Denture Stabilizing Compositions

This invention relates to improvements in adhesives, in particular, improved denture adhesives.

Ordinary removable dentures, dental plates, and the like, comprise teeth mounted in a suitable plate or base. Dentures function as a substitute for missing teeth and serve as a replacement for all or a portion of the teeth ordinarily found in the oral cavity. Although dentures generally are skillfully prepared, often they do not fit perfectly. Moreover, no matter how satisfactory at first, after a period of time the fit of the denture becomes loose and imperfect due to natural shrinkage and changes in the gums, mucous tissues, and the like. Loose and imperfectly fitted dentures usually are corrected and stabilized by the use of a denture stabilizer. Denture stabilizers are used to fill the interstices between the dentures and the gums or tissues. Prior to placement of the denture in the oral cavity, a denture stabilizer is applied to the denture-plate surface which, for a perfect fit, should uniformly contact the gums and mucous tissues. The denture stabilizer is formulated not only for its adherent properties, but also to provide a cushion or gasket between the denture and the gums or tissues, thereby positioning the denture securely in the oral cavity.

Requirements and characteristics for a satisfactory denture stabilizing composition are many and are dictated by numerous factors. Desirably, one daily application of such a composition should function as an effective means for insulating, cushioning, and securely positioning the denture. The composition should retain its characteristics and properties in the typical powder and cream forms during storage under various climatic conditions such as high temperature and humidity; be readily and easily capable of application to the denture surface; not be irritating or uncomfortable to the user; be safe and nontoxic; have no disagreeable odor or color; have no unpalatable taste; optionally provide antiseptic and germicidal properties for preventing or inhibiting the growth of organisms ordinarily found in the mouth; and function as an agent for prevention of putrefaction or adjacent to the denture. The stabilizing material must be capable of imbibing water and saliva and swelling, so as to fill the interstices between the denture and the gum or mucous tissues. The stabilizer should not attack or damage the denture, as by causing a crazing of the denture-plate material. Additionally, the stabilizer should be stable to bacteria, molds and enzyme systems found in the oral cavity, and have a pH that is nonirritating to the oral mucosa, generally 5-8.5, preferably a pH around neutrality. The mechanical strength of the stabilizing mass, be it gel or colloid, formed by inhibition of water should be great enough to securely maintain the position of the denture under normal use, and not so great as to make denture removal difficult when desired, or as to damage or injure the gums, tissues or denture upon removal.

There has been a considerable effort made over many years to develop improved denture adhesives. Both synthetic and natural polymers and gums have been used singly, in combination, and in combination with various additives.

European Patent 64,672 to Dhabhar and Schmidt, published 11/17/82, relates to a hydrophilic denture adhesive containing an adhesive polymeric fraction comprising CMC and polyethylene oxide and a hydrophilic vehicle.

European Patent Application 140,486 to A. J. Desmaris, filed 7/31/84 relates to denture adhesive compositions containing a hydrophobically modified water-soluble polymer, alone or admixed with an alkali metal salt of CMC. Hydrophobically modified hydroxyalkyl celluloses and copolymers of ethylene oxide and long chain epoxyalkanes are preferred for use in the compositions.

U.S. Pat. No. 4,280,936 to Dhabhar, Heyd and Schmidt (issued 7/28/81), relates to improved denture adhesives containing a specified ratio of CMC and polyethylene oxide in a mineral oil base.

U.S. Pat. No. 4,474,902 to Dhabhar and Schmidt (issued 10/2/84), relates to improved denture adhesives containing karaya gum in a hydrophilic vehicle. See also U.S. Pat. No. 4,514,528 (issued 4/30/85) and U.S. Pat. No. 4,518,721 (issued 5/21/85) to these same inventors, relating, respectively, to improved denture adhesives containing adhesive polymeric fractions consisting of admixtures of partial salts of lower alkylvinyl ether maleic anhydride-type copolymers with CMC or polyethylene oxide, as well as denture adhesives containing CMC and poly(ethyleneoxide). See also U.S. Pat. No. 4,522,956 (issued 6/11/85) to Dhabhar and Schmidt relating to improved denture adhesives containing polyethylene oxide as the sole adhesive component in a hydrophilic vehicle comprising certain polyethylene gylcols.

