|DENTAL SCIENCE - ORIGINAL ARTICLE
|Year : 2013 | Volume
| Issue : 5 | Page : 17-20
The effect of bleaching of teeth on the bond strength of brackets: An in vitro study
Shiji Kunjappan1, Vadivel Kumaar1, Prithiviraj1, Vasanthan1, Syed Altaf Khalid1, Joseph Paul2
1 Department of Orthodontics and Dentofacial Orthopedics, Vinayaka Missions Sankarachariyar Dental College, Salem, Tamil Nadu, India
2 Department of Conservative Dentistry and Endodontics, Vinayaka Missions Sankarachariyar Dental College, Salem, Tamil Nadu, India
|Date of Submission||02-May-2013|
|Date of Decision||04-May-2013|
|Date of Acceptance||04-May-2013|
|Date of Web Publication||13-Jun-2013|
Department of Orthodontics and Dentofacial Orthopedics, Vinayaka Missions Sankarachariyar Dental College, Salem, Tamil Nadu
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aim: To determine the reversal effect of 10% sodium ascorbate, on the bond strength of previously bleached teeth with hydrogen peroxide. Materials and Methods: Sixty extracted maxillary premolars were selected and they were divided randomly into three groups. Group A teeth were etched and bonded; Group B bleached, etched and immediately bonded; Group C was subjected to bleaching, followed by treatment with 10% sodium ascorbate solution, then etched and bonded; Then all the three groups were subjected to testing procedure for bond strength. Results: The bond strength analysis was carried out by using instron, universal testing machine. In this study Group A had the maximum bond strength of 12.24 Mpa followed by Group C 11.62 Mpa and Group B 10.96 Mpa. Conclusion: Group C the experimental group which was treated with 10% sodium ascorbate following bleaching with 35% hydrogen peroxide provided higher bond strength compared to Group B which was bonded immediately after bleaching even though it was not statistically significant.
Keywords: Bond strength, debonding, shear bond strength
|How to cite this article:|
Kunjappan S, Kumaar V, Prithiviraj, Vasanthan, Khalid SA, Paul J. The effect of bleaching of teeth on the bond strength of brackets: An in vitro study. J Pharm Bioall Sci 2013;5, Suppl S1:17-20
|How to cite this URL:|
Kunjappan S, Kumaar V, Prithiviraj, Vasanthan, Khalid SA, Paul J. The effect of bleaching of teeth on the bond strength of brackets: An in vitro study. J Pharm Bioall Sci [serial online] 2013 [cited 2022 Nov 28];5, Suppl S1:17-20. Available from: https://www.jpbsonline.org/text.asp?2013/5/5/17/113285
The most common reason for seeking orthodontic care is to improve the appearance of the face and teeth. In recent years there is an increased awareness of esthetics within the community. Every one wishes to have neatly aligned whiter and brighter teeth which typifies youth, health, and physical attractiveness. Thus a situation arises in which some adults who are interested in orthodontic treatment might have also had their teeth bleached or might be interested in bleaching, and it seems important to determine whether bleaching would significantly influence the bond strength of orthodontic bracket adhesives to the enamel surface.
Many studies have shown that the bleaching of teeth with various concentrations of bleaching agents such as hydrogen peroxide reduces the bond strength of orthodontic brackets to the enamel surface.  However recent studies have shown that certain chemicals such as Sodium Ascorbate have the ability to reverse the action of bleaching agents which reduces the bond strength.  The aim of this study was to know whether there is any significant change seen on the shear bond strength of the brackets immediately bonded to previously bleached teeth and teeth which were bonded after it was treated with 10% Sodium ascorbate solution following bleaching.
| Materials and Methods|| |
This study was done in the Department of Orthodontics and Dentofacial Orthopaedics, Vinayaka Mission's Sankarachariyar Dental College, Salem, and the bond strength analysis was carried out at CIPET, Chennai. This study was carried out with an objective of assessing the effect of in-office hydrogen peroxide containing bleaching agent on the bond strength of orthodontic brackets, and the possibility of 10% sodium ascorbate usage in reversing any effect on the bond strength. 
Sixty non-carious, sound premolar, extracted for orthodontic treatment were used for the study. Teeth with hypoplastic areas, cracks, or gross irregularities of the enamel structures were excluded. No pretreatment with chemical agents such as alcohol, formalin, or hydrogen peroxide, or any other form of bleaching was allowed. The teeth were cleaned of blood and tissue debris and stored in normal saline after extraction. The saline was changed daily to avoid bacterial contamination.
