The antibacterial properties of resins incorporating MAE‐DB and the underlying mechanisms of action were evaluated. Antibacterial effects against Streptococcus mutans were tested using the film contact method, with accumulation and membrane integrity observed by scanning electron microscopy and confocal laser scanning microscopy, respectively. Quantitative PCR was used to determine expression of the S. mutans glucosyltransferase B (gtfB) gene on the surface of resins containing 10% MAE‐DB. Bacterial growth was inhibited on resin containing 10% MAE‐DB as compared with the control at 1 day, 7 days, 30 days, or 180 days (p < 0.05). For the 10%‐MAE‐DB resin, no significant differences in bacterial viability were found regardless of the time of incubation (p > 0.05). The number of bacteria attached to resin containing 10% MAE‐DB was considerably lower than the control. The proportion of bacteria with damaged cell membranes was increased in the experimental resin over controls. Expression of gtfB was reduced by 10% MAE‐DB compared with the control (p < 0.05). These findings demonstrate that MAE‐DB can be incorporated into resin materials at sufficient concentrations for long‐term antibacterial effects against S. mutans after polymerization by attenuating gtfB expression and impairing membrane integrity. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.