Drug – bio-affecting and body treating compositions – Inorganic active ingredient containing – Silicon dioxide containing
Reexamination Certificate
1999-09-14
2002-06-04
Pak, John (Department: 1616)
Drug, bio-affecting and body treating compositions
Inorganic active ingredient containing
Silicon dioxide containing
C424S049000, C423S335000, C423S339000
Reexamination Certificate
active
06399111
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to amorphous silicas particularly used as abrasives in oral compositions. More particularly, the present invention relates to amorphous precipitated silicas with good cleaning properties associated with low abrasion characteristics which are suitable for oral compositions with low refractive index. The present invention further relates to oral compositions containing such silicas.
BACKGROUND OF THE INVENTION
Toothpaste compositions are well characterised in the literature and many compositions are disclosed in patent specifications and other literature. Toothpaste compositions contain a number of specific components for example abrasive agents, fluoride sources, binders, preservatives, humectants, anti plaque agents, colouring agents, water, flavour and other optional ingredients.
Of these components the abrasive agent is required to provide the appropriate cleaning and plaque removal without subjecting the tooth itself to excessive abrasion. Typically a toothpaste composition will contain from about 5% to about 50% preferably up to about 30% by weight of abrasive. Commonly used abrasives are aluminas, calcium carbonates and calcium phosphate. More recently synthetic silicas have been adopted because of their efficient cleaning, compatibility with other ingredients and their physical properties.
An important property of a silica for use in toothpaste formulations is its oil absorption capacity. For a material with the same particle size, this property relates directly to the thickening effect obtained when adding the silica into a toothpaste formulation; the higher the oil absorption capacity the higher the observed thickening effect. Therefore the higher the oil absorption capacity, the lower the volume of silica which can be incorporated into the toothpaste composition.
Another important property of a silica for use in toothpaste formulations is its ability to provide the appropriate cleaning and plaque removal without subjecting the tooth itself to excessive abrasion i.e. without damaging dentine or enamel. Normally cleaning capability is correlated with abrasion properties.
Another important property of a silica for use in transparent toothpaste formulations is its apparent refractive index. Any transparent toothpaste can be characterised by its refractive index. When incorporating an abrasive material into a transparent toothpaste it is important that this abrasive material remains invisible, i.e. that the clarity of the toothpaste remains the same. This is only achieved if the abrasive material has an apparent refractive index which matches the refractive index of the toothpaste. Now, toothpastes can have refractive indices ranging from 1.430 to 1.470. A refractive index of below 1.445 is generally considered as a low refractive index.
There is a market need for toothpastes in the form of clear gels which are absolutely water white. The method for assessing clarity in this invention involves use of a on a white background. This is the RIT Alphanumeric Resolution Test Object, RT 4-74, produced by Graphic Arts Research Center, Rochester Institute of Technology. The ability to discern the symbols clearly through a sample of product of standard thickness (1 cm) is measured. The symbols are numbered from −12 to +13. The higher, more positive the number, the greater the clarity. In the present invention a number of 0 or above is considered to be characteristic of a visually clear toothpaste.
In U.S. Pat. No. 5,225,177 is claimed an amorphous silica having a moisture of 10%, a 5% pH of 7, an oil absorption of less than 125 cc/100 g, a refractive index of 1.45. It is further stated that the precipitated silicas according to this document have an RDA value of at least 40, preferably 70 to 120. A detailed description of the method used for measuring the RDA value is provided and under ‘E. Test Run’ it is clear that the RDA value which is given is not the RDA of the silica but the RDA of a toothpaste containing this silica. Moreover on column 11 under ‘Calculations’ it is made clear that the RDA values are given ‘for a particular paste’. Now, It is not disclosed what is the nature of the toothpaste and, more importantly, the toothpaste silica loading is not disclosed (6% to 35% according to column 5 line 25). The RDA values therefore refer to the abrasion property of an unknown toothpaste containing an unknown amount of a specific amorphous silica and it is not possible, relying on U.S. Pat. No. 5,225,177 to know what is the RDA value of the silica.
Now, the applicant of U.S. Pat. No. 5,225,177 is marketing a product called Zeodent 115 (Average particle size 9.3 &mgr;m, refractive index 1.45, oil absorption 100 cc/100 g) which is believed to be the silica disclosed in U.S. Pat. No. 5,225,177. The RDA value of this silica is 97 which is regarded as a low to medium abrasive silica.
Commercially available silicas can be broadly categorised as low abrasion if less than 90 RDA and medium abrasion if between 110-150 RDA. Samples of commercially available toothpaste silicas were submitted to Missouri Analytical Laboratories and the RDA value of the silica was determined with the following results:
SILICA NAME
RDA
ZEODENT 113
84
ZEODENT 115
97
TIXOSIL 73
83
SIDENT 9
113
SIDENT 12
91
SORBOSIL AC77
125
SORBOSIL AC35
110
(NB: Zeodent, Tixosil, Sident and Sorbosil are registered trade marks of Huber, Rhone Poulenc, Degussa and Crosfield respectively.)
From the data, it can be seen that even current low abrasion silicas have relatively high RDA values and there is a need for an amorphous silica having a much lower RDA value which, when incorporated into an oral composition, exhibits good cleaning characteristics. There is also a need for such an amorphous silica which does not alter the clarity of the toothpaste composition to which it is added.
Now, when referring to oral compositions with good clarity, the trend in the industry is towards formulations with low refractive indices, in order to improve costs. This is because the refractive index of a toothpaste is mainly governed by its humectant/water ratio, with higher ratios giving higher refractive indices. The humectant, for example Sorbitol, is an expensive component with a high refractive index (>1.46), whereas water has a lower refractive index and is cheap.
There is therefore a need for more cost effective oral compositions, which are transparent at a refractive index lower than 1.445, in order to minimise the amount of humectant.
Tests and Definitions
i) Oil Absorption
The oil absorption is determined by the ASTM spatula rub-out method (American Society Of Test Material Standards D, 281).
The test is based on the principle of mixing linseed oil with the silica by rubbing with a spatula on a smooth surface until a stiff putty-like paste is formed which will not break or separate when it is cut with a spatula. The volume of oil used is then put into the following equation:
Oil
absorption
=
cm
3
oil
absorption
×
100
Wt
.
of
silica
sample
in
g
=
cm
3
oil
/
100
g
silica
ii) Weight Mean Particle Size
The weight mean particle size of the silica is determined using a Malvern Mastersizer model X, with a 45 mm lens and MS15 sample presentation unit. This instrument, made by Malvern Instruments, Malvern, Worcestershire uses the principle of Fraunhoffer diffraction, utilising a low power He/Ne laser. Before measurement the sample is dispersed ultrasonically in water for 7 minutes to form an aqueous suspension.
The Malvern Mastersizer measures the weight particle size distribution of the silica. The weight mean particle size (d
50
) or 50 percentile, the 10 percentile (d
10
) and the 90 percentile (d
90
) are easily obtained from the data generated by the instrument.
iii) Loose Bulk Density
Loose bulk density is determined by weighing approximately 180 ml of silica into a dry 2
Crosfield Limited
Pak John
Pillsbury & Winthrop LLP
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