GB2237199A - Oral composition comprising monodisperse colloidal silica suspension - Google Patents

Abstract

Colloidal silicas and silicates are known ingredients in oral compositions such as toothpastes. They can affect the formation of calculus, and can exert an anti-caries effect. Such silicas are only effective at relatively high levels, and such silicates tend to form a gel. By the use of monodisperse colloidal silica suspension of silicas with a nominal particle size of 7-22 nanometers which are strongly negatively charged, the tendency to form a gel is significantly reduced and lower levels of silicas are required.

Description

"Oral compositions" The present invention relates to oral compositions such as toothpastes, mouthwashes and the like.

More particularly, it relates to oral compositions which comprise, as an essential ingredient, particular colloidal silicas.

The use of colloidal silicas in oral compositions is already known from e.g. Us Patent 3, 7,521, US Patent 4,235,874, US Patent 4,348,381 and GB Patent 999,857, wherein they are described as thickening or abrasive agents. The use of silicates in oral compositions has also been described in e.g. US Patent 4,046,872, to provide compatibility of the oral compositions with unlined aluminum containers.

More recently, studies have been reported by Damen et al. and Gaare et al. in Recent Advances in the Study of Dental Calculus", IRL Press (Oxford) 1989, pp 105-114 and 115-122, concerning the effect of silicon compounds such as silicas and silicates on the formation of calculus, and their potential effect as anti-caries agents.

However, although several of the tested silicas and silicates promote the precipitation of calcium phosphate in model systems, the silicas are only effective at relatively high concentrations and the silicates suffer from the undesirable tendency to form a gel rather quickly which detraots from their efficiency.

It has now been found that this tendency to form a gel can be greatly significantly reduced by using particular colloidal silicas as hereinafter destined, Not only do these silicas stimulate hydroxyapatite nucleation at least as effectively as the above mentioned silicates, but, more importantly, they have a much-reduced tendency to gel, which potentially should improve the anti-caries effect of the oral compositions.

The particular colloidal silicas of the present invention are monodisperse colloidal silica suspensions as more fully described in US Patent 4,410,405, which is herein incorporated by way of Reference. These suspensions contain silicas with a particle size of nominally 7-22 nanometers; the particles are strongly negatively charged. They show a much increased stability to gelling at neutral pH. They are commercially available from Du Pont under the registered trade name Ludox. Ludox SM and Ludox HS40 are preferred in the present invention.

The amount of the colloidal silicas used according to the present invention ranges from 0.0001% to 15% by weight, preferably from O.l.% to 2% by weight.

The oral compositlon of this invention will contain other ingredients commonly used to formulate such products, depending on the form of the oral product. For instance, in the case of an oral composition in the form of a toothpaste the product will comprise a particulate abrasive cleaning agent, a humectant-containing liquid phase and a binder or thickener which acts to maintain the particulate solid abrasive in stable suspension in the liquid phase. A surfactant and a flavouring agent are also usual ingredients of commercially acceptable toothpastes.

Particulate solid abrasive cleaning agents commonly present in toothpaste. include silica, alumina, hydrated alumina, calcium carbonate, anhydrous dicalcium phosphate, dicalcium phosphate dihydrate and waterinsoluble sodium metaphosphate. The amount of abrasive agent is usually between about 5t and 70% by weight of the toothpaste.

Humectants commonly used are glycerol and sorbitol syrup (usually comprising an approximately 708 solution).

However, other humectants are known to those in the art including propylene glycol, lactitol, xylitol and hydrogenated corn syrup. The amount of humectant will generally range from about lot to 85% by weight of the dentifrice. The remainder of the liquid phase will consist substantially of water.

Likewise numerous binding or thickening agents have been indicated for use in dentifrices, preferred ones being hydroxyethylcelluloge, sodium carboxymethylcellulose and xanthan gum. Others include natural gum binders such as gum tragacanth, gum karaya and gum arabic, Irish moss, alginates and carrageenans. Silica thickening agents include the silica aerogels and various precipitated silicas. Mixtures of binders may be used. The amount of binders included in a dentifrice is generally between 0.1% and 10 & by weight.

It is usual to include a surfactant in a dentifrice and again the literature discloses a wide variety of suitable materials. Surfactants which have found wide use in practice are sodium lauryl sulphate, sodium dodecylbenzene sulphonate and sodium lauroylsarcosinate.

Other anionic surfactants may be used as well as other types such as cationic, amphoteric and non-ionic surfactants. Surfactants are usually present in an amount of from 0.5% to 5% by weight of the dentifrice, Flavours that are usually used in dentifrices are those based on oils of speartint and peppertint. Examples of other flavouring materials used are menthol, clove, wintergrevn, eucalyptus and aniseed. An amount of from 0.1% to 5* by weight is a suitable amount of flavour to incorporate in a dentifrice.

The oral composition of the invention may include a wide variety of optional ingredients. These include sweetening agents such as saccharin; an opacifying agent, such as titanium dioxide: a preservative, such as formalint a colouring agent; or pH controlling agent such as an acid, base or buffer, such as benzoic acid.

