WO2012119155A1

WO2012119155A1 - Antimicrobial compositions for tooth fluoridation and remineralization

Info

Publication number: WO2012119155A1
Application number: PCT/US2012/027765
Authority: WO
Inventors: Ming S. Tung
Original assignee: American Dental Association Foundation
Priority date: 2011-03-03
Filing date: 2012-03-05
Publication date: 2012-09-07

Abstract

Compositions and methods for delivering, in an oral environment, chlorhexidine in combination with beneficial ions selected from calcium, phosphate, fluoride, silver, and carbonate ions are described. These compositions and methods may involve the formation of chlorhexidine compounds either prior to use or in situ. Representative compounds include chlorhexidine fluoride (ChxF), chlorhexidine phosphate (ChxP), chlorhexidine calcium fluoride (ChxCF), chlorhexidine phosphate fluoride (ChxPF), chlorhexidine calcium phosphate (ChxCP), chlorhexidine calcium phosphate fluoride (ChxCPF), chlorhexidine silver calcium phosphate fluoride (ChxACPF) or the compositions or methods which will form these noble chlorhexidine compounds when applied to the tooth. Two or more of these chlorhexidine compounds may be formed as an aggregate, or one or more of these chlorhexidine compounds may be formed as an aggregate with calcium fluoride (CaF2).

Description

ANTIMICROBIAL COMPOSITIONS FOR TOOTH FLUORIDATION

AND REMINERALIZATION

FIELD OF THE INVENTION

[01] The present invention relates to chlorhexidine compounds and their use in tooth remineralization, fluoridation, and/or bacterial control through antimicrobial activity. The invention also relates to compositions for forming such chlorhexidine compounds in the aqueous oral environment, whereby the compounds and associated compositions can prevent dental caries and/or periodontal disease, while avoiding drawbacks associated with conventional antimicrobial agents (e.g., unpleasant taste and tooth enamel staining).

BACKGROUND OF THE INVENTION

[02] At some point during their lives, most humans suffer from tooth decay and/or periodontal disease caused by bacteria in the mouth. The field of oral health care has therefore long recognized the important benefits associated with decreasing the number of these bacteria. The common approaches to achieving this end include regular tooth brushing and flossing, combined with periodic visits to a dental hygienist for professional cleaning of the teeth and gums. Additional approaches to enhance bacterial control include the use of mouth rinses containing an antimicrobial agent. Derivatives of bisbiguanido hexane, such as chlorhexidine (l,6-di-(p-chlorophenyl biguanido) hexane) and l,6-bis(2- ethylhexyl biguanido) hexane are known to potently inhibit the growth of many detrimental microorganisms such as Lactobacillus acidophilus odontolyticus and Streptococcus mutans. Furthermore, these derivatives are also known to be effective in preventing the formation of dental plaque, calculus, gingivitis, and mouth odor. Chlorhexidine is the most widely used antimicrobial agent in the treatment of periodontal diseases.

[03] In the art of oral bacterial control, U.S. Patent No. 3,976,765 teaches the use of stable bisbiguanido hexanes contained in products possessing activity against plaque formation and mouth odor s, while also having d esirable foaming properties. U. S. Patent No. 4,666,896 teaches the use of dinalidixate and diphosphanilate salts of chlorhexidine, which are described as exhibiting synergism relative to comparable concentrations of chlorhexidine and its respective free acid.

[04] Simply rinsing the mouth with a solution of chlorhexidine or one of its derivative compounds, however, is not an entirely satisfactory solution for bacterial control. Adverse effects associated with this practice include the development of a yellow-brown stain on the teeth, tongue, and/or tooth fillings. Non-cosmetic disadvantages include taste disturbances, particularly in the perception of sweet and salt. In a minority of users, scaling and soreness of the oral mucosa can result. High concentrations of these conventional antibacterial agents, or their respective salts, can lead to any or all of these undesirable side effects.

[05] Plaque, which forms on the tooth and is the principal cause of dental decay, can contain 250 or more separate microbial species. Plaque uses sugars and other fermentable carbohydrates to produce acids, which in turn cause demineralization of the tooth surface. In its initial stages, a carious lesion is not readily apparent. However, with prolonged and repeated demineralization by plaque-created acids, a cavity will ultimately form at the lesion site. When a lesion or cavity develops on the surface of a tooth, a dentist traditionally fills it, in order to prevent further spread of the decay. However, this procedure does not restore the tooth to its original state. Thus, a considerable amount of research has been directed toward the remineralization of incipient dental lesions, with the primary objective being the re-deposition of tooth mineral lost through decay. Through remineralization, i.e., restoring the tooth mineral at the site where it was lost (e.g., with apatite, optionally containing other ingredients such as fluoride), the tooth is not merely repaired, but restored to its original form.

[06] Various approaches to remineralization and topical fluoridation are described, for example, in the background of U.S. Patent No. 6,000,341 and related patents and patent applications. The '341 patent itself teaches the use of amorphous calcium phosphate compounds, such as amorphous calcium phosphate (ACP), amorphous calcium carbonate phosphate (ACCP), amorphous calcium phosphate fluoride (ACPF), and amorphous calcium carbonate phosphate fluoride (ACCPF) for use in remineralizing teeth. Other routes for achieving tooth remineralization are described in U.S. Patent Application Publication No. 2006/0110340, where, for example, separate compositions comprising one or more soluble calcium, orthophosphate, and peroxide salts may be stabilized for storage and then activated upon use. Also, U.S. Patent Application Publication No. 2005/0281759 describes the synthesis and use of calcium peroxyphosphate compounds, in dental compositions for whitening, mineralizing, and/or fluoridating teeth.

[07] In view of the continuing prevalence of dental caries in humans and other mammals, there remains an ongoing need to develop effective compositions and methods to prevent and/or reverse this disease as well as other dental diseases caused by oral bacteria.

SUMMARY OF THE INVENTION

[08] The present invention is associated with compounds, as well as compositions that form compounds in the oral environment, whereby the compounds beneficially provide, compared to conventional chlorhexidine-containing solutions, a relatively slow release of a relatively low concentration chlorhexidine, providing prolonged antimicrobial activity with the reduction or elimination of side effects. Aspects of the invention relate to improving oral health in patients through multimodal approaches, for example decreasing disease-causing bacteria with an antimicrobial agent, in combination with strengthening/repairing the tooth with calcium, phosphate and/or fluoride. A family of chlorhexidine compounds, described herein, are useful for such multifunctional purposes, and these compounds may either be formed in situ (in the mouth) or prepared prior to application to the tooth. These compounds benefit users, for example, in preventing oral diseases, through their antimicrobial, fluoridating, and/or remineralizing activities. Agents which may be present in compositions, for delivering the compounds described herein, include peroxides (e.g., carbamide peroxide) that effect tooth whitening and/or stain removal, and/or further enhance antimicrobial activity. Compositions and methods described herein are effective for reducing oral bacteria with agents having antimicrobial activity, in addition to promoting tooth fluoridation and remineralization, with the associated prevention and/or repair of weaknesses or lesions including dental caries, exposed dentin tubules, and voids resulting from stain removal. The compositions and methods are effective for the overall improvement in aspects of oral health relating to bacteria formation in the mouth and on tooth surfaces. [09] Representative chlorhexidine compounds that may be formed either in situ, or otherwise prior to administration to the oral cavity of a patient, include chlorhexidine calcium phosphate (ChxCP), chlorhexidine phosphate fluoride (ChxPF), chlorhexidine calcium fluoride (ChxCF), chlorhexidine calcium phosphate fluoride (ChxCPF), and chlorhexidine silver calcium phosphate fluoride (ChxACPF). The compounds are normally characterized as being amorphous (i.e., non-crystalline), as can be verified using conventional analytical methods, such as X-ray diffraction (XRD). These compounds may also be characterized, in general, as solid "solutions" containing chlorhexidine, and an ion, or preferably a combination of ions, selected from calcium, phosphate, fluoride, silver, and carbonate ions. Typically, such compounds contain chlorhexidine and a combination of two or more of these ions. Solid solutions, despite having no long range structure, are nevertheless homogeneous on an angstrom scale.

[10] Particular chlorhexidine compounds may be expressed in terms of their empirical formulae or otherwise their chemical formulae using non-integer atom ratios. The atom ratios in these formulae (as ratios of the subscripts in the chemical formulae) typically also define the molar ratios of atoms or compounds used in compositions that form the chlorhexidine compounds in situ or prior to administration. For example, representative amorphous chlorhexidine calcium phosphate compounds may be represented by the formula Ca_3-xChx_x(P0₄)₂, wherein Chx represents chlorhexidine and the subscript x generally ranges (a) from greater than 0 to less than 3. In a particular embodiment, x ranges (b) from about 0.5 to 2.5, and in a more particular embodiment, x ranges (c) from about 1 to about 2.

