The Effect of Delivery System and Light Activation on Tooth Whitening Eff cacy and Hydrogen Peroxide Penetration

Transcription

1 RESEARCH ARTICLE The Effect of Delivery System and Light Activation on Tooth Whitening Eff cacy and Hydrogen Peroxide Penetration SOYOUNG PARK, BM, MM*, SO RAN KWON, DDS, MS, PhD, MS, FANG QIAN, PhD, PHILIP W. WERTZ, PhD ABSTRACT Purpose: To evaluate the whitening eff cacy of a new two-layer technology in-off ce system compared to a conventional gel-type system and determine hydrogen peroxide penetration (HPP) into the pulp cavity. Materials and Methods: Extracted molars (n 5 60) were assigned to group NC: glycerol gel; group QPRO: 20% HP varnish (Zoom Quick Pro, Philips Oral Healthcare); group ZOOM_NL: 25% HP gel (Zoom Chairside Whitening); and group ZOOM_WL: 25% HP gel (Zoom Chairside Whitening) with light-activation.hpp levels were estimated with leucocrystal-violet and horseradish-peroxidase.instrumental color measurements were performed at baseline (T 0 ), 1-day post f rst whitening (T 1 ),1-day post second whitening (T 2 ),1-day postthird whitening (T 3 ), and1-month post whitening (T 4 ).One-way analysis of variance followed by post hoctukey s HSD test was performed to detect difference in DE*and HP penetrationlevels(a ). Results: DE* of NCwaslower than other groups, whereas DE* of ZOOM_WL was greater than the other three groups, at T 3 and T 4. HPP level obtained from ZOOM_WL ( lg/ml) was signif cantly greater than those obtained fromthe other groups, whereas the mean HPP level observed in NC group ( lg/ml) was signif cantly lower than the other groups. Conclusions: Tooth whitening eff cacy and HPP levels vary based on whitening systems used. CLINICAL SIGNIFICANCE The two-layer technology in-off ce varnish system may be an alternative whitening option to reduce chair time in the off ce. (JEsthet Restor Dent 00:00^00, 2016) INTRODUCTION Tooth whitening is a conservative and effective method to lighten discolored teeth and has become an integral component of esthetic dentistry. The popularity is reflected by the wide scope of whitening options, ranging from professional inoffice procedures and custom fabricated tray-based home whitening to a variety of over-the-counter products. Among the different whitening modalities, professionally administered in-office whitening has gained popularity due to the fact that it provides instant whitening results and that there is no need to wear a tray at home. The efficacy of a variety of *Dentistry, University of Iowa College of Dentistry & Dental Clinics, Iowa City, Iowa,USA À Associate Professor, Program Director, Student Research Program, Loma Linda University School of Dentistry Center for Dental Research,11175 Campus Street CSPA1010C Loma Linda, California, 92350, USA `Associate Research Scientist/Adjunct Assistant Professor, Division of Biostatistics and Research Design and Department of Preventive and Community Dentistry, University of Iowa College of Dentistry & Dental Clinics, Iowa City, Iowa, USA Professor, Oral Pathology, Radiology and Medicine, Dows Institute for Dental Research, University of Iowa College of Dentistry & Dental Clinics, Iowa City, Iowa, USA VC 2016 Wiley Periodicals, Inc. DOI /jerd Journal of Esthetic and Restorative Dentistry Vol 00 ž No 00 ž 00^00 ž