Other denture adhesives are described in U.S. Pat. Nos. 4,530,942 (issued 7/23/85); 4,542,168 (issued 9/17/85); and 4,569,955 (issued 2/11/86).

U.S. Pat. No. 4,529,748 to H. G. P. Wienecke (issued 7/16/85), relates to dental prosthesis adhesives formed from film-forming substances such as various cellulose derivatives, acrylate polymers, methacrylate polymers, and other film-providing substances.

U.S. Pat. No. 4,138,477 to Gaffar (issued 2/6/79) discloses oral compositions to control mouth odor containing zinc-polymer combinations formed from zinc reacted with an anionic polymer containing carboxylic, sulfonic and/or phosphonic acid radicals.

U.S. Pat. No. 3,003,988, to D. P. Germann et.al. (issued 10/10/61) describes certain water-sensitized, but water-insoluble, materials for stabilizing dentures which are synthetic, hydrophilic, colloidal materials comprising mixed partial salts and esters of lower alkyl (1 to 4 carbons) vinyl ether-maleic anhydride-type copolymers, said mixed partial salts and esters containing both divalent calcium and monovalent alkali (i.e., sodium, potassium and ammonium) cations.

U.S. Pat. No. 4,758,630 to Shah et.al., issued July 19, 1988 relates to zinc and strontium partial salts of lower alkyl (C.sub.1 to C.sub.4 ) vinyl ether-maleic acid copolymers, wherein said zinc and strontium cations are "unmixed" with any other cations or ester functions in the copolymeric salt, the remaining initial carboxyl groups being unreacted. These lower alkyl vinyl ether-maleic acid copolymers are referred to hereinafter by the abbreviated term "AVE/MA copolymer" and the methyl vinyl ether-maleic acid copolymer as "MVE/MA copolymer".

It is known, therefore, that combinations of mixed partial salts of lower alkyl vinyl ether-maleic anhydride-type copolymers are useful as denture adhesive compositions. Further, there is disclosed unmixed divalent zinc and strontium salts of lower alkyl vinyl ether maleic anhydride type copolymers and their use with the lower alkyl vinyl ether maleic anhydride type copolymer containing both divalent calcium and monovalent cations, i.e. sodium, potassium, and ammonium cations to obtain a denture adhesive with stabilizing characteristics.

Yet, the search continues for denture stabilizers that will provide the above-described characteristics and, importantly, will maintain the secure fit of the denture over prolonged periods (10-14 hours) without the need for reapplication.

In accordance with the present invention, improved adhesive and other characteristics are obtained in a denture stabilizing composition by using specific single mixed partial salt(s) of a lower alkyl vinyl ether-maleic acid copolymer.

It is an object of the present invention to provide improved denture stabilizers which are easy to manufacture and that will be stable over prolonged periods in the oral cavity, yet will allow easy removal of the denture on demand.

It is a further object of the present invention to provide denture compositions which provide the user with improved sensory, such as flavor, benefits.

It is a further object to provide such stabilizers using toxicologically-acceptable, palatable materials.

It is another object herein to provide stabilizers that perform well in the presence of moisture, particularly in the presence of body fluids such as saliva, perspiration and blood.

These and other objects are secured by the present invention, in the manner disclosed hereinafter.

The present invention encompasses stabilizer compositions comprising: the mixed partial salt of a lower alkyl vinyl ether-maleic acid copolymer consisting essentially of the repeated structural unit: ##STR1## wherein R represents a C.sub.1-4 alkyl radical, n is an integer greater than one representing the number of repeated occurrences of said structural unit in a molecule of said copolymer and n is large enough to characterize said copolymer as having a specific viscosity larger than 1.2, the specific viscosity being determined in methyl ethyl ketone at 25.degree. C., said partial salts containing as the cationic salt function:

(a) from about 10% to about 65% zinc or strontium cations; and

(b) from about 10% to about 75% calcium cations

of the total initial carboxyl groups reacted.

