Evaluation of antimicrobial properties of orthodontic composite resins combined with benzalkonium chloride.

An antimicrobial agent, benzalkonium chloride (BAC), was added to a chemically cured composite resin, and the antimicrobial benefits and physical properties of the modified composite were evaluated. BAC was added to Reliance Phase II composite to create modified composites with BAC concentrations ranging from 0.25 to 2.50 wt%. Specimen disks of the modified composite were incubated with Streptococcus mutans for 48 hours, and an agar disk diffusion assay was used to measure zones of bacterial inhibition. Larger disks were suspended in brain-heart infusion medium containing 2 x 10(4) colony-forming units/mL Streptococcus sobrinus (10 mL, 2 wt% sucrose, 24 hours) to measure bacterial adherence to the adhesive; adherent cells were removed from the surface with 1 N NaOH, and the optical density of the cells was measured at 550 nanometers. Traction hooks were bonded to bovine teeth with the modified composite, and tensile bond strength was evaluated with a universal testing machine. Diametral tensile stress was also measured. The modified composite samples showed that antimicrobial activity increased with higher BAC content; no antimicrobial activity was measured for the original compound in either the disk diffusion or the bacterial adherence test. There were no significant differences (P <.05) in either tensile bond strength or diametral tensile stress among the modified composite groups and the original product. The incorporation of BAC in composite material added antimicrobial properties to the original compound without altering its mechanical properties.