Paul A. Sagel, BSChE Senior Engineer Oral Care Product Development Linda L. Odioso, MS Senior Scientist Oral Care Technology Development Donna A. McMillan, PhD Principal Toxicologist Regulatory and Clinical Development Robert W. Gerlach, DDS, MPH Principal Scientist Worldwide Clinical Investigations The Procter & Gamble Company Mason, Ohio Learning Objectives: After reading this article, the reader should be able to: describe a new trayless approach to tooth whitening. explain the whitening strip regimen and how the strips are applied. discuss the in vivo peroxide levels. compare the percentage of residual peroxide concentrations on the strip and tooth surface during use. Vital Tooth Whitening With a Novel Hydrogen Peroxide Strip System: Design, Kinetics, and Clinical Response Abstract: For many years, at-home whitening has been used with great success and produces some of the most satisfying results of all dental procedures. Historically, the most common procedure used was a custom-fabricated tray loaded with a 10% carbamide peroxide gel that was worn overnight. Today, many manufacturers offer higher concentrations (15% and 20% carbamide peroxide) for faster results. Regardless of the peroxide concentration used, the custom tray delivery system has remained essentially the same. Recently, a trayless whitening system was developed that does not require any prefabrication or gel loading. The new delivery system is a thin, conformable strip precoated with an adhesive hydrogen peroxide gel. Each preloaded strip is presented on a backing liner. To use the strip, it is peeled off of the backing liner and applied to the facial surfaces of the anterior teeth. Each strip is worn for 30 minutes, removed, and discarded. The strip holds the gel in place for sufficient time to allow the peroxide to intrinsically and extrinsically whiten the teeth. The highly flexible strips conform intimately to the tooth surface and provide a uniform, controlled application of the peroxide gel. At-home tooth whitening produces some of the most satisfying results of all oral care products. A whiter smile builds self-confidence and selfesteem. 1 In addition, tooth whitening is one treatment people feel they can use to offset the effects of aging and lifestyle habits. Peroxide-based tooth whitening is not a new procedure. As early as 1877 dental researchers discovered oxalic acid could be used to whiten vital teeth. 2 The successful advent of the nightguard vital tooth-bleaching technique in 1989 started the now common use of carbamide peroxide to whiten vital teeth. 3 Since then, several manufacturers have marketed at-home tooth-whitening kits through dental offices that included the whitening gels and the materials to fabricate the custom tray device. In the early years, the almost exclusive choice of whitening agents was the 10% carbamide peroxide gels. 2 More recently, higher concentrations of carbamide peroxide gels (up to 22%) are commonly used to achieve faster, but not necessarily better results. 4 Transient tooth sensitivity is common with virtually all tray-applied toothwhitening products. This tooth sensitivity is reported to occur in 10% to 65% of all users. 5,6 Several factors impact the rate and degree of tooth sensitivity, including concentration, wear time, and frequency of application. 7 Sensitivity usually subsides when treatment is completed or, in some cases, discontinued. Many of the new whitening products are focused on achieving faster results and reducing sensitivity. The purpose of this article is to introduce a new tray- S10 Compendium / Supplement No. 29 Vol. 21, 2000
Figure 1 The Crest Whitestrips maxillary strip. Figure 2 The Crest Whitestrips mandibular strip. Figure 3 Removing the strip from the release liner. less whitening system, which uses a novel adhesive whitening-strip delivery system that does not require custom trays. The Trayless Approach to Tooth Whitening The new whitening product, Crest Whitestrips,a, consists of a thin, flexible strip coated with an adhesive hydrogen peroxide whitening gel. The flexibility of the strip allows it to conform to the tooth surface and provide uniform, intimate contact of the whitening gel for the 30-minute wear period. The strips are made of 9-µm polyethylene and embossed with small reservoirs 0.13 cm in diameter and 0.015 cm in depth. The embossing provides capacity for the gel and also improves the conformability of the strip to the tooth surface. The strip device provides a uniform, consistent amount of whitening gel to the tooth surface and protects the gel from salivary interaction during the whitening