US3070510A

US3070510A - Dentifrice containing resinous cleaning agents

Info

Publication number: US3070510A
Application number: US850533A
Authority: US
Inventors: William E Cooley; Robert J Grabenstetter; Robert W Broge
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1959-11-03
Filing date: 1959-11-03
Publication date: 1962-12-25
Anticipated expiration: 1979-12-25
Also published as: DE1170584B; FR1360156A; GB939230A

Description

3,079,510 DENTlFRICE CONTAINING RESINOUS CLEANiNG AGENTS William E. Cooley, Cincinnati, Robert J. Grahenstetter, Colerain Township, Hamilton County, and Robert W. Broge, Wyoming, Ohio, assignors to The Procter Gamble Company, Cincinnati, Chic, a corporation or Ohio No Drawing. Fiied Nov. 3, 1959, fietxNo. 850,533 11 Claims. ((1167-93) This invention relates to a dentifrice containing a particulate synthetic resin as a cleaning agent and ionic agents to reduce tooth decay; specifically the latter are fluoride or stannous and fluoride ions.

A satisfactory dentifrice should have a cosmetic effect on the teeth, keeping them light colored. It should also have a functional effect on the teeth and mouth, keeping them clean and free from food debris, thereby aiding prevention of tooth decay. In order to achieve both ends it is necessary to brush with a dentifrice containing a cleaning agent, often called an abrasive. The purpose of the cleaning agent is to aid in removal of the tightly adherent film which, in many persons, contains pigments which color is brown or yellow. The cleaning agent should remove this pellicle film with a minimum of abrasion of the underlying tooth material. Enamel, which covers much of the exposed tooth surface, i relatively hard and is not of as much concern as the softer dentin which may be exposed by receding gums. The ideal cleaning agent is one which effects the maximum removal of the pellicle film with the minimum abrasion of dentin.

Beyond the function of a dentifrice in maintaining oral cleanliness, there is merit in including an agent which acts specifically to reduce tooth decay. Work stimulated by the discovery of the beneficial effect of fluoride in drinking water or topically applied to the teeth has led to the development of dentifrices containing stannous fluoride. The efiect of stannous fluoride in a properly formulated dentifrice in reducing incidence of caries has been well established. Recent reports of this effect in the scientific literature are listed in a publication by W. A. Jordan and J. K. Peterson in I. Am. Dental Assoc., 58, 42 (1959). Both the stannous ions and the fluoride ions are believed to contribute to the anti-caries effect. Interest has also been evidenced in dentifrices containing other inorganic fluorides than stannous fluoride and in organic fluorides such as ethanolamine hydrofluorides.

A problem recognized in the scientific and patent literature is that of formulating a dentifrice in which the stannous fluoride or other ionic anti-caries agent will remain avialable for treatment of the teeth in use rather than reacting with the cleaning agent. Major steps towards the solution of this problem have been taken. U.S. Patent 2,876,166, William H. Nebergall, March 3, 1959, teaches the improved compatibility of heat-treated calcium phosphates with fluorides in dentifrices. Means for maintaining stannous ions in a condition available for reaction with the teeth have received attention in British Patent 804,486, March 11, 1959, which teaches the use of a reservoir of stannous ion in the form of a slightly soluble compound. 7

Thepreparation'of a cleaning agent with high cleaning to abrasion ratio has been taught in U. S. Patent 2,876,- 168, R. W. Broge and R. J. Grabenstetter, March 3, 1959. This patent shows preparation and use of calcium pyrophosphate with such properties.

While the advances described are substantial, there is still opportunity to improve the compatibility of the cleaning agent with ionic ingredients such as stannous and fluoride ions and at the same time to maintain or to improve the cleaning to abrasion ratio.

An object of this invention is to provide a dentifrice in which a substantial amount of stannous and fluoride ions do not react with the cleaning agent and thus re: main available for treatment of the tooth surfaces on use.

An additional object is to provide a cleaning agent whi h is effective in removing pellicle films from the teeth and which causes a minimum of abrasion to dentin.

These and other objects are achieved in a dentifrice formulation comprising a substantially water-impervious, cross-linked, thermo-setting, highly polymerized synthetic resin in the form of particles having a specified range of mean diameters, and a water-soluble source of fluoride or fluoride and stannous ions.

Hans Schmidt in U.S. Patent 2,130,034 has taught the use of synthetic resins in dentifrices. He discloses a variety of thermo-plastic and thermo-setting resins, but does not disclose or suggest the type of particulate, highly polymerized resin employed in the formulations proposed herein.

