Comparison of antibacterial activities of root-end filling materials by an agar diffusion assay and Alamar blue assay

Background/purpose: The purpose of this in vitro study was to evaluate antibacterial activities of the leachable components of root-end filling materials (calcium silicate cement). Materials and methods: Root-end filling materials were mixed according to the manufacturers' directions and then placed into 6-mm-diameter Teflon rings with mixed materials; they were allowed to set for 24 hours and then tested. Antibacterial activities of the root-end filling materials were evaluated against Streptococcus sanguinis, Streptococcus mutans and Escherichia coli. The antibacterial activity of the root-end filling materials tested was determined by measuring the diameter of each zone of inhibition (on an agar diffusion test). An Alamar blue assay was used to detect bacterial growth. Statistical analysis was conducted using one-way analysis of variance. Results: Zones of inhibition were observed in the zinc oxide-eugenol cement (IRM) group treating S. sanguinis and E. coli agar plates in the agar diffusion test. Cultures of S. sanguinis and E. coli showed the lowest absorbances with the IRM group at different times of observation (1 hour, 3 hours, 6 hours and 12 hours) (P < 0.05). The growth of S. mutans showed no significant difference between controls and any tested materials (P > 0.05). Conclusion: We concluded that both the agar diffusion test and Alamar blue assay gave comparable findings of assessing the antimicrobial activity present in root-end filling materials. No antimicrobial activity was detected for mineral trioxide aggregate, calcium silicate cement, or amalgam after coming into contact with S. mutans, S. sanguinis and E. coli. IRM showed high antimicrobial activity against both S. sanguinis and E. coli.