الفهرس 
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Abstract
Objective: To evaluate the effect of silica dioxide (SiO2) nanofillers in different bonding systems on shear bond strength (SBS) and mode offailure of orthodontic brackets at two experimental times.Materials andMethods: Ninety-six intact premolars were divided into four groups: A) Conventionalacid-etch and primer Transbond XT; B) Transbond Plus self-etch primer; and two self-etch bonding systems reinforced with silicadioxide nanofiller at different concentrations: C) Futurabond DC at 1%; D) Optibond All-in-One at 7%. Each group was allocated into twosubgroups (n = 12) according to experimental time (12 and 24 hours). SBS test was performed using a universal testing machine. ARI scoreswere determined under a stereomicroscope. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were usedto determine the size and distribution of nanofillers. One-way ANOVA was used to compare SBS followed by the post-hoc Tukey test. Thechi-square test was used to evaluate ARI scores.Results: Mean SBS of Futurabond DC and Optibond All-in-One were significantly lowerthan conventional system, and there were no significant differences between means SBS obtained with all self-etch bonding systems usedin the study. Lower ARI scores were found for Futurabond DC and Optibond All-in-One. There was no significant difference of SBS andARI obtained at either time points for all bonding systems. Relative homogeneous distribution of the fillers was observed with the bondingsystems.Conclusion: Two nanofilled systems revealed the lowest bond strengths, but still clinically acceptable and less adhesive was left onenamel. It is advisable not to load the brackets immediately to the maximum.