Objective: This research compared the antibacterial efficacy of silver and copper oxide nanoparticles incorporated into a commercial orthodontic adhesive and their effects on shear bond strength (SBS) of stainless steel orthodontic brackets bonded to enamel surface.

Methodology: Ninety extracted premolars were randomly allocated into three groups (n = 30). Orthodontic adhesive (Enlight, Ormco) was blended with silver (100 nm, 2% w/w) and copper oxide (50 nm, 1% w/w) nanoparticles to form nano-adhesives. Antibacterial activity of control and modified adhesives were assessed against Streptococcus mutans after 24 hs by agar diffusion test. The degree of conversion for all groups was determined using a Fourier transformed infra-red spectrometer. The control and nano-modified adhesives were then used to bond brackets to the teeth after acid etching using phosphoric acid for 30 seconds, then rinsing with water for 15 seconds. Shear bond strength was assessed using a Universal testing machine and the adhesive remnant index (ARI) scores were examined.

Results: The addition of nanoparticles significantly increased the antibacterial efficiency of the adhesive against S.mutans after 24 hs (P<0.0001). The findings of the study suggest that the degree of conversion, SBS and ARI scores were not significantly different from the control group after incorporation of either Ag or CuO NPs.

Conclusion: Both nano-adhesives showed significant antibacterial activity against Streptococcus mutans with no adverse effect neither on the degree of conversion nor SBS nor adhesive remanent index.