Effect of nano–zinc oxide and nano-chitosan particles on the shear bond strength of dental composites used as orthodontic adhesive

•Adding ZnO/chitosan nanoparticles at 1% and 5% wt. preserves bond strength.•The shear bond strength of adhesive with 10% wt. nanoparticles is not acceptable.•The adhesive remnant index did not differ significantly among the groups. Background: This study aimed to evaluate the effect of the combination of zinc oxide nanoparticles (NPs) and chitosan NPs on the shear bond strength (SBS) of composites used for orthodontic bonding. Methods: Four groups of composites (n = 10), containing 0%, 1%, 5%, and 10% w/w NP fillers, respectively, were used to bond brackets to the surfaces of 40 intact bovine incisors. After 1000 rounds of thermal cycling at 5°C–55°C, all specimens were mounted in acrylic blocks. The SBS was tested using a universal testing machine, and the adhesive remnant index scores were registered using a stereomicroscope. Data were statistically analyzed using a 1-way ANOVA and the Kruskal–Wallis test. Results: The highest value of mean SBS was found in the control group, and the lowest value was found in the group with composite containing 10% NPs. The adhesive remnant index did not differ significantly among the groups (P = 0.823). Conclusions: Incorporation of 1% and 5% zinc oxide and chitosan NPs had no effect on the SBS of composite, and the obtained SBS values were similar to that of the control group.