2 systems has been investigated, and many studies have shown that increasing the exposure time and frequency will improve efficacy in terms of tooth color change. 1 4 Active concentration of the whitening material is another important factor to consider. However, several studies have shown that the higher the concentration the faster the whitening rate, 5 7 other studies did not find significant differences between various concentrations of carbamide peroxide Furthermore, activating light sources such as plasma arc lamps, laser systems with a variety of wavelengths, and light emitting diodes (LED) have been used to enhance whitening efficacy. However, study results on the use of light activation in tooth whitening have been equivocal due to the variability of study designs and the use of different whitening materials as well as different activating lights. 11 Whitening efficacy has also been related to the ability of hydrogen peroxide (HP) to diffuse into the tooth structure. 12 HP diffusion into the pulp cavity was enhanced by higher HP concentrations, 13 prolonged whitening time, 14 heat, 14 and large open dentinal tubules of young teeth. 15 LED light and laser activation demonstrated increased HP penetration levels into the pulp cavity, 16 but HP levels seemed not to be correlated with whitening efficacy. 12 With the continuous introduction of new in-office whitening systems varying in delivery method and concentration, there is lack of information on the relative efficacy of these systems. Henceforth, the purpose of this study was to evaluate the whitening efficacy of a new two-layer technology in-office system compared to a conventional gel-type system and determine HP penetration into the pulp cavity. Additionally, degree of tooth color change was correlated with HP penetration levels. The null hypotheses to be tested was that first, there would be no difference in tooth whitening efficacy in terms of tooth color change in DE*, DL*, and Db* among the three different systems tested. Second, there would be no difference in HP penetration levels into the pulp cavity among the different groups. Third, there would be no correlation between HP penetration levels and degree of post whitening overall tooth color change. MATERIALS AND METHODS Sample Selection and Preparation Sixty extracted human molars were collected prior to the study and stored in 0.1% Thymol at 48C. The University of Iowa Institutional Review Board approved the use of extracted human teeth with no identifiers in this study (IRB ID# ). Teeth were cleaned and observed for the absence of anomalies, caries, existing restorations, and deep crack lines. The roots were marked 2 mm apical to the cementoenamel junction and trimmed off with a sectioning machine (TechCut 4, Allied High Tech Products, Inc., Compton, CA, USA). A cavity was prepared by enlarging the pulp chamber with pointed tapered diamond burs (NeoDiamond, Microcopy, Kennesaw, GA, USA) toward the lingual in order to maintain intact labial tooth structure of 2 mm thickness and encompass 50 ml of acetate buffer. A circular adhesive label 6 mm in diameter was adhered at the center of the labial surface to establish a standardized color reading and whitening area. The remaining tooth was painted with gray nail varnish (Sally Hansen, New York, NY, USA), and the adhesive label removed after drying, leaving a standardized window. Whitening Protocol The specimens were randomly assigned into four groups as follows, group NC: glycerin gel (Sigma Aldrich, St. Louis, MO, USA) acting as the negative control; group QPRO: 20% HP varnish (Zoom QuickPro, Philips Oral Healthcare); group ZOOM_NL: 25% HP gel (Zoom Chairside Whitening, Philips Oral Healthcare); without light activation and group ZOOM_WL: 25% HP gel (Zoom Chairside Whitening, Philips Oral Healthcare) with LED light activation (Zoom WhiteSpeed, Philips Oral Healthcare, peak wavelength: 466 nm) set at high intensity (190 mw/cm 2 ). The varnish was a one-time application for 30 minutes whereas the HP gel was removed and replenished with a new gel after 15 minutes as per manufacturer recommendation. A jig was fabricated 2 Vol00žNo00ž00^00ž2016 JournalofEstheticandRestorativeDentistry DOI /jerd VC 2016 Wiley Periodicals, Inc.

