WO1999038481A1

WO1999038481A1 - Method for cleaning dentures

Info

Publication number: WO1999038481A1
Application number: PCT/US1998/001712
Authority: WO
Inventors: Steven Wayne Moore; Howard David Hutton; Stephen Oliver Flattery; Mark Ieuan Edwards
Original assignee: The Procter & Gamble Company
Priority date: 1998-01-29
Filing date: 1998-01-29
Publication date: 1999-08-05
Also published as: EP1049449A1; AU2347999A; WO1999038482A1; AU6255098A; WO1999038482A8

Abstract

The present invention relates to a method for cleaning dentures, and more particularly to a method requiring a small amount of liquid cleanser and made more effective by heating, particularly by microwave, to a temperature in the range from 40 °C to 90 °C. The method provides rapid, convenient cleaning and excellent plaque removal.

Description

METHOD FOR CLEANING DENTURES

TECHNICAL FIELD

The present invention relates to a method for cleaning dentures, and more particularly to a method requiring a small amount of liquid cleanser, made more effective by heating, particularly by microwave. The method provides rapid, convenient cleaning and excellent plaque removal.

BACKGROUND OF THE INVENTION

Tablets and powders for cleansing dentures and the like are well known in the art. The aim of a denture cleanser product is to clean the denture as fully and as quickly as possible and especially to remove the accumulation of plaque, mucilaginous and bacterial deposits which collect while the denture is being worn. To wear a ^η denture which has not been completely cleaned of plaque and bacterial deposits is not only unhygienic but can also within a short space of time result in a detrimental effect on the mucous membrane. Moreover bacterial deposits can lead to so-called bacterial corrosion of the plastics material used to produce the denture with consequent colour change and malodour formation.

Denture cleansers are most frequently sold in tablet or powder form and are intended to be dissolved in warm water to create a cleansing bath in which the denture is soaked, typically for a period of from five to twenty minutes, or even for several hours, such as overnight. Particularly when it is desired to cleanse the denture through the day, the extended cleaning time can be a considerable inconvenience. Much shorter soak times are usually detrimental to performance.

US 4,511,486 describes a method of cleaning dentures using an alcoholic, aerated foam. The foam compositions comprise high levels of alcohol. Cleansing times are less than one minute and described effects include the stripping away of loosely adhering plaque.

US 4,701,223 and US 4,807,649 describes liquid and gel denture cleansing compositions which allegedly improve on those of US 4,511,486 above, particularly in respect of plaque and calculus removal. Cleansing times are generally less than one minute, preferably less than 30s. Critical to the invention, however, is the combination of an anionic surfactant, especially a fatty alcohol sulphate, and an elevated level of a chelating agent.

There have also been suggestions in the prior art to use elevated temperatures for cleaning. US 5,201,411 and US 5,314,543 describe an apparatus and method for cleaning of dentures in which the denture, along with a denture cleanser, is immersed in water in a covered container which is then heated in a microwave. The period of heating is sufficient to provide a hot cleaning fluid without bringing it to a boil; two minutes is suggested for a 'regular' microwave setting when a typical 6 to 8 ounces (180 to 225g) of water is used. The denture cleanser can be a powder or a liquid but it is intended to be one which will quickly mix with and dissolve in the water to form a bath in which the denture is immersed.

Despite all the foregoing, there remains a need for improved methods for removing stains, debris and plaque from dentures, employing mild formulations which leave a pleasant taste on the denture and yet which are convenient to use.

It has now been discovered that relatively small amounts of a liquid cleaning composition can be made to perform very well both on stains and against plaque by contacting the denture with the composition, for example by spraying the composition onto the denture, and heating the composition to a temperature in the range from about 40°C to about 90°C, especially by microwaving the composition and denture. The heating process is very effective at loosening accumulated plaque which is then readily removed when the denture is rinsed.

SUMMARY OF THE INVENTION

The invention herein provides a method for cleaning a denture comprising: a) treating the denture by contacting it with from about 0.1 to about 50g of a liquid cleaning composition, which comprises an effective proportion of a cleaning agent, with the cleaning composition being heated to a temperature in the range from about 40°C to about 90°C; and b) thereafter rinsing the denture. Although many ways of delivering the heat to the denture can be used, the preferred method is to use a domestic microwave oven. In this way the denture can be cleaned in as little as 20 seconds to about a minute. A 'defrost' setting is preferably used. Preferred cleaning compositions comprise cleaning agents selected from bleaches, surfactants and solvents. Highly preferred herein are sprayable liquid compositions which can uniformly coat the denture without substantially dripping off after application. The cleaning composition can also suitably be provided in a pre-dosed, re-sealable pouch into which the denture can also be placed for the purpose of cleaning.

