Dental Whitening - Revisiting the Myths

Dental Whitening - Revisiting the Myths

Jorge Perdigão, D.M.D., M.S.,Ph.D.*:

The popularity of dental bleaching has increased with the introduction of at-home whitening. Currently available whitening methods include those prescribed by a dental professional for use at home, those applied by the professional in the dental office, a combination of the two, or systems available over the counter. This article reviews the effect, efficacy, and safety of bleaching techniques and materials. Most whitening techniques are considered effective and safe when carried out under the supervision of a dental professional.

This article also compares the efficacy and safety of some of the most popular bleaching techniques, including at-home whitening with carbamide peroxide, over-the-counter (OTC) systems, and in-office whitening. Some of these whitening techniques are illustrated in this article.


Tooth whitening was first described in the nineteenth century for the treatment of discolored pulpless teeth.1 In 1989, Haywood and Heymann introduced the nightguard vital bleaching technique (NGVB), using a concentration of 10% carbamide peroxide available over the counter as an FDA-approved antiseptic.2 The NVGB technique, or at-home whitening, became a standard and very popular technique around the world. This technique is performed at home by the patient with professional supervision, using 10%-22% carbamide peroxide in a customfitted tray. Numerous controlled clinical studies have described the effectiveness and safety of at-home whitening.3-8 According to the American Dental Association,9 “data accumulated over the last 20 years indicate no significant, long-term oral or systemic health risks associated with professional at-home tooth bleaching materials containing 10% carbamide peroxide (3.5% H2O2).”

Along with at-home whitening using a custom-fitted tray, there are currently other techniques used by dental professionals to bleach vital teeth. Among them:
• Dentist-administered in-office whitening using a high concentration of hydrogen peroxide (from 25 to 50%). The hydrogen peroxide gel can be irradiated with a heat and/or a light source or be chemically activated.
• Dentist-administered in-office whitening followed by at-home whitening with a custom-fitted tray
• Dentist-administered custom-fitted bleaching tray containing a high
concentration of carbamide peroxide (CP) (from 35 to 40%), also known
as waiting-room whitening (for periods of 30 minutes to one hour)
• Over-the-counter (OTC) products, including trays and adhesive strips
applied by the patient with or without professional supervision.

There are several variables that influence the treatment outcome, including the technique, the type of bleaching agent, the concentration, and the application time.10-12


At-Home Whitening
Carbamide peroxide in concentrations between 10% and 22%, and hydrogen peroxide in concentrations from 4% to 8%, are indicated for home bleaching for prolonged periods of time.11-13

One of the advantages of at-home whitening is its efficacy, which is readily noticed by patients.14 (Figure 1) Another advantage of at-homewhitening is its shade stability. After 10 years, 43% of patients who bleached their teeth with 10% carbamide peroxide deemed the color to be stable.15 In a clinical trial with 10% carbamide peroxide,16 teeth became eight shades lighter after two weeks of treatment when color was measured with the Vita shade guide organized by value (lighter to darker). Two years later teeth had darkened an average of two shades, which occurred during the first six weeks post-treatment. Overall patients were satisfied with the shade.

A major disadvantage of at-home whitening is patient compliance, as the dental professional is unable to monitor the daily treatment. Another disadvantage is the treatment time. In fact, at-home bleaching requires a longer treatment time than in-office bleaching, which may contribute to the higher incidence of tooth sensitivity associated with at-home whitening.

At-Home Whitening Versus OTC Whitening Systems
An increasing number of over-the counter (OTC)products have been introduced within the last few years. In some cases, the fees associated with dentist-prescribed whitening techniques have made patients opt for OTC whitening systems.17 Overall, industry sales of OTC whitening agents, including strips and trays, rose to $333 million in 2003. In 2006, sales dropped to $218 million.18 These OTC agents may work well for patients who have minor discolorations or as a touch-up method. Because the FDA does not regulate tooth whiteners, many OTC products have not been submitted to meticulous clinical testing and consequently may be of questionable efficacy and safety.19 Ill-fitting trays may result in soft tissue injury and malocclusion problems. Some dentifrices claimed to have whitening ability may work by abrasion to remove superficial stains.19

In spite of the strong impact of OTC whitening methods among consumers, at-home whitening is still the procedure of choice, particularly for the treatment of intrinsically stained teeth.29,21 A recent clinical report comparing the outcome of several whitening methods concluded that at-home bleaching was superior to a well-known OTC adhesive whitening strip.22

In-Office Whitening
In-office bleaching is performed using high-concentration HP (25% to 50%) along with some form of light energy that is assumed to accelerate the bleaching process.23 A few in-office chemically-activated hydrogen peroxide gels are available in two syringes. One of the syringes contains an H2O2 gel that has an acidic pH. When we mix the “activator” with the base gel, the pH increases and the decomposition starts by releasing oxygen. The contents of each syringe are mixed immediately prior to the pplication (Figure 2) to activate the material.

