Drug – bio-affecting and body treating compositions – Dentifrices
Reexamination Certificate
1998-04-08
2001-09-25
Harrison, Robert H. (Department: 1619)
Drug, bio-affecting and body treating compositions
Dentifrices
C423S339000
Reexamination Certificate
active
06294155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to silica compositions useful as an abrasive system in a dentifrice. The invention also relates to dentifrices, preferably toothpastes, which effectively clean teeth without a high degree of dentin and/or enamel abrasion.
2. Relevant Art
Dentifrices, e.g., such as toothpastes, are used to clean teeth. In particular, dentifrices aid in the removal of food particles, the removal of discoloration caused by substances such as tobacco or tea, and the removal of firmly adhering bacterial films, referred to as plaque, from the surface of the teeth. Abrasive substances, also referred to herein as abrasive systems, are formulated in the toothpaste as the primary cleaning agent.
To achieve cleaning, the abrasive systems in dentifrices have to provide a certain degree of abrasiveness with respect to the surface of the teeth. It is important, however, that abrasiveness with respect to dental enamel and dentine be at an acceptably low level to prevent the surface of the teeth from being damaged by the daily use of the toothpaste. The rate of enamel removal through brushing should not exceed the rate at which it is replenished through natural remineralization processes.
The abrasive system used should also be compatible with the other components of the toothpaste. It should lend itself to processing with water, humectants and consistency regulators to form a ductile paste readily dispensable from tubes or dispensers and should not adversely affect known caries inhibitors, for example, fluoride carriers, such as NaF or Na monofluorophosphate, even in the event of prolonged storage.
As illustrated in U.S. Pat. No. 3,957,968, toothpastes containing a combination of alpha-aluminum oxide (corundum) and a second abrasive having a Mohs hardness of less than about 6 are said to have good cleaning and polishing effects. Alpha-aluminum oxide, which has a Mohs hardness of 9, has a relatively strong abrasive effect on dental enamel. To reduce the enamel abrasion, certain calcium, magnesium or sodium salts have been added to a dentifrice containing the aforementioned abrasives.
U.S. Pat. No. 4,303,641 discloses an alkaline treatment for increasing the abrasiveness, and as a result its cleaning performance, of dentifrice silica gel compositions without employing the processing and drying steps typically used to prepare prior art gels. It is noted that treating silica gels with alkaline materials enhances the cleaning performance of the gels as evidenced by increased Radioactive Dentine Abrasion (RDA), defined later below. The Examples in this patent illustrate the alkaline treatment with gels having average particle sizes greater than 10 microns, e.g., about 14-16 microns. The RDA values shown for these alkaline treated gels, however, are quite high as evidenced by “powder” RDA's which this patent reports to be over 1,000 (and over 200 if measured using RDA methods disclosed herein) for some samples. This indicates that the alkaline treated gels exhibit a high degree of abrasiveness on dentin surfaces.
Non-alkaline treated silica xerogel abrasives are also well known in the art. Such gels are prepared to have median particle sizes in the range of 1 to 100 microns. Typically, these gels have particle sizes from 10 to 50 microns, depending on the ‘grittiness’ desired. The aforementioned '641 patent discloses that non-alkaline treated silica gels are effective polishing and cleaning agents while causing low amounts of damage to underlying tooth materials such as dentin and enamel. However, the aforementioned '641 patent also discloses that more effective abrasives are achieved via alkaline treatment of such silica gels.
U.S. Pat. No. 5,651,958 discloses using a combination of silicas in dentifrices to balance cleaning with minimal abrasion to dentin and enamel surfaces. The '958 patent discloses combining precipitated silica having a narrow particle size range distribution of soft particles having a mean value ranging from 8 to 14 microns with a silica gel in which 70% of the gel particles have a diameter below 25 microns and a Radioactive Dentin Abrasion from 62 to about 100. It is noted that the gel silica particles have an Einlehner hardness from about 3 to about 15 for abrasive to a brass screen.
U.S. Pat. No. 5,589,160 discloses a combination of two precipitated silicas to be used as a dentifrice abrasive. One of the precipitated silicas has a mean particle size of about 5 to 11 microns and an Einlehner hardness of 0.8 to 2.5 for abrasive to a brass screen. The other precipitated silica has a mean particle size of from about 5 to about 11 and an Einlehner hardness from about 3 to about 8 for abrasive to a brass screen.
U.S. Pat. No. 3,670,076 discloses a combination of relatively small and large alumina particles as providing superior abrasives and cleaning.
The above-mentioned measures, however, have not completely solved the problem of obtaining effective cleaning without the excessive abrasion of dental enamel. Workers in the art have continued to search for dentifrices containing abrasive systems which have reduced abrasion of dental enamel, but still effect acceptable cleaning.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide suitable dentifrices which, although achieving an optimal cleaning of teeth, can have only a mild abrasive effect. It has been unexpectedly found that such a composition is prepared from a silica composition comprising:
(a) silica gel (i) having a median particle size below 7 microns, (ii) a pH of from about 6 to about 11, and (iii) a hardness defined by powder RDA of 100 to 200, and a PCR of 100 to 150 when said silica (a) is formulated by itself into a dentifrice paste; and
(b) silica gel or precipitated silica having a median particle size of 7 microns or greater and having a hardness defined by a powder RDA of about 50 to 180, and a PCR of about 80 to 105 when said silica (b) is formulated by itself in a dentifrice paste,
further wherein the weight ratio of (b) to (a) is at least 1:1. Dentifrice compositions comprising (a) and (b) have an RDA of about 150 or below and a PCR of at least 80 and up to about 150, and an REA of less than about 30 (as measured on the IU scale). Silica gel (a) is preferably prepared by contacting a hydrous gel with an alkaline material.
The cleaning performance of silicas (a) and (b) combined is unexpected from cleaning performances of compositions comprising either (a) or (b) alone. For example, abrasives that exhibit a high degree of cleaning are also usually high in dentin or enamel abrasion. As disclosed in the above referenced U.S. Pat. No. 4,303,641, while the silica gels defined in (a) are effective for cleaning performance as a result of the alkaline treatment of hydrous gels, these materials have relatively high abrasion as defined by RDA. Conversely, while dentifrices comprising silicas defined by (b) are generally less abrasive than (a), there is room for improving its cleaning. Applicants have discovered, however, that lower RDA's and improved cleaning performance, as shown by improved PCR's, are obtained by combining (a) and (b). Indeed, silica (b) is widely used for abrasive systems in dentifrice and such systems can easily be improved by combining silica (a) according to this invention with prior art silica abrasives.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The silica gels defined by (a) can be a hydrogel, xerogel, or aerogel. A preferred embodiment is a hydrous gel which is described in U.S. Pat. No. 4,303,641, the contents of which are incorporated by reference. Such hydrous gels may be prepared from acid set silica hydrogels produced by reacting alkali metal silicate and mineral acids, e.g., sulfuric acid, in aqueous mediums. The acid and silicate are mixed under conditions sufficient to form a sol which in turn converts into a hydrogel. The gel is further aged and washed using conventional techniques to produce a gel having a pH from 2.5 to about 5. The washed gel generally con
Ernest Michael Vance
Kempske Sandra Joan
Thomas Michael Bruce
Cross Charles A.
Harrison Robert H.
W. R. Grace & Co. - Conn.
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