Effect of light curing units on color stability and mechanical properties of resin cements after aging

This study aimed to evaluate the color stability, Martens hardness (HMV), and modulus of elasticity (Eit*) of resin cements light-cured using two types of light-emitting diodes (LED) subjected to ultraviolet (UV) aging. Two resin cements were used: light-cured (RelyX Veener) and dual-cured (Variolink II). Forty discs were confectioned for each resin cement (with a diameter of 5 mm and thickness of 1.5 mm). Half of the samples were light-cured by a Radii-cal singlewave and the other half by a Valo® polywave. The specimens were then stored at 37 °C and 100% relative humidity for 24 h to ensure complete polymerization. Baseline evaluations of the color alteration, HMV, and Eit* were performed. The specimens were aged for 252 h in an UV-accelerated aging chamber. Then, a final analysis was performed. Two-way repeated-measures ANOVA was performed on the color changes. Meanwhile, three-way repeated-measures ANOVA followed by Tukey´s test was performed on HMV and Eit* to compare the means (α = 0.05). With regard to the color alteration (ΔE), there was no statistically significant difference between the materials or between the light curing units (p > 0.05). With regard to the mechanical properties, Valo® promoted high values of HMV and Eit* compared with Radii-cal (p < 0.05). With regard to the resin cements, Variolink II showed higher HMV and Eit* values than RelyX Veneer (p < 0.05), except for Eit* after UV aging. The light-curing unit influenced the mechanical properties but not the color stability of the resin cements.