Comparison of antibacterial effects of orthodontic composites containing different nanoparticles on Streptococcus mutans at different times

INTRODUCTION: Plaque accumulation can cause white spot lesions. Adding nanoparticles to composites can be effective in reducing the number and function of microorganisms. OBJECTIVE: The aim of this study was to evaluate the antibacterial effects of orthodontic composites containing different nanoparticles on Streptococcus mutans at different times. METHODS: Hydroxyapatite, titanium oxides, zinc oxide, copper oxide and silver oxide nanoparticles were prepared at 0.5% and 1% weight concentrations. Accordingly, ten study groups and one control group were obtained. Then, 26 composite discs were prepared from each group. Strain of Streptococcus mutans was cultured, and colonies of Streptococcus mutans were counted. Further bacterial culture was swapped onto enriched Mueller-Hinton agar. The composites were placed on the culture medium, and after incubation the diameter of growth inhibition was measured. To investigate the long-term effect of nanoparticles, the colonies were counted at days 3, 15 and 30. RESULTS: The results showed that 1% copper oxide and 1% silver oxide significantly reduced the number of bacteria (p< 0.05), but there was no significant difference between the other groups and control group (p> 0.05). At day three, there was a significant difference between control group and 0.5% silver oxide, 1% silver oxide and 1% copper oxide groups (p< 0.05). However, colonies had grown in all groups at day 30 but showed no significant difference with control group (p> 0.05). CONCLUSION: Addition of 1% copper oxide and 1% silver oxide has short-term antibacterial effects, so the clinical use of these nanoparticles cannot be justified.