The resins suitable for use in the present invention are substantially water-impervious, cross-linked, thermo-setting highly polymerized resins. A thermo-setting resin is one which solidifies on heating and cannot be remelted. This property arises from the formation of cross-links between polymer chains during the chemical reaction which is promoted by heat or chemical means. The resulting three-dimensional network of polymers is the type of structure which is suitable for the purposes of this invention. Some thermo-setting plastics soften at tempera tures of about C. and these are included in the term therrno-setting as it is used herein.

By substantially water-impervious is meant resins which do not take up appreciable water on prolonged contact. Preferably water absorption in 24 hours at 25 C. according to ASTM Test D-57057T is less than about 1%. The absorption of water leads to swelling and softening of the resin particles which is undesirable in a dentifrice cleaning agent. Casein resins are examples of a type of thermo-setting plastic which is unsatisfactory because of relatively high Water absorption.

Common types of thermo-setting synthetic resins which are suitable for use in this invention when highly polymerized are melamines, phenolics, ureas, melamine-ureas', cross-linked epoxies, and cross-linked polyesters. The last two types named are generally less desirable and some resins of these types are examples of the class of thermosetting resins which soften at roughly 120. C.

The thermo-plastic resins which are not generally suit able for use in this invention can be melted and resolidified without losing their original properties. Their properties, presumably lower hardness and rigidity than the thermosetting resins, are not such that they effectively remove pellicle film from teeth. Examples of commonthermo plastic resins are acrylics, cellulosics such as acetates and butyrates, polyamides, polyethylenes, polystyrene's and vinyls.

The highly polymerized synthetic resins for use in this invention are as free as possible from low molecular weight materials and extenders. They should be highly polymerized to achieve a minimum content of the low molecular weight starting material and maximum cross-linking. Low molecular weight impurities such .as monomers and other starting materials are to be avoided since theyQcan react with stannous and fluoride ions and can lead to'off odors and flavors. Extenders, which are used in the'plastics industry to inexpensively increase the bulk of the synthetic resin, should be avoided becauseof their" strong tendency to sorb ionic ingredients, elg; stannous and/ or fluoride ions. Examples of the extender materials which are commonly used in commercial practice and which should be absent in the resins used in the compositions of this invention are wood flour, cellulose, asbestos, and mica.

Melamine resins, the product of polymerization of melamine and formaldehyde, are preferred for use as cleaning agents because of their excellent physical properties and compatibility with ionic ingredients combined with freedom from color and odor.

Phenolics and ureas, i.e., phenol-formaldehyde and urea-formaldehyde resins, are desirable from the standpoint of physical properties and compatibility. Most of these resins are difiicult to obtain in a color-free highly polymerized condition and are, therefore, less desirable for the formulation of a white dentifrice.

Polyesters, or alkyd resins, are the product of esterification reactions between polyhydric alcohols and polybasic acids. In order to prepare a thermo-setting cross-linked polyester, a dihydric alcohol and a dibasic acid, either or both of which contains a double bond, are esterified and the resulting unsaturated polyester is then cross-linked by reaction with a monomer such as styrene. Commonly, a saturated dihydric alcohol, such as ethylene glycol, propylene glycol, 1,3- and 2,3-butylene glycol, diethylene glycol and dipropylene glycol, is reacted with an unsaturated dibasic acid, such as maleic anhydride or furnaric acid. The polymerizable monomer can be styrene, vinyl toluene, diallyl phthalate, methyl methacrylate or triallyl cyanurate. Heat or a peroxide catalyst, alone or in combination, are used to bring about the polymerization.

Epoxy resins are made by reacting epichlorohydrin with polyhydric compounds such as bisphenols and glycols. The resulting polymers are cross-linked to form thermosetting resins by direct reaction between epoxy groups, linkage of epoxy groups with aromatic or aliphatic hydroxyls, and cross-linking with curing agents through various radicals. The most common cross-linking agents are polyfunctional primary and secondary amines and dibasic acids or acid anhydrides.

The low molecular weight starting materials of the resins described above are polymerized in commercial practice by reactions promoted by heat, with or without a catalyst present. Pressure is sometimes used with heat in commercial practice during polymerization, such as in molding operations. The highest degree of resin polymerization found in commercial molding practice is that obtained when a resin is used in a molding process which involves high temperatures and pressures for several minutes of time. However, the molding of resins without the use of extenders would not be considered in commercial practice.

