Impact of coffee exposure on the color adjustment potential of universal-shade resin composites: an in vitro study

Objectives: This study aimed to evaluate the color adjustment potential (CAP) of a universal- shade composite resin applied to acrylic teeth of different shades under various storage conditions and over different time intervals. Methods: A universal-shade composite (Omnichroma; Tokuyama, Tokyo, Japan) and acrylic molar teeth in three shades (A1, A2, D4) were used. Two types of samples were prepared: dual-shade (Class I restorations with 5-mm diameter and 2-mm depth in acrylic teeth) and single-shade (artificial tooth replicas). Specimens were stored in either distilled water or coffee. Color measurements were performed using a spectrophotometer at baseline, 1 day, 1 week, and 1 month. Color differences (ΔE00) were calculated using the CIEDE2000 formula. ΔE00 values were analyzed with two-way ANOVA and Tukey’s tests. CAP00 values were analyzed using the three-way ANOVA for intergroup comparisons and repeated measures ANOVA with Bonferroni tests to assess time-related effects. Results: At baseline, the ΔE00 values were lowest in the A1 group for both sample types, followed by A2 and D4. After 1 month, coffee immersion led to significantly higher ΔE00 values than distilled water in all groups. CAP00 values significantly decreased between 1 week and 1 month in coffee-stored samples. All shade and storage subgroups showed a significant time-dependent increase in CAP00 (p < 0.05). Conclusions: One-month storage in distilled water enhanced CAP in all groups. In turn, prolonged coffee exposure increased color differences and diminished the color harmony of restorations over time.