Drug – bio-affecting and body treating compositions – Dentifrices – Oxygen or chlorine releasing compound containing
Reexamination Certificate
2001-08-16
2002-12-03
Rose, Shep K. (Department: 1614)
Drug, bio-affecting and body treating compositions
Dentifrices
Oxygen or chlorine releasing compound containing
C424S613000, C424S614000, C424S616000, C433S215000, C433S216000
Reexamination Certificate
active
06488913
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to teeth whiteners comprising two parts, one of which contains hydrogen peroxide (in a free form or in a form of its adduct with urea) and the other peroxides and/or percarbonates of metals belonging to the first or second group of the periodic table. More specifically, the invention relates to teeth whiteners having increased storage stability while having superior bleaching efficacy.
BACKGROUND OF THE INVENTION
Teeth whiteners, also known as teeth bleaching agents, are in widespread use as a cosmetic means to enhance appearance and, generally, to contribute to better oral health and hygiene.
Particularly popular and effective among these devices are those whose chemistry is based on peroxides, of which hydrogen peroxide and carbamide peroxide (representing an adduct of hydrogen peroxide and urea) are most frequently employed. Such peroxides are characterized by their ability to generate radical (atomic) oxygen. The chemical action of the radical/atomic oxygen is responsible for the desired whitening/bleaching effect. The generation of atomic oxygen is, however, highly undesirable during storage of such peroxide-based teeth whitening devices. Thus, in their commercial form, such devices are formulated in a manner designed to prevent and/or inhibit premature peroxide decomposition. Contact with certain foreign objects, especially materials having highly developed surface areas, certain chemicals, and elevated pH accelerate the decomposition process of said peroxides and the liberation of radical oxygen.
Stability of such teeth whitening formulations, however, is in direct conflict with the purpose and objective of their application, namely achieving the best possible whitening effect in the shortest possible time of contact with the tooth surface. Consequently, teeth whitening devices of prior art formulations typically require multiple applications stretching over a period of weeks or even months, with each recommended application time usually being from two to eight hours.
To address this conflict between stability and efficacy, two component formulations were recently developed to ensure the stability of peroxide during storage. In such formulations, the decomposition of peroxide (generation of radical oxygen) is inhibited until the two (components are mixed, these formulations allow for extended shelf life and more effective bleaching action.
In two component systems, the peroxide-containing parts are maintained at low pH and free of solid particles, conditions that are beneficial for their stability. In order to further enhance peroxide stability, special additives are used to inhibit their decomposition. Formulations based on carbamide peroxide are preferably anhydrous as the presence of water has a destabilizing effect on this compound. The second component contains materials that stimulate the decomposition of peroxides, such as alkaline substances and solid particles having highly developed surface areas. If the peroxide in the first part comprises carbamide peroxide, the medium of the second part contains water in order to minimize tissue irritation caused by the desiccating effect of anhydrous and hydrophilic mediums used in the first part.
Of the two forms of peroxides commonly used in commercial teeth whiteners, hydrogen peroxide is preferred for its greater stability, while carbamide peroxide based formulations offer advantages in terms of better compatibility with additives used to achieve more desirable consistencies and handling properties, and less risk of damage to soft tissues. Both hydrogen peroxide and carbamide peroxide-based formulations are more stable, especially the former, at low pH, preferably in the range of 3-4.5. Carbamide peroxide-based materials may, however, exhibit adequate stability even at neutral or near neutral pH. This makes such formulations more desirable in terms of better perceived compatibility with mucosa and of having no or negligible detrimental effect on tooth enamel and the health of teeth, especially those teeth which are in less than intact condition.
Carbamide peroxide formulations are particularly stable in environments containing little or no water. Examples of common commercial carriers for carbamide peroxide are glycerin and propylene glycol. While these carriers are considered nontoxic and convenient for their compatibility with desirable additives such as thickening agents, preservatives, flavors and therapeutics, their use may create some unwelcome, though generally minor, side effects. The most common is discomfort caused by their desiccating effect on mucosa, and is especially pronounced when scarified or inflamed tissue is involved. Similar responses may also be expected in cases of leaching restorations or recessed gums.
The concentrations of peroxides in commercially available teeth bleaching formulations vary greatly, generally depending on factors such as recommended time of single application, frequency and technique of application, and most significantly, the intended use: if the material is designed for professional use only, for application by the subject/patient but under professional control, or broadly available to the public for in-home, non-supervised use.
The concentration of peroxide (expressed as a percentage of H
2
O
2
) in carbamide peroxide or hydrogen peroxide based formulations sold directly to the public is generally on the order of about 3.0 to about 5.5% by weight, which corresponds to approximately 10 to 16% by weight carbamide peroxide. The concentration of H
2
O
2
in formulations designed for professional use is often higher, in the 7-15% by weight range.
To provide prolonged contact of whitening formulation with teeth while minimizing contact with the mucosa, the whitening material is usually placed on fabricated trays, preferably ones custom procured in a dentist's office to precisely fit the patient's anatomy. The use of higher H
2
O
2
concentration (faster-action) formulations calls for special measures to protect the mucosa from contact with such inherently irritating compositions. Rubber dams or curable tissue coatings are frequently used to protect soft tissues.
Attempts have been made to accelerate the teeth bleaching processes without increasing the concentration of the peroxide by using heat-generating devices, such as high intensity light emitting instruments or lasers. Because of the cost of necessary equipment and greatly increased risk of tissue damage associated with these techniques, they are designed for use exclusively by a dentist. The most effective of these techniques are those using lasers, but they also carry the highest risk of inflicting damage to the teeth and/or soft tissue. The cost of treatments is considerably higher than when conventional methods are used.
The shortcomings of the prior art formulations may be summarized as follows:
A) The inherent conflict between the requirements of shelf life stability of peroxides and the understandable demand for fast bleaching action and high efficacy of the product;
B) The carbamide peroxide based teeth whiteners (which are also more convenient and considered to be safer) require anhydrous or near anhydrous hydrophilic carriers for adequate storage stability which frequently cause user discomfort due to their desiccating effect on mucosa;
C) Storage stability requirements impose the necessity of maintaining low pH on commercial teeth whitening formulations, especially those based on hydrogen peroxide. This is objectionable from the point of view of the potentially damaging effect of such acidic materials on teeth and mucosa;
D) Formulations which exhibit adequate shelf life, as evidenced by maintaining stable peroxide concentrations over time, are intrinsically less effective due to the slow generation of radical (atomic) oxygen in the oral environment which impairs the speed and efficacy of the teeth bleaching process;
E) Fast acting techniques require the use of expensive, often unreliable equipment; they are also associated with increased risk to
Butler David V.
Orlowski Jan A.
Knobbe Martens Olson & Bear
Rose Shep K.
Scientific Pharmaceuticals, INC
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