It has been found that the resins used as the cleaning agents in the compositions of this invention should be free from extenders and should be polymerized substantially beyond the resin polymerization of commercial practice. Commercially cured resins even without extenders do not have the cleaning ability and ionic compatibility which is desired for fluoride-containing dentifrices. Commercial cures do not effect the high degrees of cross-linking and reduction of residual low molecular weight starting materials which are essential to obtain these properties.

The resinous cleaning agents used herein should undergo a heat polymerization for a period of time measured in hours at temperatures in the range of about 100 C. to about 180 C. to obtain the desired properties. Optimum temperatures vary with the resin but should be sufficient to effect polymerization without charring the resin. For example, polymerization conditions at atmospheric pressure can range from one hour at 100-120 C. for polyesters to 16-24 hours at 150-165 C. for melamine resins. Polymerization, ionic compatibility and cleaning efiectiveness of the resins increase with increased times and temperatures of treatment. Greater increases in the degree of polymerization are obtained with increased temperatures of treatment than with increases in t me of treatment. However, the times of treatment always should be substantially greater than the polymerization times found in commercial molding practice.

Some degree of polymerization can be effected with an acid and is especially useful for melamine-formaldehyde resins, urea-formaldehyde resins, and melamine-ureaformaldehyde resins, but further heat polymerization is necessary. Acid polymerization is effected by adding an acid, usually a strong acid such as HNO to the low molecular weight starting material in water. Polymerization is allowed to advance at a temperature below the boiling point of the solution.

The high degree of heat polymerization necessary to obtain the resinous cleaning agents of this invention imparts extreme rigidity or brittleness (low degree of resistance to impact) to the resins. Such a property would be undesirable in any of the conventional uses of resins such as in molding; therefore a high degree of polymerization would be avoided in such uses. However, in the resinous cleaning agent of the present invention extreme brittleness is highly desirable since it apparently is the basis for the outstanding cleaning ability of the resins as well as being an indicator of the high degree of polymerization which results in excellent ionic compatibility.

The heat polymerization of the resins should be conducted at a sutficient temperature and for sufficient time to obtain an ionic compatibility equivalent to a stannous ion compatibility of not less than about 30% as determined by the one-hour test hereinafter described in Example I. Stannous compatibility is also an indicator of cleaning effectiveness and of fluoride ion compatibility. Stannous compatibility is the severest test of the degree of polymerization, since when the stannous compatibility is satisfactory, the latter properties are at least satisfactory.

It is necessary that the resinous cleaning agent be in particulate form. If it has been prepared in bulk, it can be reduced to the desired particle size, set forth in detail hereinafter, by conventional grinding methods. Impact, ball, and tube mills can be employed for grinding highly cross-linked resins. The final heat treatment can be f0llowed by grinding, and it is desirable to grind before the heat treatment step to decrease the time required to achieve the necessary high degree of polymerization. If the resin is in the form of particles having the desired distribution of sizes during the final heat polymerization and if the desired particle size is not disturbed during the final heating, a final grinding step is not necessary.

An indication of the types of thermo-setting resins which are suitable for use in this invention has been given. So long as the resin meets the other requirements set forth, i.e. being water-impervious, being cross-linked and being thermo-setting, the exact composition of the resin, so long as it is highly polymerized, has little effect on its performance as a compatible cleaning agent in the dentifrices of this invention. Commercially available materials in various stages of polymerization can be made suitable by effecting substantial further polymerization as described above. Specific resins suitable for use in this invention and their processing are shown in examples given hereinafter.

The resinous cleaning agents are composed of particles substantially all of which have a diameter of less than 50 Larger particles tend to feel gritty in the mouth and to stick between teeth. The mean diameter of the particles of the cleaning agent is desirably from about 5a to about 401.4 and preferably Sp. to 20 for optimum performance. Preferably not more than about 10 weight percent of the particles have a diameter of less than about 1,u. Finer particles are relatively ineffective in cleaning teeth, and therefore the fraction of fines is limited. By particle is meant aggregates as well as individual particles. It might be supposed that only particles with sharp edges and corners would be effective in removing pellicle film from the teeth. However, it has been discovered that roughly spherical particles and aggregates of roughly The particle diameters referred to herein were determined by microscopic measurements using a calibrated eyepiece.

