الفهرس 
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Abstract
The aim of the present study was to assess the effect of titanium dioxide nanoparticle on the fracture toughness, surface microhardness, degree of conversion, antibacterial activity and color of an experimental resin based composite. A light curing resin matrix was made by mixing 50 wt% Bis-GMA and 50 wt% TEGDMA. Silane coated SiO2 filler (mean particle size: 0.5 µm, 5-15 nm) was added in the ratio of 65 wt% of the resin composites. Acrylic acid-modified TiO2 NPs (21 nm) were prepared and added with the ratios of 0, 0.2, 0.3 and 0.4 wt% to the experimental resin composites. Fracture toughness was evaluated using a Universal Testing Machine. Surface microhardness was measured using Vickers microhardness tester. Degree of conversion was measured using FTIR spectroscopy. The antibacterial activity was evaluated using direct contact test against streptococcus mutans and staphylococcus aureus. Color was measured using a spectrophotometer. All data were analysed using ANOVA and LSD tests. RBCS-containing different ratios of TiO2 NPs improved the fracture toughness and surface microhardness compared with the unmodified RBC. However, this improvement decreased gradually for RBCs-containing 0.3 and 0.4 wt% TiO2 NPs. The DC increased as a function of mass fraction of TiO2 NPs. RBCs-containing TiO2 NPS possessed a weak antibacterial effect. Finally, the addition of TiO2 NPs to the RBCs compromises its color.