Time-dependent color stability of three nanohybrid resin composites after cigarette smoke exposure: an in vitro study

To determine whether cigarette smoke exposure increases time-dependent color change (E00) in nanohybrid resin composites.This experimental, comparative, longitudinal in vitro study prepared 45 disc-shaped specimens, allocated to three groups (n = 15): Filtek Z350 XT, IPS Empress Direct, and Forma. Specimens were exposed daily to the smoke of six cigarettes for 28 days in a custom-built exposure chamber. Color was recorded at baseline and after 7, 14, 21, and 28 days using a VITA Easyshade spectrophotometer in the CIELAB color space. The primary outcome was color change calculated with the CIEDE2000 formula (E00). Perceptibility (0.8) and clinical acceptability (1.8) thresholds were considered. Repeated-measures ANOVA was used to evaluate the effect of time on E00.E00 increased progressively over time for all three materials (main effect of time, p < 0.001). Forma presented the lowest mean E values throughout follow-up, Filtek Z350 XT showed intermediate values, and IPS Empress Direct exhibited the highest color change. From day 14 onwards, all materials exceeded the perceptibility threshold and a relevant proportion of specimens surpassed the clinical acceptability threshold, with increasing magnitudes up to day 28.Daily exposure to cigarette smoke produced a progressive and statistically significant increase in color change (E00) in all three nanohybrid resin composites evaluated, confirming that exposure time directly influences chromatic stability.