INTRODUCTION: This study aimed to assess the effects of various nicotine concentrations in flavored electronic cigarettes (e-cigarettes) on the surface roughness, microhardness, and color stability of restorative materials and enamel structure. METHODS: The study utilized nanohybrid packable resin composite restorations, resin-modified glass ionomer (RMGI), and dental enamel samples (n=10). These samples were exposed to electronic cigarettes with different nicotine concentrations (3, 20, or 50 mg) using a customized chamber connected to a vacuum machine. A total of 3600 puffs were administered through cycles consisting of 9 puffs, with each puff lasting 4 s and an interval of 20 s between puffs, resulting in a total cycle duration of 3 min and 36 s. Before and after the exposure, the samples were tested for microhardness (MH), surface roughness (SR), and color changes (ΔE*). Data were analyzed using one-way and two-way analyses of variance (ANOVA). Multiple comparisons among different groups were conducted using Bonferroni's multiple comparison test with a p-value level set at 0.05. RESULTS: The study findings indicate that all samples - enamel, resin composite, and RMGI - experienced significant reductions in MH. However, no significant differences were observed among the enamel groups. Higher nicotine concentrations did not significantly affect the MH in the resin composite and RMGI group, but both showed significant differences compared to the lowest concentration (3 mg) (p<
0.05). At 3 mg nicotine, enamel exhibited the highest ratio (%) change (-46.81± 24.68), followed by RMGI (-23.27 ± 6.24). At the highest concentration of 50 mg nicotine, enamel demonstrated a ratio (%) change of -25.46 ± 16.39, whereas RMGI with -75.72 ± 3.46 maintained similar degradation levels to the 20 mg group. SR results revealed that while most enamel and all RMGI samples showed no significant changes after nicotine exposure, all nicotine concentrations significantly increased SR in resin composite (nicotine 3 mg: 76.00 ± 11.90 to 165.46 ± 36.06 nm
p<
0.05). Additionally, color change demonstrated that RMGI exhibited the greatest color change after exposure to both 3 mg (ΔE*=9.45 ± 2.30) and 50 mg (ΔE*=10.25 ± 1.53 nicotine concentrations (p<
0.05), while enamel and resin composite samples did not show clinically detectable color changes at the 3 mg nicotine concentration. The 20 mg nicotine concentration had the most substantial impact across the groups. CONCLUSIONS: The higher nicotine concentrations showed a greater effect among all samples in the tested groups. All concentrations of nicotine e-cigarettes (3, 20, and 50 mg) significantly affected the MH of all tested groups. In terms of SR, the only group that did not show a significant increase with all nicotine concentrations is the RMGI. In aesthetic perspective, the lower the concentration of nicotine e-cigarettes, the lower the change in color when compared to higher concentrations.