All percentages and proportions herein are by weight unless otherwise indicated. DETAILED DESCRIPTION OF THE INVENTION

Definitions

By "denture" is meant any device that is manufactured for placement within the mouth over a period of from a few hours to several days or more but that may be temporarily removed from it by the wearer for the purpose of cleaning or hygienic treatment. This includes artificial teeth and also orthodontic brackets, bridges and the like. The methods of cleaning herein take place outside of the mouth..

By "liquid cleaning composition" herein is meant a composition comprising one or more cleaning agents, other than water, which can be made to flow at 25°C at a moderate shear rate, such as less than 10 s^"1; it includes both classical liquids and gels which may appear to be solid at very low shear rates.

The present cleaning compositions comprise an "effective proportion" of a cleaning agent. An "effective proportion" of a cleaning agent is any proportion capable of measurably improving soil, stain or plaque removal from the denture, compared to the use of water alone. This amount will vary depending on the cleaning agent(s) employed. In general, however, the total amount of cleaning agent is from about 1 to 100%, preferably from about 10 to about 40% of the cleaning composition, which is preferably an aqueous composition.

By "microwaving" herein is meant exposing the denture and compositions to microwave electromagnetic radiation. This is by any conventional means such as by placing the substrate in a typical microwave such as used in homes and microwaving the substrate for a sufficient time. Microwaves have an electromagnetic radiation wavelength of from about 1cm to about lm, preferably from about 3 cm to about 30cm, more preferably from about 11cm to about 13cm. See Aust. J. Chem., 1995, 48 [10], 1665-1692, Developments in Microwave-Assisted Organic Chemistry, by Strauss and Trainor. By "defrost setting" herein is meant a microwave oven setting in which the oven is made to operate at below its maximum setting such that the maximum achievable energy delivery is less than 500W, preferably less than 300W. By "intermittent" energy or heating herein is meant the application of a heat or energy source at repeated intervals with gaps of at least 2s, preferably at least 5s between each application.

Cleaning Compositions The present cleaning compositions comprise an effective amount of a cleaning agent. Preferred cleaning compositions comprise cleaning agents selected from bleaches, bleach activators, surfactants, solvents and mixtures thereof The total amount of cleaning agent is generally from about 1 to 100%, preferably from about 10 to about 40%, more preferably from about 15 to about 30% of the cleaning composition. The cleaning composition is preferably an aqueous composition and optionally comprises additional ingredients such as thickeners, flavours, chelating agents and film-forming oils which can be useful in resisting regrowth of plaque.

In general the pH of the composition will be in the range of from about 3 to about 10 and will be chosen to enhance the performance and/or stability of the chosen ingredients. Where the cleaning composition comprises hydrogen peroxide, the pH is preferably in the range of from about 3 to about 6, more preferably from about 3.5 to about 5.

In the methods of the invention, less than about 50g of the composition is used, which is insufficient in which to fully immerse a typical denture. Accordingly, for best performance, it is preferred that the composition has a yield stress at 25°C of at least about 2 Pa, more preferably at least about 5 Pa. In this way the composition, once applied to the denture is inhibited from running off. Preferably however, the composition is for convenience a sprayable composition having a viscosity, at 25 °C, of less than about 10 Pa.s at a shear rate of 10 s^"1. The liquid composition is preferably also pseudoplastic, or shear thinning, having a viscosity, at 25°C, of greater than about 20 Pa.s at a shear rate of 0.1 s^"1. More preferably still, the liquid composition is also thixotropic to assist spreading of the composition onto the denture after being sheared, but allowing it to thicken, or even set, and avoid run-off, shortly thereafter.

