Comparative evaluation and influence on shear bond strength of incorporating silver, zinc oxide, and titanium dioxide nanoparticles in orthodontic adhesive

Objective: To investigate the influence of silver (Ag), zinc oxide (ZnO), and titanium dioxide (TiO 2 ) nanoparticles on shear bond strength (SBS). Materials and Methods: One hundred and twenty extracted premolars divided into four groups with thirty specimens in each group. Group 1 (control): brackets (American Orthodontics) were bonded with Transbond XT primer. Groups 2, 3, and 4: brackets (American Orthodontics) were bonded with adhesives incorporated with Ag, ZnO, and TiO 2 nanoparticles in the concentration of 1.0% nanoparticles of Ag, 1.0% TiO 2 , and 1.0% ZnO weight/weight, respectively. An "Instron" universal testing machine AGS-10k NG (SHIMADZU) was used to measure the SBS. The data were analyzed by SPSS software and then, the normal distribution of the data was confirmed by Kolmogorov-Smirnov test. One-way ANOVA test and Tukey′s multiple post hoc procedures were used to compare between groups. In all statistical tests, the significance level was set at 5% (P < 0.05). Results: A significant difference was observed between control (mean [standard deviation (SD)] 9.43 [3.03], confidence interval [CI]: 8.30-10.56), Ag (mean [SD]: 7.55 [1.29], CI: 7.07-8.03), ZnO (mean [SD]: 6.50 [1.15], CI: 6.07-6.93), and TiO 2 (mean [SD]: 6.33 [1.51], CI: 5.77-0.89) with SBS (F = 16.8453, P < 0.05) at 5% level of significance. Conclusion: Incorporation of various nanoparticles into adhesive materials in minimal amounts may decrease SBS and may lead to the failure of bracket or adhesive. The limitation of this study is that it is an in vitro research and these results may not be comparable to what the expected bond strengths observed in vivo. Further clinical studies are needed to evaluate biological effects of adding such amounts of nanoparticles and approve such adhesives as clinically sustainable.