# Time-Dependent Color Stability of Three Nanohybrid Resin Composites After Cigarette Smoke Exposure: An In Vitro Study

## TL;DR

This study shows that daily cigarette smoke exposure causes increasing color changes in three types of dental resin composites over 28 days.

## Contribution

The study demonstrates the time-dependent effect of cigarette smoke on color stability of nanohybrid resin composites in vitro.

## Key findings

- All three materials showed progressively higher color change (E00) over 28 days of smoke exposure.
- Forma had the lowest color change, while IPS Empress Direct had the highest among the tested materials.
- By day 14, all materials exceeded the perceptibility threshold, with many surpassing the clinical acceptability threshold by day 28.

## Abstract

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.