The preferred cleaning agents and additional optional ingredients will now be described in turn. Bleaching Agents - A preferred cleaning agent for use in the present cleaning composition is a bleaching agent. Suitable bleaching agents for use herein are listed below:

Hydrogen Peroxide Source - The compositions of the present invention preferably contain a source of oxygen bleach, preferably a source of hydrogen peroxide with or without a selected bleach activator. The preferred source of hydrogen peroxide used herein can be any convenient source. The source of hydrogen peroxide can also be any common hydrogen-peroxide releasing salt, such as sodium perborate or sodium percarbonate. For example, perborate, e.g., sodium perborate, sodium carbonate peroxyhydrate or equivalent percarbonate salts, sodium pyrophosphate peroxy-hydrate, urea peroxyhydrate, or sodium peroxide can be used herein. Sodium perborate monohydrate and sodium percarbonate are particularly preferred. Mixtures of any convenient hydrogen peroxide sources can also be used. Especially preferred for use herein is hydrogen peroxide itself, used as its commercially available 30% aqueous solution. Hydrogen peroxide sources are illustrated in detail in Kirk Othmer Review on Bleaching and include the various forms of sodium perborate and sodium percarbonate and modified forms.

Another source of hydrogen peroxide is enzymes. Examples include Lipoxidase, glucose oxidase, peroxidase, alcohol oxidases, and mixtures thereof.

Other peroxygen bleaches preferred for use herein are the alkyl and organomineral hydroperoxides disclosed in EP-A-812,906. Diacyl Peroxide Bleaching Species - The composition of the present invention may comprise diacyl peroxide of the general formula: RC(O)OO(O)CR¹ wherein R and R¹ can be the same or different and are hydrocarbyls, preferably no more than one is a hydrocarbyl chain of longer than ten carbon atoms, more preferably at least one has an aromatic nucleus. Examples of suitable diacyl peroxides are selected from the group consisting dibenzoyl peroxide, dianisoyl peroxide, benzoyl glutaryl peroxide, benzoyl succinyl peroxide, di-(2-methybenzoyl) peroxide, diphthaloyl peroxide, dinaphthoyl peroxide, substituted dinaphthoyl peroxide, and mixtures thereof, more preferably dibenzoyl peroxide, dicumyl peroxide, diphthaloyl peroxides and mixtures thereof. A particularly preferred diacyl peroxide is dibenzoyl peroxide. Chlorine Bleach - Any chlorine bleach typically known in the art is suitable for use herein. Preferred chlorine bleaches for use herein include sodium hypochlorite, lithium hypochlorite, calcium hypochlorite, chlorinated trisodium phosphates, and mixtures thereof. For more about chlorine bleaches see Surfactant Science Series, Vol. 5, Part II, pages 520-26. Suitable levels of bleaching agents for use herein are from about 1 to about 20%, preferably from about 2 to about 15%, more preferably from about 3 to about 10%.

Bleach Activators - Numerous conventional bleach activators are known. See for example activators referenced in U.S. Patent 4,915,854, issued April 10, 1990 to Mao et al, U.S. Patent 4,412,934 and WO 96/19563. Highly preferred for use herein is tetraacetyl ethylene diamine (TAED) which is highly effective without giving rise to adverse flavours. Nonanoyloxybenzenesulfonate (NOBS) or acyl lactam activators may be used, and mixtures thereof with TAED can also be used. See also co-pending application PCT US97/12217, incorporated herein by reference in its entirety, for other bleach activators. Suitable levels of bleaching activators for use herein are from about 0.5 to about 10%, preferably from about 1 to about 5%.

Solvent - An organic solvent is preferably present in the compositions of the present invention. The solvents are useful for dissolving the bleach activator and flavour oils, for removing tobacco stains such as tar, and are believed to assist in plaque removal. Preferred solvents are selected from the group consisting of alkanolamines, N-alkyl pyrrolidones, such as N-ethyl pyrrolidone, diacetone alcohol, long chain (greater than Cg) alkyl ethers, cyclic alkyl ketones, and mixtures thereof. Preferred for use herein are alkanolamines, especially N-methylethanolamine. High levels of very volatile solvents such as ethanol, are preferably avoided. Suitable levels of solvent for use herein are from about 0.2 to about 20%, preferably from about 0.5 to about 10%. Preferred levels of alkanolamine solvents are from about 0.1 to about 1.5%.