In spite of being considered less effective than at-home bleaching, in-office whitening may achieve visible results in one or two sessions.14,24  The apparent shade improvement immediately after an in-office whitening session is caused by tooth dehydration.20 One study evaluating patients’ satisfaction with in-office whitening found that a single in-office bleaching session is not sufficient to achieve satisfactory results.24 Nevertheless, some patients refuse to wear trays. For these patients, in-office whitening is the only viable treatment option as long as they are informed that at-home whitening is more effective and durable.

Manufacturers’ recommendations for using light irradiation and/or laser as an adjunct to in-office bleaching have been questioned in the literature.14,25-29 In fact, clinical research has shown that these external sources of energy do not influence the degree of bleaching, while they may potentiate tooth sensitivity.25-27 For photolysis to occur, the energy must be provided by high frequency light of wavelength 248 nm or lower. The only light to fulfill this requirement is UV, which makes its use in the oral cavity very difficult.10

Some authors have reported increased tooth sensitivity with in-office whitening and appreciable short-term color rebound after treatment.30,31 Another complication that may be caused by in-office whitening is pulp injury. The 35% H2O2 in-office bleaching gel irradiated with light resulted in trans-enamel and trans-dentinal cytotoxic effects characterized by direct damage to odontoblasts and a decrease of their metabolic activity.32 In another study, after five consecutive applications of a 35% H2O2 bleaching agent, either irradiated or not by halogen light, products of gel degradation were capable of diffusing through enamel and dentin, causing toxic effects to the cells.33 The toxic effect of high concentrations of hydrogen peroxide used with in-office bleaching depends upon the anatomy of the tooth.34 The pulp of teeth with thinner enamel and dentin, such as lower incisors, is more prone to injury. A recent study reported that 38% H2O2 for 45 minutes causes irreversible pulp damage in lower incisors but not in premolars.34


Jump-Start Technique?

Many dentists perform in-office bleaching complemented with a custom-fitted tray for at-home bleaching with carbamide peroxide. In-office bleaching is performed during the first session to provide an initial “jump-start” bleaching effect, then the patient is given a home-bleaching agent, usually carbamide peroxide, in a custom-fitted tray, which is to be used until the desired shade is obtained.35  This combination has been used assuming that it enhances the bleaching effect and improves color  stability when compared to in-office bleaching.10,35 However, clinical evidence does not support this assumption. A recent clinical study  reported that this combined in-office/at-home technique does not improve the final shade. The results were similar to those obtained with the at-home technique without the jump-start step.29 Therefore, the in-office component of this combined technique does not improve the patient’s treatment outcome, and may be considered superfluous.

Tooth Sensitivity

Peroxides diffuse very quickly into dentin reaching the pulp chamber, but the rate of penetration depends upon the concentration and composition of the whitening agent.36-38 Tooth sensitivity seems to be the most common lateral effect of whitening with carbamide peroxide, but sensitivity usually relapses with termination of treatment.39 Sensitivity is usually associated with previous history of sensitive teeth, increased frequency of application, or the utilization of higher concentrations of carbamide peroxide such as 20%.39-41 Higher concentrations of peroxides result in a faster rate of whitening than lower concentrations with a similar final result.42,43 However, a slightly higher incidence of sensitivity is associated with higher concentrations.42 Another factor that could play a role in sensitivity is the pH of the bleaching gel, as the pH of whiteners used with the at-home technique can be as low as 5.6.44

Recently some manufacturers have added potassium nitrate and fluoride to the composition of their whitening gels in order to prevent sensitivity during the treatment. One clinical study demonstrated that potassium nitrate and sodium fluoride added to a 10% carbamide peroxide gel reduced sensitivity over a two-week at-home treatment when compared to a 10% carbamide peroxide gel without those two components.45 The use of potassium nitrate/sodium fluoride gel before in-office bleaching with 35% hydrogen peroxide also reduces tooth sensitivity.46

A recent clinical study compared the efficacy of two desensitizers included in the composition of two carbamide peroxide gels. Potassium nitrate was found to be as effective as amorphous calcium phosphate (ACP) to prevent sensitivity.47 However, the carbamide peroxide gel with ACP resulted in less effective whitening than the gel with potassium nitrate.

Discoloration Caused by Antibiotics

Stains that result from chromogenic foodstuff and physiological discoloration caused by aging usually respond well to whitening.20 Tooth discoloration caused by antibiotics is more difficult to remove.

There are two situations in which tetracycline-based medications cause tooth discoloration.

First, and the more common of the two, tetracycline ingestion during tooth formation can be treated with at-home whitening with 10% carbamide peroxide to remove the staining caused by the deposition of the antibiotic on dentin. For the whitening to be successful, treatment must be carried out for up to six months in patients with brownish or grayish horizontal band discolorations.48 (Figures 3 and 4)

Because of the duration of the treatment, patients’ compliance is truly important. Therefore, the patient must commit to a two- to six-month daily treatment. The whitening effect lasts up to 7.5 years after treatment, according to a clinical report.49

It is important that the dental professional understands that teeth with extremely dark gingival tetracycline staining do not have a good prognosis, especially the dark bluish bands located at the cervical third of the teeth.20 The teeth may turn lighter, but the dark band around the cervical third will still be visible after the completion of the treatment.

