Comparison of two curing protocols during adhesive cementation: can the step luting technique supersede the traditional one?

This study aims to compare the degree of conversion of two different curing protocols used during adhesive cementation. The following resin luting agents were tested: Hri Flow (MF) and pre-heated Hri Micerium (MH); light-cure Nexus Third Generation (NX3L) and dual-cure Nexus Third Generation (NX3D); dual cured RelyX Ultimate (RXU) and light-cure RelyX Veneers (RXL). For each tested material, ten samples were prepared and divided into two groups which had different curing protocols (P1 and P2): in P1, samples were cured for 40 s; in P2, samples were cured for 5 s, and then, after 20 s, cured again for additional 40 s. The degree of conversion (DC) was evaluated both during the first 5 min of the curing phase and after 1, 2, 7, 14 and 28 days (p = 0.05). Different trends were observed in DC values after 5 min by comparing P1 and P2. In both P1 and P2, DC decreased as follows, MH > MF > NX3L > RXL > RXU > NX3D. There were significant differences of DC values among all resin luting agents (p   0.05). Both P1 and P2 protocols let achieve an acceptable DC after 28 days. The tested P2 can be safely used to lute indirect restorations, simplifying the removal of cement excesses.