Also disclosed are denture stabilizing compositions comprising these mixed partial salts, as well as denture stabilizing compositions comprising a safe and adhesively effective amount of two or more denture adhesive components wherein one of said denture adhesive components is the mixed partial salt(s) of the present invention.

Preferably these mixed partial salts are used along with a water-sensitized polymeric material selected from the group consisting of natural gums, synthetic polymers, saccharide derivatives, cellulose derivatives, and mixtures thereof.

All percentages and ratios used herein are by weight, unless otherwise specified.

The polymeric salts of the present invention are the mixed partial salt of a lower alkyl vinyl ether-maleic acid copolymer consisting essentially of the repeated structural unit: ##STR2## wherein R represents a C.sub.1-4 alkyl radical, n is an integer greater than one representing the number of repeated occurrences of said structural unit in a molecule of said copolymer and n is large enough to characterize said copolymer as having a specific viscosity larger than 1.2, the specific viscosity being determined in methyl ethyl ketone at 25.degree. C., said partial salts containing as the cationic salt function:

(a) from about 10% to about 65% zinc or strontium cations; and

(b) from about 10% to about 75% calcium cations

of the total initial carboxyl groups reacted.

R is preferably methyl.

Preferably, these mixed partial salts comprise from about 10% to about 45%, more preferably from about 15% to about 30% zinc or strontium cations (preferably zinc) and from about 25% to about 60%, more preferably from about 40% to about 60% calcium cations.

The mixed partial salts preferably further comprise from about 1% to about 20%, more preferably from about 1% to about 15% and most preferably from about 1% to about 10% sodium cations.

The subject polymeric salts are advantageously prepared by the interaction of the AVE/MA copolymer (I) with cationic calcium and either zinc or strontium compounds having a functional group typical of reactants of a carboxylic acid, such as, for example, the hydroxide, acetate, hali-ed., lactate, etc. in an aqueous medium. In a preferred embodiment, the oxide of zinc and the hydroxide of calcium are utilized. Since zinc hydroxide is not commercially available, its use as a reactant is readily and more economically accomplished by employing an aqueous slurry of particulate zinc oxide which, although practically insoluble in water, provides hydration to zinc hydroxide on the particulate surface. Calcium hydroxide as well as strontium hydroxide, on the other hand, are available in either crystalline or powder form and are soluble in about 50 parts water. Aqueous solutions of strontium oxide, however, which forms the hydroxide when treated with water (caution: heat evolution), may also be used.

Anions that form toxic, irritating or contaminating by-products should be avoided, or special precautions and treatment provided to assure the removal and absence of such by-products from the polymeric salt end-product. The particular compound used should be substantially pure to assure obtaining a substantially pure, substantially off-white polymeric salt end-product.

The lower alkyl vinyl ether maleic acid (AVE/MA) copolymers (I) are readily obtained by copolymerizing a lower alkyl vinyl ether monomer, such as methyl vinyl ether, ethyl vinyl ether, divinyl ether, propyl vinyl either and isobutyl vinyl ether, with maleic anhydride to yield the corresponding lower alkyl vinyl ether-maleic anhydride copolymer which is readily hydrolyzable to the acid copolymer (I). Both anhydride and acid forms are also available from commercial suppliers. For example, the GAF Corporation, Wayne, N.J. provides both the polymeric free acid form (I) and the corresponding anhydride form under its "GANTREZ" trademark as the "GANTREZ S Series" and "GANTREZ AN Series", respectively. In the former acid series, the GANTREZ S-97 (M. W..TM.50,000) is particularly suitable, and, in the latter anhydride series, the GANTREZ AN-149 (M. W.=50,000) the GANTREZ AN-169 (M. W.=67,000) and the GANTREZ AN-179 (M. W.=80,000) copolymers are particularly suitable. Said acid and anhydride forms of AVE/MA copolymers, having an average molecular weight of from about 50,000 to about 80,000 (as measured by membrane osmometry in 2-butanone 1-10 grams/1000 ml solution), are also characterized by having the previously described specific viscosity parameter of more than 1.2. When the anhydride copolymer dissolves in water, the anhydride linkage is cleaved so that the highly polar, polymeric free acid (I) is formed. Accordingly, the anhydride form, which is relatively less expensive than the acid form, may be used as a convenient and cheaper precursor for the acid. Elevated temperatures may be advantageously employed to enhance the rate of anhydride-to-acid hydrolysis.

