Effect of home and office bleaching methods on the shear bond strength of metal brackets (in vivo/ex vivo)

Abstract

Background: Considering the high prevalence of cosmetic treatments including bleaching and the effect of this process on the structure of tooth enamel and dentin, investigating the effect of cosmetic treatments on the results of orthodontic treatment after that is one of the essentials of orthodontic studies. Since the results of laboratory studies cannot be generalized to the clinical environment due to oral conditions such as the effects of saliva, patient nutrition and oral flora on the mineralization process, and considering that no clinical study has investigated this issue, the aim of this clinical trial study is to investigate the effect of the time interval between bleaching with two methods (at home and in the office) and the orthodontic treatment on the shear bond strength of metal brackets on the premolar teeth of patients. Materials and methods: Patients who need to have their premolar teeth extracted in the course of orthodontic treatment were asked to participate in the study by obtaining a written informed consent. The total number of studied teeth was 225 (9 groups of 25). At first, the patients were randomly divided into three groups. The two experimental groups were subjected to home or office bleaching treatment. In home bleaching group, after making a special tray, carbamide peroxide 20% was placed on teeth for three hours a day for 8 days, and in the office bleaching group, hydrogen peroxide 45% was used for three days and half an hour a day. After the bleaching stage was completed, the patients in the intervention groups were divided into 3 subgroups (n=25). In the first subgroups, 24 hours after bleaching, in the second subgroups, 1 week, and in the third subgroups, 15 days after bleaching, brackets were bonded to the tooth surface, and after 30 days, the teeth were extracted and the strength of the shear bond was determined by the materials testing machine. Also, the amount of resin remaining on the surface of the tooth was measured by an optical microscope and expressed with the Adhesive Remnant Index. Statistical analysis was performed to compare the shear bond strength by two-way analysis of variance and Tukey's post hoc test (SPSS 22.0). A significance level of less than 0.05 was considered. Results: At 24 hours after bleaching, the SBS in the control group was significantly higher than both the office and home bleaching groups (P value < 0.001). At 1 week and 15 days after bleaching, the SBS in the home bleaching group was higher than both the office bleaching group and the control group (P value < 0.001). Also, in these two time periods, no significant difference was found between the SBS in the control group and the office bleaching group (P value > 0.05). In both home and office bleaching groups, the SBS increased significantly after 1 week (P value < 0.001) and there was no significant difference between the SBS after 1 week and 15 days (P value>0.05). The amount of residual adhesive in the control group was less than both bleaching groups 24 hours after bleaching (P value < 0.001). Also, in 1 week and 15 days after bleaching, the amount of residual adhesive in the office bleaching group was higher than the home bleaching and control groups (P value < 0.001). In both bleaching groups, the amount of adhesive remaining in 24 hours is higher than in 1 week and 15 days (P value < 0.001). Conclusion: The bond strength of orthodontic brackets to tooth enamel decreases immediately after bleaching. The bond strength of orthodontic brackets increases with the delay of the bracket bond after bleaching treatment. In order to achieve the proper band strength, at least one week of time between bleaching and orthodontic treatment is necessary. Also, home bleaching reduces bond strength less than the office method