3 for each specimen by gently placing the lingual surface of each tooth into a polyvinyl siloxane impression material (Aquasil Ultra Heavy, Dentsply Caulk, Milford, DE, USA) at a 308 angle from the base. Teeth were kept at room temperature (258C) in a closed humid chamber with 100% relative humidity (General Glassblowing Co. Lab Apparatus, Richmond, CA, USA) throughout the 30-minute treatment procedure. All teeth were subjected to three whitening sessions with an interval of 3 5 days. solution (1 mg/ml), and 1 ml of acetate buffer. The final color intensity was measured in an UV/Visible Spectrophotometer (Perkin Elmer, Model Lambda 20, USA, Waltham, MA, USA) at a wavelength of 596 nm. A standard calibration curve with known amounts of HP was used to determine the amount in microgram equivalents in the samples. Statistical Analysis Color Measurements Instrumental color measurements were performed with a contact-type intraoral spectrophotometer (Vita Easyshade Compact Advance, Vita Zahnfabrik, Bad S ackingen, Germany) with a 5 mm diameter probe. The Easyshade Compact was calibrated and placed perpendicular and flush to the exposed tooth surface according to manufacturer s instruction. Color measurements were taken at baseline (T 0 ), 1-day post first whitening (T 1 ), 1-day post second whitening (T 2 ), 1-day post third whitening (T 3 ), and 1-month post whitening (T 4 ). Measurements were performed under a color controlled lightening box (MM 4e GTI Mini Matcher, GTI Graphic Technology, Inc., Newburgh, NY, USA) at CIE D 65, a color temperature of 6,500 K and light intensity of 1,200 lux. Color difference was calculated as DE* ab from the Commission Internationale de l Eclairage. 17 It was calculated from the following equation: DE ab 5 ½ðL 2 2L 1 Þ 2 1 ða 2 2a 1 Þ 2 1 ðb 2 2b 1 Þ 2 Š 1=2 Descriptive statistics were conducted to profile all variables in the study. One-way analysis of variance (ANOVA), followed by the post hoc Tukey s HSD (honestly significant difference) test, was performed to detect both the difference in color parameter values as well as the change in color parameters among the four groups at each post whitening time point. The change in each color parameter is defined as the difference between baseline and each post whitening time point. Moreover, one-way ANOVA with repeated measures, followed by the post hoc contrast test, was used to determine whether there was a significant difference in the color change in each color parameter within each experimental group. One-way ANOVA, followed by the post hoc Tukey s HSD test, was performed to assess the difference in the HPP levels among the four experimental groups. Additionally, Pearson correlation test was used to evaluate the correlation between HPP level and color change parameter DE* at 1-month post whitening. All tests utilized a significance level of SAS for Windows (v9.4, SAS Institute Inc., Cary, NC, USA) was used for the data analysis. Measurement of HP Penetration Levels HP penetration (HPP) levels were measured after the first 30-minute whitening treatment and estimated according to the method of Mottola and colleagues. 18 Acetate buffer (40 ml) retrieved from the pulp cavity was mixed with 1 ml of leucocrystal violet solution (0.5 mg/ml), 0.5 ml of horseradish peroxidase RESULTS Analysis of Color Change Parameters Baseline color parameters showed that there was no significant effect of the type of experimental groups for L*, a*, and b* (p > 0.05 in all instances). VC 2016 Wiley Periodicals, Inc. DOI /jerd Journal of Esthetic and Restorative Dentistry Vol 00 ž No 00 ž 00^00 ž

4 TABLE 1. Comparison of color change (DL*, Db*, and DE*) from baseline to each post whitening time point by group and within each group Group 1-day post first whitening 1-day post second whitening 1-day post third whitening 1-month post whitening DL_T1 Db_T1 DE_T1 DL_T2 Db_T2 DE_T2 DL_T3 Db_T3 DE_T3 DL_T4 Db_T4 DE_T aa (0.69) 0.11 aa (1.02) aa (1.02) 1.38 aa (0.68) 0.35 aa (1.20) aa (0.67) 1.60 aa (0.71) 0.20 aa (1.35) aa (0.97) 1.46 aa (0.86) 0.29 aa (1.18) NC 0.01 aa (1.03) db (2.76) db (2.82) 5.35 cb (3.12) 7.70 cb (2.70) cb (2.31) 2.41 a,bb (3.32) 6.63 ba,b (2.33) bb (2.64) 3.20 bb (3.13) 3.77 ab (2.47) aa,b (2.22) QPRO 1.95 ab (3.24) 10.0 db (2.82) db (3.06) 4.45 aa,b (2.59) 7.23 cb (2.54) cb (2.36) 3.36 ab,c (2.51) 6.17 ba,b (2.01) bb (2.24) 3.87 ab (1.58) 4.51 ab (2.14) ab,c (2.06) ZOOM_NL 3.65 ab (2.04) dc (2.20) dc (1.99) 5.87 cb (2.37) cc (2.06) cc (1.81) 4.90 b,cc (2.80) 9.56 bc (1.82) bc (2.03) 4.27 bb (1.89) 4.40 ab (1.81) ac (1.57) ZOOM_WL 2.21 ab (2.27) Within each column under each variable measured, means with the same upper letter are not signif cantly different