by PAYAM MIRFENDERESKI
Over the last two decades, increasing numbers of individuals have taken advantage of tooth bleaching in order to enhance and beautify their smiles. Tooth bleaching and tooth whitening are often used interchangeably both colloquially and in dental practice, but according to the International Organization for Standardization, the two have slightly different definitions. While both are cosmetic dental procedures designed to whiten and polish teeth, tooth bleaching is more specific. Tooth bleaching is in fact a form of tooth whitening that decolorizes teeth via chemical processes, and it is what millions of people refer to when they say they got their teeth “whitened.”  Read on to learn how tooth bleaching actually works and how you can maintain a beautiful smile without damaging your teeth!
how is tooth bleaching different from tooth whitening?
While “tooth whitening” and “tooth bleaching” seem to be interchangeable, it is useful to make a scientific distinction between the two. Tooth bleaching entails the removal of tooth discolorations through oxidation. The oxidation of pigment molecules in the teeth, in particular, is what leads to the increased perception of whiteness in the teeth.
Tooth whitening comprises a wider range of interventions, including purely mechanical ones such as polishing and brushing with disease-preventive pastes that only remove surface stains. Tooth bleaching is therefore a chemical procedure designed to alter the inherent coloration of the teeth, while tooth whitening is any set of chemical or mechanical procedures designed to polish the teeth for aesthetic reasons. 
Tooth whitening can be used in order to remove both extrinsic and intrinsic tooth stains, which may be caused by smoking, poor oral hygiene, drinking colored substances such as coffee or tea, and even aging. Intrinsic stains, such as those caused by aging, can be removed only through bleaching and not through mechanical procedures. 
how does tooth bleaching work?
The active chemical ingredient in most tooth bleaching products is hydrogen peroxide, although chlorine dioxide-based and carbamide peroxide-based products are also available. Hydrogen peroxide, chlorine dioxide, and carbamide peroxide are all molecules that commonly engage in oxidation. Bleaching products contain anywhere between 3% and 40% hydrogen peroxide by concentration, with at-home products typically containing lower hydrogen peroxide concentrations than their in-office counterparts. [1,3]
Although the chemical mechanisms of tooth bleaching are not yet fully understood, it is believed that free radicals (highly reactive ions) produced by hydrogen peroxide interact with pigment molecules in the teeth to produce a whitening effect. These interactions cause changes in the light-absorbing properties of the teeth, thereby making them appear less colored and thus “whiter” to the eye. The temporary dehydration of the enamel surface is another side effect of the bleaching procedure that visibly reduces the shade of the teeth. 
how can I get my teeth bleached?
Though originally practiced mainly in dental offices, tooth bleaching has expanded and diversified greatly over the last two decades. Individuals today may get their teeth bleached at a variety of locations via an even wider range of products. In addition to purchasing over-the-counter tooth bleaching products to apply at home, consumers can get their teeth bleached at malls, in beauty salons, and even on cruise ships. 
The types of bleaching products are also diverse, and include brushes, strips, and trays.  Most brushes and strips are over-the-counter products, purchasable without a dentist’s prescription and applied by patients themselves. Individuals can choose to attach strips coated with bleaching gel to their teeth for several hours per day for a couple of weeks until their teeth achieve the desired whiteness. Similarly, they may opt to apply hydrogen peroxide-containing gels directly to their teeth using special brushes.
Trays, also called mouthguards, are personalized dental molds typically prescribed by dentists for at-home use. At-home tray bleaching typically involves applying a bleaching gel to the inside of the tray and wearing the tray either overnight or twice a day for 2 to 4 days per week.  Tray bleaching is also common in dental offices themselves, where trays containing high concentrations of bleaching agent are applied for 30 minutes to 2 hours, producing an immediate whitening effect. 
what new methods of tooth bleaching can I use?
More creative methods of tooth bleaching are also patented and being perfected, but more research needs to be conducted in order to determine their effectiveness. One of these is the light-emitting toothbrush. Theoretically, this product would allow consumers to brush their teeth with hydrogen peroxide-containing paste while shining light onto their teeth from the same toothbrush, thereby harnessing the power of photobleaching in addition to the oxidative processes described above . Another recent invention is the dry patch, which overcomes the weak adhesion exhibited by wet, gel-coated patches and strips as well as the possibility of swallowing and ingesting some of the gel. The dry patch would sidestep this complication by containing the bleaching gel within a matrix rather than on the external surface of the strips. 
which bleaching method is the most effective?
Many factors play a role in the effectiveness of the bleaching process, the two most influential of which are the concentration of the active ingredient and the length of time that the bleaching material has contact with the enamel, the hard white tissue that covers the visible portion of the teeth. 
