A profusion of commercial bleaching systems exists on the market today. Home bleaching systems commonly utilize carbamide peroxide to deliver a more stable form of hydrogen peroxide, the active bleaching agent. Most home bleaching systems contain 10% carbamide peroxide, but different commercial brands claim superiority based on differences in the carrier of the active ingredient, which could affect material delivery, material retention in the bleaching tray (material viscosity) or patient compliance (tooth sensitivity, material taste). Although there are a few reports that compare the different bleaching systems by listing their material and marketing contents,^5-6 clinical comparisons of different bleaching systems are rare.

In this study, three commercial 10% carbamide peroxide bleaching systems were used by 24 patients in an overnight protocol maintained for two weeks to compare their subjective clinical effects.

Results

Fifteen women and nine men participated. Their mean age was 28.5 years (range 17 to 51). They did not exhibit tooth sensitivity or recession in the subject teeth before the bleaching treatment. The patients bleached their teeth for 13.5 ± 2.9 nights. Three-quarters of the patients (18 of 24) complied with the daily regimen. The other patients skipped a day or more during the treatment for sensitivity reasons. The recorded time of onset of subjective tooth whitening and the onset, frequency and duration of tooth sensitivity are listed in Table I.

Side effects of the bleaching treatment presented minimal problems to the patients. Six patients (25%) reported gum tingling, tenderness or mild sensitivity for one or two days. One patient reported a scratchy throat for one day. One patient reported sleep interruption and a sore jaw for a couple of days toward the end of treatment. Another patient reported some bruxism as a response to wearing the tray. Three patients did not like the consistency of one of the bleaching products compared with the other.

Intrapatient differences in whitening effect and tooth sensitivity by the two commercial bleaching systems used by each patient were occasionally reported; however, there was no clear trend for the intrapatient differences for the bleaching agents. No intrapatient differences in tooth whitening were noted between the left and right halves. There were no statistical differences in the time of onset of subjective tooth whitening and the onset, frequency and duration of tooth sensitivity among the three commercial bleaching systems when compared pairwise (paired t-test) or independently (ANOVA).

Discussion

A placebo gel was not included in this study because it is well known that carbamide peroxide and hydrogen peroxide bleaching materials will lighten teeth significantly more than placebo materials.7-11 The patients were aware which bleaching agents they were using. It was thought that potential bias by the patients toward a particular agent would be minimal given that the agents had the same 10% carbamide peroxide concentration, the patients had no previous bleaching experience or affiliations with any of the agents, and no marketing or extraneous packaging materials were given to the patients.

No attempt was made to quantify the degree of whitening achieved. Other studies have attempted to quantify tooth colour changes by using the Vita shade tab system or a colorimeter.7-11 The Vita shade tab system requires subjective shade matching, and the colorimeter has been criticized because of its technique sensitivity and need for a flat surface. In addition, small increments of change that could perhaps be measured by instruments such as a colorimeter would not necessarily indicate a clinically significant result. A clinically significant bleaching result necessitates a clear perception by the patient of a difference in tooth colour. In this study, therefore, a notation by the patient that the teeth became whiter was accepted as a clinically significant colour change.

Every patient reported some degree of tooth whitening. The colour changes ranged widely from very slight to dramatic. The average onset for apparent tooth colour change was 2.5 days. An early onset of bleaching effect is desirable to encourage compliance. Four patients reported the onset of tooth whitening as occurring in localized areas of their teeth, resulting in white spots. This response to bleaching has been attributed to variations in enamel structure.12 The visibility of the white spots diminishes over time as the dentin and the rest of the enamel become whiter and perhaps as some of the early enamel whitening regresses. Patients should be advised of the likelihood of initial white spots as a result of the bleaching treatment.

The advantages of overnight wear include greater patient convenience and improved material retention due to less salivation and less interference with the bleaching tray by the patient. Disadvantages are that overnight wear generally leads to longer contact times and does not allow the patient to monitor the side effects, such as tooth sensitivity.

Tooth sensitivity was the most significant side effect of this study. Its frequency was relatively high compared to other reported problems. Other clinical studies using 10% carbamide peroxide for overnight wear over a period of several weeks have reported a 9% to 100% incidence of tooth sensitivity.7,13-16 Leonard and colleagues17 suggested that the only predictors for tooth sensitivity during home bleaching were frequency of application and whether the patient had sensitive teeth before bleaching. Sex, age, day or night wear pattern, dental arch, and absence or presence of abrasion, defective restorations or gingival recession had no significant effect on the development of tooth sensitivity in their study.