[11] Therefore, representative compositions used in the preparation or formation of such amorphous chlorhexidine calcium phosphate compounds comprise a chlorhexidine salt, a calcium salt and a phosphate salt, wherein, in the composition, (I) the molar ratio of calcium to chlorhexidine is (3-x)/x, wherein x may be in any of the above ranges (a), (b), or (c) (i.e., from greater than 0 to less than 3, from about 0.5 to about 2.5, or from about 1 to about 2). Thus, in the case (c) where x ranges from about 1 to about 2, the molar ratio of calcium to chlorhexidine in the composition can range from about 0.5 (when x=2) to about 2 (when x=l). According to other embodiments, in the composition, (II) the molar ratio of calcium to phosphate is (3-x)/2, wherein x may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (III) the molar ratio of chlorhexidine to phosphate is x/2, wherein x may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition used to prepare or form the amorphous chlorhexidine calcium phosphate compound, both conditions (I) and (II) above are met (i.e., (I) the molar ratio of calcium to chlorhexidine is (3-x)/x and (II) the molar ratio of calcium to phosphate is (3-x)/2, wherein x may be in any of the above ranges (a), (b), or (c)). Likewise, according to other embodiments, in the composition used to prepare or form the amorphous chlorhexidine calcium phosphate compound, both conditions (I) and (III) above are met. According to other embodiments, both conditions (II) and (III) are met. According to other embodiments, conditions (I), (II), and (III) are met. Preferably, the chlorhexidine salt, calcium salt and phosphate salt used in compositions to form these compounds are water soluble salts.

Representative amorphous chlorhexidine calcium phosphate fluoride compounds may be represented by the formula Ca_3-xChx_x(P0₄)2_-yF_3y, wherein x and y generally range (a) from greater than 0 to less than 3 and from greater than 0 to less than 2, respectively. In a particular embodiment, x and y range (b) from about 0.5 to 2.5 and from about 0.25 to about 1.75, respectively. In a more particular embodiment, x and y range (c) from about 1 to about 2 and from about 0.5 to about 1.5, respectively.

Representative compositions used in the preparation or formation of such amorphous chlorhexidine calcium phosphate fluoride compounds comprise a chlorhexidine salt, a calcium salt, a phosphate salt, and a fluoride salt wherein, in the composition, (I) the molar ratio of calcium to chlorhexidine is (3-x)/x, wherein x may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (II) the molar ratio of calcium to phosphate is (3-x)/(2-y), wherein x and y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (III) the molar ratio of calcium to fluoride is (3-x)/3y, wherein x and y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (IV) the molar ratio of chlorhexidine to phosphate is x/(2-y), wherein x and y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (V) the molar ratio of chlorhexidine to fluoride is x/3y, wherein x and y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (VI) the molar ratio of phosphate to fluoride is (2-y)/3y, wherein y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition used to prepare or form the amorphous chlorhexidine calcium phosphate fluoride compound, two or more of conditions (I), (II), (III), (IV), (V), and (VI) above are met (e.g. , conditions (I) and (II) are met, conditions (I) and (III) are met, conditions (I) and (IV) are met, conditions (I) and (V) are met, or conditions (I) and (VI) are met). According to other embodiments, three or more of the conditions (I), (II), (III), (IV), (V), and (VI) above are met. According to other embodiments, four or more of the conditions (I), (II), (III), (IV), (V), and (VI) above are met. According to other embodiments, five or more of the conditions (I), (II), (III), (IV), (V), and (VI) above are met. According to other embodiments, all conditions (I)-(VI) are met. Preferably, the chlorhexidine salt, calcium salt, phosphate salt, and fluoride salt used in compositions to form these compounds are water soluble salts.

[14] Representative amorphous chlorhexidine silver calcium phosphate fluoride compounds may be represented by the formula Ca(3_-x-z)Chx_xAg2z(P0₄)_2-yF3y, wherein x, y, and z generally range (a) from greater than 0 to less than 3, from greater than 0 to less than 2, and greater than 0, respectively, subject to the condition that x+z is less than 3. In a particular embodiment, x, y, and z range (b) from about 0.5 to 2.5, from about 0.25 to about 1.75, and greater than about 0.25, respectively. In a more particular embodiment, x, y, and z range (c) from about 1 to about 2, from about 0.5 to about 1.5, and greater than about 0.5, respectively.

[15] Representative compositions used in the preparation or formation of such amorphous chlorhexidine silver calcium phosphate fluoride compounds comprise a chlorhexidine salt, silver salt, a calcium salt, a phosphate salt, and a fluoride salt wherein, in the composition, (I) the molar ratio of calcium to chlorhexidine is (3-x-z)/x, wherein x and z may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (II) the molar ratio of calcium to silver is (3-x-z)/2z, wherein x and z may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (III) the molar ratio of calcium to phosphate is (3-x-z)/(2-y), wherein x, y, and z may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (IV) the molar ratio of calcium to fluoride is (3-x- z)/3y, wherein x, y, and z may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (V) the molar ratio of chlorhexidine to silver is x/2z, wherein x and z may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (VI) the molar ratio of chlorhexidine to phosphate is x/(2-y), wherein x and y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (VII) the molar ratio of chlorhexidine to fluoride is x/3y, wherein x and y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition, (VIII) the molar ratio of silver to phosphate is 2z/(2-y), wherein z and y may be in any of the above ranges (a),

(b) , or (c). According to other embodiments, in the composition, (IX) the molar ratio of silver to fluoride is 2z/3y, wherein z and y may be in any of the above ranges (a), (b), or

(c) . According to other embodiments, in the composition, (X) the molar ratio of phosphate to fluoride is (2-y)/3y, wherein y may be in any of the above ranges (a), (b), or (c). According to other embodiments, in the composition used to prepare or form the amorphous chlorhexidine silver calcium phosphate fluoride compound, two or more of conditions (I)-(X) above are met. According to other embodiments, three or more of the conditions (I)-(X) above are met, four or more of the conditions (I)-(X) above are met, five or of the conditions (I)-(X) above are met, six or more of the conditions (I)-(X) above are met, seven or more of the conditions (I)-(X) above are met, eight or more of the conditions (I)-(X) above are met, nine or more of the conditions (I)-(X) above are met, or all of the conditions (I)-(X) above are met. Preferably, the chlorhexidine salt, silver salt, calcium salt, phosphate salt, and fluoride salt used in compositions to form these compounds are water soluble salts.

Other representative compounds include amorphous chlorhexidine phosphate fluoride (ChxPF) and amorphous chlorhexidine calcium fluoride (ChxCF), represented by the formulas Chx_x(P0₄)_2-yF_3y and Ca_3-xChx_xF_3y, wherein, in various embodiments, the values of x and y are any of the ranges (a), (b), or (c) as described above. Conditions (I)-(III), analogous to the conditions discussed above with respect to compositions for preparing these compounds, are also met in various embodiments of the invention.

Any of the above amorphous chlorhexidine compounds may be in their respective hydrate or solvate forms, namely in the form of a complex of the compound with molecules or ions of a solvent (e.g. , water in the case of a hydrate). In this regard, the chemical formulae given above are not intended to preclude the existence of other complexed solvent molecules (i.e. , when the compound is in the form of a solvate), such as complexed water molecules (e.g. , when the compound is in the form of a hydrate). Therefore the compounds described herein and also recited in the appended claims necessarily include all forms in which these compounds may reside, including their respective solvate and hydrate forms. The chemical formulae given above can therefore be representative of all atoms present in a compound or solid solution (i. e. , a chlorhexidine compound represented by the formula Ca3_-xCh _x(P04)₂, as described above, can consist of calcium, as well as the atoms in chlorhexidine and phosphate, in the specified ratios). However, these chemical formula are not intended to preclude, in general, the existence of other atoms, possibly present in an additional chemical group of the compound, unless otherwise stated. Therefore, a chlorhexidine calcium phosphate compound, having molar ratios calcium, chlorhexidine, and phosphate as indicated in a given chemical formula, may also have other atoms or chemical groups as part of the long range structure of the solid solution. Therefore, a chlorhexidine calcium phosphate compound, for example, can include chemical groups of other cationic antimicrobial agents described herein, including bisbiguanido hexane derivatives described below. Further examples of antimicrobial agents that can be integrated into the structures of the chlorhexidine compounds described herein include (i) peptides and saccharides, in monomeric, oligomeric, or polymeric forms or otherwise (ii) peptide derivatives and saccharide derivatives, in monomeric, oligomeric, or polymeric forms. Such peptides and saccharides and their derivatives generally have at least one positively charged (cationic) functional group, which may include a nitrogen atom, a phosphorous atom, or sulfur atom that is positively charged, preferably under physiological pH (e.g. , pH = 7.4). A representative polysaccharide is chitosan, bearing amine functional groups. Thus, for example, a chlorhexidine calcium phosphate compound can include a chlorhexidine chitosan calcium phosphate compound.

