CA1126160A - Pure alkali metal salts of lauryl (dodecyl) sulphate in oral composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Dental hygiene compositions containing as antiplaque/
antiseptic/deodorizing active ingredient highly pure alkali metal lauryl sulphate substantially free from non-lauryl alkyl salts.

Description

The present invention relates to dental hygiene compositions including, but not limited to, dentifrices in solid, powder, paste, or cream form and liquid mouth washes and rinses.
The primary use oE such compositions is in maintaining dental hygiene and it is the function of such compositions to keep the surface of the teeth as clean and shiny as possible, to preserve the health of the teeth and gums, to inhibit the formation of ~npleasant odours in the oral cavity and to freshen the user's breath. Known formulations of such compositions have been intended to provide cosmetic, cleansing, refreshing and/or deodorizing benefits/ or have provided a therapeutic e.g. anticaries activity.
The compositions of the present invention are formulated to provide a further therapeutic activity, namely an antiplaque activity. Dental plaque is considered to be a material composed largely of microorganisms and an organic matrix derived from bacteria and saliva. Dental experts generally consider that the calculus also known as tartar is a mature plaque which has crystallized with the development of an identifiable crystal structure. It is well known that even with regular and thorough brushing, the plaque ~i.e~ calciEied plaque) deposit adheres tenaciously to the teeth. Such deposits are unattractive and cause tooth decay.
It is the object of this invention to provide dental hygiene compositions, which wil:L prevent or reduce the deposit of clental plaque. It :is al90 an object oE this invention to provide formulations COntaininCJ anticaries agents such as sodium fluoride or sodium monofluorophosphate. ~ Eurther object o khis :invention is to provide dental hygiene composi-tions which will possess significant antimicrobial properties.
The present invention is based on the findiny that alkali me-tal salts of lauryl (dodecyl) sulphate when employed in a highly pure forml substantially free from other alkyl sulphates, exhibit particular advantages with respect to the formulation and use of dental hygiene compositions having antiplaque activity. The most readily-available lauryl sulphate salt is the sodium form, i.e. sodium lauryl sulphate. ~.
The potassium and other alkali metal salts are analogous to the sodium salt, although the use of the latter is normally preferred for reasons of economy. It will be appreciated, however, that the potassium and other alkali metal salts may be substituted for the sodium salt in the compositions oE
the invention and hereinafter described.

The material that is commonly commercially available under the designation "sodium lauryl sulphate" is not the pure compound sodium dodecyl sulphate C~3(CH2)10CH2OSO3Na, but is a mixture of homologous sodium alkyl sulphates with sodium dodecyl sulphate predominating. Thus, as normally employed, the designation or chemical description "sodium lauryl sulphate" refers to a material containing as impurity varying amounts of sodium salts oE non-dodecyl alkyl sulphates as well as the pure dodecyl sulphate salt. These mate:rials often also contain varying amounts of sodium salts of inorganic acids e.g. sodium chloride and sodium sulphate, and unsulphated alcohols.

Sod.ium lauryl sulphate in impure form has been employed .in t~le past in toothpaste compositi.ons as a detergent or foam-producing agent. The present inventors have :investiga-ted the specific antimicrohial activity of solutions o~ various forms of material commercially available as "soclium lauryl sulphate", including one form that has recent.ly become available from certain sources as a highly pu:re compound, substantially free from any content of non~dodecyl alkyl sulphate sodium salts. It has been found that the anti- ~;
microbial activity of the pure form of the sodium ~ s~
dodecyl sulphate material against the microorganisms considered to be responsible for plaque-formation in the human mouth is high, while the activity o-F the impure solutions combining substantial amounts of non-dodecyl alk~l sulphates against such microorganisms is inhibited to a significant extent.

