Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 13 5 2016 12 31 373 382 Pedram Baghaeian Postgraduate Student, Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Ahmad Sodagar Associate Professor, Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Abbas Bahador Associate Professor, Microbiology Department, Tehran University of Medical Sciences, Tehran, Iran Maryam Pourhajibagher PhD of Medical Bacteriology, Microbiology Department, Tehran University of Medical Sciences, Tehran, Iran Badreddin Ahmadi Educational Instructor Art and Architecture Department, Tarbiatmodares University, Tehran, Iran 2016 06 08 2016 07 24 Objectives: This study sought to assess the effect of curcumin nanoparticles (curcNPs) on antimicrobial property and shear bond strength (SBS) of orthodontic composite to bovine enamel. Materials and Methods: In this in vitro, experimental study, 1%, 5% and 10% curcNPs were added to Transbond XT composite. Stainless steel brackets were bonded to 48 sound bovine incisors in four groups (n=12) using composite containing 0% (control), 1%, 5% and 10% curcNPs. The bracket-tooth SBS was measured by a universal testing machine. The adhesive remnant index (ARI) score was calculated after debonding using a stereomicroscope. Also, 180 discs were fabricated of the four composites; 108 were subjected to eluted component test, 36 were used for disc diffusion test and 36 were used for biofilm test to assess their antimicrobial activity against Streptococcus mutans, Streptococcus sanguinis and Lactobacillus acidophilus. Results: The highest and lowest SBS belonged to control and 10% curcNP groups, respectively. The difference in SBS was significant among the four groups (P=0.008). The SBS of control group was significantly higher than that of 10% curcNPs (P=0.006). The four groups were not significantly different in terms of ARI score (P>0.05). Growth inhibition zones were not seen in any group. In biofilm test, the colony counts of all bacteria significantly decreased by an increase in percentage of curcNPs. Colony count significantly decreased only at 30 days. Conclusions: At 1% concentration, curcNPs have significant antimicrobial activity against cariogenic bacteria with no adverse effect on SBS. However, insolubility of curcNPs remains a major drawback.   https://fid.tums.ac.ir/index.php/fid/article/view/1300 https://fid.tums.ac.ir/index.php/fid/article/download/1300/914