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After a whitening appointment, dentists can provide patients with a maintenance program that effectively removes staining daily. The goal is to help the patient stay continuously within the realm of a bright, natural smile. Many "natural" maintenance options circulating on the Internet may catch a patient's eye. Dentists should understand the science behind these products and objectively identify which products work or do not work. This article reviews various whitening products, such as activated charcoal and blue covarine, with its optic blue illusion instant whitening effect, and examines how to strengthen teeth and maintain healthy smiles through solutions such as nano-hydroxyapatite and fluoride.
Mechanisms of Teeth Staining: Intrinsic and Extrinsic
In reviewing the mechanisms of teeth staining, it is useful to first examine what a classically beautiful white smile looks like esthetically. Figure 1 shows a woman who maintains her smile daily with the type of technology and techniques that will be discussed here. In a closer look at her smile, a few key qualities can be observed. A normal-colored tooth is determined by the blue, green, and pink tints of the enamel and is reinforced by yellow to brown shades beneath the dentin.1 The smile in the figure contains all the components that make up a "Hollywood beautiful" smile.
Staining is the process by which the teeth lose their brighter, whiter coloring over time. Intrinsic and extrinsic staining can occur on teeth surfaces and within the teeth themselves. The typical American diet consists of food and beverages that can quickly stain teeth. The components that cause stains are tannins and chromogens, which are present in beverages such as red wine. Other common causes of staining include black coffee, coffee with cream, cold coffee, cigarette smoking, black teas, juices, fruit-like power drinks, and even products used in dentistry, such as some mouthrinses and chlorhexidine.1
To prevent or lessen the effect of staining, intrinsic and extrinsic mechanisms must be explored further. Intrinsic staining references a change to the structural composition or thickness of the dental hard tissues that causes discoloration of teeth, including amelogenesis imperfecta, dentinogenesis imperfecta, tetracycline stain, enamel hyperplasia, aging, root resorption, and fluorosis. Intrinsic staining is difficult to resolve because it deals with the internal dentin (yellows and browns) that cannot be whitened easily. Extrinsic stain removal is more feasible. Extrinsic refers to staining that is incorporated into the pellicle and results from the stain-causing agent's basic color. The stain itself is caused by a chemical interaction at the tooth surface.1
Within extrinsic staining there are two types: metallic and nonmetallic. Extrinsic nonmetallic stains include the previously listed common liquids and foods. Chromogens and tannins are absorbed onto the tooth surface and deposited on plaque or the acquired pellicle. Beverages, tobacco, and medicaments are the main cause of these stains. Metallic stains are caused by occupational exposure to metallic salts or medicines containing metallic salts. Examples are the black staining of teeth seen in people using iron supplements, the violet to black staining produced by potassium permanganate in mouthrinses, and the golden-brown discoloration from stannous fluoride.1
Teeth Brightening and Whitening
The history of teeth brightening can be traced back to the Egyptians, who in early 2000 BC created a whitening paste using pumice stone with wine vinegar. Later cultures, such as the ancient Romans in 600 BC, used ammonia from their own urine to brighten their smiles. Around 450 BC, the Romans created a nitrum rub composed of native carbonate soda ash. Modern-day methods of brightening and whitening continue this path.2,3
Hydrogen peroxide is one of most common whitening chemicals, but it has problematic elements that are making it less and less attractive to practitioners. According to a 2016 article by Kwon,4 the limitations of hydrogen peroxide comprise sensitivity, gingival irritation, efficacy, inadequate uptake, and pulpal damage. Inadequate uptake is particularly important to the discussion of daily "white, bright" smile maintenance. Hydrogen peroxide concentrations are high during a 1-hour whitening procedure at the dental office (up to 32%), which makes them very effective on white and brown stains. Patients also use 10%, 15%, and 20% carbamide peroxide or hydrogen peroxide at home as an effective, limited-time daily-use procedure. Kwon's reflections on the inadequacy of uptake in these procedures are essential for understanding potential alternatives. In discussing pulpal damage, Kwon notes that higher peroxide penetration may adversely affect pulpal tissue. As the hydrogen peroxide uptake is closer and closer to the pulp, even the tooth itself can be damaged.4
Although tooth whitening is considered safe and effective when performed under a dentist's supervision, the mechanism underlying noncomplex treatment is not fully understood. Kwon's 2016 article states that researchers still do not understand the entire mechanism of peroxide whitening.4 According to the American Dental Association Council on Scientific Affairs, there appears to be insufficient evidence to support unsupervised use of peroxide-based bleaching materials.5 Today and likely for the foreseeable future, no extremely highly concentrated daily brush-on gels of peroxide are likely to be recommended for patient use because of the absence of supportive research. According to Kwon, the solution may be an anti-staining formulation that would prevent chromophores from bonding with the organic or inorganic content of dental hard tissues from the beginning.4 In other words, an ideal solution would prevent tannins and chromophores from readily binding to teeth. Although this type of solution does not exist, other daily solutions can remove staining effectively.