using the post hoctukey s HSD test (p > 0.05).Within each row under the same color parameter, means with the same lower letter are not signif cantly different using the post hoc contrasttests (p > 0.05). Table 1 summarizes the comparison of color change parameters from baseline to each post whitening time within each group and also comparison among the groups. Assessing the within group effects revealed that the negative control group NC showed no significant difference in DL*, Db*, and DE* at all treatment time points. Except for NC, there was a significant difference in Db* and DE* and among the four time points within QPRO, ZOOM_NL, and ZOOM_WL with each with least to highest DE* values in 1-day post first whitening, 1-day post second whitening, 1-day post third whitening, and 1-month post whitening, respectively. It is noteworthy to point out that ZOOM_NL showed no significant difference in DL* among the four different time points. When evaluating the difference among the groups at 1-day post first whitening, DE* of NC was lower than other groups although no difference was found among QPRO, ZOOM_NL, and ZOOM_WL. At 1-day post second whitening, 1-day post third whitening, and 1-month post whitening, DE* of NC was lower than other groups, whereas DE* of ZOOM_WL was greater than the other three groups. No difference was found between QPRO and ZOOM_NL. Analysis of HP Penetration Levels Descriptive statistics are presented in Table 2, and Figure 1 illustrates the HP penetration levels among the four experimental groups. Results of the one-way ANOVA showed that there was a significant effect of the type of whitening systems on the HP penetration levels (F(3,56) ; p < ), indicating a significant difference in mean HP penetration level among the four experimental groups. The post hoc Tukey s HSD test revealed that mean HP penetration level obtained from ZOOM_WL ( lg/ml) was significantly greater than those obtained from the other three experimental groups, whereas the mean HP penetration level observed in NC ( lg/ml) was significantly lower than those observed in the other three experimental groups. No significant difference 4 Vol00žNo00ž00^00ž2016 JournalofEstheticandRestorativeDentistry DOI /jerd VC 2016 Wiley Periodicals, Inc.

5 TABLE 2. Comparison of hydrogen peroxide penetration levels (lg/ml) among the four groups Group N Minimum Maximum Median NC (0.003) A QPRO (0.485) B ZOOM_NL (0.282) B ZOOM_WL (0.753) C s with the same letter are not signif cantly different using the post hoctukey s HSD test (p > 0.05). was found between QPRO ( lg/ml) and ZOOM_NL ( lg/ml). Correlation of HP Penetration Levels and Overall Color Change at 1-Month Post Whitening No significant difference was found between HP penetration levels and DE* within NC, QPRO, ZOOM_NL, and ZOOM_WL using the Pearson correlation test (p > 0.05 in all instances). However, there was a significant difference when combining all groups together (p < ). Thus, the Pearson correlation coefficient of 0.68 indicated a moderate positive relationship between HP penetration levels and overall color change Figure 2. DISCUSSION The ADA Council on Scientific Affairs advised patients to consult with their dentist to determine the most appropriate whitening treatment and emphasized that based on data accumulated over the last 20 years there are no significant, long-term oral or systemic health risks associated with professional at-home tooth whitening materials containing 10% carbamide peroxide (3.5% HP). 19 This may be the most important reason that clinicians use professional at-home tooth whitening as their first treatment option to treat discolored teeth. Other benefits include relatively low cost for the whitening treatment, reduced chair-time, allocation of most of the task to the dental staff and lower incidence and severity of tooth whitening induced sensitivity when compared to in-office whitening using highly concentrated whitening material. 20 However, it is vital to realize our patients needs and embrace alternatives to accommodate most everybody desiring whiter and brighter teeth. In-office whitening offers the benefit of faster whitening results that can motivate the patient to continue treatment. It is also highly appreciated by patients that cannot comply with wearing trays. However, the prolonged chair time, advocated use of light activating units and higher incidence of tooth sensitivity were significant drawbacks that limited its use to patients that could afford the higher cost and would tolerate the tooth whitening induced sensitivity. FIGURE 1. Hydrogen peroxide penetration levels by groups. FIGURE 2. Correlation of hydrogen peroxide penetration level to overall tooth color change. VC 2016 Wiley Periodicals, Inc. DOI /jerd Journal of Esthetic and Restorative Dentistry Vol 00 ž No 00 ž 00^00 ž