In the present study, most reports of sensitivity were mild, transient, sporadic or continuous over a few days, and were elicited by a cold stimulus. When specific teeth were indicated, they were usually the incisors and canines; the premolars were never indicated as specifically sensitive. Two patients reported episodes of spontaneous sensitivity. Two patients reported sensitivity to heat. Five patients reported one to three days of "acute," "very," "extreme," "high" or "severe" tooth sensitivity. The mean number of days of sensitivity was 5.0 ± 3.8 days. All patients should be advised of the likelihood of tooth sensitivity as part of their informed consent. They should also be told that sensitivity could be severe enough to prevent or at least delay the completion of treatment. In other studies, 2 of 17, 4 of 10 and 4 of 28 patients discontinued their bleaching treatment as a result of tooth sensitivity.7,18 In the present study, 25% of the patients skipped at least one day of bleaching for tooth sensitivity reasons but continued to bleach their teeth thereafter. One patient stopped treatment after 12 days because of sensitivity.

The patients were generally assessed within one week of the bleaching treatment. No patients reported the persistence of tooth sensitivity after the cessation of bleaching. This is in agreement with other reports, which conclude that no long-term irreversible pulpal effects are associated with these bleaching techniques.6 Electric pulp tests have indicated no significant changes in pulp response following bleaching whether the teeth were sensitive or not.7,16 Longer exposures to bleaching agents do not appear to increase the level of tooth sensitivity. In this study, tooth sensitivity often diminished during the latter part of treatment. In one 6-month clinical study, the majority of tooth-sensitive days occurred near the beginning of treatment and there were only zero to 20 days of total tooth sensitivity.18

Tooth sensitivity has been attributed to the permeation of the bleaching agent into the pulp.19 Fluoride gels in the bleaching trays have been recommended for treating tooth sensitivity;3 however, fluoride’s action in desensitization is unknown. It could be beneficial in reducing exposure of the pulp to the bleaching agents by simply supplanting the use of the bleaching agent for that day. Fluoride and other desensitizing pastes could also theoretically reduce the penetration of hydrogen peroxide into the pulp by reducing the permeability of dentinal tubules at their orifices. Nonetheless, the best ways to reduce the pulpal inflammation causing tooth sensitivity are probably to reduce the time of exposure to the bleaching agent and to administer anti-inflammatory analgesics.

Despite some reported intrapatient differences, there were no statistically significant differences among the three commercial bleaching systems with respect to tooth sensitivity.

According to information from the manufacturers, Opalescence uses glycerine and contains 20% water. Platinum has a water-based dentifrice formulation. Nite White Excel uses a polyglycol composition and is unique because it contains no water. The water content of the bleaching agent could conceivably affect both tooth dehydration and material stability. In the present study, the different water content of the three commercial bleaching systems did not appear to affect tooth sensitivity or tooth whitening.

The pH values of the three bleaching materials were measured at room temperature by a flat surface polymer body combination electrode with an Accumet 620 pH/mV meter (Fisher). For Platinum, the mean pH was 5.90 (± 0.03, standard deviation); for Opalescence, 6.40 (± 0.09); and for Nite White, 7.43 (± 0.03). Scanning electron microscope investigations have shown slight changes to enamel surface morphology after exposure to bleaching material, particularly under more acidic conditions.20 The clinical significance of these changes, however, is considered negligible or minimal for bleaching treatments of normal duration when the buffering and remineralization potential of the saliva are considered.21 Furthermore, it has been shown that the pH of a carbamide peroxide solution increases during nightguard wear as a result of urea breakdown.22 The pH of the material can affect peroxide radical liberation (and hence, bleaching effect) and material stability.23 A sufficiently low-pH material can also open exposed dentinal tubules, resulting in increased tooth sensitivity. In the present study, the different pH values of the three commercial bleaching systems did not result in clinical differences in tooth sensitivity or tooth whitening.

The selection of a bleaching product should be based on the concentration of the active ingredient, the viscosity of the bleaching agent (higher material viscosity leads to greater material retention)24 and other marketing features. It is likely that higher concentrations of carbamide peroxide will not only whiten teeth more quickly and to a greater degree, but will also lead to increased sensitivity problems. Therefore, a balance between tooth sensitivity and tooth whitening needs to be struck for each individual patient. In Canada, a concentration of 10% carbamide peroxide is significant because formulations containing greater than 10% can be used only under the supervision of dental professionals. In the United States, only 10% carbamide peroxide formulations have received the American Dental Association Seal of Acceptance from the Council on Scientific Affairs of the American Dental Association.

Bleaching methods and materials appear to be growing by leaps and bounds. This study attempts to provide some independent clinical data for dental practitioners for the most common home bleaching method using an overnight wearing regimen in a clinical setting. Further research is needed to investigate the causes of tooth sensitivity and methods to reduce its severity and frequency. n

Dr. Tam is an assistant professor, department of restorative dentistry, University of Toronto.

Reprint requests to: Dr. L. Tam, Department of Restorative Dentistry, Faculty of Dentistry, University of Toronto, 124 Edward St. Toronto, ON M5G 1G6

The author has no declared financial interest in any company manufacturing the types of products mentioned in this article.

Acknowledgments: The author thanks Mr. R. Kandola, a third-year dental student in the faculty of dentistry, University of Toronto, for his assistance in obtaining the pH measurements.

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