comparison of antibacterial effects of zno and cuo nanoparticles coated brackets against streptococcus mutans

statement of the problem: during the orthodontic treatment, microbial plaques may accumulate around the brackets and cause caries, especially in high-risk patients. finding ways to eliminate this microbial plaque seems to be essential. purpose: the aim of this study was to compare the antibacterial effects of nano copper oxide (cuo) and nano zinc oxide (zno) coated brackets against streptococcus mutans ( s.mutans ) in order to decrease the risk of caries around the orthodontic brackets during the treatment. materials and method: sixty brackets were coated with nanoparticles of zno (n=20), cuo (n=20) and cuo-zno (n=20). twelve uncoated brackets constituted the control group. the brackets were bonded to the crowns of extracted premolars, sterilized and prepared for antimicrobial tests ( s.mutans atcc35668). the samples taken after 0, 2, 4, 6 and 24 hours were cultured on agar plates. colonies were counted 24 hours after incubation. one-way anova and tukey tests were used for statistical analysis. results: in cuo and cuo-zno coated brackets, no colony growth was seen after two hours. between 0-6 hours, the mean colony counts were not significantly different between the zno and the control group ( p >0.05). during 6-24 hours, the growth of s.mutans was significantly reduced by zno nanoparticles in comparison with the control group ( p < 0.001). however, these bacteria were not totally eliminated. conclusion: cuo and zno-cuo nanoparticles coated brackets have better antimicrobial effect on s.mutans than zno coated brackets.