In general, the lower alkyl vinyl ether-maleic acid copolymer (I), or its corresponding anhydride, is added to water preheated to about 70.degree.-80.degree. C. with vigorous stirring to form a homogeneous mixture. If the anhydride precursor is utilized, it is recommended that the aqueous mixture be further heated to about 90.degree. C. with stirring to ensure complete hydrolysis of the anhydride to the acid form. Heating is then discontinued although mixing is continued until the batch turns clear with a simultaneous decrease in viscosity (about 65.degree.-75.degree. C.). An aqueous solution of the cationic zinc or strontium salt forming compound, or, for example, an aqueous dispersion of particulate zinc oxide is combined with calcium hydroxide in the form of a slurry, in an amount sufficient to provide the desired cationic content desired in the end-product, is separately prepared at ambient temperature and slowly added to the hot polymeric acid solution with continuous vigorous mixing so as to prevent localized precipitation of the cationic polymeric salt. After addition is complete, mixing is continued to ensure that all the salt forming compound is reacted with the copolymer.

Alternatively, an aqueous solution containing the zinc and calcium source is preheated to 70.degree.-80.degree. C. with vigorous stirring to form a homogeneous slurry. The lower alkyl vinyl ether-maleic acid copolymer (I) or its corresponding anhydride is then added to the slurry while further heating to 90.degree. C. and stirring to ensure complete hydrolysis.

The sum total of zinc (or strontium) and calcium cations in the resultant mixed partial salt of AVE/MA copolymers should be sufficient to give a neutralization ranging from about 10% to about 75%, preferably from about 25% to about 60% and most preferably from about 60% calcium and from about 10% to about 65%, preferably from about 10% to about 45%, and most preferably from about 15% to about 30% zinc or strontium resulting in a salt containing free acid in the range of from about 20% to about 50%.

The reaction batch is then dried such as by shallow drying trays in a convection oven maintained at about 70.degree. C. with hot air circulation to evaporate the water content and recover the polymeric salt product in dry form. Alternatively, the reaction batch is then transferred to 5 drum dryers maintained at 80-100 PSIG with hot steam to evaporate the water content and recover the polymeric salt in the flake form.

The resulting flakes may be subjected to milling and screening to yield the desired physical properties to provide satisfactory denture stabilizing properties.

Said salts are friable so that appropriate particle size and bulk density can be obtained. For best results, particles should be capable of passage through a 140- to 200-mesh sieve (U.S.B.S. series) and preferably are less than 0.74 millimeter in their largest dimension.

The subject zinc or strontium and calcium AVE/MA copolymer salts have exceptional adhesive qualities when contacted with water or saliva such that they are extremely useful as denture adhesive materials in denture stabilizing compositions. For such use the salt in particulate form is preferably characterized by a particle size of at least minus 140-mesh U.S.B.S. sieve; a bulk density greater than 0.3 gram per cubic centimeter and preferably higher then 0.6 gram per cubic centimeter; and a pH between 3 and 7.0, the pH being determined on a one percent by weight dispersion in water.

Each of the subject calcium/zinc or strontium AVE/MA copolymer salts may be utilized in effective adhesive amounts, preferably at least 25 percent by weight, as the sole adhesive component or as a co-adhesive in joint usage with other active adhesive components in denture stabilizing compositions.