The samples were divided randomly into three groups of twenty each as Group A, B and C, the acrylic blocks in which the teeth were embedded was colour coded [Figure 1]. Group A - green coloured, Group B - blue coloured and Group C - red coloured. Each tooth was mounted vertically in the self cure acrylic blocks so that the crown of the teeth was exposed. The teeth in all the groups were mounted in such a way that the buccal surface would be exposed, and a jig fabricated for mounting onto an instron universal testing machine [Figure 2].
In Group A, which was considered as control group, the teeth were etched with 37% phosphoric acid gel (3M ESPE) for 30 s, then rinsed with water and dried till the enamel surface of the teeth showed frosty white appearance of etched enamel. For those teeth that did not show white frosty appearance the above mentioned procedure was repeated. Then the pre-adjusted edgewise appliance (3M 0.022 slot) brackets of a surface area 10 mm 2 provided by the manufacturer (3M unitek) were bonded on to the etched surface using light cure composite resin (3M transbond XT) adhesive taking care to follow the manufacturer's instructions. Excess material was removed using a sharp probe and cured, using a light emitting diode (LED) light source and cured for 30 s.
In Group B the buccal surface of the tooth was bleached with 35% hydrogen peroxide containing bleaching agent (Pola office), which was mixed according to manufacturer's recommendation and applied with brush on to tooth surface in a layer of approximately 2 mm in thickness ensuring no enamel was visible. It was then cured using a LED curing light for 30 s and kept in place for 3 min before it was washed away. Immediately after this, the bonding area was etched with 37% phosphoric acid gel for 30 s then washed and dried till white frosty appearance was seen. The pre-adjusted edgewise brackets were bonded as mentioned earlier for Group A.
In Group C, the teeth were bleached in the same procedure as Group B, after washing away the bleaching agent, 10% sodium ascorbate solution was applied to the enamel surface of the embedded teeth as an irrigation solution for 10 min with the flow rate of 1 ml/min. During this period the enamel surface was continuously agitated using a sterile brush. After the antioxidant treatment the enamel surface was thoroughly rinsed with distilled water for 30 s. Then acid etched for 30 s, rinsed and the brackets bonded using LED light cure unit carried out as mentioned previously for other two groups.
The teeth in all the groups were mounted individually on to a universal testing machine for the debonding procedure.
The shear bond strength was tested in the laboratory at CIPET Chennai, following 24 h after the bracket bonding procedure for all the three groups, the Instron machine (model no: 100 K) was used in this study to record the maximum load necessary to debond the bracket, using a stiff 0.09 mm stainless steel (SS) wire hook the ends of which were embedded in an acrylic block, which was mounted on the movable crosshead of the Instron testing machine and positioned so that the hook engaged the bracket which was to be debonded.
The force required to debond the bracket was measured in Newtons (N), and the shear bond strength was calculated by dividing the force value by bracket base area (10 mm 2 , as provided by manufacturer).
Statistical analysis was done by using ANOVA (Analysis of variances) by Fishers F test. The inter comparison between the groups was calculated by Bonferroni t-test (Post hoc test). Data was fed in PC and statistical package SPSS ver. 11.5 was used for analysis.
| Results|| |
The mean shear bond strengths
The Fishers F test in [Table 1] revealed that Group A had maximum mean shear bond strength of 12.236 Mpa with standard deviation of 2.781 followed by Group C with mean shear bond strength of 11.619 Mpa and standard deviation of 2.359 and Group B mean shear bond strength of 11.293 Mpa and standard deviation of 1.965. The P value was 0.454 which was statistically non-significant.
Comparison of mean shear bond strength
Comparison of mean shear bond strength was done statistically using Bonferroni 't' test which showed that there is no statistically significant difference in the mean shear bond strength of group A and Group B (P = 0.224). There was no statistically significant difference in the mean shear bond strength of group A and Group C (P = 0.454) and Group B and Group C (P = 0.638) Thus, the inter comparison between the groups showed that there was no statistically significant difference in the mean shear bond strength of various groups.
Comparison of bond strength between the control and experiment groups
The ANOVA test procedure is used to compares mean scores of bond strength of more than two groups. The procedure assumes that the variances of the groups are equal and it was tested with Levene's test statistics and the results are given in [Table 1].
