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Nanofillers can reduce enamel demineralization without compromising physical properties of the composite. The aim of this study was to evaluate shear bond strength (SBS) and antibacterial effects of an orthodontic composite after adding titanium oxide (TiO2) nanoparticles. Light cure orthodontic composite paste (Transbond XT) was blended with TiO2 nanoparticles. A total of 30 extracted premolars were randomly allocated into two groups of 15. In order to bond brackets, Transbond XT adhesive and nanocomposite were used in each group, respectively. SBS of two groups were determined, and the adhesive remnant index (ARI) scores were assessed. A total of 45 composite discs specimen were prepared. Of the 45 discs, 30 discs were made from nanocomposite and tested for antibacterial properties immediately and 30 days after curing by direct contact test. The antibacterial properties of the remaining 15 discs that were made from the conventional composite were tested immediately after curing as control group. Student's t-test and chi-square tests were used to analyse the data with the significance level of 0.05. No significant difference was found between SBS of conventional and nanocomposites, 24 hours after curing (P = 0.58). Chi-square test showed that ARI scores of two groups were not significantly different after debonding (P = 0.69). Comparison of antibacterial effects between conventional and nanocomposite demonstrated significant difference between two groups, with nanocomposites having a higher antibacterial activity (P = 0.03). Colony count revealed no significant difference in bacterial growth immediately and 30 days after curing in nanocomposite group. Adding TiO2 nanoparticles to orthodontic composite enhances its antibacterial effects without compromising the SBS.

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The main goal of this research is to investigate the effect of nano-CaCO3 coated with different content of stearic acid on fracture toughness of HDPE/CaCO3 nanocomposite. For this purpose, HDPE/10 vol % CaCO3 nanocomposites were made using a twin-screw mixer-single-screw extruder. Nanocomposite standard samples were prepared via injection molding method. Three-point bending tests and microscopic evaluations were performed. The results of fracture toughness test showed that the addition of uncoated nano-CaCO3 to HDPE causes to decrease fracture toughness, but it can be increased slightly as stearic acid content added. Also the results showed that the stress whitening zone width depends strongly on both CaCO3 and stearic acid content