Clinical FocusTooth Whitening: What We Now Know
Introduction
The public has been influenced by the portrayal of perfect white smiles in the media. The color quality of television, movies, electronic and print media has raised self-awareness of discolored teeth. In the late 1980's several companies introduced both home-based products and professionally applied tooth whitening products into the U.S. marketplace. These have gained popularity with the public who has come to demand whiter, more perfect smiles.1 There are several different methods for whitening teeth, each with their own mechanism of action. The efficacy of these different methods is dependent upon the particular tooth discoloration that is being treated. Causes of tooth discoloration can be categorized into two main groups: intrinsic and extrinsic staining (see Figure 1). Intrinsic staining, sometimes called internal staining, can be attributed to factors such as genetics, age (from enamel wear over time exposing yellower dentin), antibiotics, high levels of fluoride, and developmental disorders and can start before the tooth has erupted. After eruption of the tooth some dental restorations can cause tooth staining. Extrinsic staining, sometimes called external staining, is largely due to environmental factors including smoking, pigments in beverages and foods, antibiotics, and metals such as iron or copper. Colored compounds from these sources are adsorbed into acquired dental pellicle or directly onto the surface of the tooth causing a stain to appear. See Figure 1 for examples of the staining from these sources.
Tooth whitening is any process that lightens the color of a tooth. Whitening may be accomplished by physical removal of the stain or a chemical reaction to lighten the tooth color. Bleaching is defined here as the chemical degradation of the chromogens. The active ingredient in most whitening products is hydrogen peroxide (H2O2) which is delivered as hydrogen peroxide or carbamide peroxide. Carbamide peroxide is a stable complex that breaks down in contact with water to release hydrogen peroxide. Because carbamide peroxide releases hydrogen peroxide the chemistry of most tooth whitening is that of hydrogen peroxide.
Tooth stains consist of compounds that have color or darker shades called chromogens that are accumulated in the tooth (intrinsic) or on the tooth (extrinsic). Chromogens fall into two categories: large organic compounds that have conjugated double bonds in their chemical structure as shown in Figure 2A; and metal containing compounds. Bleaching of the organic compounds by hydrogen peroxide involves reacting with the double bonds to oxidize the double bond as shown in Figure 2B. This causes the chromogen to become a lighter colored compound. Bleaching of the metallic compounds is much more difficult; better esthetic options may be veneers, bonding, or crowns. There are some professional products that contain sodium hypochlorite (NaOCl) which reacts with the double bonds of the chromogen in much the same way as peroxide as shown in Figure 2C.
Different product types are marketed to address the particular stain to be removed. The broad categories include: cleansers such as smokers' toothpastes which contain larger amounts of detergents and abrasives to aid in the removal of chromogens from the tooth surfaces; bleaches to react with the chromogens to lighten color; and products that have both increased cleansing and bleaching. More severe or complex stains are best lightened professionally, while over-the-counter products can be used for milder cases. The treatment time required for reaching the tooth whitening endpoint is dependent on the time of exposure and the concentration of bleaching compound. This endpoint is dependent on the type of whitening employed, usually 1–2 shades for cleansers and over-the-counter (OTC) gels, and more for professionally applied products.
Section snippets
Types of Teeth Whitening Systems
Whitening systems can be variously categorized. The following approach is in accordance with the American Academy of Cosmetic Dentistry.2
Risks Associated With Tooth Whitening
Risks commonly reported with tooth whitening include increased tooth sensitivity and mild gingival irritation. The degree of these side effects is directly related to the concentration of the peroxide bleach component, duration of the treatment, and the non-bleach composition of the product used. Tooth sensitivity usually occurs at the time of treatment and can last several days; gingival irritation begins within a day of the treatment and can also last several days. There are additional risks
What's New in Bleaching Research?
New studies have shown that aggressive tooth bleaching can cause increased tooth sensitivity, changes in tooth microstructure, and restoration changes. Aggressive bleaching can chemically react with composite restorations, glass ionomer cements, sealants, and ceramic crowns, thus reducing their stability.
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In one in vitro study seven tooth colored restoration substrates including a nanohybrid composite, a microhybrid composite, a flowable composite, and a packable composite resin, along with a
What Does This Mean?
These new studies provide a body of evidence for the profession to use in the counseling, care and treatment of the dental patient. See Box 1 for conclusions drawn from the literature.
Summary
When used following manufacturer's instructions, hydrogen peroxide and carbamide peroxide based tooth whitening is safe and effective. However as with all dental therapies, there are risks, and practices should be tailored to the needs of each individual patient, based upon type and extent of staining, dietary habits, previous restorations and other intraoral conditions. Patients should be informed of the risks associated with tooth whitening and, if using agents at home, instructed for
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