Bond Strength of Universal Adhesive/Resin Cement Combinations Relying on Touch-Cure Mechanisms

New dual-curing resin cements are constantly launched into the market to improve the bond strength between dentine and indirect restorations when light irradiation is limited by the restoration material. The present study evaluated the microshear bond strength (μSBS) of two dual-cured resin cements, Estecem II Plus (EP) and Variolink Esthetic DC (VAR), when resin composite or dentine substrates were conditioned with their corresponding universal adhesives, Tokuyama Universal Bond II (TUB) and Adhese Universal DC (ADH). The experimental groups (n = 20) were (1) TUB/EP light-cured, (2) TUB/EP self-cured, (3) ADH/VAR light-cured, and (4) ADH/VAR self-cured. A μSBS test was performed after 24 h (T0) or after thermocycling (TC), and failure modes were assessed. Data analysis was performed using three-way ANOVA and Tukey tests (p < 0.05). In composite, TUB/EP self-cured demonstrated the highest μSBS at T0 and TC. After TC, TUB/EP self-cured and ADH/VAR light-cured remained stable (p > 0.05). In dentine, TUB/EP light-cured was statistically superior to TUB/EP self-cured and ADH/VAR self-cured at T0. Thermocycling decreased the μSBS of light-curing groups. TUB/EP achieved optimal μSBS when the manufacturer's instructions were followed and the adhesive was self-cured, irrespective of the bonding substrate. However, ADH/VAR was more dependent on the type of bonding substrate than on the curing mode of the resin cement.