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The first reports describing methods for bleaching nonvital teeth appeared in the mid-19th century, when chloride of lime and Labarraque's solution (calcium hydrochlorite and acetic acid) were proposed as potential whitening agents.1,2 In 1885, the first case of teeth bleaching with hydrogen peroxide was reported,3 and in 1918, Dr. C.H. Abbot recorded the first use of a combination of superoxol (30% hydrogen peroxide) with high-intensity light to increase the temperature of the peroxide for the purpose of accelerating the bleaching process.4 Most of the teeth bleaching techniques in use today use hydrogen peroxide as the active ingredient, either directly or as the product of a chemical reaction with other ingredients such as carbamide peroxide,5,6 allowing easy penetration of enamel and dentin owing to their low molecular weights.7
During the teeth-bleaching process, hydrogen peroxide breaks down into water and peroxide radicals (oxygen ions) as it is absorbed through tooth enamel (Figure 1).8 Unstable electrons in these radicals seek to bind with unsaturated double bonds, which are typically dark- or yellow-pigmented, then alter their structure by breaking them down into single carbon bonds and reducing their absorption of light-instead reflecting light and giving teeth a whiter, brighter appearance.7,8
HYDROGEN PEROXIDE VERSUS CARBAMIDE PEROXIDE
The principal factors influencing the effectiveness of both in-office and take-home whitening treatments are the concentration of hydrogen peroxide and/or carbamide peroxide and the contact times on tooth surfaces.8 In-office bleaching is primarily performed with concentrated solutions of hydrogen peroxide, which breaks down faster and releases a greater number of free radicals owing to its higher concentration of peroxide.8 At-home tray-bleaching solutions most often use carbamide peroxide because of its lower concentration of hydrogen peroxide.8 Carbamide peroxide breaks down more slowly, and it requires longer treatment times than hydrogen peroxide. It is also less effective, but its use in lower concentrations can reduce the likelihood of tooth sensitivity and gum irritation for the patient.8,9
TOOTH DISCOLORATION: TYPES AND CAUSES
There are two types of tooth staining: intrinsic and extrinsic.8Intrinsic staining is discoloration of the tooth dentin that occurs deeper within the tooth and is caused by genetics, trauma, medications, or environment.8 Overall tooth color can also darken with age as a result of erosion and thinning of the enamel, which becomes more translucent, making the dentin more visible.10
Extrinsic staining is discoloration of the tooth enamel, typically as a result of molecules bonding to bacterial biofilm on the teeth.8This type of staining is usually caused by foods and beverages (eg, wine or coffee), smoking, or poor oral hygiene and is easier to remove than intrinsic staining.8
SAFETY AND EFFICACY: FACTORS TO CONSIDER
Teeth bleaching is a safe treatment when performed properly,11and most adverse events are limited to tooth sensitivity and gum irritation.12 However, additional side effects may include soft-tissue burns and erosion of tooth enamel,13,14 cervical resorption, release of selected components of dental restorative materials, and alteration of the enamel surface.15Although studies show that approximately 50% of patients who receive teeth bleaching treatments experience some degree of tooth sensitivity,16 with proper preparation, bleaching techniques, and postprocedural care, this side effect can be reduced or prevented. Chemical burning on intraoral soft tissues from prolonged contact with peroxide can also be minimized or eliminated with proper gingival-isolation training, techniques, and monitoring. The following are the leading considerations for avoiding side effects and achieving successful results with teeth bleaching:
• Concentration. Higer concentrations of hydrogen peroxide in the teeth-bleaching gel whiten teeth more quickly than lower concentrations.5 However, the higher the concentration of hydrogen peroxide, the greater the likelihood of side effects and adverse events.17
• Contact time. The effectiveness of a teeth-bleaching gel is directly related to its exposure time, with longer contact times corresponding to a greater change in tooth shade.8Again, however, excessive exposure times can cause side effects.8
• Temperature. Because temperature accelerates the oxi- dative reaction of peroxide decomposition,8many whitening methods use high-powered lights to increase the temper- ture of the bleaching gel. However, these lights contribute to an increase in pulpal temperatures and damage to healthy tooth structure, as well as desiccation of the teeth, thereby increasing the likelihood of sensitivity and pain both during and after the whitening treatment.8,18
• pH. For oxidative effect, the ideal pH for a tooth-bleaching or tooth-whitening gel is 9.5 to 10.8.8 The gels must be shipped and stored at a lower pH to prevent the chemical reaction from occurring before patient use.8 Hydrogen per- oxide and carbamide peroxide have a shelf-life consider- ation because of their oxidative properties.8
• Environment. For oxidation that occurs in a sealed environment, the effect of bleaching is optimized by prevent- ing oxygen ions from escaping and oxidases in saliva from neutralizing the free radicals.19
TEETH BLEACHING AND WHITENING OPTIONS
The American Dental Association (ADA) recognizes the following categories of bleaching and/or whitening procedures: in-office bleaching, take-home bleaching, and over-the-counter bleaching or whitening products.20Another category of whitening products is classified as "other," consisting of options that use natural ingredients or ingredients other than hydrogen peroxide and carbamide peroxide. With the exception of the "other" category, all these options rely on the oxidizing effects of hydrogen peroxide or a hydrogen peroxide-releasing agent (ie, carbamide peroxide). However, only in-office and take-home systems are professionally backed by a dentist and performed after an examination and clearance are given.