Surfactants - A highly preferred cleaning agent for use herein is a surfactant or mixture of surfactants. Nonlimiting examples of surfactants useful herein include the conventional C11-C18 alkyl benzene sulfonates ("LA.S") and primary, branched-chain and random C\Q- C20 alkyl sulfates ("AS"), the C JQ-CIS secondary (2,3) alkyl sulfates of the formula CH₃(CH₂)_x(CHOSO3-M⁺) CH3 and CH3 (CH₂)_y(CHOSO₃-M⁺) CH₂CH₃ where x and (y + 1) are integers of at least about 7, preferably at least about 9, and M is a water- solubilizing cation, especially sodium, unsaturated sulfates such as oleyl sulfate, the CJO- Cj8 alkyl alkoxy sulfates ("AExS"; especially EO 1-7 ethoxy sulfates), CJO-CIS alkyl alkoxy carboxylates (especially the EO 1-5 ethoxycarboxylates), the \Q-C\ glycerol ethers, the Cjo-Ci8 alkyl polyglycosides and their corresponding sulfated polyglycosides, and C12-C18 alpha-sulfonated fatty acid esters.

The conventional non-ionic and amphoteric surfactants such as the C12-C18 alkyl ethoxylates ("AE") including the so-called narrow peaked alkyl ethoxylates and C6-C12 alkyl phenol alkoxylates (especially ethoxylates and mixed ethoxy/propoxy), C12-C18 betaines and sulfobetaines ("sultaines"), and the like, can also be included in the overall compositions. C10-C20 conventional soaps may also be used. If high foaming is desired, the branched-chain C\Q-C\β soaps may be used. Mixtures of anionic and non-ionic surfactants are especially useful. Other conventional, useful surfactants are listed in standard texts. Preferred for use herein is at least one non-ionic surfactant which is able to provide a structure to the liquid composition such that it is pseudoplastic and thixotropic. Preferred liquid compositions also have a yield stress of at least about 2 Pa, more preferably at least 5 Pa. Suitable for this purpose are the alcohol ethoxylates such as Cι₂-Cι₃ pareth-3 and Cι₄-Ci5 pareth-7 available as Neodol® 23-3 and Neodol® 45-7 respectively from Shell.

Preferred for use herein, especially when both a hydrogen peroxide source and a bleach activator are employed, are mixtures of two non-ionic surfactants of differing HLB, optionally together with an anionic surfactant, as described in EP-A-598, 170. A particularly preferred surfactant system uses one non-ionic surfactant having a HLB greater than 11 and the other having a HLB less than 9. Without wishing to be bound by theory, it is believed that the dual non-ionic system absorbs the hydrophobic bleach activator into a mixed micelle, keeping it separate from the bleach activator until the emulsion is broken upon heating.

Suitable levels of surfactant for use herein are from about 1 to about 30%, preferably from about 5 to about 20%. Care should be taken in selection of surfactants to avoid those with excessively 'soapy' tastes.

Film-forming oil - A desirable, optional ingredient for use in the present cleaning composition is a film-forming oil. By "film-forming oil" herein is meant a material, or mixture of materials, that is insoluble in or immiscible with water at 40°C and is liquid at 40°C and that will spread on an acrylic plate at that temperature. More particularly the oil preferably has a contact angle with acrylic of less than 90°, more preferably less than 70°, and especially less than 50° at 40°C. Suitable film-forming oils include hydrocarbons, fluorocarbons, mineral oils and silicone oils. Highly preferred herein are silicone oils. By "silicone oil" is meant a polymer with a silicon or siloxane backbone. Suitable classes of silicone oils include, but are not limited to, dimethicones, dimethiconols, dimethicone copolyols and aminoalkylsilicones.

A highly preferred silicone oil is a dimethicone copolyol or aminoalkylsilicone antiplaque agent such as those described in WO 96/19563 and WO 96/19554.

Preferred for use herein are alkyl or alkoxy dimethicone copolyols having the formula (I): 99/38481

wherein X is selected from hydrogen, alkyl, alkoxy and acyl groups having from about 1 to about 16 carbon atoms, Y is selected from alkyl and alkoxy groups having from about 8 to about 22 carbon atoms, n is from 0 to about 200, m is from about 1 to about 40, q is from about 1 to about 100, the molecular weight of the residue (C2H4θ-)_x(C3HgO-)yX is from about 50 to about 2000, preferably from about 250 to about 1000 and x and y are such that the weight ratio of oxyethylene:oxypropylene is from 100:0 to 0:100, preferably from 100:0 to about 20:80.