The second type of antibioticrelated discoloration is caused with minocycline, a tetracycline taken by adults for the treatment of acne (Figure 5). The discoloration of hard tissues caused by the binding of minocycline to secondary dentin and bone has been known for years in the medical and dental community.50-53

Questions from Practicing Dentists About At-Home Whitening

Question #1. What do I tell my patients: Wear the tray overnight, or wear it a few hours a day?

Some patients’ lifestyles do not allow them to wear the tray during the day, while others comment that the tray interferes with their sleep. As far as efficacy and durability of the whitening effect after the treatment is completed, we strongly recommend overnight whitening. Clinical studies out the University of Indiana Operative Dentistry Clinical Research group have shown that overnight whitening is more effective and durable.21

Question #2. I’m confused: Some lecturers recommend trays with reservoirs; others recommend trays without them.

The use of reservoirs in the tray to allow for space to retain the bleaching gel is a controversial issue. In spite of spacers being recommended by some manufacturers as a light-cured block-out resin, the use of spacers to create reservoirs for the bleaching gel does not seem to increase the success of home bleaching.54 The bleaching gel, however, remains active for longer periods when reservoirs are used.55 The use of a reservoir in the custom tray for home bleaching resulted in higher rates and higher intensity of gingival inflammation.56

Question #3. Which concentration of carbamide peroxide would you recommend for at-home whitening?

A higher carbamide peroxide concentration does not increase the longevity of the whitening effect of at-home tooth-bleaching agents.43 The only concentration that at one point received the ADA seal of acceptance is 10% carbamide peroxide.20

Question #4. One of my patients has decided to refill the tray with gel after a few hours. She asked for my opinion ...

There is no need to refill the tray after a few hours. Patients who changed the whitening solution more than once a day reported significantly more side effects than did those who did not change the whitening solution.45  Additionally, the percentage of carbamide peroxide recovered from the tray and teeth is 10% at 10 h. After two hours, more than 50% of the active agent is available.57

Question #5. Do you recommend at-home whitening for two weeks, or for longer periods?

Clinical situations like the one depicted in Figures 1 and 2 usually take two to three weeks for the patient to achieve excellent results. For grayish shades (C shades in the Vita Classical Shade guide) and  reddishgrey shades (D shades), it usually takes at least four weeks for the patient to notice an acceptable improvement. In other specific situations, like brown stains from fluorosis (Figures 3 and 4) and dark bands from tetracycline ingestion, it may take up to six months of continuous at-home bleaching (Figure 3).

Question #6. Does at-home whitening work well for  discoloration-associated with fluorosis?

It depends upon the stain. At-home whitening usually lightens brown stains (Figure 6), but it does not work so well for white stains. The author has had two patients for whom at-home whitening with 10% carbamide peroxide bleached the teeth but ended up highlighting the white spots. Because these spots were not very deep, a few applications of a microbrasion58 suspension camouflaged the white spots. However, it is difficult to predict when microabrasion will remove a stain completely from a tooth. Additionally, microabrasion is not a conservative technique, as it removes a thin layer of enamel.59


Question #7. Do you recommend at-home whitening with the tray to bleach endodontically treated teeth?

No. Internal bleaching with sodium perborate/water works better than external beaching with the tray filled with carbamide peroxide. There is a clinical situation in which carbamide peroxide in a custom-fitted tray significantly improves the color of a single tooth with a discoloration caused by trauma (Figure 7). Radiographically, the pulp space is almost completely obliterated by the dystrophic calcification,60 but the tooth still responds to the peroxide action.


There are several methods and materials available for dental whitening. At-home whitening with 10% carbamide peroxide for two to three weeks is the safest and most effective method for vital teeth. If patients refuse to be treated with the at-home technique, the in-office option is available. However, the patient must be informed that, to achieve desirable results, he or she may need to supplement the in-office treatment with the at-home method. Additionally, the dental professional must use some caution with the type of in-office whitening prescribed, as there have been some reports of potential pulp injury from in-office whitening materials, either caused by the high-concentrated hydrogen peroxide gel, or by the energy source used to “activate” the gel, or by a combination of both.

Special lights are not recommended for in-office whitening because they do not increase the efficacy of whitening gels. There is no evidence that “jump-starting” the at-home method with one in-office session improves the outcome. In fact, it does not.

Dentist-supervised at-home whitening for extended periods of time (up to six months) with 10% carbamide peroxide is recommended for tetracycline-associated stains and for brown discolorations caused by fluorosis.




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The author does not have any financial interest or association with the manufacturers of the products mentioned in this article. Special thanks to the University of Minnesota School of Dentistry past and present dental students for helping with some of the clinical cases shown in this article.