6 Manufacturers have put efforts in overcoming these drawbacks and realized that they could make a more user-friendly system by changing their delivery method from the conventional gel type to a two-step varnish system. Philips Zoom Quick Pro that was used in this study is comprised of a first layer of 20% HP varnish followed by a second sealant layer that locks the HP layer into place and prevents inadvertent exposure to the surrounding tissue. The system was released in the USA in Upon application of the two layers, which takes about 5 minutes in the office, the patient can leave the office and peal off the adhesives at home after 30 minutes. This reduces the in-office chair time significantly and there is also no need for the use of light activation. However the efficacy and the incidence of sensitivity associated with this two-layer technology have not been well documented. This study evaluated the efficacy of this new varnish system compared to a 25% HP gel used with and without light activation. Based on the results, our first null hypothesis was rejected. There was a significant difference in overall color change based on the whitening system used. At 1-month post whitening the light activated group (ZOOM_WL) demonstrated the highest overall color change supporting the efficacy of light activation used in conjunction with 25% HP. This is in concordance with other studies that showed that light activation enhances the degree of lightening and reduction of chroma The use of light activation is still a topic of dispute and there are also in vitro and clinical trials indicating that light activation does not affect the change in color produced by whitening However, it important to point out that the 20% HP varnish (QPRO) was as effective as the 25% HP gel without light activation (ZOOM_NL). To the best of our knowledge there are no studies on the efficacy of this in-office varnish system compared to the gel system and although there was a difference in formulation and concentration, it was as effective in terms of overall color change. Our study used the widely adopted color difference formula within dental research, derived from the CIE-L*a*b* system. The 50:50% perceptibility threshold of DE* 5 1 which is used in a controlled environment and a 50:50% acceptability threshold of DE* was used to interpret tooth color change results. 34,35 Notably, regardless of whitening system there was a significant increase with continuous whitening sessions. The tooth is permeable and Bowles and Ugwuneri were the first to spectrophotometrically detect the amount of HP penetration into the pulp cavity. 13 This in vitro model proved useful for further studies investigating various factors that might influence HPP into the pulp cavity and was also used for this study. Our second null hypothesis was rejected, since there was a significant difference in HPP levels among the four groups with the light activated group (ZOOM_WL) demonstrating the highest HPP level and no difference between the varnish system (QPRO) and the nonlight activated (ZOOM_NL) group which interestingly followed the same pattern as for overall color change. The increase in HPP levels with light activation is very consistent with another study that has shown increased levels with laser and LED lights. 36 Increased concentration is also associated with higher penetration levels. 13,37 39 Although there was a difference in concentration between QPRO and ZOOM_NL, the concentrations of HP found in the buffer in the pulp cavities were not significantly different. The ability to penetrate into dental hard tissue has also been related to the rheologic properties of the material. 40 On the basis of viscosity difference, it would have been expected to observe more HPP with the 25% HP gel compared to the 20% HP varnish. This suggests that other proprietary factors may have been exerting a modulating influence. This may have to be investigated further to determine the effect of formulation on HP penetration. Our third hypothesis was rejected. Despite the fact that within each group there was no correlation between overall color change and HPP levels, when combining all the groups together there was a modest correlation (r ) indicating that the higher the HPP level the higher the overall color change. Studies that evaluated the correlation between HPP level to overall color change are scarce. One study compared 40% HP using a sealed technique without 6 Vol00žNo00ž00^00ž2016 JournalofEstheticandRestorativeDentistry DOI /jerd VC 2016 Wiley Periodicals, Inc.

