Objectives The primary objective of the study was to examine changes in surface microhardness, roughness, and color resulting from exposure of the material to a commercially available green smoothie, for representatives of the following main classes of contemporary restorative materials: conventional resin composites, bulk-fill resin composites, glass-ionomer hybrid materials, and so-called alkasite material. Secondary objectives of the study include investigation of color changes according to individual color axes (L*, a*, b*), analysis of the contribution of color changes according to individual axes to the overall color change, and correlation analysis for changes in the main variables (microhardness, surface roughness, and color change) during the exposure of restorative materials to the green smoothie. Materials and methods The following materials were tested: conventional composite materials Tetric EvoCeram (Ivoclar Vivadent, Schaan, Liechtenstein) and Charisma Classic (Kulzer, Hanau, Germany), alkasite material Cention N (Ivoclar Vivadent, Schaan, Liechtenstein), bulk-fill composite material Filtek One Bulk Fill Restorative (3M, St. Paul, MN, USA), glass hybrid material Equia Forte HT Fil coated with Equia Coat (GC, Tokyo, Japan), and Equia Forte HT Fil (GC, Tokyo, Japan) without coating. All materials were used in the A2 shade. The samples were prepared in a cylindric mold with a diameter of 15 mm and a height of 1 mm, using 20 samples per material. The samples were stored in deionized water at 37 ˚ C and immersed over one month for 5 minutes daily in a green smoothie "Green avocado" (Ortoromi, Borgoricco, Italy) with 47% apple juice, 25% pear juice, 20% avocado, 8% spinach, and ascorbic acid. Changes in microhardness, surface roughness, and color were evaluated after four weeks of green smoothie exposure. Statistical analysis was performed using analysis of variance (ANOVA) with Tukey post-hoc test for multiple comparisons, t-test, Pearson's correlation analysis, and principal component analysis with varimax rotation. Results Statistically significant effects of the green smoothie on the degradation of contemporary restorative materials were identified for all tested properties. Statistically significant changes in microhardness, a significantly greater increase in surface roughness, and a greater color change were observed in the green smoothie group compared to the negative control group exposed to deionized water. After 30 days of cyclic exposure to the green smoothie, microhardness values decreased by 8-28% (for composite materials) or increased up to 91% (for glass hybrid). A statistically significant decrease in microhardness was measured for Tetric EvoCeram and Filtek One Bulk Fill in both groups (experimental and control), while a significant increase in microhardness was observed in the glass hybrid Equia Forte HT in both groups. There were no significant changes in microhardness for the glass hybrid coated with Equia Coat (in both groups) or for the alkasite material Cention N in the control group. The differences in microhardness change between the control and experimental groups were statistically significant for all materials except for the glass hybrid with resin coating. The increase in surface roughness of the samples immersed in the green smoothie was 7-26 times higher compared to the control group. The increase in roughness was statistically significant in most materials, except in the control group of materials Tetric EvoCeram, Cention N, and Charisma Classic. For all materials, the increase in roughness was significantly higher in the group exposed to the green smoothie than in the control group. Observable color changes (ΔE*) in the experimental group were 3-8 times higher compared to the control group. The ΔE* values of the samples immersed in the green smoothie ranged from 3.2 to 14.2, indicating color differences visible to the human eye. Color changes differed among the materials in a wide range of values, and for all materials they were significantly higher in the experimental group exposed to the green smoothie compared to the control group. Shifts along the color axes (L*, a*, and b*) mostly occurred in the same direction in the experimental and control groups, with their extent being generally greater in the experimental group. Principal component analysis and Pearson's correlation analysis showed a prominent correlation between surface roughness changes measured in the control and experimental groups. Conclusion Based on the results of this in vitro study, it can be concluded that daily exposure of restorative dental materials to a green smoothie can significantly accelerate the degradation of their surface properties, which reflects as a decrease in microhardness, increased roughness, and observable color changes. Considering all the above, doctors of dental medicine should be familiar with the behavior of restorative materials in different nutritional conditions and be able to predict their behavior. As clinicians, we can reduce the degradation of dental restorations by informing patients about their durability, advising them on dietary habits, and applying preventive and minimally invasive treatments to extend the service life of dental restorations.