It is preferred that said calcium/zinc or strontium copolymer salt be used along with a co-adhesive in denture stabilizing compositions. Preferably, the co-adhesive is a polymeric material selected from the group consisting of natural gums, synthetic polymers, saccharide derivatives, cellulose derivatives, and mixtures thereof. In general, from about 15 to about 70 percent, based on the total weight of the composition, of said mixed calcium/zinc or strontium salt is present.

Preferred co-adhesives include a water-soluble hydrophilic colloid or polymer having the particular property of swelling upon exposure to moisture to form a mucilaginous mass. Such adhesive materials include both natural gums and synthetic polymeric gums and, among those commonly employed in denture stabilizing compositions and which are also suitable herein co-adhesive action with the subject mixed AVE/MA copolymer salts, there may be mentioned, for example, karaya gum, gelatin, algin, sodium alginate, tragacanth, methylcellulose, acrylamide polymers, ethylene oxide polymers, polyvinylpyrrolidone, cationic polyarylamide polymers and, as the most preferred, sodium carboxymethylcellulose and mixed partial salts of poly(vinyl methyl-ether maleate).

Accordingly, a preferred aspect of the subject invention provides a denture stabilizing composition having as a stabilizing component an effective adhesive amount of a mixed partial salt of a lower alkyl vinyl ether-maleic acid copolymer consisting essentially of the repeated structural unit: ##STR3## wherein R represents a C.sub.1 to C.sub.4 alkyl radical, n is an integer greater than one representing the number of repeated occurrences of said structural unit in a molecule of said copolymer and n is large enough to characterize said copolymer as having a specific viscosity larger than 1.2, the specific viscosity being determined in methyl ethyl ketone at 25.degree. C., said partial salts containing as the cationic salt function:

(a) from about 10% to about 65% zinc or strontium cations; and

(b) from about 10% to about 75% calcium cations

of the total initial carboxyl groups reacted.

Another preferred aspect of this invention provides a denture stabilizing composition comprising a safe and adhesively effective amount of at least two denture adhesive components, wherein one of said denture adhesive components is the mixed partial salt of a lower alkyl vinyl ether-maleic acid copolymer described above. Preferably the co-adhesive is as described above.

The compositions of the present invention can optionally include from about 0.01% to about 5% of one or more components which provide the user with sensory, including flavor, benefits. Suitable components include menthol, menthyl lactate, peppermint oil, spearmint oil, peppermint oil, leaf alcohol, as well as those paramenthane"carboxyamide flavoring agents available from Wilkinson-Sword (such as WS-3) which are described in U.S. Pat. No. 4,136,163 to Watson et.al., issued Jan. 23, 1979 which is incorporated by reference herein.

The compositions of the present invention are manufactured in an art-recognized manner known to those skilled in the art, such as in a powder, cream, ointment, liquid or a paste. Suitable examples of such formulations are disclosed in U.S. Pat. No. 4,518,721, issued May 21, 1985 and U.S. Pat. No. 4,514,528, issued Apr. 30, 1985, both to Dhabhar et.al. and both of which are hereby incorporated by reference herein.

The following non-limiting examples illustrate embodiments of the subject invention wherein both essential and optional ingredients are combined. It is to be understood that these examples are for illustrative purposes only and are not to be construed as limiting the scope of the invention thereto.

Into a reaction vessel equipped with a high speed stirrer and containing 92.4 parts (4.6 kg) of purified water heated to 85.C, is slowly added 0.53 parts (26.3 grams) of zinc oxide and calcium hyroxide 1.30 parts (64.6 grams). After addition is complete, the temperature of the slurry is kept constant with high speed mixing. While keeping heat and mixing constant add 5.76 parts (288 grams) of methyl vinyl ether-maleic anhydride copolymer to the reaction vessel containing the alkali dispersion over a 15 minute period. Temperature and mixing remain constant for 60 minutes. After 15 minutes the resulting adhesive polymeric dispersion is characterized by an increase in viscosity, and a decrease and stabilization of pH which is determined on a 1% by weight dispersion of said material in water, said material consisting of mixed partial calcium zinc salt of methyl vinyl ether-maleic acid copolymer.