process. The thinness of the strip makes it almost unnoticeable during the wear period. Two different strip designs are used to whiten the dentition one for the maxillary dentition and one for the mandibular dentition. The maxillary strip is rectangular with rounded corners and measures 6.5 cm long x 1.5 cm wide (Figure 1). The maxillary strip is loaded with 0.200 g of the adhesive whitening a Procter & Gamble, Cincinnati, OH 45202 Figure 4 Aligning the maxillary strip. gel and contains approximately 11 mg of hydrogen peroxide, providing delivery of approximately 1.1 mg hydrogen peroxide per square centimeter of contact. The mandibular strip is trapezoidal with rounded corners and measures 5.0 cm long x 2.0 cm wide (Figure 2). It is loaded with 0.150 g of adhesive whitening gel and contains approximately 8.3 mg of hydrogen peroxide, providing delivery of approximately 1.1 mg hydrogen peroxide per square centimeter of contact the same dose per unit area as the maxillary strip. Each preloaded strip is individually presented on a release liner. To use the product, the strip that holds the gel is peeled off of the release liner (Figure 3) and applied to the facial anterior dentition as described below. The flexibility of the strip allows it to conform to the tooth surface and provide uniform, intimate contact. Applying the Maxillary Strip The strip is applied to the maxillary dentition by aligning its upper edge along the gingival margin of the anterior teeth (Figure 4). The strip is gently pressed onto the tooth sur- Vol. 21, 2000 Compendium / Supplement No. 29 S11
Figure 5 Folding the maxillary strip. faces to ensure good contact, and the excess strip is folded to the lingual surfaces of the anterior teeth (Figure 5). The strip is designed to be wider than the incisogingival length of the teeth to accommodate tooth-size variations in a normal population. Folding the strip material onto the lingual surfaces of the teeth provides additional anchoring of the strip. The length of the strip is designed to cover at least the central six anterior teeth (cuspid to cuspid) and up to the central eight anterior teeth (bicuspid to bicuspid), depending on arch size (Figure 6). The strip provides a uniform, consistent amount of whitening gel to the tooth surface and protects the gel from salivary interaction. Applying the Mandibular Strip The mandibular strip is applied by aligning the longest (bottom) edge of the trapezoid along the gingival margin of the anterior teeth. The strip is gently pressed onto the tooth surfaces to ensure good contact, and the excess strip is folded over to the lingual surfaces of the anterior teeth (Figures 7 through 9). Similar to the maxillary strip, the mandibular strip is wider than the incisogingival length to account for variations in tooth size. The adhesive whitening gel is a viscous polyacrylic acid polymer gel (Carbopol,b ) of glycerin and water containing 5.3% hydrogen peroxide at approximately 5.8 ph. The viscous nature of the gel produces adhesiveness that holds the gel on the dentition for the required wear time and contributes to the product s resistance to saliva solubilization. b B.F. Goodrich, Charlotte, NC 28217 Figure 6 Maxillary strip applied. The solubilization resistance slows saliva and other organics from reacting with the hydrogen peroxide, allowing sufficient time to intrinsically and extrinsically whiten the teeth. Although the adhesive gel does provide some protection against salivary interaction at the edges of the strip, the strip is the primary barrier. Whitening Regimen The recommended usage regimen for the whitening strip is 30 minutes 2 times per day. As with the current tray-based products, the maxillary and mandibular strips may be used separately to allow tracking whitening progress by comparing the maxillary to the mandibular dentition. Whitening is a gradual process and having a reference point often keeps the user motivated to comply with the usage regimen. The whitening procedure can easily be incorporated into the user s morning and evening routines, and two applications a day produce noticeable results faster than once per day, motivating the patient to continue using the product. The 30-minute wear time was chosen not only because of its convenience but also because of the kinetics of peroxide on the tooth surface. After 30 minutes of wear, the peroxide level drops and the whitening efficiency decreases. Peroxide levels on the whitening strip and the tooth surface were evaluated in a crossover study. Ten adult volunteers wore 1 maxillary strip each day for 3 days. For each application, participants were assigned a specific wearing time (5, 30, or 60 minutes) based on a randomization scheme. After treatment, the strips were carefully removed, and the remaining gel was sampled from both the strip and tooth surface. Both samples were analyzed by indirect iodine titration. The mean residual peroxide concentrations on the strip and the tooth surface are summarized in Figure 10. The peroxide level S12 Compendium / Supplement No. 29 Vol. 21, 2000