The invention further relates to compositions having antimicrobial activity that can simultaneously fluoridate and remineralize a tooth (e.g. , with a final product of apatite). Representative compositions comprise a chlorhexidine salt, a calcium salt, a phosphate salt, and a fluoride salt, each of which is water soluble, in a stable delivery vehicle such as a non-aqueous carrier (e.g., used to suspend particles of the water soluble salts). Alternatively, kits may comprise two or more separate compositions of these salts, for example separate compositions of combinations of these salts (e.g. , kits having compositions in separated compartments). When the composition, or initially separate compositions, is/are exposed to the aqueous oral environment, chlorhexidine, calcium, phosphate, and fluoride ions, and optionally other ions, are released and have the multimodal therapeutic efficacy, as discussed above. For example, with the types of water soluble salts in these compositions, discussed above, the use of the proper ratios and concentrations of these salts, under the proper conditions of solid/solution solubility equilibrium and/or with particle sizes which result in the proper dissolution kinetics, etc., such compositions, when in contact with the aqueous oral environment, release ions that precipitate the chlorhexidine compounds discussed above, and optionally also form calcium fluoride (CaF₂). In the case of the formation of an amorphous chlorhexidine compound in combination with CaF₂, aggregates may be formed. Representative aggregates formed by compositions described herein therefore include calcium fluoride/chlorhexidine calcium phosphate fluoride (CaF₂-ChxCPF) aggregates or otherwise aggregates of calcium fluoride and other amorphous chlorhexidine compounds, as described herein. Alternatively, aggregates of any two or more of the amorphous chlorhexidine compounds may be formed, depending on the salts used in compositions to form these aggregates, as well as the relative concentrations of these salts. Representative aggregates therefore include chlorhexidine phosphate/chlorhexidine calcium phosphate (ChxP-ChxCPF) aggregates.

In compositions used to form amorphous chlorhexidine compounds described herein, including aggregates of such compounds as described above, representative water soluble chlorhexidine salts include the respective gluconate, acetate, fluoride, dihydrogen fluoride, and dihydrogen chloride salts and mixtures of these salts. Representative water soluble calcium salts include calcium sulfate, calcium oxide, calcium chloride, calcium nitrate, calcium acetate, calcium lactate, calcium peroxide, calcium glycerophosphate, and mixtures thereof. Representative water soluble phosphate salts include sodium phosphates, potassium phosphates, ammonium phosphates, calcium phosphates, and peroxyphosphates. Representative water soluble fluoride salts include sodium fluoride, potassium fluoride, ammonium fluoride, sodium fluorosilicate, sodium monofiuorophosphate, and silver fluoride. Representative water soluble silver salts, in the case of formation of chlorhexidine silver calcium phosphate fluoride, include silver nitrate, silver fluoride, and silver acetate. From the above description, it will be appreciated that, while in many cases four, or optionally five, separate compounds provide the sources of chlorhexidine, calcium, phosphate, fluoride, and silver, it is also possible (e.g. , in the case of a calcium phosphate-containing compound such as calcium orthophosphate) for a single compound to serve as two or three or even all four of the soluble chlorhexidine salt, soluble calcium salt, soluble phosphate salt, soluble fluoride salt, and soluble silver salt.

[20] Examples of non-aqueous carriers used to suspend particles of the chlorhexidine, calcium, phosphate, and fluoride salts include liquids such as varnishes (e.g., rosin- based), oils (e.g. , a vegetable oil, a mineral oil, or an essential oil), polyols (e.g. , glycerin), and alcohols. Liquid non-aqueous carriers will generally contain little water, for example, less than about 1 wt-% water. Often these compositions contain less than about 0.1 wt-% water or no water at all. Solid non-aqueous carriers include waxes, nonaqueous pastes and gels, and chewing gums. An especially preferred non-aqueous carrier is a varnish, which provides exceptional release characteristics that are favorable for the formation of chlorhexidine compounds described herein, either alone or in aggregate form. Varnishes have been found to provide sufficiently long contact time with tooth surfaces, together with good ion release kinetics, for the effective formation of the desired compounds. An especially preferred solid non-aqueous carrier is a wax, for example when used in the form of a waxed dental floss product.

[21] In place of, or in addition to, bisbiguanido hexane derivatives, such as chlorhexidine, representative compositions described herein may contain other cationic antibacterial agents. These include

N¹ -(4-chlorobenzyl)-N⁵-(2,4-dichlorobenzyl)biguanide; p-chlorophenyl biguanide; 4-chlorobenzhydryl biguanide; 4-chlorobenzhydrylguanylurea; N-3-lauroxypropyl-N⁵-p- chlorobenzylbiguanide; 1 -(lauryldimethylammonium)-8-(p- chlorobenzyldimethylammonium octane dichloride; 5,6-dichloro-2- guanidinobenzimidazole; N¹-p-chlorophenyl-N⁵-laurylbiguanide; 5-amino-l ,3-bis(2- ethylhexyl)-5-methylhexahydropyrimidine; and their nontoxic acid addition salts such as gluconate and acetate addition salts. The total amount of chlorhexidine and/or any of the above antimicrobial agents {e.g., a combination of chlorhexidine and one or more of the above antimicrobial agents) is generally in the range from about 0.050 to about 5% by weight, and typically from about 0.1% to about 3% by weight, in the compositions described herein.

[22] Other aspects of the invention relate to compositions and methods for reducing oral bacterial levels while simultaneously fluoridating and remineralizing a tooth. Representative methods comprise combining a first aqueous solution comprising a water soluble chlorhexidine salt and a water soluble calcium salt with a second aqueous solution comprising a soluble phosphate salt and a soluble fluoride salt to deliver a chlorhexidine compound as described herein, having the capability of simultaneously releasing, in the oral environment, beneficial chlorhexidine and one or more ions selected from, calcium, phosphate, fluoride, and silver ions, and combinations thereof. The methods further comprise, during or after combining the compositions, applying the combined composition {i.e., a composition capable of delivering a chlorhexidine compound described herein) to the tooth. Thus, the compositions of the first and second aqueous solutions may be such that, when mixed, will result in a mixture that forms or delivers any of the chlorhexidine compounds described herein, optionally in combination with CaF₂.

[23] The first and second aqueous solutions may be combined, for example, prior to applying the combined composition to teeth, for example, by using a tray such that contact is maintained between the combined composition and the surface of the teeth. According to one embodiment, an aqueous solution of the combined composition described above can prepared, prior to application. Alternatively, two or more aqueous solutions may be applied simultaneously or sequentially on the tooth, such that mixing and formation of the amorphous chlorhexidine compound, as a precipitate, occurs on the tooth.

[24] Other aspects of the invention relate to antimicrobial and tooth remineralization compositions comprising solid particles of (a) a soluble chlorhexidine salt, in combination with one or more of (b) a soluble calcium salt, (c) a soluble phosphate salt, (d) a soluble fluoride salt, and (e) a soluble silver salt. These salts in representative compositions will release chlorhexidine in combination with one or more ions selected from calcium ions, phosphate ions, fluoride ions, and silver ions when in contact with the aqueous oral environment. These ions, released in suitable concentrations and over suitable time periods, form (by precipitation), any of the chlorhexidine compounds described herein, and optionally two or more of such chlorhexidine compounds as an aggregate, or at least one of such chlorhexidine compounds as an aggregate with calcium fluoride, as discussed above.

[25] Other aspects of the invention relate to antimicrobial and tooth remineralization kits comprising a first aqueous solution comprising a chlorhexidine salt and a soluble calcium salt, and a second aqueous solution comprising a soluble phosphate salt and a soluble fluoride salt. The first and said second aqueous solutions are packaged in separate containers, and, after the solutions are combined, the resulting, combined aqueous solution, which is capable of delivering an amorphous chlorhexidine compound as described above, may thereafter be applied to the teeth.

