INTRODUCTION

Tooth whitening has become a $1.2 billion industry. Patients are requesting bleaching procedures at an ever-increasing rate and desire results as quickly as possible. Dentists are aware that rapidity and degree of whitening are dependent on many variables, including contact time and concentration of the active ingredient.

Studies^1,2 have documented discrepancies between the listed and actual concentrations of the active material in bleaching products. The concentration of bleaching agents in previously assayed products has varied from 1.08 above to 3.55 below the posted concentration. Until recently, the difference in concentration was reported as a difference from the posted label concentration. The current standard for indicating differences in listed and actual bleaching agent concentrations is to indicate the percentage loss from the label concentration. A recently established International Standard for Bleaching Products requires that the actual concentration of active ingredient “shall not exceed 10% or lower than 30% of the manufacturer's stated concentration” over the stated lifetime of the products.³

The purpose of this current study was to gather tooth-whitening agents from four different parts of the world and to determine their concentrations and if the bleaching agents in the United States were within the recommendations of the International Standard at the month of expiration. Differences from the labeled concentration may occur during manufacturing, shipping, or storage of the tooth-whitening agents. Refrigeration during transportation from the manufacturer to dentist's office, when recommended, may vary from the manufacturer's recommendations, causing a more rapid degradation of the agents. This present study examines the labeled vs measured levels of active bleaching agents in tooth-whitening products prescribed by dentists or available over the counter in China, Brazil, Saudi Arabia, and the United States. The date of manufacture was unknown for the bleaching products tested; however, all tests were accomplished shortly after the products were received by the institutions conducting the testing.

The International Standard requires that products retain a certain percentage of the concentration indicated on the label until the date of expiration. The initial evaluation was accomplished when products were acquired to determine why some products may be less effective than expected. The evaluation at product expiration was performed to determine if the use life of the agents was within the requirement of the International Standard.

METHODS AND MATERIALS

An undergraduate student wrote to all the manufacturers of tooth-whitening agents available in the United States, requesting they forward a sample of each of their products for a comprehensive photo of commercially available bleaching products. Three months were spent collecting products. Thirty-five products were received, and they were stored at room temperature after arrival at the university. The over-the-counter products were purchased at local retailers. All assays to determine the initial concentration were performed by the end of the three months. The products were maintained at room temperature in the United States. Another student determined the concentration of the products on the month of expiration. Twenty-four of the products were available for assaying at that time. In China, Saudi Arabia, and Brazil, all products that were available in their countries were purchased and kept at room temperature until they were assayed. The various participants were able to collect 13 products in China, 7 products in Saudi Arabia, and 15 products in Brazil.

The same method of determining the amount of peroxide in the agents was used at all testing sites, which is the one recommended by the United States Pharmacopeia⁴ and the International Standard.³ The specific steps in this chemical analysis have been used in multiple studies.^5–9 The testing sites were sent the specific steps and asked to become familiar with the procedure. All of the participants who performed the tests are published authors in tooth whitening.

Prior to determining the amount of peroxide in a bleaching agent, a researcher at each site indicated on a data sheet the current date, manufacturer, product, expiration date, peroxide type, peroxide concentration, and trial number. An empty 250-mL beaker was then weighed on a scale that was accurate to three decimal points. Approximately 2 g of the bleaching product was placed in the empty beaker, and another weight was taken. The sample weight was calculated by subtracting the empty beaker weight from the beaker with the sample.

Deionized water was added to the 100-mL mark on the beaker. A stir bar was added, and the beaker was allowed to mix on a stir plate until a homogeneous mixture was attained. Twenty milliliters of glacial acetic acid was added, and the beaker was immediately covered with a watch glass. Approximately 2 g of potassium iodide was added to the solution and allowed to dissolve, which turned the solution to a light shade of yellow. Three drops of ammonium molybdate were added, and the solution was allowed to again become homogenous. The beaker was then transferred to a darkened cupboard. The darkened cupboard was used to allow the chemicals to fully associate to ensure complete reaction with the available peroxide agent.

