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Year : 2013  |  Volume : 16  |  Issue : 2  |  Page : 131-134
Spectrophotometric evaluation of peroxide penetration into the pulp chamber from whitening strips and gel: An in vitro study

Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, King George's Medical University, Lucknow, India

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Date of Submission27-Aug-2012
Date of Decision10-Oct-2012
Date of Acceptance19-Nov-2013
Date of Web Publication7-Mar-2013


Aim: To investigate pulp chamber penetration of different concentration of hydrogen peroxide.
Materials and Methods: Fifty extracted human maxillary central incisor teeth were taken and grouped into five ( n = 10). All teeth were cut approximately 3 mm apical to the cemento-enamel junction. Pulp was removed and the pulp chamber filled with acetate buffer. Buccal crown surfaces of teeth in the experimental groups were subjected to whitening strip and paint on whitener gel. Control group teeth were exposed to distilled water. The acetate buffer solution in each tooth was then transferred to a glass test tube after 30 min. Leuco-crystal violet dye and enzyme horse radish peroxidase were added. The optical density of resultant blue color in the tubes was measured by UV-visible spectrophotometer. The values were converted into microgram equivalents of hydrogen peroxide.
Results: The results were evaluated statistically using nonparametric Mann-Whitney U test. Whitening strip showed the lowest pulpal peroxide penetration whereas paint on whitener gel showed highest pulpal peroxide penetration.
Conclusion: This study demonstrate that peroxide is readily penetrate into the pulp chamber of teeth.

Keywords: Bleaching gel; peroxide; peroxide penetration; whitening strips

How to cite this article:
Bharti R, Wadhwani K K. Spectrophotometric evaluation of peroxide penetration into the pulp chamber from whitening strips and gel: An in vitro study. J Conserv Dent 2013;16:131-4

How to cite this URL:
Bharti R, Wadhwani K K. Spectrophotometric evaluation of peroxide penetration into the pulp chamber from whitening strips and gel: An in vitro study. J Conserv Dent [serial online] 2013 [cited 2023 Sep 28];16:131-4. Available from:

   Introduction Top

Since past few years, aesthetic dentistry has focused on tooth whitening. Patient's demand for white teeth has increased dramatically. Numerous tooth whitening products are available in the market under various brand names. Most of these products are to be dispensed and used directly by a dentist. However, few whitening products are available over the counter that can be used by the patients themselves without supervision. [1] These over-the-counter products are either whitening strips or gel. These whitening strips are flexible, which can be applied directly to the teeth. These strips contain various concentrations of hydrogen peroxide (5.3%, 6.5%, and 14%) and eliminate the need for fabrication of custom trays for each patient.

It is reported that whitening strips are easy to use and offer comfort and shorter duration of wear compared with tray bleaching systems. [2] The whitening strips containing 5.3% and 6.5% hydrogen peroxide are used as over-the-counter materials, but the whitening strip containing14% hydrogen peroxide is marketed only for dentists. [3] However, Nathoo et al., [4] report that whitening strips are difficult to adapt onto the malposed teeth. A more recent option is paint on whiteners (gels), which may be used either during daytime or at night. These whiteners are like paint and are applied to the labial surface of a tooth with an applicator brush. They have been formulated in such a manner that they release peroxide gradually and continuously onto the tooth surface until they are removed by normal tooth brushing. [5],[6],[7],[8]

Gel contains one of these peroxide derivatives such as carbamide peroxide (CP), hydrogen peroxide (HP), or sodium per carbonate peroxide (NPP), also known as solid hydrogen peroxide. The effect of CP and NPP is similar to HP, because CP ultimately breaks down into urea and HP [9] and NPP dissociates into sodium carbonate and HP. [10] Hydrogen peroxide breaks down into free radicals, which eventually combine to form molecular oxygen and water. This oxygen oxidizes the stained areas. [9]

A major side effect of bleaching procedures is tooth sensitivity caused by the reversible pulpal damage. [11],[12],[13] Whereas Haywood and Heymann [9] and Haywood et al., [14] reported the use of carbamide peroxide as bleaching agent and evaluated as safe and tolerable with no side effects. McMillan et al., [15] and Gerlach et al.,[16] also observed that the whitening strips have no adverse impact on overall tolerance.