[26] Yet further aspects of the invention relate to a carbonated aqueous solution comprising a water soluble chlorhexidine salt, and one or more of a water soluble calcium salt, a water soluble phosphate salt, a water soluble fluoride salt, and a water soluble silver salt. In a representative embodiment, the carbonated solution comprises a water soluble chlorhexidine salt in combination with each of a water soluble calcium salt, a water soluble phosphate salt, and a water soluble fluoride salt, with representative water soluble salts as described above. The carbonated aqueous solution is stable at low pH, and precipitates at least one amorphous chlorhexidine compound described above, optionally in the form of an aggregate, as also described above, upon release of carbon dioxide from the solution. Precipitation of the desired amorphous chlorhexidine is initiated upon depressurization of the carbonated solution, which releases carbon dioxide and increases solution pH. According to preferred embodiments, the carbonated solution is applied to the teeth shortly after depressurization/release of carbon dioxide (e.g., within 10 minutes, within 5 minutes, or within 1 minute following depressurization), for example by opening a pressurized vessel, such as an enclosed plastic container, to expose the contents (namely the carbonated solution) to ambient pressure.

[27] These and other aspects and features relating to the present invention are apparent from the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

[28] FIG. 1 is an x-ray powder diffraction pattern of amorphous chlorhexidine calcium phosphate, as prepared in Example 1.

[29] FIG. 2 is an x-ray powder diffraction pattern of amorphous chlorhexidine calcium phosphate fluoride, as prepared in Example 2.

[30] FIG. 3 is an infrared (IR) spectrum of chlorhexidine calcium phosphate fluoride, as prepared in Example 1.

[31] FIG. 4 is a Scanning Electron Microscopy (SEM) image of the amorphous chlorhexidine calcium phosphate fluoride, as prepared in Example 2 and in the form of an aggregate with calcium fluoride (CaF₂).

[32] FIG. 5 illustrates the antimicrobial activity of representative chlorhexidine compound precipitating compositions, as prepared in Example 6 at differing chlorhexidine acetate concentrations in a varnish composition.

DETAILED DESCRIPTION OF THE INVENTION

[33] Dental caries (tooth decay) is a demineralization process caused by acids produced from bacteria plaque. Calcium and phosphate, as predominant constituents of tooth mineral, can be used for tooth remineralization, or reversal of the decay. Fluoride prevents dental caries by inhibiting the demineralization process and/or promoting remineralization (i.e., formation of calcium phosphate tooth mineral). Thus, fluoride, calcium, and phosphate have the ability to prevent dental caries when applied to the tooth in the proper manner. Chlorhexidine (Chx) and related bisbiguanido hexane derivatives are antimicrobial agents that can kill the bacteria that cause dental caries. Compounds containing some, and preferably all, of the beneficial ingredients, namely chlorhexidine in combination with calcium, phosphate, and/or fluoride, can promote the remineralization of the tooth while preventing bacteria growth, thereby effectively preventing and repairing dental caries. Chlorhexidine can also act to prevent periodontal diseases.

[34] Chlorhexidine fluoride and a family of other compounds based on the solid solution chemistry of chlorhexidine have been found useful for the prevention of dental caries and periodontal diseases, especially in terms of their ability to release beneficial chlorhexidine in combination with other important ions, namely calcium, phosphate, fluoride, and/or silver ions, at controlled release rates into the oral cavity. Representative chlorhexidine compounds include chlorhexidine calcium fluoride (ChxCF), chlorhexidine phosphate fluoride (ChxPF) chlorhexidine calcium phosphate (ChxCP)_, and chlorhexidine calcium phosphate fluoride (ChxCPF). Another representative compound is chlorhexidine silver calcium phosphate fluoride (ChxACPF), with the silver ions acting to provide additional antimicrobial activity. In the abbreviated formulas of the compounds described above and elsewhere herein, Chx is understood to represent chlorhexidine, C is understood to represent calcium (Ca), P is understood to represent phosphate (P0₄), and F is understood to represent fluoride (F), and A is understood to represent silver (Ag).

[35] Aggregates of two or more of these chlorhexidine compounds, or an aggregate of one or more of these chlorhexidine compounds with calcium fluoride, are also beneficial in obtaining the desired remineralization/antimicrobial activities discussed above. Representative aggregates comprise at least one of calcium fluoride, chlorhexidine fluoride, and chlorhexidine phosphate, together with at least one of ChxCF, ChxPF, ChxCP, and ChxCPF. Compounds and aggregates described herein can be prepared first and applied on the tooth in a carrier or formed in situ on and in the tooth. Aspects of the invention therefore relate to methods and compositions for preparing chlorhexidine compounds, including aggregates of such compounds, as described herein.

[36] The synthesis of chlorhexidine compounds described herein (e.g., from water soluble salts as described above), is generally carried out at ambient temperature or physiological temperature if the compound is synthesized in situ (i.e., in the mouth). Typical reaction temperatures are therefore in the range from about 15°C to about 40°C. The resulting chlorhexidine compounds are preferably mainly or substantially (e.g. , greater than about 90%, or even greater than about 95%) amorphous (non-crystalline), as confirmed using appropriate analytical methods such as X-ray powder diffraction. According to other embodiments, the chlorhexidine compound is mainly amorphous and is in the form of an aggregate with another component as described above (e.g. , CaF₂) which may be either crystalline or amorphous. In a representative embodiment, chlorhexidine calcium phosphate fluoride (ChxCPF) is prepared by combining a chlorhexidine digluconate aqueous solution (20% w/v), with calcium acetate, potassium phosphate and sodium fluoride, in solid or solution form, and these ingredients at sufficiently high concentrations precipitate amorphous ChxCPF spontaneously. Similar procedures can be followed to obtain other amorphous chlorhexidine compounds and/or aggregates of chlorhexidine compounds as described herein, by varying the types and concentrations of the starting materials. Those skilled in the art, with the knowledge gained from the present disclosure, will be able to ascertain the requisite ingredients, concentrations, and conditions. It will also be appreciated that multiple pathways exist for obtaining a given chlorhexidine compound. For example, the compound ChxF₂ may be synthesized either (1) by mixing an aqueous solution of chlorhexidine digluconate (for example, at a concentration of 20% w/v) with an aqueous solution of sodium fluoride (for example, at a concentration of 1 mol/1) or (2) by adding solid chlorhexidine to the above aqueous sodium fluoride solution.

A preferred amorphous chlorhexidine compound is amorphous chlorhexidine calcium phosphate fluoride (ChxCPF). As discussed above, this compound provides a solid solution containing chlorhexidine, together with beneficial ions, namely calcium ions, phosphate ions, and fluoride ions for combined antimicrobial and tooth remineralization properties in a single compound. Based on the descriptions above of chemical formulae for the amorphous chlorhexidine compounds, the atomic makeup of these compounds, including amorphous chlorhexidine calcium phosphate fluoride, in terms of the molar ratios of chlorhexidine, calcium, phosphate, fluoride, and optionally silver, may vary. Under physiological conditions, amorphous ChxCPF over a range of atomic makeup values, has a high solubility and can dissolve, release the chlorhexidine and the beneficial ions into the oral environment as discussed above. These ions can then in turn convert to apatite tooth mineral, allowing the antimicrobial and remineralization effects to proceed at a practical rate for therapeutic purposes. A particular subset of amorphous chlorhexidine compounds fall in the category of amorphous chlorhexidine calcium phosphate-containing compounds, and these include amorphous chlorhexidine calcium phosphate (ChxCP), as well as amorphous chlorhexidine calcium phosphate fluoride (ChxCPF), amorphous chlorhexidine calcium carbonate phosphate (ChxCCbP), and amorphous chlorhexidine calcium carbonate phosphate fluoride (AChxCCbPF), with Cb understood to represent carbonate (C0₃ ^" ). According to other embodiments, mixtures of two or more of these amorphous chlorhexidine calcium phosphate-containing compounds may be provided in any mixing ratio. Aspects of the invention therefore relate particularly to the deposition of chlorhexidine calcium phosphate fluoride-containing compounds, or aggregates of these compounds, on the tooth.

The formation of an amorphous chlorhexidine calcium phosphate-containing compound, optionally as an aggregate as described above, is particularly beneficial in that amorphous chlorhexidine compounds within this class are generally more soluble under acidic conditions than under basic conditions (e.g., more soluble at a pH of less than 7 than at a pH of greater than 7), and therefore release higher concentrations of chlorhexidine, calcium ions, and phosphate ions when the tooth is "under attack" or most susceptible to demineralization. Moreover, the dissolution of amorphous chlorhexidine calcium phosphate-containing compounds neutralizes acidic conditions in the mouth and raises oral pH to values less conducive to demineralization (i.e., more favorable to remineralization). In this manner, amorphous chlorhexidine calcium phosphate- containing compounds or aggregates of these compounds can simultaneously deliver all the necessary and desirable components for antimicrobial activity and tooth remineralization, as discussed above. Preferably, the chlorhexidine calcium phosphate- containing compound, ChxCPF is formed, by including sufficient fluoride in the composition used to form the amorphous chlorhexidine compound.