Futhermore, they may include anti-caries agents such as sodium fluoride, stannous fluoride, monosodium fluorophosphatet anti-plaque agents such as stannous pyrophosphate, zinc citrate; antibacterial agents such as 2,4,4'-trichloro-2 -hydroxy-diphenylether, anticalculus agents such as alkali metal pyrophosphates and so on.

For a fuller discussion of the formulation of oral compositions reference is made to Harry's Cosmeticology, Seventh Edition, 1982, Edited by J B Wilkinson and R J More, pages 609 to 617.

The invention also provides a method of treating the oral cavity with the above colloidal silicas. The treatment may comprise rinsing with a suspension of the colloidal silicas in water or with a flavoured mouthwash product containing the colloidal silicas or by brushing the teeth with a dental product comprising the colloidal silicas.

The invention will be further illustrated by the following Example.

Example Seeded crystal growth experiments were carried out, using the yodel system as described by Damon and ten Cate in "Recent Advances in the study of Dental Calculus", IRL Press at Oxford University Press, 1989, pages 105-104, adapted to slightly larger volumes and other test agents. A buffered, supersaturated calcium phosphate solution is stirred gently over a small quantity of hydroxyapatite seed crystals. Further hydroxyapatite is deposited on the crystals, and the fall-off in calcium concentration is monitored by a calcium ion selective electrode connected to a chart recorder. The experiments were carried out at room temperature.

Three stock calcifying solutions were made up, all buffered to pH 7.2 with 50 mM N-2-Hydroxyethylpiperazine N'-2-ethanesulphonic acid (HEPER). Solution A 15 mM KH2po4 solution B 4mM Caul2 and solution C just the HEPES. These were stored in plastic bottles. 4.0 +/- 0.1 mg hydroxyapatite (8 m2/g surface area) was weighed into a plastic bottle and 10 ml calcium solution B and 10 ml HEPES buffer C were added, together with the test agent.

The mixture was equilibrated for ca 15 min, after which the reaction was started by the addition of 20 ml phosphate solution A. To check reproducibility, runs were done in duplicate.

The test agents used were: a) Waterglass (sodium silicate solution 30% by weight si 2 and 2.5 to 1 SiO2/Na2O weight ratio, supplied by BODE) diluted and acidified to pH 7.2 with 50 mM HEPER followed by 1 M BDH AnalaR grade hydrochloric acid, to give a stock solution with a final concentration 24 mM expressed as sio2. 1 ml of this stock solution in the 40 ml reaction mixture gave 0.6 mM Si02 (17 ppm Si), with the amount of C reduced accordingly.

The stock solution tended to gel after a couple of weeks.

b) Ludox HS40 and Ludox SM colloidal silicas with nominal particle sizes 7 nm and 12 nm respectively.

These were diluted with water (BDH AnalaR grade) to give 1% (expressed as Si) stock solutions. lOo ul of stock solutions in the reaction mixture gave 25 ppm Si.

c) Fluoride: 2.5 ppm F.

d) Phosphate-free control runs, to eliminate the possibility of calcium silicate oomplexing.

The following crystal growth results were obtained, where calcium concentrations are expressed as pCa (ie -log[Ca++]).

test agent PCa after 0 1 2 3 4hrs control 3.14 3.16 3.20 3.22 3.26 0.6 itM sicat:a 3.14 3.20 3.40 3.56 Iudox SM SM (25 PEXn Si) 3.14 3.32 3,60 Ludox HS40 (25 ppm Si) 3.16 3.21 3.24 3.42 3.68 2.5 ppn fluoride 3.20 3.24 3.30 3.40 - Gelling tests were also carried out with the aforementioned waterglass or Ludox solutions.

The undiluted waterglass was pH 12 and was diluted with 50mM HEPES buffer followed by 1 M BDH AnalaR grade hydrochloric acid to a final pH of 7.2, except where this was prevented by very rapid gelling, a) solutions with 2.1% Sio2 and above gelled before pH 7.2 was reached.

b) Intermediate concentrations gave the following gel times: 1.2% SiO2 13 min (solid gel) 0.67% SiO2 (3120 ppm 8i) 2 hrs ditto 0.36% sio2 (1680 ppm Si) overnight ditto 880 ppm Si 10 days (gel formed as inhomogeneities in the liquid) c) 469 ppm Si and below did not gel over six week.

The Ludox HS40 and SM solutions were both much lesbt alkalins (ca pH 10), and showed a much reduced tendency to gel. When 1 M hydrochloric acid was added directly to the Ludox HS40, as supplied, to bring it to pH 7,2, gelling took place in four hours. The final concentration, expressed as Sio2, was 36%. A solution containing 19% sio2, buffered at pH 7.2, gelled after six weeks, but an 11% solution prepared similarly remained liquid after this time. Ludox SM is somewhat less stable, but a buffered solution containing 9.6% SiO2 took three days to gel at pH 7.2 and a 5.98 solution had not gelled after six weeks.

Claims (3)

1. An oral composition comprising colloidal silicas, characterised in that the colloidal silicas are monodisperse colloidal silica suspensions wherein the silica particles are strongly negatively charged and have a particle size of nominally from 7-22 nanometers.

2. A composition according to claim 1, characterised in that the colloidal silicas are present in an amount of 0.0001 to 15% by weight of the composition.

3. A composition according to claim 1 or 2, characterised in that it in the form of a toothpaste.