Fluorideions arean essential constituentof the dentifrices of this invention. They may be supplied by any water-soluble innocuous compound of fluorine which provides-fluoride ions ,on contact with water. By innocuous compound is meant a compound which is not undesirably toxic, highly colored, or otherwise objectionable for use in a dentifrice. Many water-soluble inorganic salts are suitable sources of fluoride ion. Among these may be mentioned sodium and potassium fluoride, which are economical and have desirable properties. Examples of other suitable ffluoride salts include ammonium fluoride, indium fluoride, i.e., InF palladium fluoride,-i.e., PdF ferrous fluoride, lithium fluoride, and

mixtures thereof. Complex water-soluble fluoride-containing salts such as fluorosilicates, i.e., Na SiF fluorozirconates, i.e., Na ZrF K- ZrF fluorostannites, i.e., KSnF fluoroborates, i.e., NaBF and fluorotitanates are also suitable for use in the dentifrices of this invention.

Mixtures of fluoride salts can be used.

It is also within the scope of this invention to supply 7 stannous ions from a compound other than a fluoride.

Suitable water-soluble stannous compounds are chloride and nitrate. A reservoir of slightly soluble tin may be provided as in British 804,486, but it is not'necessary because of the compatibility of the resinouscleaning agent.

It is not necessary that the fluoride ion be supplied by an inorganic salt. It may be suppliedby an organic fluoride which is soluble in water or at least which dissociates to give fluoride ions in contact with water. The

fluoride ions may also be supplied by organic hydrofluorides. Suitable amine fluorides disclosed in Canadian Patent 543,066 (Philip Zutavern et al., July 2, 1957) are 'the mono-, diand triethanolamine hydrofluorides. These compounds may also be named as the corresponding ethanol-ammonium fluorides. Other useful organic fluorides and hydrofluorides are disclosed in a publication by H. R. Muhlemann et al. in Helvetica Odontologica Act, vol. I, No. 2, page 23, 1957.

The essential ingredients of thdentifrices of this invention may be compounded in a number of cosmetically acceptable forms. For example, they may be compounded as a powder or as a paste. In formulating the finished dentifrice it is desirable to use only auxiliary .agents which do. not precipitate, complex, or. otherwise react with stannous or fluoride ions, thereby decreasing the advantage providedby the compatible resious cleaning agent. Some. loss ofstannous ions is probably .inevitable because of oxidation and slow hydrolysis.

Toothpastes usually contain a humectant, a sudser, a binder, a sweetener, and a flavor in addition to a cleaning agent. Fluoride ion itself is compatible with the auxiliary ingredients of the toothpaste which are conventionally used in dentifrices. If stannous ion is also present, these ingredients preferably should be-selected with greater care. Glycerine and sorbitol are humectants compatible withstannous ion. Binders of a non-ionic character are preferred, for they are generally compatible; examples are hydroxyethyl cellulose and very high molecular-weight polyethylene oxides. Nonionic and cationic detergents are compatible sudsers. Suitable nonionics include sucrose monolaurateand the condensation product of dodecyl alcohol with 1-6 moles of ethylene oxide. Many of the commonly employed flavoring oils are compatible with stannous ion. Of course, if the ingredient is present in small amounts relative to the stan- ,will be the case in the preferred embodiment of this invention, they are used at a level of from about 1000 p.p.m. to about 9000 p.p.m. The preferred level is from about 2000 p.p.m. to ,about 4000 p.p.m. since there is no need to provide an amount for reaction with the cleaning agent. Fluoride ions are present at a level of greater than about 25 p.p.m. in order to achieve the desired effect. There is little advantage in having more than about 4000 p.p.m. fluoride ions present, and preferably the fluoride level will be from about 500 p.p.m. to about 2500 p.p.m. 'In a toothpaste the cleaning agent will constitute from about 20% to about of thecomposition. Preferably malonic, formic, fumaric, methoxyacetic, and propionic.

The pI-I of toothpastes of thisinvention is higher than about 3 and lower than about 7. Lower pHs than 3 are not desirable for use in the mouth and lead to problems of hydrolysis of some of the ingredients of the paste and problems of corrosion of metal containers. When stanhigh'degree. The manufacturers recommendations were generally followed as to polymerization temperatures and nous ions are present, the pH preferably should be lower than about 5. In the absence of stronger complexing agents than fluoride, the stannous ion precipitates as hydrous stannous oxide at higher pHs. If resins, such as melamines, which have a natural alkalinity, are used as the cleaning agent, neutralization of the resins should be effected before they are associated with stannous ions.

