Drug – bio-affecting and body treating compositions – Dentifrices
Reexamination Certificate
2002-07-12
2004-01-27
Rose, Shep K. (Department: 1614)
Drug, bio-affecting and body treating compositions
Dentifrices
Reexamination Certificate
active
06682717
ABSTRACT:
International standard ISO11609 of 1995 contains the following definitions:
Dentifrice: any substance or combination of substances specially prepared for the public for cleaning the accessible surfaces of teeth.
Toothpaste: any semi-solid dentifrice preparation presented in the form of a paste, cream or gel.
This invention is concerned with toothpaste.
Toothpaste invariably contains an abrasive powder for cleaning purposes. The cleaning and abrasive properties of the toothpaste depend on the concentration of the powder, on the Moh's hardness of the abrasive, and on the shape and particle size and size distribution of the powder. The cleaning effect of toothpaste concerns its effectiveness in removing adventitious stains and other deposits from the surface of teeth and other parts of oral cavity. The abrasive effect or abrasivity concerns undesired removal of surface components of teeth including enamel and dentine, and undesired damage in the oral cavity. A toothpaste having a high cleaning effect generally has a rather high abrasivity, and vice versa. ISO11609 provides methods for testing abrasivity and sets limits on dentifrices marketed in Europe. An earlier British standard BS5136 of 1981 also sets limits on abrasivity by comparison with a standard reference toothpaste, which is also used as a reference in ISO11609, and which has the formulation:
Precipitated calcium carbonate 40% w/w.
Glycol 25% w/w
Sodium carboxymethylcellulose 1.40% w/w
Dodecyl sodium sulphate 1.00% w/w
Sodium silicate (80° TW of approximately pH 7) 0.05% w/w
Saccharin sodium 0.15% w/w
Formalin (40% (m/m) formaldehyde) 0.10 w/w
Peppermint flavouring 0.80% w/w
Water 33.05% w/w
Abrasive powders used or contemplated for use in toothpaste formulations include silicas, including gels and precipitates, sodium bicarbonate, calcium and magnesium carbonates, calcium phosphates, alumina and hydrates thereof, aluminosilicates, aluminium and magnesium silicates, and thermosetting urea-formaldehyde and other plastics materials. There is a need in the industry for an abrasive for inclusion in toothpaste formulations, which provides good cleaning properties, in particular stain removal, while showing relatively low abrasivity. In particular, there is a need for an abrasive which can be incorporated in a concentration large enough to provide an excellent cleaning effect in a toothpaste with low abrasivity which nevertheless complies with the abrasivity requirements of the above-stated standard specifications. This invention addresses that need.
U.S. Pat. No. 3,957,968 teaches the use of flat flakes of &agr;-aluminium oxide in toothpaste. The flakes have a median particle size of 2 to 7 &mgr;m. U.S. Pat. No. 4,060,599 discloses the use of a finer aluminium oxide (median 1 to 2 &mgr;m) and specifically uses Reynolds RC152DBM which has a median size of around 1.7 &mgr;m.
U.S. Pat. No. 4,632,826 teaches the use of a weakly calcined alumina polishing agent. This polishing agent consists of 10% to 50% by weight &ggr; aluminium oxide and 50% to 90% by weight &agr; aluminium oxide.
GB-A-2155333 teaches the use of calcium hydrogenphosphate anhydride and an aluminium oxide having an average particle size of 0.5 &mgr;m to 10 &mgr;m. The alumina has a high &agr;-content, as measured by X-ray diffraction.
WO-A-95/33441 teaches the use of cationically charged colloids of a metal compound. The colloid has a particle size of 0.001 &mgr;m to 0.2 &mgr;m.
GB-A-2037162 and GB-A-2009596 disclose the use of hydrated aluminas in dentifrice products.