The success of bleaching procedures is directly related to the ability of whitening agents to penetrate enamel and dentine. In recent studies, it has been shown that both hydrogen peroxide [17],[18] and CP penetrate enamel and dentin and also enter the pulp chamber [19],[20],[21] and pulpal enzymes are significantly inhibited by hydrogen peroxide. [22]

   Materials and Methods Top

In the present study, 50 extracted human maxillary central incisor teeth were taken as study samples. These teeth were approximately of the same size and free of caries or any other defects. After cleaning they were stored in distilled water. For experimentation all teeth were cut approximately 3 mm apical to the cemento-enamel junction. Pulp was removed with a round bur. All samples were then observed by stereomicroscope to see any surface defects on the surface of teeth. Then 50 teeth selected were grouped into five, each group containing 10 teeth.

Twenty-five milliliters of 2M acetate buffer was placed into the pulp chamber of each tooth to absorb and stabilize any peroxide that might penetrate into the pulp chamber. The vestibular crown surface of each tooth in group I-IV (test group) was treated by one of the following bleaching products according to manufacturer's instructions:

  • Group I: Whitening strip containing 5.3% HP (crest white strips; Procter and Gamble, Cincinnati, OH, USA)
  • Group II: Night use paint - on whitener containing 19% NPP equivalent to 5.3% HP (Crest Night Effects; Procter and Gamble, Cincinnati OH, USA)
  • Group III: Day use paint - on whitener containing 18% CP equivalent to 6.5% HP (Colgate Simply White; Colgate Palmolive Company, New York, NY, USA)
  • Group IV: Night use paint - on whitener containing 8.7% HP (Colgate Simply White Night; Colgate Palmolive Company, New York, NY, USA)
  • Group V: Control group and was exposed to distilled water only.
These bleaching products were left on tooth surfaces for 30 min at 37°C. The acetate buffer solution from the pulp chamber of each tooth was removed by means of a pasture pipette after treatment and transferred to a glass tube. The pulp chamber of each tooth was rinsed twice with a 100-μl portion of distilled water and was also transferred to the same glass tubes. Distilled water (2775 μl) was then added to the glass tube together with100 μl, 0.5 mg/ml leukocrystal violet (Aldrich: Sigma-Aldrich Chemical Co., Germany) and 50 μl, 1 mg/ml of the enzyme horse radish peroxidase (Aldrich: Sigma Chemical Co., St. Louis, MO, USA) according to the method described by Mottola et al.,[11] This procedure was repeated separately for each tooth.

The optical density of the resultant blue color in the tubes was measured by a U-V visible spectrophotometer (Shimadzu U.V 1601, Japan) at a wavelength of 596 nm at room temperature [Figure 1]. The values were converted into microgram equivalent of hydrogen peroxide using a spectrophotometer calibration curve [Table 1] obtained through dilutions of 30% hydrogen peroxide (Merk K Ga A, Darmstadt, Germany) stock solution with distilled water. After the first dilution to 0.1 M, the solution was standardized by iodometric titration. [12]
Figure 1: Spectrophotometric curve used in this study

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Table 1: Absorption of different standard concentrations of hydrogen peroxide

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Measurement of concentration of hydrogen peroxide release

The concentration of the hydrogen peroxide released was measured using a spectrophotometer. For this purpose a priming operation was performed. In priming, the absorbance of different standard concentration of hydrogen peroxide was measured. Thereafter, a scatter-plot of standard concentration of hydrogen peroxide and absorbance was drawn.

The equation of the best fit line was then computed as: y = 0.7996x + 0.0147 in which y is the value of the absorbance at 596 nm and x is the weight of hydrogen peroxide in micrograms. R²=0.9414 (regression coefficient of calibration line). The results of measurements were evaluated statistically using nonparametric Mann-WhitneyU test [Table 2].
Table 2: Penetration of hydrogen peroxide at 37°C

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   Results Top

The quantity of hydrogen peroxide in the pulp chambers of teeth exposed to 5.3% gel, 19% NPP (equivalent to 5.3% HP), 18% CP (equivalent to 6.5% HP), and 8.7% gel at 37°C are shown in [Table 2]. Pulpal peroxide was not observed in the control group teeth (group V). Group I, the whitening strip containing 5.3% HP, showed the lowest pulpal peroxide penetration. The differences in peroxide penetration were also observed within the paint-on whitener groups. The amount of hydrogen peroxide found in the pulp chamber of group IV was highest in all the five groups.