A basic Google search brings up many of the new ideas for teeth whitening that are currently circulating. Coconut oil pulling is touted as a beneficial and active means of whitening and brightening, but there is no scientific evidence on how the mechanism may occur. It may be antibacterial and beneficial in that regard. Another popular natural remedy on the Internet is apple cider vinegar. This method takes a long time to be effective in whitening teeth; additionally, apple cider vinegar is very acidic and can damage the enamel well before whitening effects are achieved. Turmeric is another substance that has little to no scientific data or medical evidence of efficacy. Awareness of these three methods is essential for clinicians so they can be discussed with patients who mention them. Finally, activated charcoal, which has been around for a long time, is of genuine interest. Activated charcoal is used in medicine to adsorb tannins, chromogens, and pigments. Applying the concept to teeth may work for stain removal.6
The Mechanism of Activated Charcoal
Common charcoal is made from peat, coal, wood, coconut shells, or petroleum products. Activated charcoal resembles common charcoal, but it is made specifically for use as a medicine. It traps chemicals and prevents their absorption into the body.6 Activated charcoal is made by burning carbon-rich materials, such as wood, at very high temperatures. The resulting product is a black, odorless powder. The charcoal is then activated through a special oxidation process that creates porosities on the charcoal particles to increase surface area and available binding sites.7 Non-dental uses for activated charcoal include treatment for poisonings. Because of its absorptive properties, charcoal has incredible surface area and will uptake the poisonous entities that are in the body. It will not bond to anything in the body but will be excreted while bound to the poisons. Although evidence of efficacy is insufficient, activated charcoal is also used to reduce intestinal gas, lower cholesterol levels, treat bile flow problems during pregnancy (cholestasis), and prevent hangovers.6
Adsorption is a chemical reaction where elements bind to a surface. The porous surface of activated charcoal has a negative electrical charge that causes positively charged toxins and gas to bond with it.8 For example, 1 mL of finely subdivided and activated medicinal charcoal has a total surface area of approximately 1,000 square meters.9 One activated teaspoon has the adsorptive properties of roughly a football field, which could be beneficial for poison control.7
Returning to the historical perspective, the first recorded application of charcoal for medicinal purposes was cited in Egypt around 1500 BC. The principal use appears to have been the application of charcoal to adsorb odorous vapors from putrefying wounds. One of the first revolutionary industry usages of activated charcoal was in an English sugar refinery, which successfully wielded wood charcoal for the decolorization of sugar syrups. This led to an entire industry dedicated to changing colors for many different textiles and other products.10
An interesting study of activated charcoal was done by French chemist M. Bertrand, who decided to demonstrate its efficacy by ingesting 5 g of arsenic mixed with charcoal. Amazingly, he survived.11 The history of warfare also made use of charcoal. After poisonous gases were introduced into the battlefields during World War I, large-scale production of an absorption method was needed immediately. The gas mask was invented to resolve this problem. A gas mask made with adsorbent activated charcoal was then used in the military. Around 1918, the first extraction of charcoal from coconut and almond shells utilizing zinc chloride occurred.10 This method is used for the mass production of activated charcoal in a much more economical manner.
