table 6 (for which the chemical composition is given in Table 5) were evaluated for their effect on the color formation of chlorhexidine in the presence of tea. The polymers were adsorbed separately from 1 wt/vol% IMS/water (1:1) solutions. 0.2, 0.02 and 0.002% by weight aqueous solutions of chlorhexidine were used. The discs were scanned using UV/visible reflectance spectrophotometry, and the O.D. were measured at 266, 410 and 510 nm. O.D. for the tea blanks were also measured at these wavelengths, and these values were subtracted from the slices treated with chlorhexidine or the polymer/chlorhexidine combinations. Table 6 gives the results at 510 nm. They are expressed as ratios relative to the coloring produced by a tea blank test = 1.0. Similar results were obtained at 2 66 nm and 410 nm. In CT 18 the polymer was omitted, i.e. that chlorhexidine per se was used.

From Table 6 it can be seen that at the two higher chlorhexidine concentrations (i.e. 0.2 and 0.02%) the presence or nature of the polymer had no significant effect on the amount of color produced when treating HAP discs. At the lowest concentration (i.e., 0.002%) of chlorhexidine used, most samples show a significant reduction in staining that was equal to or less than the minimal levels produced by exposing the HAP discs to the tea solutions. However, it will be understood from the results in examples 10-20 and 6-9 that with approximately the same staining as the control, more chlorhexidine was adsorbed on the polymers, which exhibited an increased antibacterial effect.

Example 30-31

These examples show the increase in the amount of chlorhexidine adsorbed on a disc of hydroxyapatite treated with a mixture of chlorhexidine and Polymer 93W compared to treating the HAP disc with a chlorhexidine solution per se.

An IMS solution (2 wt/vol%) of Polymer 9 3W was mixed with an appropriate (0.04 wt/vol%) solution of chlorhexidine in water, at a solution ratio of 1:1 by volume. The discs of hydroxyapatite were allowed to stand in the mixture for 1 hour, and were then washed 5 times with water. The amount of chlorhexidine adsorbed on the discs was determined by UV reflectance spectrophotometry as described in Examples 10-20 (the optical density was measured at 266 nm). In the comparative tests 2 0 and 21, the discs were treated for 1 hour with respectively 0.2 and 0.02% solutions of chlorhexidine in a 1:1 mixture by volume of industrial methylated spirit and water.

The results are shown in table 7. From table 7 it can be seen that the treatment of a HAP with Polymeren 93W/chlorhexidine mixture results in more chlorhexidine being adsorbed than from chlorhexidine solution per se.

Example 32-33

These examples demonstrate the increased "kill" of a Polymer93W/chlorhexidine mixture, compared to that observed with pure chlorhexidine solution.

The wafers prepared in Examples 30-31 were washed overnight

n in water, and subjected to an experiment with a covering layer of S. mutans agar. They were placed in a Petri dish and covered with BHI agar (25 ml). S. mutans (100 µl), grown in a fermenter (as described above) and diluted x 100 in Ringer's salt solution, was pipetted onto the agar and spread evenly. The bacteria were grown overnight at 37°C; "lawns" of bacteria and "clear zones" free of bacteria were noted and measured. The results are shown in table 8.

The clear zones, i.e. zones where no growth occurs are shown as 1% of the area of the disc. It will be understood that where "% area of disc where there was no growth" is more than 100, this shows that the inhibition spread to the agar layer outside the circumference of the disc.

From table 8 it can be seen that the mixture has increased antibacterial activity compared to chlorhexidine per se.

Example 34-65

These examples show that the combination of an anti-adhesive compound Ise, Polymer 93W, and chlorhexidine, reduces the amount of staining, compared to chlorhexidine per se, produced on several different surfaces found in the oral environment. These surfaces include the teeth, composite filling materials, e.g. Occlusin and Opalux, and a methacrylate-based resin commonly used in the manufacture of dental prostheses (hereafter for convenience referred to as "PR").

Samples

Remnants of flesh were removed with a scalpel from freshly extracted teeth, and the teeth were then tumbled for 20 min. in 50% sodium hypochlorite solution and washed externally with distilled water. These and teeth containing fillings were ultrasonically treated in alcohol for 10 min., and then dried.

Samples of DR (25 mm x 10 mm x 3 mm) and slices of the aforementioned composite fillings were washed in alcohol and dried.

Solutions

a) 1% and 0.5% solutions of Polymer 93W (lg) in a mixture of industrial methylated spirit (50 ml) and water (50 ml).

b) Solutions (0.2%, 0.02% and 0.002%) of chlorhexidine in water.

c) Appropriate mixtures of Polymer 93W and chlorhexidine were obtained d by mixing equal volumes of solutions from a) and b) to g

in the concentrations shown in the following tables.

d) Human saliva was obtained by taking samples (20 ml) from each of 6 volunteers, centrifuging for 20 min. at 2,500 rpm and test

vein together.

e) Tea solutions were prepared by boiling a sample (8 g) of a commercial type of tea in distilled water (80 ml) for 2 min.,

cool the product to room temperature and filter away the remaining tea leaves.

Evaluation

All surfaces were treated for 10 min. with a sample of saliva. Excess saliva was washed away.

In Examples 34-49, the surface was subjected to a first treatment for 10 min., the surface was washed with distilled water, subjected to the second treatment for 10 min., rinsed and then immersed in the tea solution for 1 hour; the procedure was repeated, the sample was left in the tea solution overnight and the entire procedure repeated every day for 5 days.

In examples 50-65, the 5-day procedure above was repeated, except that the first treatment took place for 5 min. and the second treatment was omitted, the samples were treated with appropriate mixtures of Polymer 93W and chlorhexidine.

The coloring of the surfaces was compared visually with the same surface treated only with water and judged according to the following scale.