   Discussion Top

Lampros et al.,[13] evaluated in their study that the dental hard tissues possess a significant degree of permeability. They showed that iodide ions could readily pass through the coronal wall of tooth. This study indicates that dental hard tissues exhibit substantial permeability of hydrogen peroxide and permeability increases with increased concentration of applied hydrogen peroxide.

Sowjanya and Chaudhary [14] examined the effect of hydrogen peroxide containing bleaching agents on the morphology of human enamel. They found that in SEM study of enamel surfaces treated with hydrogen peroxide, bleaching agents have shown a little alteration in the surface morphology.

In 1993, Hanks et al., [15] observed that the diffusion of hydrogen peroxide through dentine depends on the original concentration of the bleaching agent and the length of time the agent is in contact with the tooth. The results obtained in this study shows that the control group exposed to distilled water do not show any peroxide penetration into the pulp chamber as none of the peroxide preparation was used. In the experimental groups, groups I, II, III, and IV showed positive pulpal peroxide penetration into the pulp chamber.

Peroxide from both whitening strips and paint-on whiteners penetrated into the pulp chamber of an extracted tooth. A large amount of pulpal peroxide was found in the paint-on whitener, group IV (maximum mean concentration 0.398 ± 0.073), than in the whitening strips, group I (maximum mean concentration 0.138 ± 0.017). A difference in peroxide penetration in these groups was due to different concentration of H 2 O 2 in the bleaching products. As strips have 5.3% H 2 O 2 and group IV paint-on whitener has 8.7% H 2 O 2 , it is generally accepted that use of higher hydrogen peroxide concentration containing bleaching products (Gel or strips) causes higher pulpal peroxide penetration. [1],[3],[16] This may have resulted from differences in the composition of the bleaching products (paint on whitener/strip). Paint-on products have been reported to gradually release H 2 O 2 , [4],[6] but the active ingredient of bleaching products might have affected peroxide penetration. Among the bleaching products used in this study, one of the paint-on whiteners and strips contained sodium per carbonate peroxide (NPP) and carbamide peroxide, respectively, as an active ingredient. For bleaching to occur, CP and NPP must be broken down first into the active form, that is, H 2 O 2 . [9],[10] Hence, paint-on whitener has been thought to demonstrate low pulpal peroxide penetration than the whitening strip group, [17] although initial H 2 O 2 concentration released from these two paint-on whiteners were reported to be similar or higher than that released from the strip. [5],[6],[18]

In vitro studies may have the limitations of inability to simulate the clinical conditions. In vital pulp, the pulpal fluid pressure is capable of reducing inward diffusion of chemicals. [19],[20] Tse et al.,[21] reported that there are sufficient mechanisms in the pulp that protect tissue from radicals generated from the reaction of hydrogen peroxide reaching into the pulp and defense mechanism of pulp would significantly reduce the available level of hydrogen peroxide. Therefore, the amount of hydrogen peroxide reaching the vital pulp may be less than in in vitro conditions. It is assumed that penetration of peroxides observed in this study does not affect treatment negatively.

   Conclusion Top

On the basis of these results and within the limitation of this in vitro study, it may be concluded that hydrogen peroxide from paint-on whiteners and whitening strips readily penetrates into the pulp chamber. Higher the concentration of hydrogen peroxide used higher is the penetration into the pulp chamber. Further long-term studies are required to be carried out in detail to evaluate the clinical behavior and other properties of these bleaching products.

