Antibacterial Activity of a Novel Silver Nanoparticle-Loaded Orthodontic Band Cement

Method: 16 groups of AgNP-loaded OBC were formulated with varying concentrations of benzoyl peroxide (BPO; 0.5, 1, 1.5, 2 wt%), 2,2-(p-Tolylimino)diethanol (P-TIDE; 0.5, 1 wt%), and silver benzoate (AgBz; 0.5, 1 wt%). Controls included OBC and OBC formulated at UTHSCSA (UTOBC).  Cements were light-cured and tested with Rockwell_15T hardness and near-infrared FTIR (Near-IR) for degree of cure (DoC), and 3-point bending for mechanical properties.  In vitro Ag⁺ ion release was measured for 4 months.  0.5 wt% BPO/0.5 wt% P-TIDE formulation had the best combination of mechanical properties and Ag⁺ ion release, so two additional groups with 0.1 and 0.25 wt% AgBz were made and tested to better assess antimicrobial activity.  

Result: OBC had significantly (p<0.5) higher hardness, modulus and ultimate transverse strength (UTS) than all groups despite having lower DoC. This may be due to better filler dispersion. In general, UTOBC and some 0.5 wt% AgNP-loaded groups had significantly higher hardness than 1 wt% AgNP-loaded groups, but modulus and UTS were mostly not different. Additional BPO and P-TIDE increased DoC, modulus and UTS of AgNP OBC groups to comparable levels as those of UTOBC.  Ag-NP OBC made with 0.1 and 0.25% AgBz had higher hardness than the corresponding 1 wt% AgBz group but there were no differences in DoC, modulus or UTS.  Ag⁺ ion release was observed for all AgNP-loaded groups for 4 months, and, based on previous work, are expected to have significant antibacterial activity.

Conclusion: AgNP-loaded OBC has comparable mechanical properties as UTOBC. All experimental groups released significant amounts of Ag⁺ ions in vitro up to 4 months. We are currently conducting in vitro antibacterial tests to determine antibacterial activity.