Scale

0: No staining (i.e. water control taken as 0, although there was slight discoloration);

1: Slight discoloration;

2: Moderate discoloration;

3: Strong discoloration;

4: Very strong discolouration.

In tables 9, 10 and 17

OC = Occlusin

OP = Opalux

T = Tooth

PR = Prosthetic resin

A = 0.5% Polymer 93W

AA = 1% Polymer 93W

B = Water

X = 0.1% chlorhexidine

XX = 0.2% chlorhexidine

Y = 0.01% chlorhexidine

YY = 0.02% chlorhexidine

Z = 0.001% chlorhexidine

ZZ = 0.002% chlorhexidine

W = 0.0001% chlorhexidine

From table 9 it can be seen that a low concentration (e.g. 0.002%) of chlorhexidine staining of dental fillings, teeth or prosthetic resin is reduced, if the surface thereof is first treated with a specific polymer. It can also be seen (Examples 46-49) that where the surface is treated with a chlorhexidine solution and then with Polymer 93W, the discoloration is reduced to the control level.

Table 10 reveals the results obtained by treating Occlusin and Opalux surfaces with mixtures of chlorhexidine and Polymer 93W. There is a significant reduction in the discoloration of Occlusin, to the control level at chlorhexidine concentrations of 0.01% and less; a similar tendency is evident with Opalux.

Table 11 shows the results obtained when treating tooth surfaces and a prosthetic resin with a mixture of chlorhexidine and Polymer 93W. The trend in the reduction in discoloration is similar to that observed with Occlusin and Opalux.

Where a tooth with an Occlusin implant was submitted to the evaluation, the tooth and the implant were slightly discolored to the same extent, so that the contours of the implant were further reduced.

Claims (12)

1. Oral hygiene preparation, characterized in that it comprises (i) 0.001-10% by weight of at least one cationic antibacterial agent; and (ii) 0.05-30% by weight of at least one polymer bearing associated polyalkylene oxide side chains, the polymer comprising one or more repeating units of general structure A and one or more repeating units of general structure B wherein X, which in the repeating units of structure A may be the same or different, and Y, which in the repeating units of structure B may be the same or different, are hydrocarbyl, or substituted hydrocarbyl residues, which provide a backbone for the polymer; Z is -CHR^CHR<2-> or -(CH2)m-; in which R<1>, as in the same repeating unit with the structure B reaches n or q is 2 or more or in different repeating units of the structure B may be the same or different, is hydrogen or a hydrocarbyl group; and R<2>, as in the same repeating unit with the structure B reaches n or q is 2 or more or in different repeating units of the structure B may be the same or different, is hydrogen or a hydrocarbyl group; except that R<1> and R2 in a single unit-CHR<x->CHR<2->0- cannot both be hydrocarbyl; R<3>, which in the same repeating unit of structure B when q is 2 or more or in different repeating units of structure B may be the same or different, is hydrogen or a hydrocarbyl group or an acyl group derived from an alkanoic acid having up to 5 carbon atoms; m, when present, is a number from 3 to 10; n is a number from 1 to 60; and p is a number from 1 to 4; and q is a number from 1 to 4; all CO 2 H groups are linked via one or more intermediates L to the hydrocarbyl residue X, and in cases where p is 2 to 4 may be linked with L to the same or different carbon atoms in X; L may be the same or different in the repeating units of the structure A and selected from one or more direct bonds and one or more groups of atoms, all the groups forming a chain of one or more atoms to link a CO 2 H group with X except that more than two CO 2 H groups cannot be directly bonded to the same carbon atom in X; all (Z0)nR3) q groups are linked via one or more intermediates M to the hydrocarbyl residue Y, and in cases where q is 2 to 4 may be linked with M to the same or different carbon atoms in Y; M can be the same or different in the repeating units of the structure B, and is selected from one or more direct bonds and one or more groups of atoms, all the groups forming a chain of one or more atoms to bind together a (ZO)nR <3->group with Y, except that more than two (ZO)nR<3->groups cannot be directly bonded to the same carbon atom in Y; the ratio of the number of CO 2 H groups to the number of (ZO) n R < 3 -> groups, in particular, where Z is -CH 2 CH 2 -, is within the range of 1:20 to 20:1. 2. Oral hygiene preparation according to claim 1, characterized in that the cationic antibacterial agent is a polybiguanide or a salt thereof. 3. Oral hygiene preparation according to claim 2, characterized in that the polybiguanide is a bis-biguanide. 4. Oral hygiene preparation according to claim 3, characterized in that the bis-biguanide is chlorhexidine. 5. Oral hygiene preparation according to claim 1, characterized in that, where Z is -CHR^-CHR<2> both R<1> and R2 are hydrogen. 6. Oral hygiene preparation according to claim 1, characterized in that R3 is methyl. 7. Oral hygiene preparation according to claim 1, characterized in that, in the structure A, L is a direct bond, -CH2-, -CH2-CH2-, -CH2-CH =, -NH-CO-, -CONHCH(CH3) - or - CONHCH(OH)-. 8. Oral hygiene preparation according to claim 1, characterized in that, in the structure A, p is 1 or 2. 9. Oral hygiene preparation according to claim 1, characterized in that, in the structure B, M is C00 or CONH. 10. Oral hygiene preparation according to claim 1, characterized in that, in structure B, g is 1 or 2. 11. Oral hygiene preparation according to claim 1, characterized in that A or B represents the repeating unit which can be derived by addition polymerization of a polymerizable olefinic unsaturated carboxylic acid or, respectively, an ester or an amide derivative thereof. 12. Oral hygiene preparation according to claim 11, characterized in that the polymerizable olefinically unsaturated carboxylic acid is acrylic acid or methacrylic acid.