Once the sample had been in a darkened area for at least 10 minutes, it was placed on the stir plate. Gradually, 0.025 N sodium thiosulfate was triturated into the solution, using a 50-mL burette, until the sample turned a pale shade of yellow. Three milliliters of a 1.0% starch indicator was added to the solution, turning the solution a dark purple. More sodium thiosulfate was titrated into the solution, using a 10-mL burette, until the solution turned colorless, which was the end point of the assay. All chemical analyses of concentrations were performed in triplicate.

The concentration of the bleaching agent was determined by the following formula:

where TS is sodium thiosulfate and PW is product weight.

RESULTS

United States

Thirty-two products dispensed to dentists were within 15% of the active agent concentration listed on the label (Table 1). Three products had a 15% lower but not more than a 30% lower concentration of active agent than that listed on the label. All of the tooth-whitening agents dispensed to dentists in the United States that were assayed in this study were within the requirements established by the International Standard upon delivery to the testing site.

Table 1:  Bleaching Agents Available to Dentists Only in the United States Listed by Manufacturer, With Lot Number, Type of Peroxide, Label Concentration, Average Concentration, and Concentration Difference (cont.)

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In the United States, the concentration of the active agent in the bleaching products available over the counter was also assayed. Manufacturers are not required by the Food and Drug Administration to list the active agent concentration of cosmetic products, only to list the ingredients found in the product. The new International Standard requires manufacturers of all tooth-whitening products to list the concentrations of the active bleaching agent on the packaging. Since the products were not required to identify the concentration on the label, it was not possible to identify the concentration differences at the time of testing. The over-the-counter product concentrations of carbamide peroxide (CP) ranged from 10% to 23% CP, and the hydrogen peroxide (HP) concentrations ranged from .09% to 10% HP (Table 2).

Table 2:  Over-the-Counter Bleaching Agents in the United States Listed by Manufacturer, With Lot Number, Type of Peroxide, and Average Concentration

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Twenty-four products were tested at the month of expiration. Three products were found to have concentrations less than that accepted by the International Standard (Table 3).

Table 3:  Bleaching Agents in the United States Assayed During the Month of Expiration, Listed by Manufacturer, With Lot Number, Type of Peroxide, Label Concentration, Mean Concentration of Three Trials, and Concentration Difference

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China

The concentration testing for the tooth-whitening agents that were available on the Chinese market was accomplished at Wuhan University in Wuhan, China. Thirteen products were secured and assayed. Nine of the products had CP as the active agent, with agent concentrations ranging from 8% to 19% CP. Four of the products had HP as the active agent, with agent concentrations ranging from 6-10% HP. Six of the products were available over the counter, and the other seven were available from dental offices. Ten of the products were within 15% of the concentration on the label. Three products had concentrations that were lower than 15% of the indicated concentration but were not more than 30% lower than the listed active agent concentration on the label (Table 4).

Table 4:  Bleaching Agents in China Listed by Manufacturer, With Product Name, Type of Peroxide, Label Concentration, Average Concentration, and Concentration Difference

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Brazil

The concentration testing for the bleaching products that were available on the Brazilian market was accomplished at the University of Santa Catarina in Florianopolis, Brazil. Fifteen products were secured and assayed. Twelve of the products contained CP and had concentrations ranging from 9% to 37% CP. Three of the products contained HP and had concentrations ranging from 6% to 7.5% HP. No tooth-whitening products were available over the counter. Six of the products were within 15% of the concentration on the label. Six products had concentrations that were lower than 15% of the indicated concentration but were not more than 30% lower than the listed concentration of the active agent. Three of the products had a loss of more than 30% of the concentration indicated on the label (Table 5).