Figure 7 Aligning the mandibular strip. Figure 8 Folding the mandibular strip. Peroxide Concentration vs Wear Time 6 Figure 9 Mandibular strip applied. on the strip was initially 5.3% and decreased to 3.3% at 5 minutes, 2.7% at 30 minutes, and 2.2% at 60 minutes. The peroxide on the tooth surface was initially 5.3% and decreased to 2.5% at 5 minutes, 1.9% at 30 minutes, and 1.4% at 60 minutes. The peroxide level likely decreased as a result of a reaction with salivary components, dilution, and the transportation of peroxide into the tooth. Figure 11 shows a cross section of a tooth with the whitening strip applied. For the peroxide to whiten the intrinsic stains, many of which are at the dentin level, the peroxide must transport to the stain and then react with it. The concentration gradient between the peroxide at the tooth surface and the lack of peroxide at the stain sets up a concentration gradient that causes the transport of peroxide to the stain. The exact mechanism of transport is unknown and could be a capillary rise through enamel interprismatic spaces, convective mass transfer, or classical molecular diffusion based on a random molecular path. After the peroxide reaches the stain, the whitening kinetics are a function of the peroxide concentration in the area of the stain and the stain concentration. If peroxide is the limiting reactant in the whitening process, the delivery of the peroxide to the stain may be the rate-limiting step in the whitening process. This is a reasonable assumption because teeth generally do not continue to whiten after the delivery 5 4 % Hydrogen Peroxide 3 2 1 0 % Hydrogen peroxide on strip % Hydrogen peroxide on teeth 0 10 20 30 40 50 60 Wear Time (min) Figure 10 Peroxide concentration on the strip and tooth surface. system (tray or strip) is removed. This is also why many treatments are needed to actually whiten the teeth. As the concentration of peroxide on the strip begins to diminish during the wear time, the transport of peroxide to the stain begins to slow. As the delivery of peroxide slows, whitening efficiency decreases. The thinness of the strip makes it almost unnoticeable during the wear period. Efficacy Detailed clinical efficacy is beyond the scope of this article, but a brief review of two studies (reported separately in this supplement) is warranted. In a 70-subject, placebocontrolled clinical trial, twice-daily application (30 minutes each wearing) over 14 days resulted in significant improvements in tooth Vol. 21, 2000 Compendium / Supplement No. 29 S13
Gingiva Stain Pulp Dentin Enamel Strip Whitening Gel Enamel Dentin Peroxide Molecules Figure 12A Photograph taken before using maxillary Crest Whitestrips. Note there was no pretreatment prophylaxis. Figure 11 Cross section of a tooth with strip applied. shade relative to baseline and placebo control. Participants wore the whitening strips without receiving a dental prophylaxis before treatment. Nearly four shades of improvement were observed relative to baseline. 8 In another blinded, comparative study where tooth color was measured objectively in Commission International de l Eclairage ([CIE] International Commission on Illumination) lab color space, Gerlach et al 9 reported that use of the whitening strips for 30 minutes twice a day provided efficacy similar to a marketed, traybased 10% carbamide peroxide (Opalescence,c ) used 2 hours a day for 2 weeks. There were no reports of tooth sensitivity among participants in the whitening-strip group. In this trial, the 5.3% hydrogen peroxide (equivalent to 16% carbamide peroxide) whitening strips provided There were no reports of tooth sensitivity among participants in the whiteningstrip group. a benefit similar to the 10% carbamide peroxide tray-based product with half the total wear time. Gerlach et al also found the strip to provide a more uniform and predictable whitening benefit as evidenced by a 50% reduction in the standard deviation for the whitening-strip group compared to the tray system. This reduction in variability is likely a result of the controlled and uniform application of the whitening gel with the strip device. 