Effect of light-unit and exposure time on composite-resins discoloration

Objectives: To evaluate the effect of light-curing-units (LCUs) and exposure times on composite-resins discoloration over a period of 30 days immersed on red wine. Methods: Composite discs 2 mm thick x 5 mm diameter were fabricated from four composite-resins: Filtek Supreme Plus/3M ESPE , Durafill/Heraeus Kulzer, Filtek Z250/3M ESPE and Venus/Heraeus Kulzer. The LCUs used were Halogen–Optilux501/Demetron and Blue LED–EliparFreeLight2/3M ESPE. The photo-emission times were half-, full- and double the time recommended by the manufacturers. After 24h in distilled water at 37^oC, the specimens were polished and baseline measurement of the CIE-L*a*b* color was obtained using a spectroradiometer and an external light source with a noncontacting 45-degree illumination and 0-degree observation optical configuration. Specimens were stored in red wine (37^oC) and color measurements of both top and bottom surfaces were obtained after 1-, 2-, 7-, 14-, 20- and 30-days in wine. The red wine was renewed every week and its pH was ~3.2. Statistical analysis was performed using Repeated Measures ANOVA (alpha=0.05). Results: For all three color directions (L*, a*, and b*), each of the factors studied (Resin, LCU, Cure Time Factor, Days in Red Dye, and Surface) was a statistically significant factor (P<0.05) either overall or in an interaction with one or more other factors.  As examples, at 30 Days for the Bottom Surface:

 Conclusion: The effects of changes in curing time on discoloration by red wine vary significantly by the composite resin being stained, as do the effects of the LCU.