AbstractObjectives: (1) To evaluate and compare the flexural strength, flexural modulus, compressive strength, surface roughness, and gloss for two nanohybrid composites (Herculite XRV Ultra, and Tetric Evo Ceram) and two microhybrid composites (Filtek Z250, and Venus). (2) To evaluate the differences in surface roughness and gloss between the materials. (3) To evaluate the effect of polishing and toothbrushing abrasive on surface roughness and gloss. (4) To assess the relationship between 2D surface roughness and 3D surface roughness parameters.Materials and methods: Compressive strength, Flexural strength, and Flexural Modulus of each material were determined using a universal testing machine (each test n=10). Flexural strength and flexural modulus were evaluated by using a three-point bending test. The results were statistically analyzed, with psmaller or equal to 0.05. Surface roughness and gloss of each material were evaluated by a 2D contact stylus profilometer: before polishing, after polishing, and after abrasive toothbrushing. Three surface roughness parameter were used in this study (Ra, Rt, Rsm). The results were analysed to evaluate the effect of polishing and toothbrushing abrasive by t-test for paired data and Oneway (ANOVA) test, followed by Tukey`s post hoc test, for multiple comparisons. 3D surface roughness measurements (Sa, St, Sds) were recorded using 3D non contact stylus profilometer. 3D surface roughness (Sa) and 2D surface roughness (Ra) for all tested materials were plotted to show the relationship between Sa and Ra after polishing and after brushing.Results: For the mechanical tests, Filtek Z250 exhibited the highest flexural strength (136.71 MPa), flexural modulus (7.9 GPa), and compressive strength (405.33 MPa) among all materials tested, while Tetric Evo Ceram showed the lowest mean values for compressive strength (237.74 MPa) and flexural strength (83.75 MPa).For Surface roughness after polishing, Ra, Rt, aand Rsm of the materials did not differ significantly from each other, whereas after brushing there were significant differences between the materials. Tetric Evo Ceram exhibited the rougher surface after brushing. The gloss results showed significant differences in gloss between the materials tested after polishing and after brushing. Herculite XRV exhibited the highest surface gloss after polishing (74.85) and was the best at retaining the gloss after brushing, whereas Venus recorded the lowest result for gloss after polishing (52.28). However, Filtek Z250 had the lowest gloss retention after brushing. Also the results showed a positive correlation between 3D surface roughness (Sa) and 2D surface roughness (Ra) for all materials tested after polishing: r2=0.9 and after brushing: r2=1. Conclusion: While nanohybrid composites may have certain advantage, such as higher gloss, over microhybrid composite resin, their mechanical properties were not superior to those of the microhybrid composites which were tested.