Without being bound by theory, representative compositions, used to prepare amorphous chlorhexidine compounds and their aggregates, have the ability to quickly release chlorhexidine, calcium, phosphate, fluoride, and optionally silver and/or carbonate, in sufficient amounts and at the appropriate ratios, such that the desired compound or aggregate (e.g., an aggregate of calcium fluoride and an amorphous chlorhexidine calcium phosphate-containing compound as described above) is produced (e.g., by precipitation). Although the release of ions and formation of the amorphous chlorhexidine compound may occur in situ (e.g. , in the aqueous, oral environment), these events may otherwise occur at some time prior to the application of the formed amorphous chlorhexidine compound or aggregate to the tooth. In either case, an aggregate of both calcium fluoride and an amorphous chlorhexidine calcium phosphate- containing compound, as described above, can be formed, with the aggregate components acting together to promote the advantageous antimicrobial, tooth fluoridation and remineralization properties, as described above. Preferably, the aggregates are nanoaggregates (i.e. , are composed of nanoparticles of the components), with representative aggregates comprising a nano amorphous chlorhexidine compound and nano calcium fluoride (either crystalline or amorphous), or, according to other embodiments, comprising two or more nano amorphous chlorhexidine compounds. Particular nanoaggregates of interest comprise two or more of nano calcium fluoride, nano chlorhexidine fluoride, nano chlorhexidine phosphate, nano chlorhexidine calcium fluoride and nano chlorhexidine calcium phosphate fluoride.

Several types of systems, including the precipitating compositions described herein, have the potential to form a desired, multifunctional, therapeutic amorphous chlorhexidine compound or aggregate thereof (e.g., with calcium fluoride). For example, a stable, single phase non-aqueous medium or carrier may be used to suspend (or mix with) solid particles of a chlorhexidine salt, a calcium salt, a phosphate salt, and a fluoride salt, with each of these salts being water-soluble. Upon application of this composition to the tooth (i.e., in the aqueous environment of the mouth), the salts dissolve readily in sufficient concentrations causing the resulting saliva-containing solution to become supersaturated with respect to a desired amorphous chlorhexidine compound or aggregate thereof (e.g., a desired aggregate of calcium fluoride and one or more amorphous chlorhexidine calcium phosphate-containing compounds, as described above). The supersaturated solution (of saliva) then rapidly precipitates and forms the desired amorphous chlorhexidine compound or aggregate. [41] Suitable non-aqueous carriers for use in representative compositions i nclude liquids, pastes, and gels (e.g. , tooth varnishes, dental resins, dental adhesives, dental composites, dental pick, pit and fissure sealants). Other suitable non-aqueous media or carriers include oils (e.g., vegetable oils, mineral oils, and essential oils), waxes, esters, alcohols, and polyols. Essential oils have antiseptic and antimicrobial effects, and include thymol, menthol, eucalyptol, and eugenol. Other non-aqueous media or carriers, as discussed above, are varnishes, which typically comprise a natural polymer (e.g. , a rosin such as colophony or a pine resin-based material) or synthetic polymer (e.g. , a polyurethane based resin or a polymethacrylate based resin such as polymethyl methacrylate) in alcoholic solution. Other non-aqueous carriers can include reactive monomer systems (e.g., in the form of a paste with suitable fillers) that cure or polymerize in the presence of radiation (e.g. , UV light) or moisture. Reactive monomer systems thus include one-part systems that can be cured, as well as two-part resin systems that cure via chemical reaction, upon combining the two parts. Such reactive monomer systems which are useful for oral applications are known in the art and described, for example, in U.S. Patent Nos. 5,508,342 and 6,649,669, the description of these monomer systems being incorporated by reference. Varnishes have been used for sustained-release tooth fluoridation and are also applicable as carriers in the precipitating compositions described herein. Tooth varnishes are generally compounds that are topically applied to teeth with a special brush, cotton, or tray and harden over a short time by contact with saliva, air, or both.

[42] Solid materials (e.g. , dental flosses, floss waxes, confections, chewing gums, and polymeric matrices) as described in U.S. Patent No. 5,993,786 may also function similarly as carriers to provide the calcium, phosphate, and fluoride ingredients in sufficient quantities and ratios to cause aggregate formation in the aqueous environment of the mouth. Suitable polymers which may be used in a solid polymeric matrix carrier are described, for example, in U.S. Patent No. 5,508,342, the description of the disclosed polymeric carriers being incorporated by reference. Chewing gum compositions as nonaqueous media include natural or synthetic gum base materials, such as natural tree resins and latexes, as well as synthetic polymers. Examples include chicle and other polyterpenes and isoprenes, styrenes, butadienes, poly(vinyl acetate), or polyethylene. A waxed dental floss product provides a suitable carrier in a composition comprising the water soluble salts, as described above.

[43] Any of these non-aqueous carriers may contain minor quantities of water but are generally essentially or completely free of water (e.g. , contain less than 1 wt-% water, less than 1000 ppm water, or less than 100 ppm water). It is also possible to provide the chlorhexidine salt, calcium salt, phosphate salt, fluoride salt, and/or silver salt in a solid powder comprising solid particles of these salts without any carrier, or with an inert material (e.g. , a water-soluble solid such as a starch). Because the salts are soluble in aqueous media, they will dissolve and form a precipitating composition in situ (i.e. , in the aqueous, oral environment). Whether solid particles of water soluble salts are suspended in a non-aqueous medium or used without any medium, small particle sizes will improve dissolution rate in the mouth as well as minimize any unpleasant, gritty texture. The average particle size, with respect to at least one of these salts, at least two of these salts, or all of the salts used in the precipitating composition, will generally be less about 150 microns (μιη), typically from about 1 to about 100 μπι and often from about 5 to about 100 pm.

[44] Another type of system for forming and delivering the desired amorphous chlorhexidine compound or aggregate thereof involves the use of separate, aqueous solutions. One solution, for example, can comprise a soluble chlorhexidine salt and a soluble calcium salt, and a second solution can comprise a soluble phosphate salt and a soluble fluoride salt. This allows the chlorhexidine, calcium, phosphate, and fluoride ions to be solubilized in separate, stable environments prior to being combined in amounts and ratios which lead to the precipitation or formation of the desired amorphous chlorhexidine compound or aggregate, as described above. While this delivery system is thus exemplified by the use of two aqueous solutions, those skilled in the art having knowledge gained from the present disclosure can readily contemplate alternative delivery systems within the scope of the invention, including those with more than two (e.g. , three) aqueous solutions or with aqueous solutions having varying compositions (e.g. , where the soluble phosphate salt is distributed between the first and second solutions). The overriding consideration is maintaining the aqueous solutions and their respective ingredients, namely chlorhexidine and ions of one or more of calcium, phosphate, fluoride, and silver, in stable concentrations under storage conditions, such that precipitate formation is avoided, before the solutions are combined. Upon mixing or combination of the solutions, the resulting mixture has the desired properties which allow the formation and delivery of an amorphous chlorhexidine compound or aggregate thereof, as described above, to the tooth, thereby resulting in antimicrobial activity, remineralization (e.g., through the formation of apatite upon release of the beneficial ions of tooth mineral, such as calcium and phosphate) and fluoridation (e.g., by maintaining the fluoride concentration in mouth). Tooth kits may therefore comprise two or more aqueous solutions that, when combined, result in the formation of an amorphous chlorhexidine compound or aggregate thereof, such as a calcium fluoride/amorphous chlorhexidine calcium phosphate-containing compound aggregate. The two or more aqueous solutions, containing the soluble chlorhexidine, calcium, phosphate, fluoride, and/or silver ingredients, may also be effectively separated in stable concentrations, by using separate layers in a gel or polyol carrier. In this manner, for example, a soluble chlorhexidine salt and a soluble calcium salt can be contained in one layer of a gel and soluble phosphate and soluble fluoride salts in another layer. A gel, such as a polyol, can be used as a carrier for either or both (or all) layers that are combined to yield the precipitating composition (in this case a gel composition). When the gel is applied to the teeth, the soluble salts are combined to form and deliver the amorphous chlorhexidine compound or aggregate thereof, as described above. In another representative embodiment, one of the solutions may be microencapsulated and suspended in another solution. In this case, the two solutions are mixed just before or during application.

Solutions of soluble salts of chlorhexidine and one or more of soluble calcium, phosphate, fluoride, and silver salts, as described above, may therefore be mixed or combined prior to the application to the tooth surface, such that the combination and application steps are performed sequentially. For example, a first aqueous solution comprising a soluble chlorhexidine salt and a soluble calcium salt may be first combined and mixed thoroughly in a container, such as a cup or a tray, with a second aqueous solution comprising a soluble phosphate salt and a soluble fluoride salt. In this manner, the amorphous chlorhexidine compound or aggregate thereof is formed in an aqueous composition prior to and/or during application to the teeth. Alternatively, the compositions may be mixed on the teeth at the time of application (i.e. , use) to the teeth in a simultaneous manner. Thus, simultaneous mixing and application (i. e. , for delivery of the amorphous chlorhexidine compound or aggregate thereof) includes methods wherein a first, chlorhexidine- and calcium-containing aqueous composition is applied onto the surface of the tooth (e.g., applying a solution with a cotton tip) and a second phosphate- and fluoride-containing aqueous composition is then applied, such that it is combined with the applied first composition.