Thus as between pure and impure solutions containing equivalent amounts of the pure compound, a higher specific activity will be exhibited by the solution that is substantially free of non-dodecyl alkyl sulphate salts, and therefore, by employing sodium dodecyl sulphate material in a form that is of high purity, there can be provided a composition having an effective level of antiplaque activity at a relatively lower content of the alkyl sulphate salt. The level of the alkyl sulphate is a matter of practical importance as the concentration of alkyl sulphate that needs to be employed in a mouthwash or toothpaste composition can be an important factor in the formation of a product that meets with consumer acceptance.
In the mouth, sodium dodecyl sulphate and other alkyl sulphates have an astringent effect. Depending on the nature and proportions of the ingredients in the formula-tion, a small variation in the alkyl sulphate content can ma}ce the difference between a product that is acceptable to the consumer and one that is unacceptable as having a harsh and unpleasant taste or that gives an unpleasant sensation in the mouth owing to thP physiolog.ica:L action o~ the alkyl su:Lphate on -the mou-th and dental tissues. ~oreover, an excessive content oE alkyl sulphate is normally to be avoided as in use oE the composition this can lead to an over-abundant degree of ~oaming in the mouth.

The present invention provides a dental hygiene composition having antimicrobial activity ayainst plaque-forming microorganisms and comprising an effective amount of from 0.1 to 2.0 per cent o~ one or more highly pure alkali metal salts of dodecyl sulphate substantially free from non-dodecyl alkyl sulphate salts, dissolved in one or more vehicles physiologically compatible with the teeth and mouth tissues.

All parts and percentages herein are ~y weight unless specified otherwise.

Any suitably pure form of sodium dodecyl sulphate or other alkali metal dodecyl sulphate salt may be employed in the compositions of the invention. The amount of non-dodecyl impurity that can be tolerated in the composition without significantly detracting from the antiplaque activity depends in each case on the quantity of the pure sodium or the alkali .
metal dodecyl sulphate that is present, and the percentages o~
impurity are therefore best expressed in terms of the ~eight of alkali metal dodecyl sulphate. In the preferred forms~ the compositions of the invention contain less -than 5% of salts of non-dodecyl alkyl sulphate, based on the weight of alkali metal dodecyl sulphate, more preferably less than 2~ and still more preferably less than 1% based on the weight of the alkali metal dodecyl sulphate salt. One especially preferred source of the alkali metal dodecyl sulphate salt for use in the composition of the invention is the highly pure form of sodium dodecyl sulphate that is a~ailable under the trade mark TEXAPON L-100 from Henkel Chemicals (Canada) Ltd., Toronto, Canada. This mater:Lal has a washing actlvity of 99~, indicat.incJ a content o~ pure soclium dodecyl sulphate oE about 99%, and conta:ins less than 0.63 of alkaJ.i metal chloride and sulphate and has a zero conterlt of unsulphated alcohols. As far as the inventors are aware, the TEXAPON L-100 material is unique among other commercially-available forms of "sodium lauryl sulphate" in its .
high content of the pure dodecyl sulphate salt, but it will be appreciated that the invention is not necessarily limited to : ~ .

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the use of the TEXAPON L-100 material and that such other highly pure forms of the dodecyl sulphate salt as may be available, or may in the future become available~ having a similar high degree o~ purity, preferably at least 95%, may be employed.

It may be noted that the preferred compositions are substantially free from any content of fatty acid based soaps or detergents other than said dodecyl sulphate salts, as these may impart an undesirable taste without contributing to the antiplaque activity of the pure dodecyl sulphate salt, and therefore the desirable antiplaque activity of the compositions is exhibited to the best advantage when solutions free from these materials were employed.

The antimicrobial activity of the compositions of the invention varies with pH and the optimum activity of the dodecyl sulphate salts has been found to occur when the salts are acidulated to about pH 2. However, under extremely acid conditions, the alkali metal dodecyl sulphate salt tends to undergo hydrolysis so that -the antiplaque activity diminishes over prolonged periods e.g. during stora~e. At pH in the range 3.0 to 5.0 satisfactory antiplaque activity can usually be achieved without undue loss of activity occurring during storage of the made-up compositions and therefore this range of pH is generall~ prefe~rred. Optimum antiplaque activity extending over normal storage liEe can be obtained at about plI 4.5 and this pEI is thereEore most preEerred or present purposes. However, in order to ach:i.eve this pll depending on the basicity of other :ingredients of the composition, it may be necessary to add considerable quantities of aqueous solutions o~ acid, and in some ~ormulations, particularly in the case o~ toothpastes and like solid or semi-solid dentifrices containing abrasives or other materials that exhibit a buffering action tending to maintain a pH higher , ~
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than 4.5, the amount of liquid that can be added is limited owing to the requirement for a viseous consistency. In sueh cases p~l somewhat higher than 4.5 will normally be employed, i.e. pH 4.5 to 5.0 consistent with maintaining a desired solids content in the composition. ~ny physiologically aceeptable acid may be employed to adjust the pH to -the desired value.
Suitable examples include dilute hydrochloric acid and phosphoric acid. Physiologically aeceptable acidie buffers e.g. buffering salt pairs such as the well-known aee-tate or citrate buffers i.e. sodium aeetate-aeetie aeid buffer or sodium trieitrate/eitric acid buffer, or buffer compounds such as dibasie sodium phosphate may be added, typically in an amount of about 0.01 to about 0.2%, to maintain the eompositions at the desired pH during mixing and storage.