9 c Ultradent Products, Inc, South Jordan, UT 84095 Figure 12B Typical whitening benefit of Crest Whitestrips. As with other peroxide-based whitening products, a whitening benefit is usually evident within a few days of using the whitening-strip system. Kugel has reported the results of two case studies using the whitening strips. 10 Using the whitening strip twice a day produced 4- to 6-shade improvements in 14 days in these 2 case studies. Overall, this 14- hour/28-strip regimen was described as easy-touse and well tolerated. The whitening strips did not interfere with work, speech, or similar daily activities. 10 Figures 12A and 12B depict the whitening benefit achieved with twice-daily use of Crest Whitestrips. In this case, treatment was initiated on the maxillary arch only without first performing a dental prophylaxis. Note the modest level of extrinsic stain apparent in the baseline view. While the primary effect is improvement in intrinsic tooth color, there is also reduction in extrinsic or superficial staining following treatment. Figures 13A and 13B depict the response after use of Crest Whitestrips on the maxillary and mandibular arches simultaneously. Discussion The new Crest Whitestrips provide a convenient and efficient method of whitening the anterior teeth. The unique delivery device is virtually unnoticeable when worn and eliminates the need to custom fabricate trays. The efficacy of the product demonstrates that only S14 Compendium / Supplement No. 29 Vol. 21, 2000
Figure 13A Before treatment with Crest Whitestrips. Figure 13B Two-week results of the simultaneous treatment of the maxillary and mandibular arches. a relatively small amount of peroxide is needed to effectively whiten teeth. For comparison, a single 15-mL rinse with 3% H 2 O 2 delivers 450 mg of hydrogen peroxide to the oral cavity, a typical 0.75-g dose of 10% carbamide peroxide bleaching gel applied with a tray delivers 25 mg of hydrogen peroxide, and Crest Whitestrips deliver 11 mg of hydrogen peroxide. Considering that 10% carbamide peroxide tray systems typically treat more teeth, the peroxide delivered per tooth Using the whitening strip twice a day produced 4- to 6-shade improvements in 14 days in these 2 case studies. area is similar. Therefore, it is not surprising that the efficacy is similar when the 10% tray is used for 2 hours/day vs the whitening strips used for 1 hour/day. The time-efficiency advantage of the strip is likely a result of faster delivery of the peroxide due to the larger concentration gradient established when the strip is applied. Conclusions The whitening strips described in this article represent a convenient and efficient method of whitening the anterior teeth. The unique whitening strip is easy to apply and conforms to the target teeth. Thus, whitening is achieved without prefabrication of a custom tray. The whitening strips are almost invisible when worn and usually do not interfere with talking or most social activities. In addition, the thinness of the product does not impact occlusal vertical dimensions. In summary, it has been found that Crest Whitestrips are a safe and effective approach for vital tooth whitening. References 1. Haywood VB, Heymann HO: Nightguard vital bleaching. Quintessence Int 20(3):173-176, 1989. 2. Freedman G, McLaughlin G: Color Atlas of Tooth Whitening. Pacific, MO, Ishiyaku EuroAmerica Inc, pp 1-10, 1991. 3. Haywood VB, Robinson FG: Vital tooth bleaching with nightguard vital bleaching. Curr Opin Cosmet Dent 4:45-52, 1997. 4. Leonard RH, Sharma A, Haywood VB: Use of different concentrations of carbamide peroxide for bleaching teeth: an in-vitro study. Quintessence Int 29(8):503-507, 1998. 5. Matis BA, Cochran MA, Eckert G, et al: The efficacy and safety of a 10% carbamide peroxide bleaching gel. Quintessence Int 29(9):555-563, 1998. 6. Li Y: Biological properties of peroxide containing tooth whiteners. Food Chem Toxicol 34:887-904, 1996. 7. Leonard RH, Haywood VB, Phillips C: Risk factors for developing tooth sensitivity and gingival irritation associated with night guard vital bleaching. Quintessence Int 28(8):527-534, 1997. 8. Kugel G, Kastali S: Tooth-whitening efficacy and safety: a randomized and controlled clinical trial. Compend Contin Educ Dent 21(suppl 29):16-21, 2000. 9. Gerlach RW, Gibb RD, Sagel PA: A randomized clinical trial comparing a novel 5.3% hydrogen peroxide whitening strip to 10%, 15%, and 20% carbamide peroxide tray-based bleaching systems. Compend Contin Educ Dent 21(suppl 29):22-28, 2000. 10. Kugel G: Nontray whitening. Compend Contin Educ Dent 21(6):524-528, 2000. Vol. 21, 2000 Compendium / Supplement No. 29 S15