Objective: To contribute to the understanding of the basic shrinkage phenomena exhibited by contemporary resin-cements with varying cure. Methods: Variolink 2 (VL2), Multilink Automix (MA), Multilink Sprint (MS, all Ivoclar-Vivadent), Nexus 2 (NX2), Maxcem (MX, both Kerr) and RelyX Unicem (RX; 3M Espe) were tested for shrinkage-strain VS and shrinkage-stress SZ. MS, MX and RX are self-adhesive; others require additionally etching and bonding. All materials were tested self-cured only (sc) and dual-cured (dc); NX2 and VL2 additionally light-cured only (lc). Light-cure was achieved by a QTH-lamp at circa 500 mW/cm2. VS was measured by the bonded-disk method (Watts and Cash, 1991), SZ by the Bioman device (Watts et al., 2003). Shrinkage-strain and -stress rates with the respective time were calculated. Data were analysed by One-Way ANOVA with Bonferroni's adjustment and T-Test at p<0.05.
Results: Ranged from 1.77 to 5.29% for shrinkage-strain and 3.36 to 10.37 MPa for shrinkage-stress. NX2 and VL2 were not significantly different, light-cured only (p>0.05). VS: MX showed the highest VS, RX the lowest, sc as well as dc. When sc, RX initially expanded up to a maximum of <0.5% at t5 min. Dc did generally not result in a higher VS compared to sc. Except for RX, sc and dc varied maximally 0.4%. SZ: The highest stress with sc was exerted by MX, with dc by MS. RX exerted in both groups the lowest stress, whereas no expansion stress was measured. Sc resulted for all materials, except MX, in statistically lower shrinkage-stress values (p<0.05).
This is in line with the rate of polymerization, which was for all materials significantly higher by lc and dc than by sc (p<0.001). Significance: Shrinkage data of resin cements are of intrinsic clinical importance. Considering the results of this study, RX represents an alternative to the non-self-adhesive resin cements. As assessed by the pattern of shrinkage-strain, dual-curing is not required for optimal setting, whereas the it leads to higher stresses compared to self-curing. Polymerization-rate and shrinkage-stress development are related to cure mode.