A balance of desirable consumer properties and effectiveness is attained in the preferred pH range of from about pH 3.5 to about pH 5.0. When stannous ions are not present, the preferred pH range is somewhat higher, being'from about pH 4.5 to about pH 7. It is necessary to insure that the toothpaste does not attack the teeth. Lower pH values are safer in the presence of stannous ions than in their absence. Lower pHs are generally preferred if other heavy metal ions such as indium ions are present.

- Example I The resins listed in this example are all substantially water-impervious, cross-linked, thermo-setting, highly polymerized resins which are suitable for use in the dentifrices of'this invention. These resins were obtained from their manufacturers and were further polymerized to a proportions of ingredients. However, a substantial additional period of heating was employed to effect a high degree of polymerization. "The treatment each resin received is set forth in the table. All of the resins were tested to assay their suitability for use in a dentifrice.

The fluoride compatibility of these resins is very high, i.e., there is very little reaction or strong sorption of fluoride ion by the resins, particularly as compared to calcium pyrophosphate, the preferred abrasive heretofore used with fluoride. Compatibility with stannous ion varies somewhat and is listed in the table. These results were obtained by slurrying particulate resin with a stannous fluoride solution and measuring the stannous ion remaining in solution after various periods of tir ne. The results given are based on a scale established by mixing 10 grams of particulate resin with ml. of- 0.1% SnF solution at room temperature. After one hour a sample of the supernatant was analyzed for stannous ion, and

the percent of that originally present was calculated. This test is much more severe than the conditions existing in a toothpaste because of the diluteness of the slurry and the absence of the non-aqueous ingredients. An arbitrary scale used is: -30%, poor; -60%, fair; good; and 90100%, excellent. Calcium pyrophosphate examined in this rigorous test rates poor although it is the preferred abrasive used heretofore with tin.

The cleaning ability of the resins was ascertained by a standard test as described in US. Patent 2,876,168, cited hereinbefore, involving the removal of a lacquer film from a plastic block. The results are reported on a scale of from 0 to 10 in which a conventional dentifrice cleaning of such powders is by the weight loss of a lead strip brushed mechanically under standardized conditions with the resin powder. A realistic but laborious test involving the mechanical brushing of radioactive dentin from extracted human teeth, as described in US. 2,876,168 cited hereinbefore, was used on certain samples when so indicated. Instead of calculating an abrasion value as was done in the cited reference, the micrograms of dentin removed per double strokes with the test cleaning agent is simply compared with the same figure for a standard sample of high cleaning to abrasion ratio calcium pyrophosphate. These values for the two samples indicated in the table and the values for the control are as follows.

agent, dicalcium phosphate dihydrate, rates 5 and the 15 high cleaning calcium pyrophosphate rates about 6.5 to 9. Mlcrograms of dentln An estimate of abrasiveness compared to the high Resin A 70 cleaning-low abrasion calcium pyrophosphate is given. Resin B 60 A quick laboratory means of comparing the abrasiveness Ca P O 115.450 MELAMINE-FORMALDEHYDE Properties of finished resin Trade name and manufacturer Description of product received gggg Rockwell Compressive 25 0., hardness strength, 24 hrs. p.s.i.g. percent Resimene 817, Monsanto Chemical Spray-dried soluble powder made in accordance with the process Company. described in US. Pat. 2,485,059.

Cymel 404R, American Cyanamide Co- Granular molding material 0.3-0. 5 E 40,00045,000 Cymel 405, American Cyanamide Co..- Soluble powder- M PHENOL-FORMALDEHYDE Resin #71, Marblette Corp.-- Casting resin 0. 02 M20-M50 13, 000

Resin A, Union Carbide Plastics Co Alkaline condensed, high formaldehyde water dispcrsable phenolic resin 01 the type disclosed in US. Patent 2,190,762. Resin B, Union Carbide Plastics 00-- 702%811131e0us soln. trimethylolphenol as described in U.S. Patent M93 NorE.-Resiu A" and Resin B are not trade names.

UREA-FORMALDEHYDE Plaslron 360, Allied Chemical Corp Powder.

UREA-MELAMINE-FORMALDEHYDE UMF, experimental resin, Monsanto A physical mixture of Resimene 817 and UF71 which is a powder Chemical 00. made in accordance with the process dcscrihed in U.S. Patent 2,485,059 except that urea is substituted for the melamine.