The resultant solution of the calcium zinc salt of methyl vinyl ether-maleic acid (MVE/MA) copolymer is then transferred to shallow stainless steel drying trays and the trays placed in a hot air convection oven at 70.degree. C. for a sufficient time to evaporate the water content (about 16-18 hours). The thus obtained dried calcium zinc MVE/MA copolymer salt is then ground in a milling apparatus and screened through a 140-mesh sieve and then through a 200 mesh sieve (U.S.B.S. sieve series). The powder has an apparent bulk density of about 1.0-1.2 gram per cubic centimeter, and a pH of 5.4 for a one percent solution in water. Analysis of the salt indicates about 47.5 percent neutralization with calcium, 17.5 percent neutralized with zinc with 35% remaining carboxyl groups. This particular salt will be referred to hereinafter by the abbreviated term, "47.5% Ca/17.5% Zn partial salt of MVE/MA copolymer".

The product, when used in conjunction with conventional denture adhesives and applied to wet dentures with normal usage, provides denture stabilizing characteristics superior to those obtained by the particular conventional denture adhesive itself.

The procedure of Example I is repeated except that the following amounts of reactants are employed: 5.74 parts (516 grams) of the anhydride copolymer, 92.32 parts (8.31 kg) purified water; and 0.374 parts (33.6 grams) of zinc oxide; 0.074 parts (6.60 grams) of sodium hydroxide and 1.50 parts (134.40 g) calcium hydroxide.

The resultant powder has an apparent bulk density of about 0.8-1.2 grams per cubic centimeter and a pH of 5.8 for a one percent solution in water. Analysis of the salt indicates about 55 percent calcium neutralization of the total initial carboxyl groups in the copolymer salt molecule; 12.5 percent neutralization with zinc and 2.5% neutralization with sodium will be referred to hereinafter by the abbreviated term "55% calcium/12.5% zinc/2.5% sodium partial salt of MVE/MA copolymer".

By following the general procedure of Example I, except that an appropriate amount of zinc oxide is utilized to provide the tabulated zinc substitution, the following calcium/zinc/sodium salts of MVE/MA copolymer are obtained:

Each of the indicated MVE/MA copolymer salts, having an apparent bulk density for the minus 140-mesh U.S.B.S. sieve powder greater than 0.5 gram per cubic centimeter, provides markedly beneficial denture stabilizing characteristics. Each of the indicated salts may be abbreviated by the percent of calcium/percent of zinc/percent sodium neutralization as done in Examples I and II.

The MVE/MA copolymeric anhydride-to-acid hydrolysis procedure outlines in Example I is repeated. To a vessel containing 93.49 parts *1.8 kg) of purified water heated to 85.degree. C. is added 1.40 parts (28 g) of strontium hydroxide octahydrate. With vigorous mixing, 1.0 parts (20.0 g) of calcium hydroxide is slowly added. After addition is complete, the temperature of the slurry is kept constant with high speed mixing. While maintaining the heat and constant mixing, 4.10 parts *78.0 g) of methyl vinyl ether-maleic anhydride copolymer are added to the reaction vessel containing the alkali dispersion over a 20 minuted period. This produces a mixed partial calcium strontium salt of methy vinyl ether-maleic acid copolymer.

Denture stabilizing powder compositions are prepared by blending together the following:

In use, the above powders (typically 2.14 10 g) are placed on a premositened denture, allowed to hydrate briefly, and the denture is inserted in the mouth and pressed into place, all in the manner of denture adhesives well-known in the art.

Liquid-type denture stabilizing compositions are prepared by mixing together the following:

Cream-type denture stabilizing compositions are prepared by mixing together the following: