Compositions – Oxidative bleachant – oxidant containing – or generative – Composition containing a stabilizer or a product in the form...
Reexamination Certificate
1999-10-28
2003-04-29
Anthony, Joseph D. (Department: 1714)
Compositions
Oxidative bleachant, oxidant containing, or generative
Composition containing a stabilizer or a product in the form...
C252S186280, C252S186290, C424S053000, C424S613000, C424S616000, C433S215000, C433S216000
Reexamination Certificate
active
06555020
ABSTRACT:
TECHNICAL FIELD
This invention pertains to bleaching gels for use in bleaching teeth. More specifically this invention relates to the production of stable aqueous bleaching gels that contain a very high percentage of hydrogen peroxide and methods for their use in bleaching teeth.
BACKGROUND ART
A gel is a colloid produced by combining a dispersed phase with a continuous phase (i.e. a dispersion medium or matrix) to produce a viscous, jelly-like, semisolid material. In the dental industry, gels are utilized as vehicles for applying a variety of dentifrices, bleaching aids, and fluoride compounds to teeth. A “dental bleaching gel” is a gel that carries a bleaching agent that can be safely applied to teeth.
Hydrogen peroxide has become the bleaching agent of choice for use in dental bleaching gels. Hydrogen peroxide is a powerful oxidizer which serves to bleach the colored materials in the teeth, thereby, producing a whiter appearance.
Unfortunately, at room temperature, hydrogen peroxide will attack the gelling agents used to make the dental bleaching gels. As a result of this attack, the gelling agents break down over time. Eventually, the gelling agents break down to such a degree that the gel's viscosity becomes too low to be suitable.
Viscosity is very important to the effectiveness of dental bleaching gels. If the viscosity is too low, the gel will flow uncontrollably from the dispensing tube and become difficult to manipulate for the purposes of varying or equalizing the bleaching treatment applied to the teeth. More importantly, if the viscosity is too low, the gel is more likely to flow away from the teeth, resulting in a reduced residence time. Residence time is the time the dental bleaching gel actually contacts the tooth enamel. The effectiveness of a dental bleaching gel is directly proportional to its residence time.
In addition, hydrogen peroxide tends to decompose at room temperature. The rate of this decomposition is dependent upon many factors. The presence of various metallic impurities, such as iron, manganese, copper and chromium, catalyze the decomposition. Furthermore, the stability of hydrogen peroxide decreases with increasing alkalinity and temperature. Because the whitening ability of a dental bleaching gel depends on the hydrogen peroxide concentration, premature decomposition diminishes the ability of the gel to whiten.
To combat these problems, dental bleaching gels containing high concentrations of hydrogen peroxide are generally refrigerated until immediately prior to use. Refrigeration slows down the hydrogen peroxide attack on the gelling agent and also slows down hydrogen peroxide decomposition. However, refrigeration is both expensive and inconvenient.
Various stabilizing agents have been investigated in an attempt to develop hydrogen peroxide containing dental bleaching gels that are stable at room temperature. Unfortunately, to date, these stabilizing agents have either proven ineffective.
The instant invention solves these stability problems by providing, for the first time, an effective bleaching gel that is stable at room temperature and that contains a large concentration of hydrogen peroxide. There appears to be very little prior art that is relevant to this invention. The most relevant prior art known to the inventors includes the following:
U.S. Pat. Nos. 5,422,073, 5,500,186, 5,593,637 and 5,756,045 teach a method for disinfecting a contact lens which includes contacting the lens with an isotonic aqueous solution comprising 0.6 to 2 weight percent tromethamine. Other aspects include adding to the solution a chelating agent (preferably disodium EDTA) and/or additional microbicide. The microbicide may be a very low concentration of hydrogen peroxide, e.g., 50 to 200 ppm. The disodium EDTA is not used as a stabilizer for the hydrogen peroxide.
U.S. Pat. No. 5,759,440 teaches an aqueous solution (as opposed to a gel) of hydrogen peroxide stabilized by incorporation of a composition containing a mixture of an alkali metal pyrophosphate or alkaline earth metal pyrophosphate with a stabilizer belonging to the category of aminopolycarboxylic acids. The solution finds application for bleaching textiles and paper pulps.