[Table 1] displays the descriptive statistics of the sample size, mean, standard deviation and standard error. [Table 1] also shows that the F statistics, calculated as the ratio of the variances. The column P value shows the probability value from the F distribution. Since the P value is greater than 0.05 there is no significant difference in the mean bond strength among the three groups.
[Table 1] also shows that the t statistics, calculated as the ratio of the difference between sample means divided by the standard error of the difference. The column P value shows the probability value from the t distribution. Since the P value is greater than 0.05 there is no significant difference in mean bond strength among the control group and the experimental Group B.
| Discussion|| |
There are number of studies regarding the interaction between the bleaching agents such as carbamide peroxide, hydrogen peroxide, and bond strength of the composite resin to enamel. The studies conducted by Adanir, et al.  in 2007 and Dishman,  in 1994 has found that there is reduced bond strength when the teeth is treated with the 35% hydrogen peroxide and immediately bonded with the light cure composite for bonding procedure. Several authors have reported significant reduction in the bond strength of brackets bonded to enamel, immediately after bleaching. One of the reasons suggested for the reduced bond strength is because of the release of free oxygen radical of the bleaching agents on the tooth surface.
The study carried out by Lai, Tay et al.  in 2002 found that resin - enamel interface in bleached teeth exhibited more extensive nano-leakage in the form of isolated silver grains and bubble like silver deposits. Reduction of resin enamel bond strength in bleached etched enamel is likely to be caused by delayed release of oxygen that affects polymerization of resin components. Studies have been done using several antioxidants such as 10% sodium ascorbate, catalase, glutathione peroxide, acetone, ethanol, 7% sodium bicarbonate helps in removal of the free oxygen radical from the tooth surface before bonding. Studies conducted by Torres et al.  in 2006, Muraguchi et al.  in 2007, found out that treating the bleached teeth with antioxidants will reverse the reduced bond strength. The bond strength of the human enamel could be reversed by delaying the bonding procedure following 1 week after the bleaching, Studies conducted by Machado, et al.  2007, Bishara, et al.  Bulut, et al.  2006, the results showed that if the bonding procedure on the bleached teeth is delayed for 1 week the bond strength will be reversed.
Study by Turkun et al.  in 2009 found that the concentration of 10% sodium ascorbate will be effective in reversing the bond strength of the bleached teeth to the normal. Study conducted by Muraguchi,  showed that the antioxidant treatment immediately after office-bleaching was effective in reversing the bond strength of both adhesive systems.
The results of this study conducted on 60 premolar teeth extracted for orthodontic purpose showed Group B (bleached and immediately bonded) teeth had the least bond strength this could be due to the reduced bond strength following bleaching procedure.
Group C (bleached and 10% sodium Ascorbate treated and bonded) teeth had higher value than Group B possibly due to the antioxidant effect on the surface of the enamel by removing the free oxidant radical formed during bleaching, Group C had comparatively less shear bond strength than Group A (control group) which had not undergone the bleaching procedure, but not statistically significant. Even though the Group B had the least bond strength when compared with the other two groups, the mean value suggests that the bond strength is still above the clinical requirement as suggested by Reynold and Lopez. According to Lopez, a maximum bond strength of seven Mpa is adequate for successful clinical bonding. Hence orthodontic brackets can be bonded immediately after bleaching without significant reduction in the bond strength. Thus effective bonding can be done on the teeth immediately after bleaching. When increase in bond strength is desired in bleached teeth, 10% sodium ascorbate treatment was found to increase the bond strength by 6.027%.
| Conclusions|| |
The following conclusions can be drawn from the result of present study:
It can be concluded that in office bleaching 35% hydrogen peroxide though reduces the bond strength, it is not significantly reducing the bond strength below the required level of seven Mpa. It is also found that the sodium ascorbate treatment increases the bond strength.
- The control group (Group A) brackets bonded without bleaching had the maximum bond strength when compared to the three groups.
- Bleaching with 35% hydrogen peroxide in-office bleaching system immediately before bonding does not significantly reduce shear bond strength of adhesive to the enamel.
- Though the shear bond strength was comparatively less for bleached tooth immediately bonded group (Group B) when compared to control group (Group A), it was above the minimal bond strength required for orthodontic bonding.
- The shear bond strength of bleached enamel surface treated with 10% sodium ascorbate was higher when compare to the bonding done immediately after bleaching and less when compared to control group.
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[Figure 1], [Figure 2]
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