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Table of Contents   
ORIGINAL RESEARCH  
Year : 2016  |  Volume : 27  |  Issue : 4  |  Page : 410-414
Assessing the effects of hydrogen peroxide bleaching agent on the shear bond strength of orthodontic brackets


1 Department of Orthodontics, Latin American Institute of Dental Research and Education, Curitiba, Paraná, Brazil
2 Department of Orthodontics, University of São Paulo State (UNESP), Araraquara, São Paulo, Brazil

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Date of Submission25-Jan-2016
Date of Decision23-Feb-2016
Date of Acceptance01-Jun-2016
Date of Web Publication10-Oct-2016
 

   Abstract 

Background: Tooth bleaching is, today, one of the most widespread cosmetic treatments in dental practice,  so it is important to determine whether it can interfere with orthodontic bonding or not.
Aim: The aim of this study was to assess the in vitro effects of 35% hydrogen peroxide bleaching agent on the shear bond strength of orthodontic brackets.
Materials and Methods: Forty-five upper bicuspids were divided into three groups (n = 15). In the control Group (C), the brackets were bonded without previous bleaching treatment. Group 1 (G1) was treated with 35% hydrogen peroxide bleaching agent 24 h before bracket bonding. Group 2 was also bleached, and the brackets were bonded after 30 days. The shear bond strength of the brackets was measured using an EMIC machine, and the results were analyzed by ANOVA.
Results: There were no statistically significant differences between the three groups (P > 0.05), with Group C showing a mean bond strength of 9.72 ± 2.63 MPa, G1 of 8.09 ± 2.63 MPa, and G2 of 11.15 ± 4.42 MPa.
Conclusion: It was possible to conclude that 35% hydrogen peroxide bleaching agent does not affect the shear strength of orthodontic brackets bonded 24 h and 30 days after bleaching.

Keywords: Dental bonding, hydrogen peroxide, shear strength, tooth bleaching

How to cite this article:
Andrighetto AR, de Lećo Withers EH, Grando KG, Ambrosio AR, Shimizu RH, Melo AC. Assessing the effects of hydrogen peroxide bleaching agent on the shear bond strength of orthodontic brackets. Indian J Dent Res 2016;27:410-4

How to cite this URL:
Andrighetto AR, de Lećo Withers EH, Grando KG, Ambrosio AR, Shimizu RH, Melo AC. Assessing the effects of hydrogen peroxide bleaching agent on the shear bond strength of orthodontic brackets. Indian J Dent Res [serial online] 2016 [cited 2020 Oct 21];27:410-4. Available from: https://www.ijdr.in/text.asp?2016/27/4/410/191891
Tooth bleaching is, today, one of the most widespread cosmetic treatments in dental practice. Such growth is encouraged by advances in dental products that have been increasingly improved results within a shorter time frame and decreased discomfort for patients, as well as a wider range of options for professionals. These materials involve easy and simple methods which, when properly applied, yield a very good esthetic outcome while preserving tooth structure integrity.[1]

Despite some orthodontists believe it is preferable to use whitening products after fixed appliances are removed,[2] it is becoming increasingly common for orthodontists to treat patients whose teeth have been bleached, or who wish to have them bleached prior to placement of the fixed orthodontic appliance. It is therefore important to ascertain that this procedure does not statistically significantly interfere with bracket/enamel bond strength.[3]

While some authors have found that neither at-home[4] nor in-office[3],[5] bleaching affects the shear bond strength of orthodontic brackets, other researchers have posited that this procedure can reduce such strength.[6],[7],[8],[9],[10],[11],[12],[13],[14],[15] In addition, although discussions about the amount of time and the necessary conditions for the restoration of enamel are frequent, there is as yet no consensus in the literature regarding this issue.

Thus, these controversies surrounding the influence of this bleaching agent on the bonding and debonding of orthodontic brackets probably led Thickett and Courbone[16] to assert: "A significant number of orthodontists are reluctant to perform tooth bleaching in their clinical practice."

Therefore, in view of increasing demand by orthodontic patients who wish to undergo dental bleaching and the need to provide efficient and effective treatment, the authors of this study undertook to evaluate in vitro the shear bond strength of orthodontic brackets bonded to human teeth 24 h and 30 days after tooth bleaching with 35% hydrogen peroxide.


   Materials and Methods Top


The sample consisted of 45 premolars with no defects, cracks, or restorations kept in 0.1% thymol solution. After 24 h under running water to eliminate residues, 48 h in a solution of artificial saliva, and 5 min in distilled water to remove excess saliva, the roots were attached to Speedex condensation silicone (Vigodent, Rio de Janeiro, RJ, Brazil). The specimens were randomly divided into three groups: The control Group (C), which was not subjected to bleaching (n = 15); Group 1 (G1), which had brackets bonded 24 h after bleaching (n = 15), and Group 2 (G2), which had brackets bonded 30 days after bleaching (n = 15).

