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IntroductionStreptococcus mutans is a bacterium mainly responsible for dental caries. From a socioeconomic point of view, a simple and inexpensive solution is necessary. This study aims to evaluate the antibacterial effect and determine the minimum inhibitory concentration of synthetic and natural curcumin on strains of Streptococcus mutans in biofilm mode. Materials and methods The Streptococcus mutans strain was isolated from saliva samples using a special kit (CRT Bacteria® Ivoclar) at the conservative endodontics department of CHU Tlemcen. The minimum inhibitory concentration was determined using the dilution technique in 96-well microplates with double serial dilutions of synthetic curcumin (Sigma-Aldrich, Saint-Quentin-Fallavier, France) and natural curcumin (99% pure curcumin from India), prepared in Brain Heart Infusion Broth (BHIB) (Conda Pronadisa, Madrid, Spain) up to a final volume of 100 μl per well. Next, an observation using an environmental scanning electron microscope was performed on glass slides immersed in a Streptococcus mutans suspension, incubated for 48 hours at 37 °C and subsequently immersed for 30 minutes in a curcumin solution at its minimum inhibitory concentration. Results The minimum inhibitory concentration of curcumin was 64 μg/ml and scanning electron microscopy revealed a significant reduction in the adhesion of Streptococcus mutans strains. Conclusion Curcumin is a promising antibacterial agent for the prevention of dental caries.