Note: Descriptions are shown in the official language in which they were submitted.
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Oral Compositions
Technical Field
The present invention relates to oral compositions. In particular, it
relates to so-called baking soda dentifrice compostions containing
pyrophosphate anticalculus agents and which have improved stability and
aesthetics.
Background
Dental calculus, or tartar as it is sometimes called, is a deposit
which forms on the surfaces of the teeth at the gingival margin.
Supragingival calculus appears principally in the areas near the orifices of
the salivary ducts; e.g., on the lingual surfaces of the lower anterior teeth
and on the buccal surfaces of the upper first and second molars, and on
the distal surfaces of the posterior molars.
Mature calculus consists of an inorganic portion which is largely
calcium phosphate arranged in a hydroxyapatite crystal lattice structure
similar to bone, enamel and dentin. An organic portion is also present
and consists of desquamated epithelial cells, leukocytes, salivary
sediment, food debris and various types of microorganisms.
As the mature calculus develops, it becomes visibly white or
yellowish in colour unless stained or discoloured by some extraneous
agent. This is undesirable from an aesthetic standpoint.
Mechanical removal of calculus periodically by the dentist is routine
dental office procedure. A variety of chemical and biological agents have
also been suggested to retard calculus formation or to remove calculus
after it is formed. Pyrophosphate salts are chemical agents knows to
have the ability to retard calculus formation as described, for example, in
U. S. Patent 4,999,184, to Parran, Jr. et al., issued March 12, 1991.
Dentifrice compositions containing pyrophosphate salts and sodium
bicarbonate (aka, baking soda) are also known, having been described for
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example, in U.S. Patent No. 5,180,576, to Winston et al., issued January
19, 1993. Obtaining stable dentifrice compositions containing sodium
bicarbonate and pyrophosphate effective for inhibiting dental calculus
formation, however, presents a processing challenge. Pyrophosphate
dissolved in these dentifrice compositions is subsequently likely to
recrystallize in the form of tetrasodium pyrophosphate decahydrate
crystals. These crystals can grow into large, glass-like particles which
have negative aesthetics and also have tartar control ef$cacy concerns.
U.S. Patent No. 5,180,576 apparently recognises this
problem and describes avoiding it by a manufacturing process
whereby the sodium bicarbonate is used to salt out the alkali
metal pyrophosphate. The amount of dissolved pyrophosphate salt is
therefore said to be relatively low in the final composition and the
remaining pyrophosphate particles are said to be undissolved tetrasodium
pyrophosphate decahydrate salted out by the sodium bicarbonate. These
undissolved pyrophosphate crystals dissolve very quickly, however,
when the composition is diluted with water as occurs during use. This
then is just another way of practicing the invention disclosed and
claimed, for example, in U.S. Patent 4,684,518, to Parran, Jr. et al.,
issued August 4, 1987.
It is also lmown from PCT application US94/03280 that
pyrophosphate/sodium bicarbonate-containing dentifrice compositions
which are aesthetically acceptable and efficacious may be prepared by
controlling the process conditions to insure that less than about 20% of
the pyrophosphate is solubilized at any point in the process mixture. In
practice, the process described in the above application still leads to
solubilization of about 5% of the total pyrophosphate level. In order to
minimise the risk of recrystallization of pyrophosphate decahydrate
crystals, it would be desirable to reduce the soluble pyrophosphate level
still further.
It is therefore an object of the present invention to provide an easily
controlled process for preparing a stable dentifrice composition
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containing sodium bicarbonate and pyrophosphate salts. An object is
also to provide stable dentifrice compositions containing sodium
bicarbonate and tetrasodium pyrophosphate salt particles of
predetermined and/or consistent size. Another object of this invention is
to prepare such stable compositions by a process controlling the
processing conditions such that the level of pyrophosphate ion dissolved
in the composition is less than 100 ppm, preferably less than 10 ppm.
These and other objects of the present invention will become readily
apparent from the detailed description which follows.
All percentages and ratios used herein are by weight, and all
measurements are made at 25°C , unless otherwise specified.
Summary of the Invention
According to a first aspect of the invention, there is provided a
dentifrice composition comprising:
a) from about 5% to about 50% by weight of sodium
bicarbonate;
b) a soluble fluoride ion source in an amount suffcient to provide
from about lOppm to about 3500ppm of fluoride ion;
c) at least about 1.5% by weight of tetrasodium pyrophosphate,
of which some or all of the tetrasodium pyrophosphate is in the
form of undissolved anhydrous tetrasodium pyrophosphate
particles; and
d) from about 50% to about 94% dentifrice carrier materials;
and wherein further said composition has a soluble pyrophosphate ion
content in the range from about 1 to about 100ppm, preferably from
about 1.5 to about lOppm, more preferably from about 2 to about Sppm.
The present invention also relates to a method of making the above
dentifrice composition comprising the steps of
a) forming a premix of dentifrice carrier materials comprising one
or more materials selected from binder/thickening agents,
humectants, buffering agents, abrasive polishing materials,
surfactants, sweetening agents, flavoring agents, titanium dioxide,
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and mixtures thereof, said premix including at least one or more
binder/thickening agents and one or more buffering agents sufficient
to provide a pH in step b) hereof greater than about pH 8;
b) forming a paste by adding water to the premix in an amount
sufficient to hydrate the binder/thickening agent;
c) adding sodium bicarbonate to the resulting paste;
d) thereafter adding tetrasodium pyrophosphate, all at once or in
portions, to the paste at a temperature less than about 30°C,
preferably less than about 25°C and preferably at a pH of greater
than about pHB.
Preferably, the tetrasodium pyrophosphate is added to the mixture
a$er all other sodium-containing salts present in the composition have
been added thereto. In preferred embodiments, moreover, the
binder/thickening agent and buffering agent are added batchwise to the
premix so as to provide multiple alternate layers of binder/thickening
agent and buffering agent in the final premix, this being valuable from the
viewpoint of achieving optimum paste rheology during the binder
hydration step.
The present invention relates to a method of manufacturing a baking
soda dentifrice composition containing pyrophosphate tartar control
agent. The dentifrice compositions produced by the present process may
be in the form of toothpastes or gels. The term "toothpaste", as used
herein, means paste and gel formulations unless otherwise specified. The
present invention also relates to baking/pyrophosphate tartar control
dentifrice compositions comprising anhydrous tetrasodium pyrophosphate
particles.
The present process and compositions comprise several essential
components, as well as optional components. A detailed description of
these components and the present process conditions are described
hereinafter.
A) Pyrophosphate Salts
The pyrophosphate salts used in the present process and
compositions must include tetrasodium pyrophosphate. This material
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may be the anhydrous salt form or the decahydrate form, or any other
species stable in solid form in the dentifrice compositions. The salt is its
solid particle form, which may be its crystalline and/or amorphous state,
with the particle size of the salt preferably being small enough to be
aesthetically acceptable and readily soluble during use.
While tetrasodium pyrophosphate salt particles are a necessary
component of the present process and compositions, it is to be recognised
that low levels of other pyrophosphate salts may be included in the
process and compositions. Specific salts include tetra alkali metal
pyrophosphate other than tetrasodium pyrophosphate, dialkali metal
diacid pyrophosphates, triallcali metal monoacid pyrophosphate and
mixtures thereof, wherein the alkali metals are sodium or potassium.
(Pyrophosphate salts are described in more detail in Kirk & Othmer,
Encvclooedia of Chemical Technology. Second Edition, Volume 15,
Interscience Publishers ( 1958)). These salts are useful in both their
hydrated and unhydrated forms. Because such salts are typically
more soluble than the tetrasodium pyrophosphate salt, their inclusion
in the process and compositions of the invention should be limited to
avoid preparing compositions containing soluble pyrophosphate ion,
and exclusion of such more soluble salts is preferred.
The amount of pyrophosphate salt useful in these compositions is
any tartar control effective amount, and is generally enough to provide at
least about 1.0%, preferably from about 1.5% to about 10%, more
preferably from about 3.0% to about 6% P20-~~, by weigh~f the
compositions. It is to be appreciated that the level of P20~ is that
amount capable of being provided to the composition (i.e., the theoretical
amount a~ an appropriate pH) and that other pyrophosphate forms (e.g.,
HP20~ ) may be present when a final product pH is established. The
level of tetrasodium pyrophosphate salt preferably used in the present
methods and compositions is therefore from about 1.5% to about 15%,
and more preferably from about 2% to about 10%, by weight of the
dentifrice composition.
B) Sodium Bicarbonate
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Sodium bicarbonate, also known as baking soda, is a household
product with a variety of uses including use in dentifrices and
mouthrinses. It is a white powder that is soluble in water and unless
stabilised, tends to release carbon dioxide in an aqueous system. The
present compositions contain from about 5% to about 50%, preferably
from about 10% to about 30% sodium bicarbonate by weight of
composition.
C) Soluble Fluoride Ion Source
A soluble fluoride ion source is also incorporated in the present
compositions. The soluble fluoride ion source is used in amounts
su~cient to provide from about 10 to about 3500 ppm of the fluoride ion.
Preferred fluorides are sodium fluoride, stannous fluoride, indium
fluoride, and sodium monofluorophosphate. Norris et al., U.S. Patent
2,946,1735, issued July 26, 1960 and Widder et al., U.S. Patent
3,678,154, issued July 18,1972 disclose such salts as well as others.
D) Dentifrice Carrier Materials
In preparing the present toothpaste process compositions, it is
desirable to add one or more dentifrice carrier materials to the
compositions. The tenor "dentifrice carrier materials", as used herein,
means any material safe and effective for use in the toothpaste
compositions prepared according the present invention. Such materials
are well known in the art and are readily chorea by one skilled in the art
basod on the physical and aesthetic properties desired for the dentifrice
composition being prepared. Dentifrice carrier materials typically
comprise from about 50% to about 94%, preferably from about 60% to
about 80% by weight of the present compositions.
The present compositions typically contain a binder/thickening
material to provide a desirable consistency. Preferred binder/thickening
agents are carboxyvinyl polymers, carrrageenan, hydroxyethyl cellulose
and water soluble salts of cellulose ethers such as sodium carboxymethyl
cellulose and sodium carboxymethyl hydroxyethyl cellulose. Natural
gums such as gum karaya, zanthan gum, gum arabic, and gum tragacanth
can also be used. Colloidal magnesium aluminium silicate or finely
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divided silica can be used as part of the thickening agent to further
improve texture. Thickening agents can be used in an amount from about
0.2% to about 5.0% by weight of the total composition.
it i5 also desirable to include some humectaiit rilaterial in a
toothpaste to keep the composition from hardening upon exposure to air.
Certain humectants can also impart a desirable sweetness or flavour to
toothpaste compositions. Suitable humectants include glycerin, sorbitol,
other edible polyhydric alcohols, and mixtures thereof, at a level of from
about 15% to about 70% by weight of composition.
Titanium dioxide can also be added to the present compositions.
Titanium dioxide is a white powder which adds pigment to the
compositions. Titanium dioxide generally comprises from about 0.25%
to ab(~ut 1 % by ~Vet_'g~'1_t of rn~npneitin~,
v
Water is also present in the compositions of this process. Water
employed in the preparation of commercially suitable toothpastes should
preferably be deionized and free of organic impurities. Water generally
comprises from about 12% to about 45%, preferably from about 15% to
about 35%, more preferably from about 20% to about 30% by weight of
composition. These amounts of water include the free water which is
added plus that which is introduced with other materials such as with
sorbitol.
The pH of the present compositions is adjusted through the use of
buffering agents. Buffering agents, as used herein, refer to agents that
can be used to increase the pH of the compositions to a range of above
about pH 8 as preferred for addition of the sodium bicarbonate and
tetrasodium pyrophosphate. These agents include trisodium phosphate,
sodium hydroxide and sodium carbonate. Sodium carbonate is preferred
at a level of from about 0.5% to about 2% by weight of composition.
An abrasive polishing material can also be included. The abrasive
polishing material contemplated for use in the compositions of the present
invention can be any material which does not excessively abrade dentin.
These include, for example, silicas including gels and precipitates,
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calcium carbonate, dicalcium orthophosphate dihydrate, calcium pyrophosphate,
tricalcium phosphate, calcium polymetaphosphate, insoluble sodium
polymetaphosphate, hydrated alumina, and resinous abrasive materials such as
particulate condensation products of urea and formaldehyde, and others such as
disclosed by Cooley et al. in U.S. Patent 3,070,510, December 25, 1962.
Mixtures
of abrasives can also be used.
Silica dental abrasives, of various types are preferred because of their
unique
benefits of exceptional dental cleaning and polishing performance without
unduly
abrading tooth enamel or dentin. The silica abrasive polishing materials,
useful
herein, as well as the other abrasives, generally have an average particle
size
ranging between about 0.1 and 30 microns, preferably 5 and 15 microns. The
silica
abrasive can be precipitated silica or silica gels such as the silica xerogels
described
in Pader et al., U.S. Patent 3,538,230, issued March 2, 1970 and DiGiulio,
U.S.
Patent 3,862,307, June 21, 1975.
Preferred are the silica xerogels marketed under the trademark "Syloid" by W.
R. Grace & Company, Davison Chemical Division. Preferred precipitated silica
materials include those marketed by the J. M. Huber Corporation under the
trademark "Zeodent", particularly the silica carrying the designation "Zeodent
119".
These silica abrasives are described in U.S. Patent 4,340,583, July 29, 1982.
The abrasive is preferably present at a level of from about 6% to 70%, more
preferably from about 15% to about 25% by weight.
The toothpaste compositions can also contain surfactants. Suitable surfactants
are those which are reasonably stable and foam throughout a wide pH range,
including non-soap anionic, nonionic, cationic, zwitterionic and amphoteric
organic
synthetic detergents. Many of these suitable agents are disclosed by Gieske et
al. in
U.S. Patent 4,051,234, September 27, 1977. Sodium alkyl sulphate and
polyethylene glycol are preferred for use herein at a level of about 4% to
about 3%
by weight of compositions respectively.
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Flavouring agents can also be added to the present compositions.
Suitable flavouring agents include oil of wintergreen, oil of peppermint,
oil of spearmint, oil of sassafras, and oil of clove. Sweetening agents
which can be used include aspartame, acesulfame, saccharin, dextrose,
levulose and sodium cyclamate. Flavouring and sweetening agents are
generally used in toothpastes at levels of from about 0.005% to about 2%
by weight of composition.
The present invention compositions can also contain optional
pharmaceutical agents (e.g., triclosan) and other tartar control agents.
Optional tartar control agents include such known materials as synthetic
anionic polymers (including polyacrylates and copolymers of malefic
anhydride or acid and methyl vinyl ether (e.g., Gantrez), as described for
example in U.S. Patent No. 4,627,977 to Gaffar et al., as well as, e.g.,
polyamino propane sulfonic acid (AMPS)), polyphosphates (e.g.
tripolyphosphate; hexametaphosphate), diphosphonates (e.g. EHDP;
AHP), polypeptides (such as polyaspartic and polyglutamic acids), and
mixtures thereof.
The toothpaste compositions are prepared by mixiag together the
components described above according to the method of manufacturing.
This method comprises the steps of
a) forming a premix of dentifrice carrier materials comprising one
or more materials selected from binder/thickening agents,
humectants, buffering agents, abrasive polishing materials,
surfactants, sweetening agents, flavoring agents, titanium dioxide,
and mixtures thereof, said premix including at least one or more
binder/thickening agents and one or more buffering agents sufficient
to provide a pH in step b) hereof greater than about pH 8;
b) forming a paste by adding water to the premix in an amount
sufficient to hydrate the binder/thickening agent;
c) adding sodium bicarbonate to the resulting paste;
. d) thereafter adding tetrasodium pyrophosphate, all at once or in
portions, to the paste at a temperature less than about 30°C,
preferably less than about 25°C and at a pH of greater than about
pHB.
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Preferably, the amount of pyrophosphate dissolved in the mixture for the
methods and composition of the present invention is in the range from
about 1 to about 100ppm, preferably from about 1.5 to about lOppm,
more preferably from about 2 to about Sppm, measured as pyrophosphate
ion. A method of measuring the amount of pyrophosphate dissolved in
the mixture and compositions is described and exemplified hereina$er in
the Examples. .
The following examples further describe and demonstrate embodiments
within the scope of the present invention.
EXAMPLES
The followins are examples of paste ~nrl uel c~Pntifric~PC having a
pyrophosphate ion content of about 3.3%.
In edient Paste Gel
Sodium Bicarbonate 20.000 20.000
Water 19.773 19.773
Silica 15.000 15.000
Glycerin 15.000 15.000
Sorbitol (70%) 14.061 14.111
Tetrasodium Pyrophosphate 5.045 5.045
Sodium~Alkyl Sulphate (28%) 4.000 4.000
PEG-6 3.000 3.000
Sodium Carbonate 1.250 1.250
Flavour 1.000 1.000
CarboxymethylCellulose 0.800 0.800
Sodium Saccharin 0.400 0.400
Titanium Dioxide 0.350 0.000
Sodium Fluoride 0.321 0.321
FD & C Blue No. 1 0.000 0.300
The paste compositions are prepared as follows. To the
humectants (sorbitol, glycerine, PEG-6) at ambient temperature is added
a particulate mix of sodium saccharin, sodium fluoride, sodium
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carbonate, sodium carboxymethylcellulose and titanium dioxide, the
sodium carbonate and sodium carboxymethylcellulose (CMC) being each
added to the particulate mix in two equal batches in the order carbonate,
CMC, carbonate, CMC to provide a so-called "layered" particulate
mixture. To this liquid premix is then added water in amount suffcient to
hydrate the binder, followed by silica . To this mixture is added sodium
bicarbonate, followed by tetrasodium pyrophosphate, in solid form. The
final paste product is then obtained by addition of flavour and sodium
alkyl sulphate solution.
Measurement of the level of soluble pyrophosphate in these compositions
is accomplished as follows.
3 .OOg ~ 0.001 g toothpaste is weighed into a SOmI polypropylene
centrifuge tube; deionised water (9.Om1) and six glass beads are then
added. Stopper and thoroughly mix for exactly 2 minutes on the vortex
mixer. Transfer the contents to a 25m1 centrifuge tube, stopper and spin
at 15,OOOrpm at 10°C for 15 minutes. Pipette l .Oml of the clear
supernatant into a 100m1 volumetric flask and dilute to volume with
deionized water, mixed well. Dilute l Oml of this solution with deionized
water and mix well. Analyse by ion chromatography.