It is also possible to maintain solubilized chlorhexidine, calcium, phosphate, and fluoride salts in a single, stable aqueous composition having the desired amounts and ratios of ingredients, such as ions, which "self assemble," to form an amorphous chlorhexidine compound or aggregate thereof, for example in combination with calcium fluoride. In this case, the precipitation or formation of the chlorhexidine compound or aggregate thereof is effected through changing one or more conditions (e.g., pH or temperature) of the aqueous composition to destabilize it, such that the solution becomes supersaturated and precipitation ensues. For example, a pH change for inducing precipitation of the chlorhexidine compound or aggregate c an result from the release of carbon dioxide pressure. During storage under the pressurized carbon dioxide atmosphere, a single solution can stably maintain relatively high concentrations of, for example, chlorhexidine, calcium, phosphate, and fluoride ions at a relatively low pH. When the gas is released upon, or shortly before, application to the tooth, the aqueous solution pH rises, resulting in an unstable, supersaturated condition under which the chlorhexidine compound or aggregate described above is readily formed. Another method for causing supersaturation with subsequent precipitation involves increasing the aqueous solution temperature from a stable and relatively lower storage temperature (e.g., refrigeration temperature) to an unstable and relatively higher use temperature, such as room temperature or body temperature (i.e., in the mouth). Thus, altering pH and/or temperature to induce instability and precipitation therefore represents an alternative method of forming the chlorhexidine compound or aggregate, either in situ or prior to use.

Regardless of the particular method and precipitating composition used (e.g. , a suspension of salts in an non-aqueous carrier, a mixture of more than one aqueous solution, a single aqueous solution which has become destabilized/super saturated, etc.), it has been found that various amounts and ratios of the chlorhexidine, in combination with one or more of calcium, phosphate, fluoride, and silver, generally lead to the effective formation of the desired, chlorhexidine compound or aggregate {e.g., a two-component aggregate) as described above.

[48] For example, good results may be obtained with precipitating compositions generally having an initial concentration of calcium (as total Ca) of greater than about 3 millimolar (mM) (e.g., from about 3 to about 500 mM), an initial concentration of phosphate (as total P0₄) of greater than about 5 mM (e.g., from about 5 to about 200 mM), a concentration of fluoride (as total F) of greater than about 3 ppm by weight (e.g., from about 3 to about 6000 ppm), and a pH of greater than about 6 (e.g., from about 6 to about 10). The initial concentrations refer to those achieved in oral environment when the system is applied and is dissolved, and prior to precipitation. The concentrations and the pH are such that the oral environment becomes supersaturated with respect to the desired amorphous chlorhexidine compound or aggregate as the soluble salts dissolve.

[49] Therefore, regardless of type of precipitating composition or method used to obtain the composition (e.g., by combining two aqueous solutions), including the compositions and methods described herein, an important property is the ability of the composition to provide, in the oral environment, a solution that is supersaturated with respect to the amorphous chlorhexidine compound or aggregate (e.g., an aggregate of calcium fluoride and an amorphous chlorhexidine calcium phosphate-containing compound).

[50] Examples of aqueous compositions, as discussed herein, include those resulting from combining two or more aqueous solutions or those resulting from the release of carbon dioxide pressure to effect a pH change. In such aqueous precipitating compositions, the property of being supersaturated with respect to components of the aggregate (e.g., calcium fluoride, chlorhexidine fluoride, or chlorhexidine phosphate or other chlorhexidine calcium phosphate-containing compound) is readily verified by determining the chlorhexidine concentration as well as the concentrations of ions of calcium, phosphate, fluoride, silver, carbonate, etc. after preparation of the aqueous precipitating composition (e.g., after combining aqueous solutions, releasing carbon dioxide pressure, etc.) but prior to the formation of any precipitate. The property of being supersaturated with respect to any chlorhexidine compound or aggregate thereof may also be analytically determined (e.g. , by diluting, prior to any precipitate formation, a sample of the resulting precipitating composition such that it is no longer supersaturated, measuring the ion concentrations, and calculating the ion concentrations prior to dilution).

[51] In the case of a precipitating composition, as described herein, in which the carrier is a non-aqueous liquid or solid, the property of supersaturation is based on an approximation of conditions in the oral environment when the non-aqueous composition is introduced and mixes thoroughly with saliva. For example, a convenient test involves vigorously mixing the non-aqueous composition (e.g. , containing water-soluble chlorhexidine, calcium, phosphate, and fluoride salts) with an equal volume of de-ionized water at 25°C and pH=7, for a specified time period (e.g., 30 seconds or 1 minute) and then evaluating the resulting aqueous phase in the manner described above, to determine whether it is supersaturated with respect to an amorphous chlorhexidine compound or aggregate. Another test for supersaturation involves vigorously mixing the non-aqueous composition (e.g. , containing water-soluble chlorhexidine, calcium, phosphate, and fluoride salts) with an equal volume of de-ionized water at 25 °C and pH=7, as described above, but for a longer time period (e.g. , 30 minutes), and then filtering the solution to determine the precipitates formed. The fact of the precipitation establishes that a given solution is supersaturated with respect to an amorphous chlorhexidine compound or aggregate. A subsequent analysis of the precipitate can further characterize the precipitate in terms of the particular amorphous chlorhexidine compound or aggregate formed, including the chemical formula(ae) of the precipitated component(s).

[52] The conditions required for the formation of the amorphous chlorhexidine compound or aggregate, for example, using a composition comprising a non-aqueous carrier, include the proper pH, ion molar ratios, and dissolution equilibria and kinetics (which depend on temperature and particle size). These necessary criteria are described herein or are otherwise apparent, through routine experimentation, to one having ordinary skill in the art, having regard for the teachings of the present disclosure. The presence of a chlorhexidine-containing precipitate may be verified by known analytical techniques such as X-ray Powder Diffraction (XRD) and Infrared Spectroscopy (IR).

[53] Mixtures of soluble chlorhexidine salts, mixtures of soluble calcium salts (e.g., a mixture of calcium chloride and calcium lactate), as well as mixtures of soluble phosphate salts, and/or mixtures of soluble fluoride salts may be used in the precipitating compositions described herein.

[54] The precipitating compositions, or any or all of the solutions which are combined to form it (e.g., aqueous solutions comprising one or more of a soluble chlorhexidine salt, a soluble calcium salt, a soluble phosphate salt, a soluble fluoride salt, and/or a soluble silver salt, as described above) may also contain a tooth whitening agent such as peroxide or otherwise may be essentially or completely free of peroxide (e.g., contain less than 10 ppm of peroxide, less than 5 ppm of peroxide, or less than 1 ppm of peroxide). In the case where a single aqueous solution or a combination of aqueous solutions is used to form the precipitating composition, any or all of these aqueous solutions may be essentially or completely free of non-aqueous constituents such as alcohols, ketones, nonaqueous gels, etc. (e.g., the composition may contain less than 10 ppm, less than 5 ppm, or less than 1 ppm of non-aqueous constituents). Additionally, the precipitating composition, or any or all of the solutions used to form it, may contain an antimicrobial agent such as chlorhexidine or other antimicrobial agents described herein, such as chitosan.

[55] Soluble chlorhexidine salts referred to herein include chlorhexidine digluconate, chlorhexidine diacetate and chlorhexidine difluoride. Soluble calcium salts referred to herein include salts that either contain calcium ions or decompose when used orally to yield calcium ions. Soluble calcium salts refer to those having calcium ion solubility in water of at least about 14 mM (or at least about 560 ppm) at 25°C and pH of 7.0. When exposed to saliva, soluble calcium salts therefore provide a source of calcium in sufficient concentration for the formation of a desired amorphous chlorhexidine compound or aggregate, as described herein. Soluble calcium salts include, but are not limited to, calcium sulfate (e.g. , plaster of Paris), calcium chloride, calcium nitrate, calcium acetate, calcium bromide, calcium gluconate, calcium benzoate, calcium glycerophosphate, calcium formate, calcium fumarate, calcium oxide, calcium lactate, calcium butyrate, calcium isobutyrate, calcium malate, calcium propionate, and calcium valerate.

