United States Patent 3,325,368 DENTIFRICE COMPOSITION George Dennis Wood, Bedfont, Feltharn, England, as-
signor to Lever Brothers Company, New York, N.., a corporation of Maine No Drawing. Filed June 18, 1964, Ser. No. 376,226 Claims priority, application Great Britain, June 21, 1963, 24,743/ 63 1 Claim. (Cl. 167-93) This invention relates to a polishing agent suitable for use in dentifrices.
The function of a polishing agent in a dentifrice is to remove food debris and adherent. films on the tooth sur face such as plaque, pellicle, cuticle (referred to hereinafter as plaque), and to give a polish to the tooth surface itself. The polishing agent should not unduly scratch or abrade the surface of the tooth enamel or other hard tissue.
One method of avoiding scratching the surface unduly is to use very small particles of submicron size, having a Mohs hardness greater than 6. Unfortunately, such materials are not very effective in the polishing process since they can not readily penetrate the film of plaque attached to the tooth surface.
In order to remove the plaque it is normal practice to use larger particles, having an average particle size usually between 5 and 20 microns. It is essential however that materials used for this purpose must not have a Mohs hardness greater than about 6, lest they cause undue scratching and abrasion of the tooth enamel. Thus materials suitable for plaque removal are not very efiective in giving a polish to the tooth surface. One method of obtaining the desired polishing effect, without undue abrasion, is by using a mixture of two abrasives of the types referred to above. A particular example of this type of system is described in British patent specification 840,161.
The present invention has as an object the provision of a polishing agent.
The polishing agent of the invention consists of particles of a material having a Mohs hardness less than 6, prefer- 3,325,368 Patented June 13, 1967 that they are or can become exposed during tooth cleanmg.
As abrasive materials there may be used, for example, aluminas, natural or synthetic silicas, calcium phosphates such as beta tricalcium orthophosphate, and thermoset-ting resins such as urea-formaldehyde or melamine-formaldehyde resins. Particularly suitable is Linde Type A alphaalumina.
The carrier particles may be composed of a polymeric material of which examples are the following thermoplastic materials: natural and synthetic rubbers, for example ably less than 4, and an average size in the range 1 to 50 material of thecarrier particles, preferably greater than 6,
such as from 7 to 9, and an average size of less than 1 micron. Preferably at least 70% by weight of the abrasive particles have particle sizes of less than 1 micron. It is furthermore preferred that the abrasive particles have an average size of from 0.01 to 0.5 microns. The larger abrasive particles will usually be used with the larger sized carrier particles.
The amount of the abrasive present in the carrier particles is preferably between 1 and of the weight of the carrier material. Amounts of from 530% are especially suitable, although the amounts used for any particular combination of abrasive and carrier materials will be determined by the physical properties of the materials employed.
The polishing agent of the invention enables the desired effect of polishing.
The abrasive particles may be embedded in the carrier particles in such manner that a substantial proportion of the abrasive particles project from the surface of the carrier particles so as to present a relatively large exposed surface of abrasive material, or the abrasive particles may be randomly distributed throughout the carrier particles, so that some of the abrasive particles project or are located close to the surface of the carrier particles so styrene-butadiene copolymers; polyolefines, for example polyethylene and polypropylene; polyvinyl-chloride and copolymers of vinyl chloride and other unsaturated monomers such as vinyl acetate or vinylidene chloride; nylons; polyacrylates and polymethacrylates. The extent of softness of the plastic can be modified by crosslinking the polymers during polymerization with such materials as divinyl benzene. External plasticisers may be used, for example sucrose benzoate for polyvinylchloride.
Carrier particles of a plastics material may be prepared by suspension polymerisation. In the suspension of the monomer the finely-divided abrasive material is dispersed. On polymerisation the abrasive material and polymer become firmly bound. At the end of the polymerisation reaction the particles of the plastics with embedded abrasive are washed and are ready for compounding with the other ingredients of a dentifrice. There will usually be present with these plastic particles a proportion of unfilled plastic particles as well'a's'free abrasive particles. When plastics materials of the smaller particle sizes are'to be used as the carrier particles, these may alternatively be made by an emulsion polymerisation method.
