Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 14 6 2017 12 16 337 343 EN Fariba Motevasselian Assistant Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Restorative and Aesthetic Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Ensieh Zibafar Assistant Professor, Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Esmail Yassini Professor, Department of Restorative and Aesthetic Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Mansoreh Mirzaei Associate Professor, Department of Restorative and Aesthetic Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Naser Pourmirhoseni Dentist, Private Practice, Tehran, Iran 2017 06 17 2017 10 17 Objectives: Streptococcus mutans (S. mutans) is a cariogenic microorganism. The restorative materials which harbor a biofilm with high levels of S. mutans can accelerate the occurrence of dental caries. The purpose of this study was to evaluate the influence of different restorative materials on S. mutans colonization in a simple in-vitro biofilm formation model. Materials and Methods: Thirteen discs of each material (nanohybrid resin composite, microhybrid resin composite, and amalgam) were prepared, polished, and sterilized in a gamma radiation chamber. The saliva-free specimens were exposed to the S. mutans bacterial suspension (0.5 McFarland) and were incubated for 4 hours. Afterwards, the specimens were rinsed and sonicated in normal saline. 10µl of the obtained suspension was cultured in a sterile blood agar medium. After 24 hours, the number of colony forming units (CFU) of S. mutans was counted. A sterility test control was considered for each group of materials. The data were analyzed by one-way ANOVA at 5% significance level. Results: The means and standard deviations of the logarithmic values of the colonies on the surfaces of amalgam, microhybrid, and nanohybrid resin composites were equal to 3.76±0.64, 3.91±0.52 and 3.34±0.74, respectively. Conclusions: There were no significant differences between the restorative materials in terms of S. mutans adhesion rate. The evaluated resin composites showed comparable numbers of CFUs, which could imply the importance of the polishing procedures. https://fid.tums.ac.ir/index.php/fid/article/view/1974 https://fid.tums.ac.ir/index.php/fid/article/download/1974/980