Soluble phosphate salts refer to those having a phosphate ion solubility in water of at least about 40 mM (or at least about 3800 ppm) at 25°C and pH of 7.0, thus providing a source of phosphate sufficient for formation of a desired amorphous chlorhexidine compound or aggregate and subsequent remineralization. Preferred soluble phosphate salts include the alkali metal, alkaline earth metal, and ammonium phosphate salts. Representative soluble phosphate salts include monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, monoammonium phosphate, diammonium phosphate, triammonium phosphate, monocalcium phosphate monohydrate (MCMP), and monocalcium phosphate anhydrate (MCPA). Other phosphate salts are the more highly oxidized peroxyphosphates, which include peroxymonophosphates (PO₅ ^"3) and diperoxymonophosphates (P0₆ ^"3) such as the alkali metal, alkaline earth metal, and ammonium salts of peroxymonophosphate and diperoxymonophosphate. Representative Peroxymonophosphate salts include monopotassium peroxymonophosphate, dipotassium peroxymonophosphate, tripotassium peroxymonophosphate, monosodium peroxymonophosphate, disodium peroxymonophosphate, trisodium peroxymonophosphate, monoammonium peroxymonophosphate, diammonium peroxymonophosphate, and triammonium peroxymonophosphate and calcium peroxymonophosphates. Representative Diperoxymonophosphate salts include monopotassium diperoxymonophosphate, dipotassium diperoxymonophosphate, tripotassium diperoxymonophosphate, monosodium diperoxymonophosphate, disodium diperoxymonophosphate, trisodium diperoxymonophosphate, monoammonium diperoxymonophosphate, diammonium diperoxymonophosphate, and triammonium diperoxymonophosphate.

Soluble fluoride salts refer to those having a fluoride ion solubility in water of at least about 1000 ppm at 25°C and pH of 7.0, thus providing a source of source of fluoride sufficient for formation, for example, of nano calcium fluoride, as a component of an aggregate of an amorphous chlorhexidine compound, as well as possibly the formation of nano amorphous chlorhexidine calcium phosphate fluoride, either alone or as another component of a nanoaggregate. Representative soluble fluoride salts include sodium fluoride, potassium fluoride, zinc fluoride, stannous fluoride, zinc ammonium fluoride, sodium monofluorophosphate, sodium hexafluorosilicate, potassium monofluorophosphate, laurylamine hydrofluoride, diethylaminoethyloctoylamide hydro fluoride, l-ethanol-2-hexadecylimidazoline dihydrofluoride, dodecyltrimethylammonium fluoride, tetraethylammonium fluoride, didecyldimethylammonium fluoride, cetylpyridinium fluoride, dilaurylmoφholinium fluoride, N-carboxymethyl-N-dodecyldiethylammonium fluoride, sarcosine stannous fluoride, glycine potassium fluoride, glycine hydrofluoride, sodium monofluorophosphate, and silver fluoride.

[58] The precipitating compositions may contain one or more conventional additives such as surfactants (e.g. , anionic, cationic, nonionic, and zwitterionic surfactants), cosurfactants or cleansing agents, soaps, flavoring agents, sweetening agents (e.g. , xylitol, licorice extract), aroma agents, astringents, anti-plaque agents, anti-calculus agents, anti-bacterial agents (e.g., silver nitrate, cetyl pyridinium chloride, triclosan, or chlorhexidine), additional preservatives and/or stabilizers, sudsing agents, humectants, thickening agents (including inorganic thickeners such as hydrated silica), binding agents or cothickeners, coloring agents, abrasive polishing agents, buffering agents, alkali metal halide salts, desensitizing agents, healing agents, other preventative caries agents, vitamins, amino acids, proteins, opacifiers, antibiotics, anti-enzymes, enzymes, oxidizing/whitening agents, antioxidants, chelating agents, etc. When used, these additives are present in amounts that do not substantially adversely affect the desired precipitating capabilities of the composition, as discussed above.

[59] Examples of oxidizing and whitening agents which are beneficially present in the precipitating compositions include peroxides and hexametaphosphates. I f peroxide is used, it may be initially stabilized for storage by maintaining it at an acidic pH in a stabilized aqueous peroxide solution, optionally containing the soluble phosphate salt and/or the soluble fluoride salt. The stabilized aqueous peroxide solution may then become destabilized, or reactive for tooth whitening upon use, by increasing pH and/or removing phosphate. Destabilization of peroxide in this manner results in the formation of perhydroxyl anions/radicals, which are beneficial for stain removal and whitening. [60] For purposes of this disclosure, concentrations which are expressed in "ppm," "wt-%," or simply "%" are all based on weight. Therefore, a solution containing 1000 ppm of a salt will contain 1 gram of that salt per kg of solution.

[61] Throughout this disclosure, various aspects are presented in a range format. The description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc. , as well as individual whole and fractional numbers within that range, for example, 1, 2, 2.6, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[62] In view of the above, it will be seen that several advantages may be achieved and other advantageous results may be obtained. As various changes could be made in the above compositions and methods without departing from the scope of the present disclosure, it is intended that all matter contained in this application, including all theoretical mechanisms and/or modes of interaction described above, shall be interpreted as illustrative only and not limiting in any way the scope of the appended claims.

[63] The following examples are set forth as representative of the present invention. These examples are not to be construed as limiting the scope of the invention as these and other equivalent embodiments will be apparent in view of the present disclosure and appended claims.

EXAMPLE 1

Chlorhexidine calcium phosphate (ChxCP) was synthesized by mixing 10 ml of 1.5 mol/1 calcium acetate and 20 ml of 0.22 mol/1 chlorhexidine digluconate which was then added to 16 ml of 1 mol/1 dipotassium phosphate under stirring. ChxCP precipitated immediately. The precipitate was filtered after 9 min and washed with 2% ammonium hydroxide, followed by ethanol, and then dried. The x-ray powder diffraction pattern in FIG. 1 indicates that the precipitate is amorphous with a broad band of amorphous ChxCPF with maximum around 2 Θ = 30. The infrared spectrum in FIG. 3 shows the wave numbers of amorphous bands of phosphate at 564 and 1040 and absorption bands of chlorhexidine at 726, 830, 1416, 1495, 1533, 1582, and 1635. The Scanning Electron Microscopy (SEM) image depicted in FIG. 4 illustrates that the amorphous chlorhexidine compound was precipitated as nanoparticles.

EXAMPLE 2

[64] Chlorhexidine calcium phosphate fluoride (ChxCPF) was synthesized by mixing 10 ml of 1.5 mol/1 calcium acetate and 20 mL of 0.22 mol/1 chlorhexidine digluconate. The mixture was then added to a solution of 16 ml of 1 mol/1 dipotassium phosphate and 1 mol/1 sodium fluoride under stirring. ChxCPF precipitated immediately. The precipitate was filtered after 9 min and washed with 2% ammonium hydroxide, followed by ethanol, and then dried. The x-ray powder diffraction pattern in FIG. 2 shows that the precipitated chlorhexidine compound is amorphous.

EXAMPLE 3

[65] Chlorhexidine silver calcium phosphate fluoride (ChxACPF) was synthesized by mixing 16 mL of 0.225 mol/1 calcium acetate, 6 ml of 0.2 mol/1 silver nitrate, and 6 ml of 0.22 mol/1 chlorhexidine digluconate. The mixture which was then added to a solution of 11 ml of 1 mol/1 dipotassium phosphate and 0.2 ml of 1 mol/1 sodium fluoride under stirring. ChxACPF precipitated immediately. The precipitate was filtered after 9 min and washed with 2% ammonium hydroxide, followed by ethanol, and then dried.

EXAMPLE 4

Chlorhexidine fluoride is synthesized by two alternate methods: (1) mixing of a chlorhexidine digluconate aqueous solution (20% w/v) with a sodium fluoride solution (1 mol/1) and (2) adding solid chlorhexidine to the above sodium fluoride solution.

EXAMPLE 5

A non-aqueous, rosin-based varnish contains 10 wt-% chlorhexidine diacetate, 10 wt-% calcium sulfate (Plaster of Paris), 6 wt-% disodium phosphate, and 5 wt-% sodium fluoride and has a calculated F/Ca molar ratio of 1.7. Each of these chlorhexidine, calcium, phosphate, and fluoride salts is present in the varnish in the form of solid particles, having an average diameter of about 25 μιη. When this varnish is applied to the surface of a tooth inside the mouth, the salts dissolve readily in aqueous saliva, resulting in sufficient concentrations of chlorhexidine, in combination with ions of calcium, phosphate, and fluoride, in the proper ratios for the precipitation of chlorhexidine calcium phosphate fluoride. The precipitate then releases chlorhexidine and the beneficial ions over time to the tooth surface. These ions convert to fluoride-containing apatite, the tooth mineral.

