Application of Langer

• Decision Date: 03 October 1974
• Docket Number: Patent Appeal No. 9239.
• Citation: 503 F.2d 1380
• Parties: Application of Horst G. LANGER.
• Court: U.S. Court of Customs and Patent Appeals (CCPA)

503 F.2d 1380

Application of Horst G. LANGER.

Patent Appeal No. 9239.

United States Court of Customs and Patent Appeals.

October 3, 1974.

Bernd W. Sandt and Theodore Post, Midland, Mich., attorneys of record, for appellant.

Joseph F. Nakamura, Washington, D. C., for the Commissioner of Patents, Jack E. Armore, Washington, D. C., of counsel.

Before MARKEY, Chief Judge, and RICH, BALDWIN, LANE and MILLER, Judges.

LANE, Judge.

This appeal is from the decision of the Patent Office Board of Appeals, adhered to on reconsideration, affirming the rejection of all the claims, claims 1-20, for "lack of proof of utility (operativeness) of the claimed subject matter for its intended purpose" under 35 U.S.C. § 101, of patent application Serial No. 29,281,¹ filed April 16, 1970, for "Dentrifices and Method for Reducing Enamel Solubility." We reverse in part and affirm in part.

The Specification

Appellant's specification describes the invention in the following way:

The present invention concerns compositions and methods using a new source of stannous² tin for incorporation in dentifrices by which term is meant mouth washes, tooth pastes, tooth powders and chewing gums, i. e., compositions for introduction into the oral cavity as cleansing compositions.

The novel dentifrices contain tin in the stannous form as a substantially water-insoluble, non-ionizing chelate³ of a synthetic amino carboxylic acid having an Sn:N ratio of the chelate moieties of 1:1, in the amount of 0.00001 to 15 weight percent. The dentifrices of this invention thus make possible a method for supplying and contacting tooth enamel several times daily with a minor to trace source of reactive tin which reacts with exposed tooth enamel to form a highly insoluble basic stannous phosphate.

* * * * * *

An effective amount of topical application of stannous tin for the purpose of enamel solubility reduction can be had by employing as a component of the novel dentifrices herein taught at least 0.00001 weight percent of a stannous chelate of a chelating agent corresponding to the following general formula:

(HOOCCH2)2NR

(I)

wherein R is selected from the group consisting of H and (CH2)n -N-(CH2COOH)m CH2COOH (II) wherein n represents an integer which is 2, 3, or 4, and m represents an integer which is 0, 1, 2, 3, or 4, and of the alkali metal salts of such chelating agents, wherein one or two of the -CH2COOH groups may be replaced by a -CH2CH2OH group, resulting in a stannous tin chelate represented by the formula

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wherein 1 or 2 of the -CH2COOH groups may be replaced by a -CH2CH2OH group when m of moiety (II) above is 1, 2, 3, or 4. All of such stannous chelates are substantially water insoluble, i. e., have a water solubility generally less than one percent by weight at room temperature, all the chelate moieties have an Sn to N ratio of 1 to 1, and all provide a source of tin reactive with tooth enamel when introduced into the oral cavity as chewing gum or other dentifrice, to reduce the enamel solubility.

Representative of the foregoing stannous chelates are distannous chelate of ethylenediaminetetraacetic acid⁴ (Sn2EDTA) also referred to as Sn2 (II) EDTA; distannous chelate of hydroxyethyl ethylenediaminetriacetic acid⁵ Sn2HEDTA; monostannous chelate of nitrilotriacetic acid⁶ SnNTA; monostannous chelate of iminodiacetic acid⁷ SnIDA; and of N-substituted iminodiacetic acids such as monostannous chelate of N-methyl-, N-ethyl-, N-propyliminodiacetic acid, etc.; distannous chelate of propylenediaminetetraacetic acid⁸; distannous chelate of triimethylenediaminetetraacetic acid⁹; distannous chelate of tetramethylenediaminetetraacetic acid¹⁰; and generally the stannous chelates described in U.S. Patent 3,152,155. Bracketed insertions ours.

Appellant's specification also gives the following proposed theoretical explanation of how the invention operates:

Unlike the stannous salts of the prior art, e. g., stannous fluoride and chloride, which are water soluble and unstable in aqueous media, or other chelates which are water soluble, unstable and too tightly chelated to be effective, the stannous chelates used in the dentrifices of this invention are substantially insoluble in water and stable in aqueous media and provide an effective source of stannous tin. The distannous chelate of ethylenediaminetetraacetic acid, for example, has a water solubility of less than 0.05 weight percent at room temperature and is stable in aqueous formulations. The low solubility in water contributes to the oxidation resistance of such chelates. In solution in saliva, the minor to trace amount of dissolved stannous chelate gives an acid reaction which, in the presence of naturally occurring chelating agents normally present in the mouth, such as sugars, proteins, amino acids and lactic acid, is believed to promote a reaction according to the following simplified equations:

In the equations, SnR represents a water-insoluble chelate as utilized in the dentrifices herein, R'H2 represents a naturally occurring chelating agent normally present in the mouth, which compound has reactive hydrogen groups and the SnOH+ cation represents a species which has been demonstrated polarographically to form by hydrolysis of tin (II) salts and complexes in aqueous solution; Acta Chemica Scandinavica, 12 (1958), 198-223. The SnOH+ cation can react with the calcium hydroxyapatite of the enamel to form the insoluble basic stannous phosphate, in the same manner as stannous fluoride is believed now ultimately to react to form the same basic stannous phosphate. Because of the complexities of the above reactions involving minute quantities of reactants, it has not yet been possible conclusively to demonstrate by present analytic techniques that such reactions do, in fact, take place. Consequently, it is not desired to be bound by this theory, even though (1) the theory is consistent with all experimentally determined results, i. e., the formation with enamel of the basic stannous phosphate when a dentifrice containing one of the claimed stannous chelates is used and (2) such experimentally determined results are entirely consistent with said theory. In any event, there is an exchange of the calcium of the enamel for stannous tin provided by the chelate. As this exchange proceeds, a further minor to trace amount of stannous chelate dissolves and the exchange of stannous tin for calcium continues at the exposed surface of the tooth enamel while the dentifrice is in the mouth. Since the exposed tooth enamel surface in the mammalian mouth is relatively small, and the dentifrices are used on a continuing basis several times a day, an amount of stannous chelate as low as 0.00001 weight percent is effective in reducing enamel solubility. The exposure of enamel surfaces to the stannous chelates of the dentifrices herein described thus provides the tooth enamel with a surface of an insoluble basic stannous phosphate; J. of Dent.Res., 39, 740, July-August 1960; Myers, J.Am.Dent.Assn., 77, 1308, Dec. 1968. The compositions and methods disclosed are useful inter alia in the reduction of enamel solubility of valuable domesticated animals, such as, for example, dogs. Emphasis and bracketed insertion ours.

The specification contains sixteen "examples" of various types. Example 1 in the specification describes the results of a test where Sn2EDTA (see note 4, supra) was added to the diet of separate groups of rats at levels of 200 parts per million (p.p.m.) for Group A, 300 p.p.m. for Group B, and none for Group C (control). At examination following sacrifice, Group A had 9.1 caries lesions (average) per animal and a tin level of 160 p.p.m. (average) in their tooth enamel, Group B had 7.5 caries lesions (average) per animal and a tin level of 225 p.p.m. (average) in their tooth enamel, and Group C (control) had 12.2 caries lesions (average) per animal and a tin level of 4 p.p.m. in their tooth enamel.

Example 2 describes a tooth paste formulation where "preferably 3% by weight of tin chelate, e. g., distannous ethylenediaminetetraacetic Sn2EDTA, is incorporated in this paste, but it can be varied from about 1% to about 15%." Example 3 describes another tooth paste formulation where "to the paste is preferably added about 4% by weight of the tin chelate, distannous ethylenediaminetetraacetic Sn2EDTA." Example 4 describes a tooth powder formulation containing 7.5 parts of Sn2EDTA. Example 5 describes a mouth wash formulation containing Sn2EDTA "to the limit of solubility." Example 6 describes an astringent mouth wash formulation containing Sn2EDTA again "to the limit of solubility." Examples 7 and 8 describe chewing gum formulations containing Sn2EDTA where the amount of the chelate "can be varied from about 0.00001% to about 15% by weight."

Example 9 describes a chewing gum formulation to which "five parts of stannous chelate of iminodiacetic acid SnIDA, see note 7, supra is added."

Example 10 describes a chewing gum formulation containing "twelve parts distannous chelate of propylene diaminetetraacetate see note 8, supra."

Example 11 describes a chewing gum in which the stannous chelates incorporated in the gum mix can be "distannous chelate of ethylenediaminetetraacetic acid Sn2EDTA; distannous chelate of hydroxyethylethylenediaminetriacetic acid Sn2HEDTA, see note 5, supra; monostannous chelate of nitrilotriacetic acid SnNTA, see note 6, supra; distannous chelate of propylenediaminetetraacetic acid see note 8, supra; distannous chelate of trimethylenediaminetetraacetic acid see note 9, supra; and distannous chelate of tetramethylenediaminetetraacetic acid see note 10, supra."

Examples 12 and 13 are both entitled "Artificial Mouth Test: Enamel Solubility Reduction." They are preceded by the following explanatory paragraph.

To measure the effect on tooth enamel of enamel solubility reducing agents in dentifrices, dental researchers frequently use as an indicator the reduction in the

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