Before bleaching, the teeth were cleaned with pumice and water, then rinsed with water and dried with oil-free compressed air. At that time, 35% hydrogen peroxide bleaching agen t (Whiteness HP Maxx 35 - FGM, Joinville, SC, Brazil) was applied to Groups 1 and 2 according to manufacturer's directions. The bleaching gel layer was 0.5-1 mm thick. A Radii-cal LED curing light (SDI, Bayswater, Vic, Australia) was used twice with 1200 mW/cm΂ intensity for 10 s to speed up the process, keeping a distance of 5-10 mm from the surface of the gel. The tooth bleaching agent was left on the tooth surface for a total of 15 min. Removal of the gel was performed with a suction tube, and the teeth were then cleaned with gauze in preparation for a second gel application, which was completed with compressed water/air, drying, and application of 2% Desensibilize KF (FGM, Joinville, SC, Brazil) for 10 min. The teeth were polished with Diamond Excel polishing paste and Diamond Flex felt discs (FGM, Joinville, SC, Brazil).

While in G1 the brackets were bonded after 24 h of storage in artificial saliva at room temperature, in G2 the brackets were bonded 30 days after daily replacement of saliva to prevent bacterial growth.

Prior to bonding the brackets in the center of the clinical crown, the teeth underwent the same protocols for removing artificial saliva and prophylaxis described above, before bleaching. Enamel etching with 37% phosphoric acid lasted 20 s, followed by rinsing for 20 s and drying for 10 s. Gemini premolar brackets (MBT, slot 0.022" × 0.030" - 3M Unitek, USA) were bonded with the Transbond™ XT primer/adhesive system (3M Unitek, Monrovia, CA, USA) following manufacturer's directions, with a Radii-cal curing light (SDI, Bayswater, Australia) 25 s after position adjustment, light pressure, and removal of excess resin. Thereafter, the teeth were removed from the silicone for specimen fabrication.

Specimen fabrication began with a straight guide [Figure 1], which provided the same spatial positioning for all brackets, regardless of bonding height and crown convexity, due to the fact that the wire filled the bracket slot with virtually no slack.
Figure 1: Brackets positioning guide

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The brackets were tied to the steel wire with elastic ligatures. The tooth roots were inserted in the cylindrical base of PVC tubes (Tigre, Joinville, SC, Brazil) filled with colorless acrylic resin (JET, Brazil). With this standardization, the working tip of the shear machine could touch all specimen brackets at the same inclination and angulation.

The specimens were kept in artificial saliva and after 12 h, shear strength tests were performed with a universal electromechanical microprocessor centrifuge test machine (DL500, EMIC, São José dos Pinhais, PR, Brazil), with 500 kgf (5 kN) capacity and test speed of 0.5 mm/min [Figure 2], with TESC testing software (EMIC, São José dos Pinhais, PR, Brazil), linked up to a device designed for shear tests in brackets, custom-developed for this investigation. The working tip of the bracket shear test device (ODEME, version OD07, Odeme Dental Research, Luzerna, SC, Brazil, with a chisel actuator) was positioned in the occlusogingival direction in contact with the bracket, between tie-wing and base, flush with the base [Figure 3].
Figure 2: Universal testing machine - EMIC

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Figure 3: Tooth positioned on testing machine

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The Kolmogorov-Smirnov test was used to test the normality, and the Cochran test was used to check if the groups had the same variance. To compare the groups, the ANOVA parametric test, with significance level of 5%, was employed.


   Results Top


[Table 1] shows the descriptive statistics of the shear strength test results for each group studied.
Table 1: Descriptive statistics of shear bond strengths


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Analysis of the normality using the Kolmogorov-Smirnov test is shown in [Table 2], and points to a normal distribution since the P > 0.05.
Table 2: Kolmogorov-Smirnov normality test


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By means of the Cochran test, equality was observed between the variances given that P > 0.05 (P = 0.31). [Table 3] shows a comparison between the groups according to ANOVA parametric test at 5% confidence level. No statistically significant difference was found between the means of the three groups.
Table 3: One-way ANOVA for shear bond strengths


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   Discussion Top


This study assessed whether the prior application of 35% hydrogen peroxide bleaching gel would influence the bond strength of orthodontic brackets. Shear bond tests, which accurately reflect occlusal forces,[17] showed that bond strength was not significantly affected. After periods of (a) 24 h and (b) 30 days following bleaching (and this applies to the control group as well, which was not subjected to tooth bleaching), the average bond strength was higher than the level accepted as clinically adequate in orthodontics, which is between 6 and 8 MPa.[17] No significant difference was found between the three groups (P = 0.09).