Certain types of liquid dental hygiene formulations, espeeially mouthwashes and rinses, eonventionally eontain substantial quantities of ethyl aleohol as an astringent and antiseptie agent. It has been found that in the presenee of substantial quantities of alcohol the desired antiplaque activity ean be aehieved with a reduced eontent of the pure dodeeyl sulphate salts of the invention, and it is suggested that the presenee of ethyl aleohol potentiates the antiplaque aetivity of the dodeeyl sulphate salts. Aeeordingly, in liquid mouthwash eompositions eontaining substantial quantities of ethyl aleohol, in the range 10 to 30%, a somewhat smaller uantity of the al]cali metal clodecy:l sulphate salt may be employed, prePerably :in the range 0.1 to 0.5~.

The eompositions of the invent:ion may be flavoured with eonventional essential oil flavours e.g. thymol, euealyptol, methyl salicylate, and peppermint and spearmint oi.ls, typically in an amount of 0.2 to 3.0%. In the ease of eompositions eombining water or an aqueous vehicle, t:hese oils may if neeessary be maintained in dispersion wit:h the aid of suitable dispersing agents. The use of cationic detergents is to be avoided for this purpose as these materials tend to reduce the efficacy of the alkali metal dodecyl sulphate salts and the preferred dispersing agents are nonionic surfactants advantageously in an amount to form 0.1 to 0.~%.
As an example of a nonionic surfactant, there may be mentioned the water-soluble TWEEN ( trade mark~ materials, which are polyoxyethylene derivatives of fatty acid partial esters of sorbitol anhydrides, but these tend to have a pronounced taste that may not be desired in all instances and therefore the preferred nonionic surfactants are the water-soluble P~URONIC
(trade mark~ material available from BA~F Wyandotte Corporation. These are alpha-hydro omega-hydroxy poly-oxyethylene block copolymers. Especially preferred on account of its excellent dispersing and solubilizing activity and because it is relatively tasteless, is the PLURONIC F-127 nonionic surfactant which is available as a white solid, of average molecular weight 12,~00, in prill or flake form.

In -the case of compositions in accordance with the invention that are formulated as liquid mouthwashes or rinses, it is further preferred to add zinc chloride as an astri.ngent, suitably in an amount of 0.01 to 0.05~. This material has mouth deodorizing activity and in presence of sodium dodecyl sulphate this activity is potentiated.

It has been further :Eound thal composit.ions conta.ining a mixture oE the pure al]cali metal dodecyl sulphate together with alkali metal N-acyl sarcosinates exert a g.reater antiplaque activity than compositions containiny equi.valent weights of ei.ther of these compounds without the other, or that, in other words, the combination of the dodecyl sulphate salt with the N-acyl sarcosinate achieves a synergistic effect. For example, in comparisons of the antiplaque activity of five toothpaste compositions that .

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contained 2% alkali metal dodecyl sulphate, 2% alkali metal N-acyl sarcosinate, and 2% of a mixture o the said sulphate and sarcosina~e in the ratios 1~ 2, and 2:1, respectively, there were observed percentage reductions of plaque of 50%, 40%, 78%, 61% and 60% respectively. This ac-tion o~ the N aeyl sarcosinates in potentiating the aetivity of the alkali metal dodecyl sulphates may be exploited in the formulation of toothpaste and like dentifrices in solid, powder, paste, or eream form, where a composition of high solids content with an enhanced antiplaque aetivity may be aehieved at a relatively low eontent of the alkali metal dodecyl sulphate through inclusion of the N-aeyl sarcosinate, in the formulation. The preferred material is sodium N-lauroyl sareosinate added in an amount 0.5 to 2.0% by weight, more preferably in 1:1 to 1:3 ratio to the weight of alkali metal dodecyl sulphate, the latter preferably also being present in an amount of 0.5 to 2.0% by weight.