Under the conditions of shear encountered during the tooth cleaning operation, the relatively soft particles of the carrier material may deform to present a large polishing surface to the tooth enamel. Under these shear conditions any particles of the abrasive material normally located beneath the surface of the carrier particle may become exposed and effective to polish the tooth surface. The polishing agent of the invention is of particular value in those dentifrices where problems of compatibility of certain constituents of the dentifrice, such as watersoluble fluorides, with the commonly used polishing agents occur. By the use of a material for the carrier particles which is compatible with the system, the abrasive material used may beone which would otherwise be incompatible, providing that in this special case the abrasive is completely or substantially completely embedded in the carrier. Again, under the influence of shear during use, the carrier can flow away from the region undergoing shear to expose the polishing surface of the occluded filler when the carrier is in contact with the tooth enamel.
Suitable amounts of the polishing agent of the invention which may be included in a dentifrice composition are from 10 to 99.5% by weight of the total composition. Dentifrice pastes suitably comprise from 10 to and dentifrice powders from 80 to 99.5% by weight of the polishing agent.
In addition to the polishing agent, the dentifrice may contain optional ingredients such as soap or synthetic detergent, fiavouring materials, buffers, sweeteners, colouring materials and therapeutic materials, for example sodium fluoride, stannous fluoride and sodium monofluorophosphate. If the dentifrice is in the form of a paste it will contain a carrier, for example glycerine or sorbitol, and a binder, for example gum tragacanth, sodium carboxymethylcellulose, hydroxyethyl cellulose, Irish moss and its derivatives. The dentifrice may also contain conventional abrasives or cleaning agents such as chalk or dicalcium phosphate. Further, one may include, if desired, particles of a polymeric material which are not impregnated with abrasive particles, or particles of thermosetting resins.
The following examples illustrate the invention. All parts are by weight. Example 1 describes a method of making the polishing agent of the invention and Examples 2 and 3 concern dentifrice formulations which include the polishing agent produced by Example 1.
Example 1 The following materials were charged into a glass reactor equipped with a stirrer, reflux condenser and thermometer pocket.
. Parts Ethyl acrylate 100 Distilled water 400 Alpha-alumina, Linde Type A (average particle size about 0.3 microns; Mohs hardness of 9) 20 Benzoyl peroxide 0.1
The monomer ethyl acrylate used was a commercial material which contained a phenolic inhibitor to prevent premature polymerisation. Before the monomer was used the inhibitor was removed \by washing the monomer several times with 2% aqueous caustic soda and then washing with distilled water until neutral to litmus.
The mixture was polymerised at 70 C. with constant stirring (700 rpm.) for 4 hours and allowed to cool to room temperature, with continuous stirring.
A mixture was then prepared under nitrogen consisting of Parts Na4P2O7-1 H O FeSO .7H O 1.39 Distilled water 100 The mixture was warmed in an oven at 60 C. for 45 minutes. Into the reactor was then injected snfficient of this mixture to give 0.446 part of hydrated sodium phosphate and 0.278 part of hydrated ferrous sulphate. The temperature was then raised to 70 C. over a period of 4 hours, again with continuous stirring.
The reactor was then allowed to cool whereafter the particles comprising those of the polymeric material having abrasive particles embedded in them were washed with ,water. The particles not containing abrasive were separated from those containing abrasive by a flotation method. The particles containing embedded abrasive had an average size of about 20 microns. The polymeric material had a Mohs hardness well below 4.
Examples 2 and 3 Denti-frice compositions were made having the compo sitions indicated below:
The dentifrices of these examples are effective in the cleaning and polishing of teeth.
What is claimed is:
A dentifrice composition consisting essentially of from 10% t0 99.5% by weightof thermoplastic carrier particles selected from the group consisting of rubber, polyethylene, polypropylene, polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate, copolymers of vinyl chloride and vinylidene chloride, nylon, polyacryl-ate and polymethacrylate, said carrier having an average particle size between about 1 and 50 microns and having a Mohs hardness of less than about 6, there being embedded in and projecting from the surface of said thermoplastic carrier particles a plurality of abrasive particles selected from the group consisting of alpha-alumina, silica, calcium phosphate, urea-formaldehyde resin and melamineformaldehyde resin, said abrasive particles having a Mohs hardness greater than 6 and an average particle size of less than 1 micron, the weight of abrasive material embedded in said carrier mate-rial being from about 1% to about 50% by weight of the carrier material.
References Cited UNITED STATES PATENTS 3,070,510 12/ 1962 Cooley et al. 1679'3 3,151,027 9/1964 Cooley et al. l6793 3,156,545 11/1964 Kistler et al. 51-298 3,175,894 3/1965 FOOt 51-298 LEWIS GOTTS, Primary Examiner.
RICHARD L. HUEF, Assistant Examiner.