POLYESTERS Selectron 5003, Pitts. Plate Glass 00---. Fluid resin with 34% styrene 0.3 M110-M1l5 23,000 Arcopol 7120, Archer-Daniels-Midland Fluid resin with 33% Styrene EPOXY Resiweld #101, H. B. Fuller Company Fluid rcsin MELAMINE-FORMALDEHYDE Approx. Trade name Treatment of product received mean Cleaning Abrasion Compatibility with particle 5 1+ diameter, p

Resimene 817 fieigggdom hrs. Sit 0.; ground in a Pulva-Sizer; reheated 16 hrs. at 30 8 Less.-- Excellent (100%).

.;s1eve Cymel 404R--." Ground in a Raymond hammer mill; heated 1 hr. at 165 0.; sieved.... 75 6 Equal"--. Do. Cymel 405 Hegggdglfi llllS. (at 150 0.; ground in a Pulva-Sizer; reheated 16 hrs. at 30 9 Less Fair (56% s eve PHENOL-FORMALDEHYDE Resin #71 Resin and accelerator 342 mixed; heated 4.5 hrs. at 100 0.; ground in a 75 4 Less Excellent (100%).

Raymond hammer mill; sieved.

Resin A Heated 1 hr. at 0.; ground with Dry Ice Pulva-Sizer; sieved 30 9 Less Fair (30%). Resin B- do-- 30 3 0. Good (85%).

Radioactive test.

tfected, and a fair estimate of cleaning and UREAJORMALDEHYDE Approx. Trade name Treatment of product received mean Cleaning Abrasion Compatibility with particle Sn++ diameter, a

Plaskon 3G0 3 parts mixed with 2 parts water; heated 16 hrs. 105 0.; ground with Dry 30 4 Fair (35%).

Ice in Raymond hammer mill; sieved.

UREA-MELAMINE-FORMALDEHYDE UMF Sewith HNOs; dried; heated for 16 hrs. at 110 0.; ground in Pulva- 30. 8 Less Excellent (100%).

izer.

POLYESTERS Selectron 5003..- Heated 3 hrs. 165 0.; powdered in Raymond hammer mill, sieved 75 2 Less. Excellent (100%). 'Aropol 7120 ..do. 75 2 do Do.

EPOXY Resiweld #l01- Heated 2 hrs. 175 0.; ground in a Raymond hammer mill; sieved 75 Less Good (75%).

Other dentin abrasion data obtained on resinous clean- Percent ing agents suitable for use in this invention are summarized below. All are effective in removing pellicle film and are compatable with stannous and fluoride ions. The starting materials are further identified in the foregoing table.

Sodium coconut sulfate 0.70 Melamine-formaldehyde resin (specified below) Hydroxyethyl cellulose 1 1. Flavor 0.85 Distilled water Balance Viscosity of'-a- 2%- solution zit-20 C.-is75-1-25 centipoises using Brookfield No. 2 spindle30 r.p.m.

Thispaste, of good consistency, had a final pH of 6.52. I

:The resinous cleaning agent did not react withor Dentin abrasion, I Particle micrograms Trade Treatment diameter, name p I Sample Ca=P2O 35 control Cyme1404R Heated 16 hrs. at 30 (mean)- '90-115 95-120 160O., Pulva- Sizer, sieved Oymel 405 do do 55 130 40 Resimeno 817-. Heated 16 hrs. at do 40 115 150C., Pulva- Sizer, sieved Cyme1404R... HeagedC 16f hrst. at 10 (max); 10-20 115 1 h 0 15 rac ion less than 10 miargert an 5 crons separated electrostatically 4 5 In the tests reported here it was not convenient to re-' duce the particle size of the resins indicated as having a mean particle diameter of 7 5,41. to within the limits which eliminate the gritty feel in the month. However, the results of the compatibility tests are not appreciably afabrasion can be made.

The data quoted under the heading Properties of Finished Resins are supplied by the manufacturer.

' in use; i.e.,

strongly absorb fluoride ion. The etficacy or this toothpaste in reducing acid attack on teeth in a biological medium was great. The toothpastes cleaning grade obtainedin'the standard testwas l0.

Examplev III The following toothpaste was prepared and was found to have a desirable consistency and'desirable properties the resinous cleaning agent did not feel gritty'and was well adapted for removing pellicle film from the teeth.

These data are generally obtained by following the pro- Percent cedure of the ASTM Test D590 for water adsorption, Stannous fluoride (1070. pp 3300 pp D785 for hardness, and D695 for compressive strength. gsnfi) 0 44 While the cleaning effectiveness of the individual sam- Saccharin I ples varies from poorer to much better than a conven- Sucrose monomyristate tional dentifrice abrasive, the compatibility with fiuo- Flavor ride and tin is outstanding and the abrasiveness is, in Glycerin "I: most samples, less than that of calcium pyrophosphate, Hydmxyethyl Cellulose (See,EXamp1e H) which is currently a commercial choice for its high cleaning to abrasion ratio.