7 replenishment of the whitening material versus the conventional technique where the material is replenished every 20 minutes. 12 However, another study compared the use of 40% HP with and without light activation. 23 Both studies found that there was no correlation between HPP levels and overall color change. 12,23 This may seem contradictory to our results; however, it important to notice that even in our study we did not find any correlation within the four groups. It was only when we combined all groups together that we found a modest correlation. It is noteworthy to emphasize that penetration levels cannot be measured clinically. It is also important to point out that penetration studies are limited by the absence of the dynamics in the oral environment including the absence of positive pulpal pressure. Additionally, the pulp cavity has to be enlarged to enable quantification using acetate buffer, leucocrystal violet, and horseradish peroxidase that compromises the resemblance to in vivo. Despite these limitations higher HPP levels may be also associated with higher incidence and severity of tooth whitening induced sensitivity. As such, it would be beneficial to develop or aim for a whitening system with minimal HPP without compromising tooth whitening efficacy. Within the limitations of this study it can be concluded that the two-layer technology in-office varnish system was as effective as the conventional geltype system without light activation and that light activation enhanced the whitening efficacy. The hydrogen peroxide penetration levels were positively correlated with overall tooth color change. Future studies addressing the clinical efficacy, incidence and severity of tooth sensitivity, patient satisfaction, and acceptance toward this new in-office varnish system are needed to support the evidence behind this new technology. DISCLOSURE AND ACKNOWLEDGEMENTS The authors do not have any financial interest in the companies whose materials are included in this article. This study was supported in part by funding from the Dows Student Research Fellowship and Iowa Dental Research Grant, the University of Iowa College of Dentistry. Whitening materials were kindly provided by Philips Oral Healthcare. REFERENCES 1. Kihn P, Barnes DM, Romberg E, et al. Clinical evaluation of a 15% in-office HP tooth-whitening touch-up agent. Comp Contin Educ Dent 2002;23: Al SS, Matis BA, Cochran MA, et al. A clinical evaluation of two in-office bleaching products. Oper Dent 2003;28: de Silva GM, Brackett MG, Haywood VB. Number of inoffice light-activated bleaching treatments needed to achieve patient satisfaction. Quint Int 2006;37: Matis BA, Cochran MA, Franco M, et al. Eight in-office tooth whitening systems evaluated in vivo: a pilot study. Oper Dent 2007;32: Sulieman M, Addy M, MacDonald E, Rees JS. The effect of HP concentration on the outcome of tooth whitening: an in vitro study. J Dent 2004;32: Auschill TM, Hellwig E, Schmidale S, et al. Efficacy, sideeffects and patients acceptance of different bleaching techniques (OTC, in-office, at-home). Oper Dent 2005;30: da Costa JB, McPharlin R, Paravina RD, Ferracane JL. Comparison of at-home and in-office tooth whitening using a novel shade guide. Oper Dent 2010;35: Matis BA, Mousa HN, Cochran MA, Eckert GJ. Clinical evaluation of bleaching agents of different concentrations. Quint Int 2000;31: Krause F, Jepsen S, Braun A. Subjective intensities of pain and contentment with treatment outcomes during tray bleaching of vital teeth employing different carbamide peroxide concentrations. Quint Int 2008;39: Meireles SS, Heckmann SS, Leida FL, et al. Efficacy and safety of 10% and 16% carbamide peroxide tooth-whitening gels: a randomized clinical trial. Oper Dent 2008;33: Buchalla W, Attin T. External bleaching therapy with activation by heat, light or laser: a systematic review. Dent Mater 2007;23: Kwon SR, Wertz PW, Dawson DV, et al. The relationship of HP exposure protocol to bleaching efficacy. Oper Dent 2013;38: Bowles WH, Ugwuneri Z. Pulp chamber penetration by HP following vital bleaching procedures. J Endodont 1987;13: Rotstein I, Torek Y, Lewinstein I. Effect of bleaching time and temperature on the radicular penetration of HP. Endodont Dent Traumatol 1991;7: Camps J, de Franceschi H, Idir F, et al. Time-course diffusion of HP through human dentin: clinical significance VC 2016 Wiley Periodicals, Inc. DOI /jerd Journal of Esthetic and Restorative Dentistry Vol 00 ž No 00 ž 00^00 ž