   References Top

1.Cooper JS, Bokmeyer TJ, Bowles WH. Penetration of the pulp chamber by carbamide peroxide bleaching agents. J Endod 1992;18:315-7.  Back to cited text no. 1
2.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 Suppl 2000;29:S22-8.  Back to cited text no. 2
3.Gokay O, Mujdeci A, Algn E. Peroxide penetration into the pulp from whitening strips. J Endod 2004;30:887-9.  Back to cited text no. 3
4.Nathoo S, Stewart B, Zhang YP, Chaknis P, Rustogi KN, DeVizio W, et al. Efficacy of a novel, nontray, paint-on 18%carbamide peroxide whitening gel. Compend Contin Educ Dent 2002;23:26-31.  Back to cited text no. 4
5.Slezak B, Santarpia P, Xu T, Monsul-Barnes V, Heu RT, Stranick M, et al. Safety profile of a new liquid whitening gel. Compend Contin Educ Dent 2002;23:4-11.  Back to cited text no. 5
6.Date RF, Yue J, Barlow AP, Bellamy PG, Prendergast MJ, Gerlach RW. Delivery, substantivity and clinical response of a direct application percarbonate tooth whitening film. Am J Dent 2003;(Spec No. 16):3B-8.  Back to cited text no. 6
7.Gambarini G, Testarelli L, Dolci G. Clinical evaluation of novel liquid whitening gel. Am J Dent 2003;16:147-51.  Back to cited text no. 7
8.García-Godoy F, Villalta P, Bartizek RD, Barker ML, Biesbrock AR. Tooth whitening effects of an experimental power whitening toothbrush relative to an 8.7% hydrogen peroxide paint-on gel control. Am J Dent 2004;(Spec No. 17):25A-30A.  Back to cited text no. 8
9.Haywood VB, Heymann HO. Nightgaurd vital bleaching: How safe is it? Quintessence Int 1991;22:515-23.  Back to cited text no. 9
10.Kaneko J, Inoue S, Kawakami S, Sano H. Bleaching effect of sodium percarbonate on discolored pulpless teeth in vitro. J Endod 2000;26:25-8.  Back to cited text no. 10
11.Mottola HA, Simpson BE, Gorin G. Absorptiometric determination of hydrogen peroxide in submicrogram amounts with LeucoCrystal Violet and peroxidase as catalyst. J Anal Chem 1970;42:410-411.  Back to cited text no. 11
12.Adibfar A, Steele A, Torneck CD, Titley KC, Ruse D. Leaching of hydrogen peroxide from bleached bovine enamel. J Endod 1992;18:488-91.  Back to cited text no. 12
13.Lampros D, Lykakes-Lampros K. Contribution to the research of permeability of the hard tissues of teeth. Stomatol Chron (Athenai) 1967;10:217-25.  Back to cited text no. 13
14.Sowjanya T, Chaudhary MT. Effect of hydrogen peroxide containing bleaching agents on the morphology of human enamel. Journal Conservative Dentistry 2003;6:99-102.   Back to cited text no. 14
15.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;72:931-8.  Back to cited text no. 15
16.Benetti AR, Valera MC, Mancini MN, Miranda CB, Balducci I. In vitro penetration of bleaching agents into the pulp chamber. Int Endod J 2004;37:120-4.  Back to cited text no. 16
17.Gokay O, Mujdeci A, Algin E. In vitro peroxide penetration into the pulp chamber from newer bleaching products. Int Endod J 2004;37:120-4.  Back to cited text no. 17
18.Mahony C, Barker ML, Engel TM, Walden GL. Peroxide degradation kinetics of a direct application percarbonate bleaching film. Am J Dent 2003;(Suppl.):9B-11B.  Back to cited text no. 18
19.Matthews G, Pashley DH. Effects of pulpal pressure on inward diffusion across dentin in vitro. J Dent Res 1992; 71,124.  Back to cited text no. 19
20.Mathews B, Vongsavan N. Interactions between neural and hydrodynamic mechanisms in dentin and pulp. Arch Oral Biol 1994;(Suppl.):87S-95S.  Back to cited text no. 20
21.Tse CS, Lynch E, Blake DR, Williams DM. Is home tooth bleaching cytotoxic? J Esthet Dent 1991;3:162-8.  Back to cited text no. 21
22.Bowles WH, Thompson LR. Vital bleaching: The effects of heat and hydrogen peroxide on pulpal enzymes. J Endodo 1986;12,108-112.  Back to cited text no. 22

Correspondence Address:
Ramesh Bharti
Department of Conservative Dentistry and Endodontic, Faculty of Dental Sciences, King George's Medical University, Chowk - 226 003, Lucknow
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.108192

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  [Figure 1]

  [Table 1], [Table 2]

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