The composition may contain the conventional humectants such as glycerine and/or sorbitol. In the case of mouthwashes containing relatively large quantities of water e.g.
in the range 50 to 90~, the humeetants may be present in an amount up to about 20%, more typically about 10%. In the case of toothpaste and like products where the moisture content plays a more important role in preserving a desired consisteney and vise~sity o~ the product, somewhat greater ~uantitles oE humectant e.(3. :in the range 20 to 40% may be used.

Typically, toothpaste formulat:ions in accordance with the invention will contain abou-t 25 -to 40% particulate dental abrasive, 1 to 4% thickener such as carboxymethyl cellulose derivatives and/or polyethylene glycols, together wit~ -the humectant, dodeeyl sulphate salt, and N-acyl sarcosinate salt, if used, and may also contain a physiologically acceptable pigment, an artificial sweetener agent e.g sodium saccharin or ? `~ ! - 8 -~2~

sodium cyclamate, an acid and buffer to maintain a desired pH, and an essential oil flavour.
Both the liquid and the solid or semi-solid, e.gO
paste, formulations in accordance wi-th the invention may contain small amounts of conventional fluoride anticaries agents. In the case o~ liquid mouthwashes or rinses this may suitably comprise sodium fluoride in an amount of 0.01 to 0.05~ and in the case of toothpaste the preferred material is sodium monofluorophosphate in an amount of 0.5 to 2.0%, although other anticaries fluoride e.g. stannous fluoride or sodium fluoride may also be used.
' Althouyh khe above descrip-tion provides ample informatlon for those skilled in the art to formulate dental hygiene formulation in accordance with the invention having antiplaque activity, for the avoidance of doubt cer-tain speci~ic form~lations will be given, by way of example only, together ' with a test method for determining antiplaque activity, _ample 1 The ingredients listed in Table 1 were mixed together in the percentages by weight lndicated, to obtain a clear solution.
Table 1 also indicates preferred ranges of percentages by weight ~or the various ingredients.
E~ple 2 The ingredients listed :in Table 2 were blended t,oyether in the percentac3es by weiyht indicatecl, to yield a smooth paste.
Ranges o~ preferred percen-tayes by weiyht are also indicated.

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Test Method The antimicrobial activity of sodium lauryl sulphate containing solutions can be determined as ~ollows.
Tooth units are pre~ared in the form of 24 x 10 x 3 mm acrylic plastic tiles.
A medium is prepared comprising Trvpticase soy broth obtained from Baltimore Biological Laboratories with 5% added sucrose sterilized by autoclaving in 500 ml quantities. The 500 ml quantities are then inoculated with a standard quantity of plaque-forming microorganisms. In successive tests, the inoculum consists of 0.5 ml from human saliva, and bacterial cultures of S~ aureus St. faecalis, Ps. aeruginosa, E. coli, C. albicans, S. cerevisiae, and A. viscosus, each containin~
uniform n~mber of cells, suitably of the order o 5 x 10 cells per inoculum. After inoculation, 10 ml aliquots are aseptically transferred to ste~ile 150 x 20 mm test tubes containing the plastic tiles. The tuhes are incubated at 37C for 24 hours.
The tubes are then shaken on a ~70r-tex ~ixer for 10 seconds to xemove loose pellicle which is allowed to settle. The tiles are then transferred to test tubes containing the tesk solutions for 30 seconds and are then put into tubes containing sterile distilled water for the same period~ Control tiles receive two 30 seconds treatment with sterile water. The tiles are then replaced into the test tubes containing inoculated medium broth and are incubated at 37C~ After 3 treatments, khe plaque aclhering on the tiles is measured employing a conventional chemical protein-del:ermination procedure~

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Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Dental hygiene composition having antimicrobial activity against plaque-forming microorganisms and comprising an effective amount of from 0.1 to 2.0 percent by weight of one or more highly pure alkali metal salts of dodecyl sulphate substantially free from non-dodecyl alkyl sulphate salts, dissolved in one or more vehicles physiologically compatible with the teeth and mouth tissues.

2. Composition as claimed in claim 1, having a content of less than 5% non-dodecyl alkyl sulphate salts, based on the weight of dodecyl sulphate salt.

