Comparison of photo-activation versus chemical or dual-curing of resin-based luting cements regarding flexural strength, modulus and surface hardness

This study investigated the efficiency of chemical activation of dual-cure resin-based luting cements as compared with light- and dual-curing. Curing was performed by (i) mixing base and catalyst without subsequent irradiation (chemical curing = CC), (ii) mixing base and catalyst with direct irradiation (dual-cure = DC) or with (iii) irradiation through 2.5 mm of leucite-reinforced glass-ceramics (IPS Empress, Ivoclar) (dual-cure through porcelain = DCtP), (iv) using only the base paste with direct irradiation (light-curing = LC) or with (v) irradiation through porcelain (fight-curing through porcelain = LCtP). Specimens of four fine-hybrid DC resin composites and one self-cure hybrid resin composite (only CC) were prepared and tested after 24 h for flexural strength, modulus of elasticity (ISO 4049) and surface hardness (Vickers). For all materials and parameters, dual-curing produced higher values than LC, even when irradiation was performed through porcelain. Following self-curing without photo-activation, flexural strength was 68.9-85.9%, the modulus 59.2-94.5% and Vickers hardness 86.1-101.4% of the corresponding values obtained by dual-curing with direct irradiation. Light-curing through porcelain as compared with direct irradiation reduced the values for most parameters and materials. In contrast, dual-curing maintained flexural strength for an, the modulus for three and the hardness for one of the materials. The mechanical properties of the self-curing resin cement ranged between those of the DC materials.