In preferred embodiments, the dimethicone copolyol is selected from C 2 to C20 alkyl dimethicone copolyols and mixtures thereof. Highly preferred is cetyl dimethicone copolyol marketed under the Trade Name Abil EM90 from TH. Goldschmidt.

When used, the silicone antiplaque agent is generally present in a level of from about 0.0001% to about 5%, preferably from about 0.1% to about 3%, more preferably from about 0.2% to about 1.5% by weight.

An optional, additional ingredient of the liquid compositions of the invention is a silicone surfactant having the general formula (I)

99/38481

wherein X is selected from hydrogen, alkyl, alkoxy and acyl groups having from about 1 to about 16 carbon atoms, Y is CH₃, q is 0, n is from about 1 to about 100, m is from about 1 to about 40, the molecular weight of the residue (C2H4θ-)_x(C₃HgO-)yX is from about 50 to about 2000, and x and y are such that the weight ratio of oxyethylene.oxypropylene is from about 100:0 to about 0: 100.

The silicone surfactant, itself a dimethicone copolyol, assists in dispersion of the silicone antiplaque agent in aqueous media whilst still allowing the antiplaque agent to deposit onto dentures. In preferred embodiments, the silicone surfactant is selected from dimethicone copolyols having a HLB value in the range from about 8 to about 14, more preferably from about 9 to about 12, and mixtures thereof. A suitable example of such a material is that marketed under the Trade Name Silwet L7230. The silicone surfactant is generally present in a level of from about 0.0001% to about 5%, preferably from about 0.1 to about 3%, more preferably from about 0.3% to about 1.5% by weight of the composition. In general, the level of the silicone surfactant should be chosen such that the ratio of silicone surfactant to the silicone antiplaque agent is from about 0.5:1 to about 5:1, more preferably from about 0.8:1 to about 3:1, most preferably from about 0.9:1 to about 2:1 by weight.

Thickeners - Thickeners for use herein can be selected from polyacrylates, clays, gums, carboxymethyl cellulose, and mixtures thereof. Preferred for use herein are polyacrylates. If clays are used then care should be taken over the selection to avoid unwanted decomposition of hydrogen peroxide by metal ions in the clay.

Bleach catalysts - If desired, cleaning compositions herein may additionally incorporate a catalyst or accelerator to further improve bleaching. Any suitable bleach catalyst can be used. Suitable catalysts are described in co-pending application PCT/US97/12217. Enzymes - Suitable enzymes include proteases, amylases, lipases, cellulases, peroxidases, and mixtures thereof of any suitable origin, such as vegetable, animal, bacterial, fungal and yeast origin. Preferred selections are influenced by factors such as pH-activity and/or stability optima, thermostability, and stability to active bleach, detergents, builders and the like. In this respect bacterial or fungal enzymes are preferred, such as bacterial amylases and proteases, and fungal cellulases. In practical terms the compositions herein may comprise from about 0.001% to about 5%, preferably 0.01%-1% by weight of a commercial enzyme preparation. Protease enzymes are usually present in such commercial preparations at levels sufficient to provide from about 0.005 to about 0.1 Anson units (AU) of activity per gram of composition. Flavour oils - The cleaning compositions herein preferably comprise a flavour oil which imparts a fresh or pleasant taste to the denture. When the composition is designed for use in a microwave, spray-dried flavour oils, which typically comprise a starch carrier are preferably avoided. Starches absorb microwave energy very efficiently and can become caramelised. Suitable oils such as peppermint oil are well known in the art, they are preferably used at a level of from about 0.001 to about 2%, more preferably at a level of from about 0.01 to about 1% by weight of the composition.

Chelating Agents - The cleaning compositions herein may also optionally contain one or more chelating agents for alkaline earth or transition metal ions. Such chelating agents can be selected from the group consisting of amino carboxylates, amino phosphonates, polyfunctionally-substituted aromatic chelating agents and mixtures thereof, all as hereinafter defined.

Amino carboxylates useful as optional chelating agents include ethylenediamine- tetracetates, N-hydroxyethylethylenediaminetriacetates, nitrilo-triacetates, ethylenediamine tetraproprionates, triethylenetetra-amine-hexacetates, diethylenetriaminepentaacetates, and ethanoldiglycines, alkali metal, ammonium, and substituted ammonium salts therein and mixtures therein.