Table 5:  Bleaching Agents in Brazil Listed by Manufacturer, With Product Name, Type of Peroxide, Label Concentration, Average Concentration, and Concentration Difference

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Saudi Arabia

The concentration testing for the bleaching agents that were available on the Saudi Arabian market was accomplished at King Saud University in Riyadh, Kingdom of Saudi Arabia. Seven products were secured and assayed. The labels indicated that six of the products contained CP and had concentrations ranging from 10–22% CP; one of the products contained HP, and the label indicated a 7.5% HP concentration of the active agent. No tooth-whitening products were available over the counter. One of the products was within 15% of the concentration on the label. Five products had concentrations that were lower than 15% of the indicated concentration but were not more than 30% lower than the listed concentration of active agent. One of the products had a loss of more than 30% of the concentration indicated on the label (Table 6).

Table 6:  Bleaching Agents in Saudi Arabia Listed by Manufacturer, With Product Name, Type of Peroxide, Label Concentration, Average Concentration, and Concentration Difference

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DISCUSSION

It is well accepted that bleaching effectiveness depends on the time the agent is in contact with the teeth and on the concentration of the agent. The Clinical Research Associates Newsletter has stated that “storage for extended time or in warm temperature, faulty packaging, and other problems can cause bleaches to lose potency.”⁹ The Clinical Research Associates performed their study using a different assay methodology. Of the 12 products they assayed, eight were within 1 of the concentration indicated on the label. Four products were more than 1 higher than the label indicated, and one product was more than 1 lower than the label indicated.

Previous studies in which concentrations were assayed evaluated products as a combined total of all similar products by specific manufacturers and not as individual products. In a report in 2000, the mean decrease in the concentrations of 10%, 15%, and 20% in Contrast PM products was 3.55 less than the label indicated. Rembrandt products of 10%, 15%, and 22% were 1.08 higher than the label indicated.¹ In a report published in 2003, Stark White products of 10%, 16%, and 22% were found to be 2.64 less than the label indicated.²

In Brazil, tooth-whitening agents are required to put the date the product was manufactured, instead of the lot number, on the label. The manufacturing date was not evident on the products in the other countries. It is possible to use the lot number to determine the time of production by contacting the manufacturer, if there is a need to know that at some point in time.

In the past, the consumer had no way of knowing the concentration of active agents in the products sold over the counter in the United States. The International Organization of Standardization now requires manufacturers to list the concentrations of active agents on all tooth-whitening agents. Patients are now able to make an informed decision as to the concentration of over-the-counter products they are purchasing.

Manufacturers have a responsibility to deliver products to the dental practitioner with the bleaching agent concentrations that are listed on the label. It is known that HP is not as stable as CP. The urea in CP stabilizes the HP. HP degrades less rapidly in cold and away from sunlight. Dental practitioners need to keep the products that recommend refrigeration in a cool area to lower the rate of degradation before use.

Manufacturers need to review the expiration dates they place on tooth-whitening agents to ensure the product they market remains within the labeled concentration required by the International Organization of Standardization. Universities around the world need to assay tooth-whitening agents and publish the results in their national dental journals to indicate which ones are at lower concentration than the label indicates at the time of delivery and those that are within the standard at the month of expiration. This will encourage manufacturers to reevaluate the priority they place on maintaining concentrations of products at the appropriate level.

Manufacturers need to adjust the expiration dates, place another agent in the active agent to reduce the degradation of their products, or encourage dental practitioners to keep their products in a cool place so the products will be at the full strength indicated on the label when patients use their products. This will give practitioners the confidence to expect predicted results.

CONCLUSION

The tooth-whitening products available in the United States and China were all within the newly established International Standard. One product in Saudi Arabia and three products in Brazil had a loss of at least 30% or more of the concentration indicated on the label by the manufacturer. These products were assayed after securing the products in the respective country. When testing was accomplished at the month of expiration in the United States, three products had a loss of more than 30% of the concentration indicated on the label. Products with a loss of at least 30% of the listed concentration at any time before the expiration date do not meet the International Standards for tooth-whitening agents.