Objective:To investigate the influence of silver (Ag), zinc oxide (ZnO), and titanium dioxide (TiO2) 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 TiO2 nanoparticles in the concentration of 1.0% nanoparticles of Ag, 1.0% TiO2, 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 TiO2 (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.

Objective: To determine the antimicrobial efficacy of silver, titanium dioxide and zinc oxide nanoparticles against Streptococcus mutans. Material and Methods: Serial dilution method was employed for preparing 1%, 0.5%, 0.25% concentrations of the three test compounds. ATCC 25175 strain of streptococcus mutans was used to assess the antimicrobial activity of test compounds. Equal quantity of BHI broth was dispensed in test tubes containing sectioned tooth and to this the prepared bacterial inoculum was added. Prepared concentrations of test compounds were added accordingly and incubated for 24hrs at 37 0 C. Then, the sectioned tooth was removed and the adherent bacteria were transferred into saline solution by vortexing. These suspensions were transferred onto sterile blood agar plate to make lawn culture and were further incubated at 37 0 C for 24hrs to determine viable bacterial count. The number of colonies were counted manually from each plate and recorded for further analysis. Decrease in number of colonies represents the effective concentration of the test compound against the inhibition of biofilm formation. Results: A significant difference in the colony forming units among all three concentrations of silver (Ag), titanium dioxide (TiO2) and zinc (ZnO) nanoparticles was noted and the antimicrobial effect of nanoparticles was concentration dependent. Inter group comparison of colony forming units with 1%, 0.5% and 0.25% of the test compound revealed that the colony forming units on the ZnO nanoparticles demonstrated highest value followed by TiO2 and the least were with that of the Ag nano particles. Conclusion: Silver, Zinc oxide and Titanium dioxide showed significant antimicrobial effects and the antimicrobial effect of nanoparticles was concentration dependent.

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