Antibacterial Properties of Restorative Materials: Amalgam and Composite Resins

OBJECTIVES: The antibacterial properties of dental restorative materials, such as amalgam and composite resins, may have an impact on the restorative treatment. This study evaluated the antibacterial effect of three composite resins: Z250, P60, Tetric Ceram and dental amalgam in vitro, using two cariogenic oral bacteria: Streptococcus mutans and Actinomyces viscous. METHODS: The antibacterial effect was assessed by the agar diffusion test (ADT) and by the direct contact test (DCT). For purposes of comparison, the effect of the tested materials on planctonic bacterial growth was assessed. The antibacterial effect was quantified by computerized spectrophotometric microanalysis. The relative antibacterial potency of the tested materials was calculated by analyzing the regression line of the linear portion of the growth curve measured in each well of a 96-well microtiter plate. RESULTS: In the ADT an antibacterial halo was detected in amalgam only. All the restorative materials revealed various degrees of antibacterial properties in both tests, i.e., after direct contact and planctonic bacterial growth. Amalgam showed the most potent antibacterial effect in all phases, and the effect lasting for at least one week. In contrast, the effect of the composite resins on bacterial growth was limited and of short duration. Furthermore, after one week of aging an increase in the growth rate of S. mutans was observed. CONCLUSION: The present findings demonstrate the strong and lasting antibacterial properties of amalgam, properties lacking in composite resins.