Because this is a laboratory study, some methodological aspects should be highlighted such as the method used to store the teeth during the experiment. Titley et al. carried out a study[8] in which 35% hydrogen peroxide bleaching gel was applied to the teeth, and one of the groups was maintained in distilled water for 24 h before resin cylinders were bonded to them. In their study, maintaining teeth in distilled water did not improve bond strength since both bleached groups showed lower bond strength values compared to the control group, which were subjected only to a saline solution. On the other hand, Dishman et al.[9] and Miles et al.,[10] who also noted significant bond strength reduction in the experimental group bonded after bleaching, contended that the use of distilled water as a medium to maintain the teeth was able to restore bond strength values to normal, since in both studies these values were restored after a week in this medium. For Hussain and Wang[18] immersion in deionized water was sufficient to restore bond strength within a period of 24 h after bleaching, but insufficient if this period was curtailed to 1 h. Similarly, Bulut et al.[11] and Uysal and Sisman[14] used artificial saliva instead of distilled water and observed that both after 7 days[11] and after 30 days[14] bond strength values also returned to normal. Corroborating Bishara et al.[5] in this study, the artificial saliva may have been responsible for the absence of significant differences between the three experimental groups. Bulut et al.,[11] in addition to use artificial saliva, also reported that the application of an oxidizing agent on the enamel immediately after bleaching could also restore shear bond strength to normal.

Reduction of bond strength to tooth enamel when using hydrogen peroxide as bleaching agent was reported in the literature by several authors.[6],[7],[8],[9],[12],[13],[14],[15],[19],[20] These results are in disagreement with this study as well as other studies,[3],[5] which showed that the hydrogen peroxide bleaching agent was capable of interfering with bond strength. Minoux and Serfaty[21] reported that bleaching agents do not induce significant modifications in enamel structure, which may justify the fact that identical results were found for the three groups in this study. Abe et al.[22] also found no statistically significant shear strength differences between a control group and another group where brackets were rebonded 1 week after bleaching. However, statistically significant differences were found in the first bonding, performed 1 week after bleaching, as well as in a group where bonding was carried out immediately after bleaching, thereby underscoring the effects of time.

Yeh et al.[23] reported that bleached teeth had greater density and surface porosity. On the other hand, these authors further observed that teeth which were bleached and subsequently etched with 37% phosphoric acid had a clear, visible enamel prismatic structure, and that prior bleaching enhanced enamel solubility to acid etching. In this study, no records were made of the enamel surface. However, these potential changes did not affect the bracket/enamel bond strength, perhaps due to the fact that the specimens were stored in artificial saliva between bleaching and subjected to acid etching prior to orthodontic bonding.

Dishman et al.[9] and Sundfeld et al.[1] reported the presence of resin tags, which appeared shorter and scarcer when bonding was performed on an area of enamel that had been previously bleached. In addition to finding a reduction in bond strength, Torneck et al.[6] observed by scanning electron microscopy unbounded areas where the resin had a granular, less homogeneous appearance. Other authors[6],[8],[9],[16] believe that such reduction in bond strength may be caused by peroxide residues or other peroxide-related substances present on the enamel surface. In this study, bond strength reduction was found, possibly due to the elimination of these peroxide-related substances in some of the experiment phases.

Türkkahraman et al.[13] observed significant reduction in the shear bond strength of brackets when teeth were subjected to bleaching and desensitizing agents, which is at odds with the results obtained in this study. It should be emphasized that their study made use of different commercially available hydrogen peroxide and desensitizing products. In addition, their sample (n = 12) was smaller than the sample used in this study (n = 15). The authors of the aforesaid study recommend that these products be applied after orthodontic treatment, which would not be clinically justifiable since all groups in their experiment showed bond strength values above acceptable values, i.e. between 6 and 8 MPa.

Similarly, to the present study, Uysal et al.[3] did not observe statistically significant differences between the three groups in their experiment. They recommend that 2-3 weeks be allowed to elapse after bleaching to perform bonding, which is also unjustified since all the results obtained at the time were above clinically acceptable values. Similarly, in 2008, Uysal and Sysman[14] compared a control group, a group where bonding was carried out immediately after bleaching and a third group bonded 30 days after bleaching using self-etching adhesive systems. Although the bond strength values of the group bonded immediately after bleaching were significantly lower, they were still within the limits of acceptable bond strength in orthodontic practice. Martins et al.[24] also found that the shear bond strength values became significantly lower when the bracket was bonded immediately after bleaching and quickly returned to control level in 24 h. However, given the limitations of in vitro studies and since the patterns of adhesive remnants were quite distinct - with the group bonded immediately after bleaching showing a much greater amount of adhesive remnants - the authors further recommend that enough time be allowed to go by until the enamel recovers similar structural characteristics to those of the control group. Similarly, Bishara et al.[5] did not note statistically significant differences between the five groups of their experiment. These authors, however, recommend that at least 2 weeks elapse before bonding-in cases of in-office bleaching-due to the fact that a wide variation was obtained after just 7 days (5.1 ± 5.3 MPa), which yielded values below the acceptable clinical level.