The phrase “alumina” is sometimes loosely used to cover a number of aluminium oxide, oxide hydroxide and trihydroxide compounds. The correct designations and some crystalline phases are shown below:
Accepted
Mineral
Crystallographic and
Name
Chemical Composition
Chemical Designation
Gibbsite
Aluminium trihydroxide
&ggr;-Al(OH)
3
Bayerite
Aluminium trihydroxide
&agr;-Al(OH)
3
Nordstrandite
Aluminium trihydroxide
Al(OH)
3
Boehmite
Aluminium oxide hydroxide
&ggr;-AlOOH
Diaspore
Aluminium oxide hydroxide
&agr;-AlOOH
Corundum
Aluminium oxide
&agr;-Al
2
O
3
This invention is concerned with alumina that is essentially Corundum. Corundum is produced by calcination of aluminium trihydroxides and oxide hydroxides. Depending on the form of aluminium trihydroxide and oxide hydroxide starting material, a number of forms of alumina (often described as activated aluminas) are produced before corundum is formed. Another form of alumina chemical is aluminium hydroxide gel, which is often formed by the neutralisation of an aluminium salt solution.
The invention provides a toothpaste comprising as an abrasive an alumina in the form of particles having d
10
below 3.5 &mgr;m, d
50
below 1.0 &mgr;m, and specific surface area below 6 m
2
/g.
According to a further aspect of the present invention, there is provided the use of alumina as an abrasive in toothpaste, wherein the alumina is in the form of particles having d
10
below 3.5 &mgr;m, d
50
below 1.0 &mgr;m, and a specific surface area below 6 m
2
/g.
According to a further aspect of the present invention, there is provided the use of alumina as a whitening agent in toothpaste, wherein the alumina is in the form of particles having d
10
below 3.5 &mgr;m, d
50
below 1.0 &mgr;m, and a specific surface area below 6 m
2
/g. In this way the alumina may serve the purpose of replacing titania or the like in conventional products, thus resulting in a cost saving.
The surface area is measured by the following method. A sample of alumina of sufficient weight to give an estimated surface area of about 0.5 to 25 m
2
is degassed in a Micrometrics Desorb 2300B at about 150° C. until a stable reading is obtained. The sample is then transferred to a Micrometrics Flowsorb II 2300, cooled and immersed in a mixture of 30% N and 70% He gas. The total amount of N absorbed is measured from the change in thermal conductivity of the gas mixture preferably during desorption as the temperature is raised again to room temperature. Surface area per gram is then calculated from the total gas absorbed and the weight of the sample.
The particle size is measured as follows. Particle size distribution of a sample of alumina is measured in a Sedigraph 5100 instrument supplied by Micrometrics Products.
The abrasive is preferably an anhydrous alumina, generally a calcined alumina or alternatively a tabular or fused alumina. Calcination is effected at a temperature of at least 900° C. Higher calcination temperatures result in harder products. The alumina used in this invention is preferably fairly hard, such as may be obtained by calcination at above 1000° C. The alumina in this invention is an &agr;-alumina. Preferably, the &agr; content is greater than 90%, preferably greater than 93%, even more preferably greater than 95% as measured by X-ray diffraction. In a preferred embodiment, the &ggr;-content is less than 1%.
The abrasive is used in the form of particles having d
10
below 3.5 &mgr;m, preferably below 2.5 &mgr;m. (d
10
, d
50
and d
90
are used in conventional manner to indicate that 10, 50 or 90 wt % of the product has a particle size above the stated value). Preferably, the alumina abrasive is a sub-micron product, having d
50
of 0.1-1.0 &mgr;m. Preferably the alumina abrasive has a relatively narrow particle size distribution, e.g. with d
10
being no greater than four times d
50
.
The alumina abrasive has a specific surface area below 6 m
2
g, preferably in the range of 4.5-5.0 m
2
/g. The specific surface area is related to the aforesaid parameters of hardness (harder products have lower specific surface areas) and particle size (more finely divided products have larger specific surface areas).
Alumina products of the kind described are readily available commercially, for they are produced in substantial quantities mainly for use in refractories and ceramics. Grinding may conveniently be effected by fluid energy or vibratory milling (micronising) or preferably by ball milling.
When an abrasive powder has excellent stain removal properties in one toothpaste, it is generally
Duncan Iain Stewart
Wills Kevin John
Alcan International Limited
Cooper & Dunham LLP
Rose Shep K.
LandOfFree
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