Overall, porous carbon materials have many uses. They can separate, store gases, purify water, and remove solvents.12 For tooth surface stain removal, carbon adsorbs a wide range of impurities and contaminants, including pigments. As a result, it will adsorb tannins and phenols.13
A chromogen is a substance that lacks definite color but may be transformed into a pigment. It is also defined as a strongly pigment-generating or pigmented organelle, organ, or microorganism.14 Tannins are polyphenols that are used in clarifying wine and beer. They contain naturally occurring compounds such as tannic acid and are also found in coffee and tea.15 Tannins are made up of large and medium-sized molecules. Carbons consisting of a combination of macropores and mesopores can adsorb these differently sized tannin molecules. Activated carbon will adsorb tannins. Adsorption isotherm data indicate that tannic acid binds strongly to charcoal.16 Compounds that contain chromogenic groups are often strongly adsorbed on activated carbon.17 Consequently, if activated charcoal adsorbs tannins, pigments, and chromogens, and if those same substances form the stains that are adsorbed to the pellicle and plaque of teeth, it would be logical that activated carbon applied to teeth with a soft toothbrush would remove the stains. Looking at a wide breadth of different products and technologies, Cooley and Tuson18concurred that activated carbon formed the best known tooth powder because it both whitened the teeth and deodorized breath.
Figure 2 through Figure 7 show "before," "during," and "after" photographs of healthy patients throughout the process of charcoal application for whitening. To promote their practice, dentists can employ a social media marketing strategy that challenges patients to take the "charcoal test" and videotape their teeth before, during, and after use. The best application of charcoal is to apply it to the brush and gently make round, circular motions. The charcoal should be allowed to sit for a few minutes; then, the patient should rinse thoroughly and expectorate. Even if ingested, the activated charcoal will be expelled along with tannins from the body. Increased use of activated charcoal over an extended period can lead to greater whitening effects, but daily removal of staining and maintenance between patient office visits are the primary concerns. Patients must understand the limitations of viable whitening options, as well as what works and what does not.
Very soft brushes are ideal for use with activated charcoal because they can greatly reduce abrasiveness. Softness combined with many bristles enables a brush to move around the tooth effectively, slightly subgingival on the buccal and lingual surfaces and interproximal into the embrasure spaces. The average brush in the United States has about 2,500 bristles of nylon; new soft brushes have more than 5,000 bristles of soft polyester fine fiber.19,20
Immediate Effect of Blue Covarine
Other products to enhance whiteness include blue covarine, a component that is now available for daily applications. Also known as optic blue or pigment blue, it is a new optical approach to tooth whitening that enhances the measurement and perception of tooth whiteness using blue-colored materials deposited directly onto the tooth surface. Blue covarine gave a mean Vita shade change of 1.18 compared with a water control of 0 and showed an increase in an objectively measured whiteness index. Essentially, when brushed on the tooth surface, blue covarine creates an illusion of whiteness. The mode of action involves deposition and retention on tooth surfaces, where it alters the optical properties of the tooth, increasing the overall measurement and perception of tooth whiteness. The optic blue is deposited on the tooth surface, and blue covarine is left over after brushing, reflecting light as a white color. Because of this, there is a whiter, brighter presentation of teeth immediately after using blue covarine.21 However, it is not particularly long-lasting.
Acidity Versus Remineralization: Nano-Hydroxyapatite and Fluoride
Acidity is another aspect of staining that must be understood for better teeth whitening. If teeth are worn down with acid erosion, staining is more evident and difficult to control. Clinicians may want to recommend components in daily care that help strengthen and remineralize teeth, such as sodium fluoride and nano-hydroxyapatite. Most dentists are familiar with the benefits of sodium fluoride; fluoridation has dramatically improved the overall health of tens of millions of Americans.22 However, it has been battled ever since it has been available, and there is now unfounded conversation on the Internet about the carcinogenic properties of fluoride as well as possible side effects leading to mental illness and other scientifically unproven results. Dentists must be aware of these perceptions so that they can respect their patients' decisions to use or not use sodium fluoride. If patients decide not to use it, clinicians may prefer a viable alternative for the daily care of teeth to correct acid erosion.
