Both direct and indirect techniques are used for composite resin material (CRM) restorations. Polishing processes are needed in both techniques after intraoral adjustment. However, it is unclear as to which polishing technique should be preferred with respect to decreasing biofilm. The purpose of thisin vitro study was to evaluate the surface properties and Streptococcus mutans biofilm formation on direct and indirect CRMs after using different polishing techniques. Two CRMs (direct and indirect) and four polishing techniques (aluminium oxide discs, diamond polishing paste, aluminium oxide polishing paste, and silicon carbide brush) were evaluated. The specimens were prepared for taking scanning electron microscopy images (n = 2) and determining surface roughness, surface free energy, and bacterial biofilm formation (BBF) with colony-forming unit counting and confocal laser scanning microscopy assays (n = 7). The data were analysed using two-way analysis of variance with Bonferroni as a post hoc test and Pearson's correlation (p < .05). The surface roughness values in the control group were higher than those in the diamond polishing paste group (p = 0.025), but the values in the aluminium oxide polishing paste and silicon carbide brush groups were comparable with those in the control group (p = 0.156 and p = 1.000, respectively). The highest surface free energy values were recorded in the silicon carbide brush group (p < 0.001), whereas there were no differences found among the other groups (p > 0.05). The highest BBF was seen in the silicon carbide brush (p < 0.001) and direct CRM (p < 0.001) groups. BBF on the surface of direct CRMs differed from that on indirect CRMs after polishing the surface. The tested polishing techniques significantly influenced surface properties and BBF. In situations that require the intraoral adjustment of CRMs, polishing with a diamond polishing paste seems to be a good option to polish the surface of both direct and indirect CRMs because the diamond polishing paste results better in terms of decreasing biofilm formation and improving surface properties. Copyright © 2019 Elsevier Ltd. All rights reserved.