1. The Field of the Invention
The present invention relates to dental bleaching compositions and methods for treating tooth surfaces. More particularly, the present invention is directed to a stable one-component viscous/gelled dental bleaching composition that has a high concentration of bleaching agent. The dental bleaching compositions of the present invention can optionally include a radiant-energy and/or heat-energy absorbing substance which can absorb these forms of energy and cause the bleaching agent to more quickly bleach the tooth surfaces.
2. The Relevant Technology
The use of certain foods and tobacco, the process of aging, diseases, trauma, medications, some congenital conditions, and environmental effects can cause teeth to become discolored. Because white or whitened teeth are usually considered to be aesthetically superior to stained or discolored teeth, there has been a heightened level of interest of late in developing compositions and methods for bleaching teeth.
A tooth is comprised of an inner dentin layer and an outer hard enamel layer that is slightly porous. The natural color of the tooth is opaque to translucent white or off-white.
Some dentrifices, like toothpastes, gels, and powders, contain active oxygen or hydrogen peroxide liberating bleaching agents. Such bleaching agents include peroxides, percarbonates and perborates of the alkali and alkaline earth metals or complex compounds containing hydrogen peroxide. Also, peroxide salts of the alkali or alkaline earth metals are known to be useful in whitening teeth.
The most commonly used dental bleaching agent is carbamide peroxide (CO(NH.sub.2).sub.2.H.sub.2 O.sub.2), also called urea hydrogen peroxide, hydrogen peroxide carbamide, and perhydrol-urea. Carbamide peroxide has been used by dental clinicians for several decades as an oral antiseptic. Tooth bleaching was an observed side effect of extended contact time. Over-the-counter compositions of 10% carbamide peroxide are available as "GLY-OXIDE.RTM." by Marion Laboratories and "PROXIGEL.RTM." by Reed and Carnrick. An extended-contact application of bleaching gel held in a dental tray is available as "OPALESCENCE.RTM." by Ultradent. Other bleaching agents such as peroxyacetic acid (CH.sub.3 C.dbd.OO--OH) and sodium perborate, are also known in the medical, dental and cosmetic arts.
Patients who have desired to have their teeth whitened have typically done so by applying a bleaching composition to the teeth by means of the dental tray for repeated treatments, or they had to submit to conventional in-office bleaching techniques that required from 4 to 10 visits to the dental office before clinically significant results were achieved. Less effective teeth whitening was also done by the use of toothpastes or polishes that were applied by brushing. Clinically significant results are quantifiable such as by measuring gray scale, L*, and as to yellowness or blueness, b*, in the CIE.RTM. system of color measurement or by equivalent methods.
Bleaching compositions have been manufactured in one-part and two-part systems. A one-part system consists of a compound in which the active bleachant is dispersed into inert components to form an emulsion or gel. One-part systems can also further consist of mixtures in which stabilizers are used to prevent premature decomposition of the peroxide in the bleaching composition. The advantage of a one-part system is ease of use and convenience. The main disadvantage is that prior art one-part viscous/gelled bleaching compositions generally contain relatively low concentrations of peroxide. High concentrations in pre-mixed gells have not been stable. Thus, current one-part systems have a low potency and are slow to react. Most one-part systems in the past have included active peroxide in a range of up to about 3.5% by weight. Due to the relatively low concentration of active bleaching agent in one-part systems, about 10 applications on average are necessary for effective bleaching.
In a two-part system, aqueous hydrogen peroxide is mixed with other components to achieve a preferred higher viscosity. These components are mixed just prior to bleaching due to the incompatibility of the other components with hydrogen peroxide. The main advantage of a two-part system is that it allows for much higher concentrations of active peroxide that cannot exist stably as a one-part system for incidental off-the-shelf use. This results in faster bleaching of the patient's teeth due to the higher peroxide concentration. Faster bleaching is desirable, especially where patient compliance with longer bleaching regimens is problematic, or if only one or a few teeth need individual bleaching.
Another example of a two-part system is microencapsulation of the bleaching agent and a stabilizer. The microcapsules would separate the bleaching agent from the carrier and other materials and would rupture only upon physical shear caused by a tooth brush. The dental bleaching effect of the microencapsulation system is only visible after prolonged use due to its low peroxide concentration or low activation rate.
Although positive results using the foregoing techniques have been reported, the effectiveness of the techniques depends upon such factors as type and intensity of the stain, bleaching agent contact time on the teeth, the amount of available active bleachant in the bleaching agent, and the persistence of the individual in applying the treatment until the desired result is accomplished.
Notwithstanding the foregoing advantages, there remain some important disadvantages to current one-part and two-part systems. A disadvantage to the two-part system is that the bleaching composition must be mixed on-site in the operatory immediately before application to the patient's tooth. Mixing requires additional time by the dental professional, which lowers efficiency and represents an extra preparatory procedure. Mixing in proper amounts is also important in order to yield consistent results.
Another disadvantage where high peroxide concentrations are used is that bleaching compositions that must be mixed on-site in the operatory subject the dental professional to the possibility of burns due to mixing splatter. Additionally, high concentrations of hydrogen peroxide are strong oxidizers.
Another disadvantage with two-part bleaching compositions is that, once mixed, the bleaching compositions must be used soon, since they are unstable and tend to decompose through the release of oxygen from the peroxide moieties. Often, the constituents of the bleaching compositions themselves accelerate decomposition rates. While such accelerants are useful in promoting faster bleaching, they yield a composition having a very short lifespan. Because known accelerants are chemical in nature, they cannot be added until bleaching is to commence. Otherwise the premature release of active oxygen will quickly decrease the potency of the bleaching composition. Moreover some accelerant(s) or peroxide indicators are unstable in that they themselves are consumed by the peroxide. The tendency of prior art accelerants or indicators to be themselves consumed has the effect of reducing the concentration of both the peroxide and the accelerant over a short period of time, thus reducing the effectiveness of each.
From the foregoing, it will be appreciated that what is needed in the art are stable, one-part, pre-mixed viscous/gelled bleaching compositions and methods for treating tooth surfaces that allow for greatly increased bleaching rates compared to existing one-part systems.
Additionally, it would be a significant advancement in the art to provide stable, one-part, pre-mixed viscous/gelled dental bleaching compositions for treating tooth surfaces that included means for accelerating the release of active oxygen from the bleaching agent when needed but which do not cause premature decomposition of the active dental bleaching agent or destruction of the bleaching agent activator.
It would still be a further advancement in the art to provide stable, one-part, pre-mixed viscous/gelled dental bleaching compositions that included higher concentrations of bleaching agent compared to existing one-part compositions that are made at the time of manufacture.
Such stable, one-part, pre-mixed dental bleaching compositions and methods for bleaching tooth surfaces are disclosed and claimed herein.