3. Composition as claimed in claim 2 wherein said content is less than 2%.

4. Composition as claimed in claim 2 wherein said content is less than 1%.

5. Composition as claimed in claim 1 containing physiologically-acceptable acidic buffer at pH in the range 3.0 to 5Ø

6. Composition as claimed in claim 5 wherein said vehicle comprises water and said pH is about 4.5.

7. A liquid mouthwash composition having antimicrobial activity against plaque forming microorganisms and comprising from 0.1 to 2.0 percent by weight of one or more highly pure alkali metal salts of dodecyl sulphate substantially free from non-dodecyl alkyl sulphate salts dissolved in one or more vehicles physiologically compatible with the teeth and mouth tissues, and 10 to 30% by weight ethyl alcohol.

8. A liquid mouthwash composition as claimed in claim 7 containing 0.1 to 0.5% of said highly pure dodecyl sulphate salt.

9. A liquid mouthwash composition as claimed in claim 7 or 8 containing water or an aqueous vehicle, 0.2 to 3.0% by weight essential oil flavour and 0.1 to 0.2%
by weight non-ionic surfactants as dispersing agent therefor.

10. A liquid mouthwash composition as claimed in claim 7 or 8 having a water content of 50 to 90% by weight and containing 0 to 20% by weight humectant.

11. A liquid mouthwash composition as claimed in claim 7 or 8 containing 0.01 to 0.05% by weight zinc chloride dissolved in water or an aqueous solution as said vehicle.

12. A liquid mouthwash composition as claimed in claim 7 comprising 0.1 to 0.5% of highly pure sodium dodecyl sulphate, 10 to 30% ethyl alcohol, 0.01 to 0.05% zinc chloride, 0 to 20% humectant, 0.2 to 3.0% essential oil flavour, 0.1 to 0.2 non-ionic dispersing agent, 0.002 to 0.005% dye, physiologically acceptable acid in an amount sufficient to bring the pH of the composition to pH 3.0 to 5.0, buffer solution for maintaining the pH of the composition at a pH in the range 3.0 to 5.0, 0.01 to 0.05% fluoride, anticaries agent and the balance water, all percentages being by weight.

13. A composition as claimed in claim 1 comprising 0.5 to 2.0% by weight of said highly pure dodecyl sulphate salt and 0.5 to 2.0% by weight of alkali metal N-acyl sarcosinate.

14. A composition as claimed in claim 13 wherein said sarcosinate is N-lauroyl sarcosinate.

15. A composition as claimed in claim 14 wherein said sarcosinate is sodium N-lauroyl sarcosinate.

16. A toothpaste composition having antimicrobial activity against plaque-forming microorganisms and comprising an effective amount of from 0.5 to 2.0% of one or more highly pure alkali metal salts of dodecyl sulphate substantially free from non-dodecyl alkyl sulphate salts dissolved in one or more vehicles physiologically compatible with teeth and mouth tissues, 0.5 to 2.0% of alkali metal N-acyl sarcosinate, 25 to 40% particulate dental abrasive, 1 to 4% thickener, and 20 to 40% humectant, and the balance comprising water, all percentages being by weight.

17. A toothpaste composition as claimed in claim 16, wherein said sarcosinate is N-lauroyl sarcosinate.

18. A toothpaste composition as claimed in claim 16 wherein said sarcosinate is sodium N-lauroyl sarcosinate.

19. A toothpaste composition as claimed in claim 16 containing a fluoride anticaries agent.

20. A toothpaste composition as claimed in claim 19 wherein said fluoride is sodium monofluorophosphate.

21. A toothpaste composition as claimed in claim 16 comprising 0.5 to 2.0% highly pure sodium dodecyl sulphate, 25 to 40% particulate dental abrasive, 1 to 4% thickener, 0.5 to 3.0% physiologically-acceptable pigment, 0.5 to 2.0% sodium N-lauroyl sarcosinate, 20 to 40% humectant, 0.1 to 0.3% sweetener, about 0.5 to 1% fluoride anticaries agent, about 1.0 to 5.0%
phosphate buffer, sufficient phosphoric acid to adjust the pH
of the composition to about pH 5.0, about 0.5% essential oil flavour, and the balance water, all percentages being by weight.