A considerable amount of surface remineralization of the enamel is achieved after treatment with 1.1% fluoride toothpaste,23 supported by study after study. Dentists also see the results clinically. If the patient is adamant about not using sodium fluoride or needs more support, nano-hydroxyapatite is an option. Nano-hydroxyapatite reveals higher remineralization effects when used daily. A study by Tschoppe et al24 showed that both nano-hydroxyapatite and sodium fluoride can greatly enhance remineralization and increase tooth microhardness. Similarly, Haghgoo et al25 found that these materials are ideal in combination. The data allow clinicians to adjust their recommendations when dealing with fluoride-wary patients. The clinician can suggest a lower dose of sodium fluoride in toothpaste combined with a dose of nano-hydroxyapatite in the same paste.
In summary, multiple options are relevant to patients outside of higher-strength hydrogen peroxide. Patients can try activated charcoal, purchasing it either in capsule form, jars, or bottles. They can use it daily in conjunction with a daily toothpaste that contains either nano-hydroxyapatite or sodium fluoride (or both) to help strengthen and remineralize the surface of the teeth. Lastly, they can brush with a blue covarine-containing paste. The relative dentin abrasivity (RDA) rating should also be considered.26
A Comprehensive Teeth-Whitening Program
A comprehensive teeth-whitening program can include increasing recare, decreasing cancellations, and decreasing no-shows in hygiene, as well as boosting revenue with sales of a product. All these improvements can be beneficial to a dentist's bottom line. An in-office 1-hour 32% hydrogen peroxide whitening visit may be a specific recommendation to patients. It is important for dentists to be conservative in their projections of whitening because patient expectations may not align with the actual change these treatments can effect. These treatments remove the extrinsic yellow-brown stain but also reveal the intrinsic gray stain. In the whitening program fee, it may be beneficial for dentists to include a continuum of whitening at home. This idea is based on the German Kor whitening philosophy.27
Kor whitening is used for extremely grayed teeth that are stubborn when it comes to whitening. Mild tetracycline stains are examples. A Kor technique includes in-office whitening visits along with intense, lengthy home whitening that relies on precisely fitted trays for a longer period. Kor whitening can be used for most patients, considering many are not satisfied by 1-hour whitening results. Dentists can offer a home whitening tray that contains either 10%, 15%, or 20% carbamide peroxide, depending on whether the patient plans to sleep while using it. If the patient is extremely sensitive, the best recommendation, based on the author's experience, may be mild 20% used for the 1-hour treatment "boost" in the office and 10% at home for 5 ,10, and even 20 days. Clinicians can recommend a maintenance program that includes a toothpaste composed of activated charcoal, sodium fluoride, nano-hydroxyapatite, and blue covarine. They can also recommend a very soft, multi-tufted polyester brush for thorough activation.
Finally, programs such as Whitening for Life, Keeping It White, and Stay White are used for hygiene recare recall. Signing patients up for these programs can decrease hygiene cancellations and no-shows. When patients follow through with all the elements of recommended whitening treatments, the program allows them to return for their scheduled hygiene appointment and receive a free tube of whitening gel. This simple incentive system is both a reward for keeping the appointment and a way of telling the patient how important hygiene is for the maintenance of a healthy, bright smile. If patients do not have whitening trays, they can be issued peel-away whitening application devices for upper and lower to complete an overnight "bump" in whitening. The program ensures that if patients cancel their appointments, they are only allowed a week to reschedule or they lose their whitening. This helps maintain the flow of a dentist's hygiene program.
Proper teeth whitening recommendations and maintenance for patients depend on a science-based understanding of products on the market. Dentists face a challenge in deciding which options most effectively remove stains daily. Patients are attracted to whitening programs that show immediate and long-term whitening results. Therefore, they may benefit most from a program that uses both in-office and at-home treatments. Dentists can also recommend certain toothpaste and toothbrush products that combine the benefits of activated charcoal, sodium fluoride, nano-hydroxyapatite, and non-abrasive bristles. Blue covarine is an additional option that leads to instant, although not long-term, improvements. Fundamentally, patients are drawn to whitening programs capable of providing simple solutions that encourage them to return to the practice for regular hygiene appointments.
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