Impact of Curing Protocols on Dual-Cure Resin Cements Properties

Objectives: This study aimed to evaluate how different activation protocols and light sources affect the properties of two dual-cured resin cements with distinct photoinitiators when used for the cementation of glass fiber posts.
Methods: Five activation protocols were tested: chemical activation, immediate photoactivation with Elipar or Grand Valo, and photoactivation after 5 minutes with Elipar or Grand Valo. Two dual resin cements, Multilink Automix and Variolink Esthetic DC, were evaluated. For degree of conversion test, cement samples were analyzed by a FTIR spectrometer (n=5). For the push-out bonding strength test, micropermeability and mechanical properties, fiberglass posts were cemented in single-rooted premolars using the two cements and activation protocols studied. The samples were sectioned to obtain slices of cervical, middle and apical thirds of the root. Bond strength was evaluated through a push-out test using an universal testing machine (n=13). For micropermeability analysis, the slices were stained with 0.1% Rhodamine B and then examined under a confocal microscope (n=5). The nanomechanical properties of the cement layer were analyzed in a nanoidentor machine (n=3). The mean values were submitted to ANOVA and Tukey's test (α=0.05).
Results: Multilink showed higher degree of conversion (75.90 ± 22.11%) than Variolink (61.60 ± 12.78%) (p<0.001). Chemical curing promoted lower conversion values. For Variolink, immediate activation with Valo promoted lower conversion degree values compared to immediate activation with Elipar (p=0.009). Multilink showed higher bond strength (12.81 ± 3.44MPa) than Varionlink (10.79 ± 4.01MPa) (p<0.001). Bond strength values reduced apically. Variolink had the highest reduced elastic modulus (6.87 ± 1.76GPa) and hardness (166.89 ± 56.77MPa).
Conclusions: Delayed photoactivation did not affect the degree of conversion, bond strength or micropermeability of dual-cured cements. Light source significantly influenced conversion, with immediate exposure of Variolink to Valo impairing its performance. Bond strength decreased apically, and cement type had a greater impact on nanomechanical properties.