Polyfunctionally-substituted aromatic chelating agents are also useful in the compositions herein. See U.S. Patent 3,812,044, issued May 21, 1974, to Connor et al. Preferred compounds of this type in acid form are dihydroxydisulfobenzenes such as 1,2-dihydroxy- 3,5-disulfobenzene. A preferred biodegradable chelator for use herein is ethylenediamine disuccinate ("EDDS"), especially the [S,S] isomer as described in U.S. Patent 4,704,233, November 3, 1987, to Hartman and Perkins.

If utilized, these chelating agents will generally comprise from about 0.1% to about 10%, more preferably from about 0.1% to about 3.0%, by weight of the cleaning compositions herein.

Methods

The methods herein comprise, as essential features: a) treating the denture by contacting it with from about 0.1 to about 50g of a liquid cleaning composition, which comprises an effective proportion of a cleaning agent, with the cleaning composition being heated to a temperature in the range from about 40°C to about 90°C; and b) thereafter rinsing the denture. 99/38481

11

It is, of course, preferred that all parts of the denture which are desired to be cleaned, are contacted with the liquid composition at some point during the cleaning process, generally the whole denture will be contacted with the liquid composition. Highly preferred for use herein is a sprayable liquid composition, enabling the denture to be completely or nearly completely coated with the liquid composition before heat is applied. This is not always essential however. Preferred compositions of the invention foam when heated, especially to temperatures greater than 60°C, and more particularly when the heating is effected by microwaving. In such cases it may be sufficient to stand the denture in a pool of the composition and allow the composition to foam up over the denture. In general, however, if the denture comprises a metal portion, at least the metal portion should be coated first to prevent arcing.

Alternatively the composition can be brushed or sponged onto the denture or it can be supplied as a coating on the interior of a resealable pouch into which the denture is inserted. When the pouch is heated the composition can foam or drip over the denture. The pouch is advantageous in that it can be pre-dosed at manufacture with a suitable amount of liquid composition and may conveniently be used for placing the denture in a heat source such as a microwave oven, dishwasher or even a conventional gas or electric oven. Other containers, such as conventional denture baths, may also be used for holding the denture bath and composition. A preferred denture bath for this purpose, having a double outer wall which remains cool to the exterior even though the interior is hot, is described in co-pending application GB 97/23826.5. Where commercial denture baths are used then it is preferred that any internal cradles supplied are not used since these can allow the liquid composition to drain away from the denture before the cleaning process is complete. Suitable amounts of the cleaning composition for use in the method of the invention are from about 0.1 to about 50g, preferably from about 1 to about 20g, more preferably from about 2 to about lOg. Although cleaning can be effected with quite low amounts of the composition the larger amounts are useful as heat transfer media and for providing a heat sink to avoid overheating of the denture, particularly when microwaved. The composition can of course, if required, be manufactured as a concentrate to be diluted prior to use.

The cleaning composition is heated to a temperature in the range from about 40°C to about 90°C, higher temperatures can run the risk of deforming the denture, which are typically made from an acrylic. Preferably the cleaning composition is heated to a temperature in the range from about 55°C to about 85°C, more preferably from about 65°C to about 75°C. The temperature can be monitored by thermometer or by use of a 99/38481

12

temperature sensitive strip, the latter can conveniently be incorporated into purpose designed apparatus such as the pouches and baths mentioned above.

Included within the scope of the present invention are methods whereby the liquid composition is heated before being applied to the denture. Generally this is less convenient than applying the composition to the denture first since it then requires handling the hot fluid.

Any convenient energy source can be used for heating the denture, provided it is safe to the denture. Suitable energy sources for use herein are microwaves, dishwashers, conventional ovens and hot water baths such as a wash basin filled with hot water. Where a hot water bath is used the denture and liquid composition is preferably enclosed within a waterproof, heat conducting container to avoid the composition being washed away from the denture before effective cleaning takes place. Where the composition is a slowly soluble, stiff gel however, even this may be unnecessary.

Highly preferred herein is a method wherein the heat is supplied by a microwave energy source, particularly by a domestic microwave oven. The oven is preferably used on a 'defrost' setting. The lower energy settings of a domestic microwave oven have the added advantage of providing an intermittent energy source. Intermittent heating has been found to be beneficial in plaque removal. Without wishing to be bound by theory it is believed that it introduces stress into the plaque which cause it to become loosened from the denture.

