This study evaluated the effects of thiourethane (TU) additives on the flexural strength (σf) and elastic modulus (Ef) of a resin cement, and on a possible strengthening of ceramic restorations. Methods: Two TUs (ARomatic and ALiphatic) were added at 0 (control—EC) or 20 wt% to photopolymerizable resin cements. RelyX Ultimate (RU) was the commercial control. Flexural strength (σf) and elastic modulus (Ef) of the cements were measured in three-point bending (n = 8). Biaxial flexural strength (σbf) of ceramic discs with and without cement layering were determined using a ball-on-ring setup. The σbf of cement-coated specimens was calculated at positions z = 0 (ceramic surface, bonded interface) and z = −t2 (cement surface above ring). Data were analyzed with one-way ANOVA/Tukey test (α =.05). Results: σf of AR was significantly higher than for AL and RU, and Ef was lower. The Ef of RU was significantly higher than all other groups. At z = 0, all resin-coated groups had higher σbf. The σbf of RU, AR, and AL were significantly higher than EC and unfilled resin group. At z = −t2, RU had significantly higher σbf. Significance: All resin cements were able to strengthen the ceramic, with the TU-modified material presenting similar results to the commercial material.