Over-the-Counter Products
Because of their widespread popularity and easy accessibility, over-the-counter (OTC) whitening products make up the largest and fastest growing category of teeth-whitening procedures.21OTC whitening treatments are widely commercially available in the form of strips, wraps, stock trays, paint-on gels, and more.21These products use hydrogen peroxide or carbamide peroxide but often in much lower concentrations than are used with take-home and in-office treatments.22
The greatest drawback to OTC products is that patients generally do not consult with a dental professional beforehand, and thus there is no opportunity to properly examine and diagnose the patient to ensure whitening is appropriate for the patient per ADA recommendations.23 OTC options rely solely on the patient for proper administration and post-treatment compliance to achieve and maintain results. Examples of OTC products are Crest® 3D Whitestrips® (The Procter & Gamble Company), Opalescence Go® (Ultradent Products, Inc.), and Colgate®(Colgate-Palmolive Company).
"Other" Whitening Options
The "other" category contains a new wave of products for lightening teeth. Products such as coconut oil, charcoal powder, "whitening" toothpastes, and chewing gum whiten or lighten teeth by removing extrinsic stains only. Whitening toothpastes and mouth rinses do not provide adequate contact time to have a dramatic bleaching effect. Overall, methods in the "other" category offer only minimal, fleeting results or are ineffective-and some can even damage tooth enamel.19
Take-Home Bleaching Products
Often referred to as "tray bleaching," take-home bleaching products require a professional dental examination and records to fabricate custom-fitted trays that hold bleaching material.13 Take-home products allow for customized treatment planning for each patient based on their bleaching needs, with the dentist choosing the ideal gel concentration and determining the amount of time required for each treatment.
Several take-home options are currently available. The most important factors to consider are their shelf-life, the contact time, and the patient's susceptibility to sensitivity. If a patient prefers a quick teeth bleaching, a gel containing a high concentration of n hydrogen peroxide would be the product of choice. If the patient has deeper staining, has higher susceptibility of sensitivity, and/or is able to allot more time for bleaching, a gel containing carbamide peroxide would the product of choice.
Opalescence™ Go™ (Ultradent Products, Inc.) is a take-home whitening system using prefilled trays containing 10% or 15% hydrogen peroxide to be used for 5 to 10 days.24 The 10% peroxide tray is to be worn for 30 to 60 minutes; the 15% peroxide tray is to be worn for 15 to 20 minutes.24 Pola Office (SDI® Limited) offers a couple of take-home bleaching product options. The Pola Day CP treatment consists of 35% carbamide peroxide to be applied for 15 minutes once or twice per day.25,26 Pola Day offers 7.5% and 9.5% concentrations of carbamide peroxide, to be worn once or twice daily for 30 minutes or once daily for 45 minutes (7.5% concentration) or once daily for 30 minutes (9.5% concentration) during the day.27 Pola Night offers 10%, 16%, and 22% carbamide peroxide concentrations, to be worn for 1 to 2 hours once daily (10% concentration), 90 minutes once daily (16% concentration), or 45 minutes once daily (22% concentration).27
KöR whitening® (Evolve® Dental Technologies) offers KöR-Day™and KöR-Night™, a daytime and nighttime at-home whitening treatment under the KöR home brand.28 KöR-Night consists of 16% carbamide peroxide, and its treatment regimen is 2 weeks of at-home nighttime whitening and periodic at-home maintenance.28 KöR-Day™ is 9% hydrogen peroxide, and its treatment regimen is 2 or more weeks of at-home daytime whitening used once or twice daily and periodic at-home maintenance.28 The daytime treatment is recommended for patients who prefer not to or are unable to wear trays during sleep, or for the patient with high dentin sensitivity who can tolerate wearing whitening trays only for very short periods.28
In-Office Bleaching Products
The most effective option, in-office teeth bleaching offers rapid results and does not rely on patient compliance. The safety of the treatment is directly related to the product that is chosen and to the monitoring that is provided by a licensed dental professional. With a typical hydrogen peroxide concentration range of 20% to 38%, in-office treatments require the use of soft-tissue barriers to prevent chemical burns, and sometimes combine ultraviolet light to increase the temperature of the gel, thus increasing its oxidative capabilities.
The most important considerations when choosing an in-office bleaching system are consistency of results and patient experience. The bleaching system must successfully lighten tooth shade for all patients, with minimal side effects.
Philips® Zoom WhiteSpeed (Koninklijke Philips N.V.) provides light-accelerated whitening, with a hydrogen peroxide concentration of 25%29 and an expected treatment duration of 45 minutes.29,30 GLO™ (GLO Science, Inc.) is a newer system that features the use of heat and light activation with LED light to accelerate the whitening process.31 Its gels are available in hydrogen peroxide concentrations of 24% and 30%,31 and treatment time is approximately 30 minutes.32With Opalescence™ Boost™ (Ultradent Products, Inc.), heat and light are not used and the hydrogen peroxide concentration is 40%.33 Pola Office is a single-use in-office system with a chairtime of approximately 30 minutes and a hydrogen peroxide concentration of 35%.34 The TheraSmile system (Mavrik Dental Systems®) delivers a fully automated teeth whitening treatment.35 With this system, a customized mouthpiece creates a vacuum seal, forming chambers around the teeth through which treatment fluids flow.36 This whitening system provides 360-degree coverage of the treatment area (first molar to first molar) and full-coverage gingival isolation to protect intraoral soft tissues from highly concentrated fluids.35,36
CONCLUSION
For patients who desire teeth bleaching, selection of a teeth bleaching or teeth whitening procedure or product must take into consideration the needs of the individual patient, including the degree of tooth staining, the patient's susceptibility to side effects such as sensitivity, and the time that the patient has available. Once the patient's needs have been identified, successful results will rely primarily on the concentration of the whitening gel and contact time of the gel on the teeth. Take-home products allow for customized treatment planning for each patient based on their individual requirements. However, although patients may prefer the convenience of take-home bleaching products, in-office teeth bleaching is the most effective option and does not depend on patient compliance. Several in-office bleaching systems are available, which vary in terms of their side effect profile and their whitening effects.
References
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