The denture can be treated with the liquid cleaning composition over a period of from a few seconds to several minutes or even an hour. In general, only a short exposure is necessary, however in certain circumstances a longer period, such as an entire dishwasher cycle may be convenient. In preferred methods herein, the denture is treated with the liquid cleaning composition over a period of from about 5 s to about three minutes, preferably from about 30s to about 90s and more preferably from about 30s to about one minute. In an especially preferred method according to the invention the denture is contacted with the liquid cleaning composition and microwave energy is applied intermittently over a period of from about 5s to about 2 minutes, preferably from about 30s to about 90s.

After treating the denture with the cleaning composition it should then be rinsed to remove any residue from the composition and loosened soil. The denture can optionally be brushed at this point. 13

The following examples illustrate sample cleaning compositions and methods according to the present invention.

Example Compositions 1 to 7

1 Silwet® L7230, commercially available from Witco The cleaning compositions of Examples I - V are prepared by mixing the surfactants and water with a standard three blade propeller at 500rpm for five minutes. The pH of the surfactant mix is adjusted into the range of from pH 3.8-4.0 using dilute sulphuric acid and where used, the TAED bleach activator, flavour oil and silicones are added. An emulsion is formed under high shear mixing using a Turax® T25 Ultra Disperser with a S25N-25F dispersing element at greater than lOOOrpm for five minutes. The hydrogen peroxide is added in and mixing is continued for a further 2 minutes on a propeller stirrer at 500rpm. Finally, the solvent is added. The precise amount of solvent added may be varied from those shown in order to adjust the composition rheology.

Example 8 Each of example compositions 1 to 7 was used in the following method. A hand operated spray gun as used to deliver 3.5g of the composition into the bottom of a Kukident® commercial denture bath, as marketed in Italy. A full denture was then placed into the bath and a further 3.5g of the composition was sprayed evenly over the top of the denture. The bath was cover with its lid and placed into a commercial, 800W microwave oven. The oven was then run on its defrost setting for a period of one minute after which the bath and denture were allowed to stand for a further 30s to one minute before removing the denture and rinsing under running water. Excellent plaque removal was observed, as determined by visual grading against a 1-10 scale.

Claims

1. A method for cleaning a denture comprising: a) treating the denture by contacting it with from 0.1 to 50g of a liquid cleaning composition, which comprises an effective proportion of a cleaning agent, with the cleaning composition being heated to a temperature in the range from 40┬░C to 90┬░C; and b) thereafter rinsing the denture.

2. A method according to Claim 1 wherein the cleaning composition comprises from 10 to 40% of the cleaning agent.

3. A method according to Claim 1 wherein the heat is supplied by a microwave energy source.

4. A method according to Claim 3 wherein the microwave energy is applied intermittently over a period of from 5 s to 2 minutes, preferably from 30s to 90s.

5. A method according to Claim 3 or Claim 4 wherein the microwave energy source is a domestic microwave oven used on a defrost setting.

6. A method according to any preceding claim wherein the cleaning composition is heated to a temperature in the range from 55┬░C to 85┬░C, preferably from 65┬░C to .75┬░C.

7. A method according to any preceding claim wherein the cleaning composition comprises a bleaching agent.

8. A method according to Claim 6 wherein the bleaching agent is hydrogen peroxide.

9. A method according to Claim 7 or Claim 8 wherein the cleaning composition further comprises a bleach activator.

10. A method according to Claim 9 wherein the bleach activator is TAED.

11. A method according to any preceding claim wherein the cleaning composition comprises a surfactant or mixture of surfactants.

12. A method according to Claim 11 wherein the cleaning composition comprises a mixture of two non-ionic surfactants, one having a HLB greater than 11 and the other having a HLB less than 9.

13. A method according to any preceding claim wherein the cleaning composition comprises an organic solvent.

14. A method according to Claim 13 wherein the organic solvent is N-methyl- ethanolamine.

15. A method according to any preceding claim wherein the cleaning composition comprises from 0.01% to 1% flavour oil.

16. A method according to any preceding claim wherein the cleaning composition is a sprayable liquid.

17. A method according to any preceding claim wherein the liquid cleaning composition is both pseudoplastic and thixotropic.

18. A method according to Claim 17 wherein the liquid cleaning composition has a yield stress of at least 2 Pa.