Effect of Light Intensity and Curing Time on Color Stability of a Methacrylate-Based Composite Resin Using an LED Light-Curing Unit

Background: Despite improvements in the optical properties of composite resins, their color stability is still a matter of discussion. This study sought to assess the effect of light intensity and curing time by a light-emitting diode (LED) light-curing unit on color stability of a methacrylate-based composite resin. Methods: In this in vitro study, 60 discs (8 × 2 mm) were fabricated of A2 shade of Z250 composite. Specimens were polished and divided into 4 groups (n=15) for curing for 20 or 40 seconds with a light intensity of 600 or 1200 mW/cm2 . After immersion in distilled water at 37°C for 24 hours, colorimetry was performed using a spectroradiometer. The specimens were then immersed in tea solution for 7 days (3 times a day, each time for one hour) and were subjected to colorimetry again. Color change (∆E) was calculated and analyzed using two-way ANOVA. Results: Significant color change was noted following an increase in curing time (P<0.05). No improvement in color stability was noted after increasing the light intensity (P>0.05). The interaction effect of light intensity and curing time on color change was significant (P<0.05). Conclusions: Curing time is an important factor affecting the color stability of composite resin polymerized with LED light curing unit. On the other hand, increasing the light intensity over the standard threshold showed no significant effect.