For convenience, many patients use daytime or nighttime bleaching trays. Comparing the results of nighttime trays, daytime trays, in-office hydrogen peroxide products, and over-the-counter hydrogen peroxide products, a 2009 review published in Operative Dentistry found that dentist-prescribed nighttime tray bleaching is the most effective of the four. According to the review, the whiteness achieved by nighttime trays surpasses that achieved by the other three systems.  While in-office procedures may induce a white appearance immediately after bleaching, the necessarily shorter contact time of the active agent appears to make them less effective in providing long-term results. In comparison to over-the-counter strips, moreover, trays are also less likely to allow hydrogen peroxide to get into the saliva, therefore decreasing the likelihood of adverse effects.  For these reasons many dental offices tend to recommend tray systems as a follow-up to in-office procedures. 
how safe is tooth bleaching?
hydrogen peroxide products
The presence of free radicals in bleaching materials has sparked a fair deal of concern throughout the years. While oxidative processes involving free radicals have been shown to be associated with aging, stroke, and other degenerative diseases (diseases which progress over time), hydrogen peroxide-based tooth bleaching is not known to produce these effects. Indeed, only very low concentrations of hydrogen peroxide are released into the mouth during the bleaching process, and the body’s natural defense mechanisms resist the little hydrogen peroxide that is swallowed and ingested during the process. 
It is important to note, nonetheless, that high hydrogen peroxide concentrations may cause burns to gingival (gum) tissue upon contact. While hard enamel tissue protects the surface of the teeth from such burns, the soft tissue of the gums are quite vulnerable to ulcers, or sores on the tissue. If these burns are immediately detected (the gingival sores typically appear as white, swollen areas), water can be applied to the ulcerated area to bring the tissue color back to normal. If the bleaching gel remains in contact with the enamel for a longer period of time, though, the ulceration takes much longer to resolve. Vitamin E, rather than mere water, must then be applied to aid in the healing process. 
chloride dioxide products
Tooth bleaching products containing chlorine dioxide are known to be more harmful than other bleaching products. Chlorine dioxide products are much more acidic than their hydrogen peroxide or carbamide peroxide counterparts and therefore tend to erode the enamel. Chlorine peroxide products may cause not only an irreversible reduction in enamel luster, but also increased sensitivity, irritation, and roughness in the teeth and a greater susceptibility to restaining. [1, 7]
While tooth bleaching has been claimed to be associated with an increased risk of oral cancer, research has not provided much evidence in favor of this assertion. A 2004 study published in Food and Chemical Toxicology determined that hydrogen peroxide-based tooth bleaching products is not correlated with oral cancer in either children or adults. According to the study, hydrogen peroxide is only genotoxic, or able to cause mutations in genes and thereby cancer, in vitro (within test tubes or petri dishes), and not in vivo (within the body). Moreover, due to the negligible contact of hydrogen peroxide with the mouth tissue throughout the bleaching process, bleaching products are highly unlikely to pose an increased risk for oral cancer. 
Nonetheless, other research is less inclined to dismissing the oral cancer debate. A 2006 review published in the British Dental Journal concluded that until further clinical research is conducted to address the question of possible carcinogenicity (ability to cause cancer), patients should not use tooth-bleaching products containing concentrated hydrogen peroxide without gum protection, and those with already damaged or diseased gums should avoid hydrogen peroxide-containing products. Patients using trays should also avoid high concentrations of hydrogen peroxide (i.e. greater than 30%) and prolonged exposures to the bleaching material. 
what are the more common side effects of tooth bleaching?
With a reported incidence of between 5 and 50%, gingival irritation is commonly due to an ill-fitting tray, high concentrations of hydrogen peroxide, and possible contact of the hydrogen peroxide with the gums. Thus, trimming the ill-fitting tray and applying gels with lower concentrations of hydrogen peroxide should be able to reduce the risk of gingival irritation. [1, 3]
Tooth sensitivity, which has an incidence of up to 50%, may be caused by the penetration of the hydrogen peroxide into the pulp. The pulp constitutes the interior tissue of the teeth, and as it contains nerves and blood vessels, is particularly sensitive to hydrogen peroxide. Nonetheless, tooth sensitivity may also be prevented to some extent by using lower concentrations of hydrogen peroxide. [1, 9]
While often accompanied by mild adverse effects such as tooth sensitivity and gingival irritation, tooth bleaching can be a safe and relatively comfortable way of whitening one’s teeth. High concentrations of hydrogen peroxide in the bleaching material may lead to complications such as burns in gingival tissue, but the more minor side effects of tooth bleaching may often be reduced through proper application and care. The effectiveness and safety of tooth bleaching depend on many factors, including application time, active agent concentration, and the type of bleaching product. Whether performed by the dentist or by patients themselves, tooth bleaching requires regulation and monitoring. New methods of tooth bleaching are being continuously invented and promoted, and it is very likely that this simple way of enhancing one’s smile will continue to be sought after by the millions.
Summer 2015 | Vol. 15 | Issue 2
- “Safety issues of tooth whitening using peroxide-based materials.” Brit Dent J. (2013).
- “Tooth-bleaching procedures and their controversial effects: A literature review.” The Saudi Dental Journal. (2014).
- “Hydrogen peroxide tooth-whitening (bleaching) products: Review of adverse effects and safety issues.” Brit Dent J. (2006).
- “Patches for teeth whitening.” patft.uspto.gov. (2004).
- “Light-emitting toothbrush and method of whitening teeth.” patft.uspto.gov. (2003).
- “Review of the Effectiveness of Various Tooth Whitening Systems.” Oper Dent. (2009).
- “Influence of bleaching agents on surface roughness of sound or eroded dental enamel specimens.” J Esthet Restor Dent. (2010).
- “Tooth whitening products and the risk of oral cancer.” Food Chem Toxicol. (2006).
- “Incidence of tooth sensitivity after home whitening treatment.” J Am Dent Assoc. (2003).