8 for young tooth internal bleaching. J Endodont 2007;33: Camargo SE, Cardoso PE, Valera MC, et al. Penetration of 35% HP into the pulp chamber in bovine teeth after LED or nd:yag laser activation. Euro J Esthet Dent 2009; 4: CIE (Commission Internationale de l Eclairage). Colorimetry: Technical Report. CIE Pub. Bureau Central De La CIE Mottola HA, Simpson BE, Gorin G. Absorptiometric determination of HP in submicrogram amounts with leuco crystal violet and peroxidase as catalyst. Anal Chem 1970; 42: American Dental Association Council on Scientific Affairs. Tooth whitening/bleaching: treatment considerations for dentists and their patients. Chicago: ADA; Rezende M, Loguercio AD, Kossatz S, Reis A. Predictive factors on the efficacy and risk/intensity of tooth sensitivity of dental bleaching: a multi regression and logistic analysis. J Dent 2016;45: New Dental Product: Philips Zoom QuickPro In Office Whitening System New-Dental-Product-Philips-Zoom-QuickPro-In- Office-Whitening-System/ (accessed May 10, 2016). 22. Ontiveros JC, Paravina RD. Color change of vital teeth exposed to bleaching performed with and without supplementary light. J Dent 2009;37: Kwon SR, Oyoyo U, Li Y. Effect of light activation on tooth whitening efficacy and hydrogen peroxide penetration: an in vitro study. J Dent 2013;41(Suppl 3):e Luk K, Tam L, Hubert M. Effect of light energy on peroxide tooth bleaching. J Am Dent Assoc 2004;135: Torres CR, Barcellos DC, Batista GR, et al. Assessment of the effectiveness of light-emitting diode and diode laser hybrid light sources to intensify dental bleaching treatment. Acta Odontol Scand 2011;69: Klaric E, Rakic M, Marcius M, et al. Optical properties of experimental light-activated bleaching procedures. Photomed Laser Surg 2014;32: Young N, Fairley P, Mohan V, Jumeaux C. A study of hydrogen peroxide chemistry and photochemistry in tea solution with relevance to clinical tooth whitening. J Dent 2012;40(Suppl 2): Kwon S, Kurti SR, Oyoyo U, Li Y. Effect of light activated tooth whitening on color change relevant to artificial stain color. J Esthet Restor Dent 2015;27:s Hein DK, Ploeger BJ, Hartup JK, et al. In-office vital tooth bleaching-what do lights add? Compend Contin Educ Dent 2003;24: Marson FC, Sensi LG, Vieira LC, Araujo E. Clinical evaluation of in-office dental bleaching treatments with and without the use of light-activation sources. Oper Dent 2008; 33: Lima DA, Aguiar FH, Liporoni PC, et al. In vitro evaluation of the effectiveness of bleaching agents activated by different light sources. J Prosthodont 2009;18: Hahn P, Schondelmaier N, Wolkewitz M, et al. Efficacy of tooth bleaching with and without light activation and its effect on the pulp temperature: an in vitro study. Odontology 2013;91: Nutter BJ, Sharif MO, Smith AB, Brunton PA. A clinical study comparing the efficacy of light activated in-surgery whitening versus in-surgery whitening without light activation. J Dent 2013;41(Suppl 5):e Kuehni RG, Marcus RT. An experiment in visual scaling of small color differences. Color Res Appl 1979;4: Ragain JC Jr., Minimum color differences for discriminating mismatch between composite and tooth color. J Esthet Restor Dent 2001;13: Camargo SE, Cardoso PE, Valera MC, et al. Penetration of 35% hydrogen peroxide into the pulp chamber in bovine teeth after LED or nd:yag laser activation. Eur J Esthet Dent 2009;4: Hanks CT, Fat JC, Wataha JC, Corcoran JF. Cytotoxicity and dentin permeability of carbamide peroxide and hydrogen peroxide vital bleaching materials, in vitro. J Dent Res 1993;72: G okay O, M}ujdeci A, Algin E. Peroxide penetration into the pulp from whitening strips. J Endod 2004;30: Palo RM, Valera MC, Camargo SE, et al. Peroxide penetration from the pulp chamber to the external root surface after internal bleaching. Am J Dent 2010;23: Kwon S, Dawson DV, Schenck D, et al. Spectrophotometric evaluation of potassium nitrate penetration into the pulp cavity. Oper Dent 2015;40: Reprint requests: So Ran Kwon,DDS,MS,PhD,MS, Associate Professor, Program Director, Student Research Program,Loma Linda University School of Dentistry Center for Dental Research,11175 Campus Street CSPA1010C,Loma Linda,CA 92350,USA;Tel.: ; sorankwon@llu.edu 8 Vol00žNo00ž00^00ž2016 JournalofEstheticandRestorativeDentistry DOI /jerd VC 2016 Wiley Periodicals, Inc.