Abstract
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) in P1, while no significant differences existed between MH and MF, and NX3L and RXL in P2. At 1, 2, 7, 14 and 28 days the light curing luting agents had a higher DC than the dual luting agents (p < 0.05). P1 and P2 were not statistically different at each time point (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.
Highlights
The development of reliable adhesive systems between the tooth and resin-based materials (RBM) has led to more conservative dental treatments
Samples were divided into two groups and submitted to the following curing protocols: five samples were cured for 40 s (P1); the other five samples were cured for 5 s, and after 20 s, cured again for additional 40 s (P2)
The longevity of an indirect restoration is directly affected by the resin luting agent [14, 15], and by its degree of conversion (DC), whose evaluation may be performed by spectroscopic analysis [12, 16]
Summary
The development of reliable adhesive systems between the tooth and resin-based materials (RBM) has led to more conservative dental treatments. Resin luting agents are intermediates between the tooth substrate, with or without a bonding agent, and the indirect restoration. They can be divided into two categories: traditional resin-based composites and resin cements. These latter can be divided into light, self or dual cured according to the curing procedure, depending on own monomers and formulation. A free radical reaction allows resin luting agents to move from a viscous to a rigid state in a process called polymerization. The formation of free radical varies with the activator system [1]
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