U.S. Pat. No. 5,641,386 teaches a process for the bleaching of pulp comprising the step of bleaching the pulp with hydrogen peroxide and an effective amount of at least one biodegradable 1-amino-alkane-1,1-diphosphate chelating agent to enhance the bleaching of the pulp.
U.S. Pat. No. 4,812,173 teaches stabilized hydrogen peroxide disinfecting solutions containing diphosphoric acids (such as hydroxyethylidene diphosphoric acid), and glycerin.
U.S. Pat. No. 5,248,389 teaches a process for peroxygen bleaching of high yield pulp in which sodium carbonate replaces sodium hydroxide and sodium silicate.
U.S. Pat. Nos. 5,098,303, 5,376,006 and 5,725,843 teach high viscosity sustained release dental compositions, such as tooth bleaching or fluoride compositions, for treating tooth surfaces. The sustained release dental compositions include a high carboxypolymethylene concentration (typically greater than 3.5%) which results in very high viscosity. The bleaching gels can contain from about 3 to about 20% carbamide peroxide, preferably about 4% to about 15% carbamide peroxide. Alternatively, the bleaching gels can contain hydrogen peroxide in a preferred range of from about 2% to about 10%.
U.S. Pat. No. 4,226,851 teaches a stable dental hygiene composition comprising a mixture of hydrogen peroxide and zinc chloride. The mixture is stabilized by the addition of water soluble vitamin E.
Ultradent, produced by Ultradent Products of South Jordan, Utah, offers a 35% hydrogen peroxide bleaching gel product called Opalescence Xtra. The package contains a prominent warning which states “REFRIGERATION REQUIRED!” Similar warnings appear in two places on the package insert. Opalescence Xtra is a gel that is red in color due to the presence of &bgr;-carotene. Opalescence Xtra turns into a colorless, runny liquid in less than two weeks when stored at room temperature.
None of the aforementioned references describes the stabilization of gels with respect to both gel stability and hydrogen peroxide stability.
SUMMARY OF THE INVENTION
This invention is directed to aqueous gels useful for bleaching teeth comprising: (i) water; (ii) polyacrylic acid thickening agent; (iii) at least one bleaching agent selected from the group consisting of hydrogen peroxide and compounds that release hydrogen peroxide in water; and (iv) aminocarboxylic acid/salt stabilizing agent. Preferably the gel also comprises (v) a neutralizing agent that serves to neutralize the polyacrylic acid. Ideally, these gels are fast acting bleaching gels that contain 20 to 50% by weight bleaching agent.
The combination of polyacrylic acid thickener and the aminocarboxylic acid/salt stabilizer provides a gel that can be loaded with hydrogen peroxide and remain sufficiently stable to provide a suitable gel (from a viscosity standpoint) after 4 to 12 weeks storage at room temperature. In addition, the gels exhibit little hydrogen peroxide decomposition.
These gels may be applied by a method comprising the following steps: (a) protecting the soft tissue surrounding the teeth with a covering; (b) applying the aforementioned aqueous gel to the teeth; and (c) removing the gel. Preferably, prior to removal, the gel is treated with a laser or heat lamp to accelerate bleaching.
DISCLOSURE OF THE INVENTION
As stated, the instant invention is directed to aqueous gels that contain hydrogen peroxide and that are stable at room temperature for up to twelve weeks. These gels comprise: (i) water; (ii) thickening agent; (iii) bleaching agent; (iv) stabilizing agent; and, optionally, (v) neutralizing agent.
Water is the principle component of the aqueous gels. Preferably, water is present in an amount over 50% by weight. More preferably, water makes up the remainder of the gel after removal of the thickening agent, bleaching agent, stabilizing agent and neutralizing agent.
The thickening agent (a.k.
Chadwick Thomas C.
Hunt Heather L.
Anthony Joseph D.
Den-Mat Corporation
Dorsey & Whitney LLP
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