Example 11 The following toothpaste was prepared.

Melamine-formaldehyde resin (specified below)" 37 Water Balance The melamine-formaldehyderesin was prepared by "the reaction 'of 3 moles of formaldehyde -per mole'of "melamine, and" thepolymerization-was carried to a high degree ofadvancement. Thepolymerwas then acidified topHd'and theresulting *solid' cured for 16. hours at C. Thesolid-was then-ground in a Pulva-Sizer (Pulvette) impact mill and heated for 20 hours at The resulting material, after beingball milled for three days, had ameanspartiele. diameterof 10a; less 1 1 than was smalled than 1a, and substantially no particles had a diameter greater than a.

The toothpaste was stored at room temperature; periodically samples were taken, diluted with 3 parts water to 1 part toothpaste and the available stannous tin determined. The results obtained follow.

Time, days: Percent Sn remaining 3 71 10 55 21 47 50 49 The fluoride ion suffered substantially no loss in availability in this time. This test when conducted for 10 days or more is as severe as the 1 hour Sn compatibility test described in Example I.

Example IV The following toothpaste was prepared and found to have a good consistency.

Melamine-formaldehyde resin (specified below)-.. 44 Water Balance A solution of Resimene 817, melamine-formaldehyde resin, was acid-set with nitric acid at 60 C. The resulting solid was dried, heated at 110 C. for 16 hours, and then was ball-milled for 16 hours. The mean particle diameter was 6:1,u. Substantially no particles had a diameter greater than 10 and the weight percent of particles smaller than 1a was less than 10%. These particles were observed under the miscroscope to be roughly spherical.

The pH of this toothpaste was 3.68. The toothpaste cleaned well, giving a cleaning grade in the standard test of 6.5. The abrasiveness of the paste was satisfactorily low.

Example V Resin 5379-1 was obtained from the manufacturer (Union Carbide Plastics Co.) as a coarse, light tan powder which had been heat treated for 16 hours at 110 C. It is an amine-modified phenol-aldehyde resin. The powder was mixed with Dry Ice, ground in a Pulva-Sizer impact mill, and sieved. The mean particle diameter was about 30,12, and there were substantially no particles of diameter greater than 50 less than 10% of the particles were smaller than Lu.

The radioactive dentin abrasion test showed that the resinous particles were about equal in abrasiveness to calcium pyrophosphate. A grade of 7.5 was obtained in the cleaning test.

The amine-modified phenol-aldehyde resin proved to be highly compatible with stannous ions in a toothpaste of the following composition. The resin is also compatible with fluoride.

Percent Stannous fluoride (1000 p.p.m. F, 3000 p.p.m.

Sn++) 0.40 Flavor 0.50 Saccharin 0.20 Color 2.0 Hydroxyethyl cellulose (see Example H) 2.0 Glycerin 28 Amine-modified phenol-aldehyde resin particles ground material prepared as above) 36 Water Balance 12 the tests described in Example III, was found to be 81%. The tin remaining was 74% after 12 days.

Toothpastes formulated with the resinous cleaning agent described in the first paragraph of this example clean the pellicle film from teeth effectively and maintain stannous and fluoride ions in an available condition.

What is claimed is:

l. A dentifrice, effective in removing dental plaque films with minimum abrasion of exposed tooth surfaces comprising:

(a) from about 25 p.p.m. to about 4000 p.p.m. of fluoride ions supplied by a water-soluble, anti-caries fluoride salt; 7

(b) as an abrasive cleaning agent, an effective amount of a substantially water-impervious, cross-linked, thermosetting, highly polymerized, synthetic resin in the form of particles having a mean diameter of from about 5 microns to about 40 microns, substantially all of said particles having a diameter of less than about 50 microns and not more than about 10 weight percent of said particles having a diameter of less than 1 micron, said resin being characterized by inertness to ionic ingredients in said dentifrice, having been heat polymerized to a fluoride ion compatibility equivalent to a stannous ion compatibility of at least about 30% according to the one hour test described in the specification.