EXAMPLE 6

Three varnishes with 0, 9.1, and 35.1 % of chlorhexidine acetate, together with suspended particles of calcium and phosphate salts, were tested for their antimicrobial activity. The two compositions containing chlorhexidine acetate, together with calcium and phosphate salts, were capable of precipitating an amorphous chlorhexidine calcium phosphate compound as described herein. One drop of each varnish composition was applied on an agar dish containing Streptococcus mutans with an optic density of 4.0. The dish was incubated at 37°C and 100% humidity for 2 days. The dish is shown in FIG. 5 with inhibiting rings. The relative antimicrobial activities are demonstrated by the radii of the inhibiting rings, minus the radii of the samples, and these values are 0.2, 0.4, and 0.6 cm for varnishes with 0, 9.1, and 35.1 % of chlorhexidine acetate respectively. In FIG. 5, the varnish sample used at the upper left section is the control without chlorhexidine, whereas the varnish sample used at the lower section is the 9.1% sample, and the varnish sample used at the upper right section is the 35.1% sample.

Claims

WHAT IS CLAIMED IS:

1. An amorphous chlorhexidine compound, comprising chlorhexidine, and an at least one ion selected from the group consisting of calcium, phosphate, fluoride, and silver ions.

2. The amorphous chlorhexidine compound of claim 1, which is selected from the group consisting of chlorhexidine calcium phosphate, chlorhexidine phosphate fluoride, chlorhexidine calcium fluoride, chlorhexidine calcium phosphate fluoride, chlorhexidine silver calcium phosphate fluoride, amorphous chlorhexidine calcium carbonate phosphate, and amorphous chlorhexidine calcium carbonate phosphate fluoride.

3. The amorphous chlorhexidine compound of claim 1, which is in the form of an aggregate with calcium fluoride.

4. The aggregate of claim 3, in which the amorphous chlorhexidine compound and calcium fluoride are present as nanoparticles.

5. The aggregate of claim 3, which is an aggregate of calcium fluoride and an amorphous chlorhexidine calcium phosphate-containing compound.

6. The amorphous chlorhexidine compound of claim 1, which is amorphous chlorhexidine calcium phosphate having the formula:

Ca_(3-x)Chx_x(P0₄)₂

wherein Chx is chlorhexidine and x is greater than 0 and less than 3.

7. The amorphous chlorhexidine compound of claim 1, further comprising chitosan.

8. The amorphous chlorhexidine compound of claim 1, which is chlorhexidine chitosan calcium phosphate.

9. The amorphous chlorhexidine compound of claim 8, in which the chl orhexidine chitosan calcium phosphate is present as nanoparticles.

10. The amorphous chlorhexidine compound of claim 1, which is amorphous chlorhexidine calcium phosphate fluoride having the formula:

Ca_(3-x)Chx_x(P0₄)_(2-y)F_3y

wherein Chx is chlorhexidine; x is greater than 0 and less than 3; y is greater than 0 and less than 2.

11. The amorphous chlorhexidine compound of claim 1 , which is amorphous chlorhexidine silver calcium phosphate fluoride having the formula:

Ca_(3-x-z)Chx_xAg_2z(P0₄)_(2-y)F_3y

wherein Chx is chlorhexidine; x is greater than 0 and less than 3; y is greater than 0 and less than 2; z+x is less than 3; and z is greater than 0.

12. An antibacterial composition for fluoridating and remineralizing a tooth comprising: a chlorhexidme salt

a calcium salt,

a phosphate salt, and

a fluoride salt, wherein (a), (b), (c), and (d) are water-soluble salts suspended in a carrier, wherein, when applied onto the tooth, said composition releases chlorhexidine, calcium, phosphate, and fluoride ions.

13. The composition of claim 12, wherein, when applied onto the tooth, said composition releases chlorhexidine, calcium, phosphate, and fluoride ions and forms an amorphous chlorhexidine compound.

14. The composition of claim 13, wherein, when applied onto the tooth, said composition releases a nanoaggregate of calcium fluoride and an amorphous chlorhexidine calcium phosphate-containing compound.

15. The composition of claim 13, wherein, when applied onto the tooth, said composition releases a nanoaggregate of chlorhexidine fluoride and a chlorhexidine calcium phosphate-containing compound.

16. The composition of claim 13, wherein, when applied onto the tooth, said composition releases a nanoaggregate of chlorhexidine phosphate and a chlorhexidine calcium phosphate-containing compound.

17. The composition of claim 12, wherein said calcium salt is selected from the group consisting of calcium sulfate, calcium oxide, calcium chloride, calcium nitrate, calcium acetate, calcium lactate, calcium gluconate, calcium lactate gluconate, calcium lysinate, calcium glycerophosphate, and mixtures thereof.

18. The composition of claim 12, wherein said phosphate salt is selected from the group consisting of a sodium phosphate, a potassium phosphate, an ammonium phosphate, a calcium phosphate, and a peroxyphosphate.

19. The composition of claim 12, wherein said fluoride salt is selected from the group consisting of sodium fluoride, potassium fluoride, ammonium fluoride, sodium monofluorophosphate, sodium silicate hexafluoride, and calcium silicate hexafluoride.

20. The composition of claim 12, wherein said aqueous carrier is selected from the group consisting of a varnish, a dental resin, a dental composite, a dental cement, a pit and fissure sealant, a prophylaxis paste, a dentifrice, a dental wax, a dental floss, a chewing gum, confections, unsaturated monomer systems and a polymeric matrix.

21. An antibacterial dental cement composition for fluoridating and remineralizing a tooth, comprising a chlorhexidine material, a calcium material, a phosphate material, and a fluoride material.

22. A method for the simultaneous removal of oral bacteria and remineralization and fluoridation of tooth surfaces, the method comprising applying the composition of claim 12 to said tooth.

23. An method for the simultaneous removal of oral bacteria and remineralization and fluoridation of tooth surfaces, the method comprising:

(a) combining a first aqueous solution comprising a soluble chlorhexidine salt and a soluble calcium salt with a second aqueous solution comprising a soluble phosphate salt and a soluble fluoride salt to obtain a precipitating composition, and

(b) during or after step (a), applying said precipitating composition to said tooth.

24. The method of claim 23, wherein said second aqueous solution further comprises a peroxide.

25. The method of claim 23, wherein said precipitating composition, obtained in step (a), is applied to said tooth in step (b) using a tray.

26. A method for the simultaneous removal of oral bacteria and remineralization and fluoridation of tooth surfaces, the method comprising:

(a) applying a first aqueous solution comprising a soluble chlorhexidine salt and a soluble calcium salt to said tooth, and (b) after step (a), applying a second aqueous solution comprising a soluble phosphate salt and a soluble fluoride salt to said tooth, wherein an amorphous chlorhexidine calcium phosphate fluoride-containing composition is formed on the tooth.

27. The method of claim 26 wherein said second aqueous solution further comprises a peroxide.

28. A method for the simultaneous removal of oral bacteria and remineralization and fluoridation of tooth surfaces, the method comprising:

(a) applying a first gel comprising a soluble chlorhexidine salt and a soluble calcium salt to said tooth, and

(b) after step (a), applying a second gel comprising a soluble phosphate salt and a soluble fluoride salt to said tooth, wherein an amorphous chlorhexidine calcium phosphate fluoride-containing composition is formed on the tooth.

29. The method of claim 28, wherein said second gel further comprising a peroxide.

30. A dental caries prevention kit for preparing a precipitating composition, said kit comprising:

(a) a first aqueous solution comprising a soluble chlorhexidine salt and a soluble calcium salt, and

(b) a second aqueous solution comprising a soluble phosphate salt and a soluble fluoride salt, wherein said first and said second aqueous solutions are packaged in separate containers, and when combined, form a chlorhexidine calcium phosphate fluoride- containing compound.

31. The kit of claim 30, wherein said second aqueous solution further comprises a peroxide.

32. The kit of claim 31, wherein said second aqueous solution further comprises carbonate.

33. A pressurized, carbonated aqueous solution comprising a soluble chlorhexidine salt, a soluble calcium salt, a soluble phosphate salt, and a soluble fluoride salt, wherein said solution precipitates a chlorhexidine calcium phosphate fluoride-containing compound upon release of carbon dioxide pressure from said solution.

34. The solution of claim 33, further comprising a peroxide.

35. A method for the simultaneous removal of oral bacteria and remineralization and fluoridation of tooth surfaces, the method comprising contacting a dental restorative with the tooth, said dental restorative comprising in combination a carrier and a chlorhexidine calcium phosphate fluoride-containing compound.

36. The method of claim 35, wherein said carrier is selected from the group consisting of a dental pit and fissure sealant, an unsaturated monomer system, a polymer matrix, a dental cement, and a varnish.