Silver Nanoparticles to Improve Antimicrobial Properties of Orthodontic Bracket-Bonding Cement

Objectives: To test the hypothesis that incorporating silver nanoparticles (SN) into an orthodontic adhesive (Sondhi Rapid-Set Indirect, 3M Unitec, St. Paul, MN) improves its physical and antimicrobial properties. Methods: SN were treated chemically and incorporated into a bis-GMA based resin, GTE (37.5%-BisGMA, 25wt%-TEGDMA, 37.5wt%-BisEMA) and cured. The sample was ground and sieved to produce powder particles ≤63.5mm and incorporated into the benzoyl-peroxide containing component (Part-B) of the resin cement. 1%, 0.5%, 0.25% and 0.125% and 0% (control) w/v of the SN-GTE were combined with the amine containing resin (Part-A) and cured to form rods and discs. The rods were used to determine degree of monomer-to-polymer conversion using Fourier Transform Infrared Spectroscopy. Flexural strength, modulus and energy to break the cured adhesive samples was measured using an Instron three point bending test. Antimicrobial activity was determined by measuring the zones of growth inhibition of Streptococcus mutans around the discs. The ability of S. mutans to grow in broth and attach to the test discs was examined by serial dilution and plating. Transmission electron microscopy (TEM) evaluated the dispersion of the SN-GTE particles within the cured resin. Results: The degree of conversion was significantly greater in the SN samples compared to the control. Flexural strength and energy to break were not significantly different (F(4,82)=1.4;p=0.231) (F(4,82)=0.1;p=0.98). The modulus of the 1% SN sample was significantly smaller than all others. TEM confirmed the presence of SN particles. No zones of inhibition were observed. After growing for 12 hours there was approximately a 100-fold decrease in the number of S. mutans cells attached to the 1% discs compared to the control. Conclusion: SN at less than 1%w/v did not decrease the modulus, no leaching effect was observed but may have reduced the attachment of S. mutans. This new material may inhibit biofilm formation.