2. The dentifrice of claim 1 in which the synthetic resin is melamine-formaldehyde.

3. The dentifrice of claim 1 in which the water-soluble fluoride salt is an ionizable stannous salt and the said resin has been heat polymerized to a fluoride and stannous ion compatibility equivalent to a stannous ion compatibility of at least about 30% according to the one hour test described in the specification.

4. A toothpaste, effective in removing dental plaque films with minimum abrasion of exposed tooth surfaces comprising:

(a) from about 25 p.p.m. to about 2500 p.p.m. of fluoride ions supplied by a water soluble, anti-caries fluoride salt;

(b) as an abrasive cleaning agent, from about 20% to about 50% by weight of a substantially waterimpervious, cross-linked, thermo-setting, highly polymerized, synthetic resin in the form of particles having a mean diameter of from about 5 microns to about 20 microns, substantially all of said particles having a diameter of less than about 50 microns and not more than about 10 weight percent of said particles having a diameter of less than 1 micron, said resin being characterized by inertness to ionic ingredients in said toothpaste, having been heat polymerized to a fluoride ion compatibility equivalent to a stannous ion compatibility of at least about 30% according to the one hour test described in the specification;

the pH of said toothpaste being from about 4.5 to about 7.0.

5. The toothpaste of claim 4 in which the synthetic resin is melamine-formaldehyde.

6. A toothpaste, effective in removing dental plaque films with minimum abrasion of exposed tooth surfaces comprising:

(b) from about 1000 p.p.m. to about 9000 p.p.m. of stannous ions supplied by a water soluble'stannous salt;

(0) as an abrasive cleaning agent, from about 20% to. about 50% by weight of a substantially waterimpervious, cross-linked, thermo-setting, highly polymerized, synthetic resin in the form of particles having a mean diameter of from about 5 microns 13 to about 20 microns, substantially all of said par-= ticles having a diameter of less than about 50 microns and not more than about 10 Weight percent of said particles having a diameter of less than 1 micron, said resin being characterized by inertness to ionic ingredients in said toothpaste, having been heat polymerized to a fluoride and stannous ion compatibility equivalent to a stannous ion compatibility of at least about 30% according to the one hour test described in the specification; the pH of said toothpaste being from about pH 3.5 to about pH 5.0.

7. The toothpaste of claim 6 in which the synthetic resin is melamine-formaldehyde.

8. The dentifrice of claim 1 in which the synthetic resin is urea-formaldehyde.

. 14 9. The dentifrice of claim 1 in which the synthetic resin is urea-melamine-formaldehyde.

10. The toothpaste of claim 6 in which the synthetic resin is urea-formaldehyde.

11. The toothpaste of claim 6 in which the synthetic resin is urea-melamine-formaldehyde.

References Cited in the file of this patent UNITED STATES PATENTS Schmidt Sept. 13, 1938 Wessinger Dec. 31, 1957 Kunin: Robert-Ion Exchange Resins, 1950, pp. 26, 38 and 39.

Claims

1. A DENTIFRICE, EFFECTIVE IN REMOVING DENTAL PLAQUE FILMS WITH MINIMUM ABRASION OF EXPOSED TOOTH SURFACES COMPRISING: (A) FROM ABOUT 25 P.P.M. TO ABOUT 4000 P.P.M. OF FLUORIDE IONS SUPPLIED BY A WATER-SOLUBLE, ANTI-CARIES FLUORIDE SALT; (B) AS AN ABRASIVE CLEANING AGENT, AN EFFECTIVE AMOUNT OF A SUBSTANTIALLY WATER-IMPERVIOUS, CROSS-LINKED, THERMOSETTING, HIGHLY POLYMERIZED, SYNTHETIC RESIN IN THE FORM OF PARTICLES HAVING A MEANS DIAMETER OF FROM ABOUT 5 MICRONS TO ABOUT 40 MICRONS, SUBSTANTIALLY ALL OF SAID PARTICLES HAVING A DIAMETER OF LESS THAN ABOUT 50 MICRONS, AND NOT MORE THAN ABOUT 10 WEIGHT PERCENT OF SAID PARTICLES HAVING A DIAMETER OF LESS THAN 1 MICRON, SAID RESIN BEING CHARACTERIZED BY INERTNESS TO IONIC INGREDIENTS IN SAID DENTIFRICE, HAVING BEEN HEAT POLYMERIZED TO A FLUORIDE ION COMPATIBILITY EQUIVALENT TO A STANNOUS ION COMPATIBILITY OF AT LEAST ABOUT 30% ACCORDING TO THE ONE HOUR TEST DESCRIBED IN THE SPECIFICATION.