Not only the extracoronal bleaching procedures were tested, Gungor et al.[20] found that intracoronal bleaching also significantly affected the shear bond strength of brackets on human enamel.

Several authors recommend that professionals wait a while before bonding to bleached enamel. Titley et al.[8] and Miles et al.[10] recommended a week. Uysal et al.[3] recommended 2-3 weeks, while Minoux and Serfaty,[21] Hussain and Wang,[18] Patusco et al.[15] and Martins et al.[24] recommend at least 24 h. However, for Patusco et al.,[15] 24 h are sufficient only when bleaching is performed with 10% carbamide peroxide, since 35% hydrogen peroxide - the same agent used in this study - yielded bond strength values below the minimum clinically acceptable. This finding was not confirmed by Scougall-Vilchis et al.[19] and Hussain and Wang,[18] who found no statistically significant differences in a similar setting, namely, 24 h after bleaching, between 10% carbamide peroxide and 38% hydrogen peroxide. There was, however, one important difference because for Scougall-Vilchis et al.,[19] values were significantly lower compared to the control group, whereas for Hussain and Wang,[18] the values were adequate and comparable to the control group and were even greater when curing time was increased. In this study, it was observed that 24 h after bleaching, with the teeth being kept in artificial saliva, the bond strength values were ideal and the teeth ready for bonding.

When other materials were used for bonding, such as resin modified glass ionomer and enamel etching with 10% polyacrylic acid, Cacciafesta et al.[12] noted a reduction in bond strength in bleached groups. Despite this reduction, all groups showed clinically acceptable bond strength.

It is noteworthy that the experiment in this study was conducted in vitro and that in vivo variations are likely to occur since it is not possible to reproduce in vitro, the complex environment of the oral cavity with absolute accuracy as it involves changes in temperature, moisture, pH, and ions present in natural saliva and patient habits.


   Conclusions Top


  • Shear bond strength tests did not reveal any statistically significant differences in bond strength between brackets bonded 24 h and 30 days after bleaching with 35% hydrogen peroxide
  • There was no statistically significant difference in bond strength between the experimental versus control group.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Sundfeld RH, Briso AL, De Sá PM, Sundfeld ML, Bedran-Russo AK. Effect of time interval between bleaching and bonding on tag formation. Bull Tokyo Dent Coll 2005;46:1-6.  Back to cited text no. 1
    
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3.
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4.
Bishara SE, Sulieman AH, Olson M. Effect of enamel bleaching on the bonding strength of orthodontic brackets. Am J Orthod Dentofacial Orthop 1993;104:444-7.  Back to cited text no. 4
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Cacciafesta V, Sfondrini MF, Stifanelli P, Scribante A, Klersy C. The effect of bleaching on shear bond strength of brackets bonded with a resin-modified glass ionomer. Am J Orthod Dentofacial Orthop 2006;130:83-7.  Back to cited text no. 12
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13.
Türkkahraman H, Adanir N, Güngör AY. Bleaching and desensitizer application effects on shear bond strengths of orthodontic brackets. Angle Orthod 2007;77:489-93.  Back to cited text no. 13
    
14.
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19.
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20.
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22.
Abe R, Endo T, Shimooka S. Effects of tooth bleaching on shear bond strength of brackets rebonded with a self-etching adhesive system. Odontology 2011;99:83-7.  Back to cited text no. 22
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24.
Martins MM, de Oliveira Almeida MA, Elias CN, de Moraes Mendes A. Bleaching effects on shear bond strengths of orthodontic brackets. Prog Orthod 2012;13:23-9.  Back to cited text no. 24
[PUBMED]    

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Correspondence Address:
Prof. Augusto Ricardo Andrighetto
Department of Orthodontics, Latin American Institute of Dental Research and Education, Curitiba, Paraná
Brazil
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.191891

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]

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2 In vitro bleaching effect of hydrogen peroxide with different time of exposition and concentration on shear bond strength of orthodontic brackets to human enamel: A meta-analysis of in vitro studies
Mohammad Moslem Imani,Fatemeh Azizi,Kiana Bahrami,Amin Golshah,Roya Safari-Faramani
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