Abstract
The concern with the polymerization shrinkage of restorative resin composites also applies to resin cements. The aim of this study was to evaluate the influence of volume and polymerization mode on forces generated during polymerization shrinkage (FGPS) of resin cements. Two light-cured resin cements--Variolink II (VL; Ivoclar Vivadent) and Nexus 3 (NX; Kerr)--and two self-cured resin cements - Multilink (ML; Ivoclar Vivadent) and Cement Post (CP; Angelus) - were inserted between two rectangular steel bases (6x2 mm) with distance set at 0.1, 0.3 and 0.5 mm, establishing a variation of volume. These steel bases were attached to a universal test machine with 50 kg load cell and forces (N) were registered for 10 min. Values of maximum forces generated by each material were subjected to two-way ANOVA and Tukey's test for individual comparisons (α=0.05). VL, NX and CP developed increasing FGPS as the volume of material increased, while ML presented the opposite behavior. It may be concluded that higher volume increases FGPS even with a concomitant decrease of C-factor, unless the resin cements present lower force generation rates as a function of time in combination with a low C-factor, resulting in stress relief and consequently lower values of FGPS.
Highlights
The evolution of indirect restorative systems has widened their indications [1], increasing the importance of luting procedures that promote adhesion, durability and aesthetics
Polymerization shrinkage forces are able to break cured resin composites to the lower flow capacity during adhesive links between resin composite and tooth, causing polymerization process
Due to the increased use of resin cements, the forces generated during polymerization shrinkage (FGPS) of increase of FGPS is a common characteristic of lightthese materials have been investigated [7,13,14,15]
Summary
The evolution of indirect restorative systems has widened their indications [1], increasing the importance of luting procedures that promote adhesion, durability and aesthetics. For this reason, resin cements became even more relevant, since this group of materials provides improved physical properties and aesthetics [2,3]. Resin cements became even more relevant, since this group of materials provides improved physical properties and aesthetics [2,3] Despite these advantages, the use of resin materials requires some care, especially as regards polymerization shrinkage. Volume is considered especially important for light-cured restorative resin composite, in which the pre-gel phase is shorter and may not allow stress relief even with a lower C-factor. Stress relief is time-dependent, and the shorter time for polymerization process is responsible for generation of higher forces of light-cured resin composites when compared with the self-cured resin composites [11]
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