Objective To investigate the effects of incorporating three different zinc oxide（ZnO） on the antibacterial activity of composite resin. Methods The minimal inhibitory concentration（MIC） and minimal bactericidal concentration（MBC） of nano -ZnO, tetrapod -like zinc oxide whiskers（T -ZnOw）, micro -ZnO against Streptococcus mutans were examined by the broth dilution test. Then the three different ZnO were added to the powder of one kind of bicomponent self -cured composite resin at 5% respectively, and the antibacterial activities of the resin specimens were evaluated using the membrane covering method before and after 3-month accelerating aging. Results The MIC values of the three different ZnO against Streptococcus mutans were 78.13, 312.50 and 1 250.00 μg/mL respectively and the MBC values were 156.25, 625.00, 1 250.00 μg/mL respectively. The antibacterial ratios of the resin specimens incorporating with 5% of the three different ZnO were （93.58±5.95）％, （89.42±4.11）％ and （78.97± 3.90）％ respectively, while after 3-month accelerating aging those were （89.01±7.91）％, （84.63±4.72）％ and （72.27± 3.89）％. Conclusion The three different ZnO could improve the antibacterial activity of the composite resin. The nano-ZnO exhibit the strongest antibacterial activity, while the micro-ZnO weakest. The T-ZnOw presents comparatively strong antibacterial activity although with smaller specific surface area.
