Polymerization shrinkage kinetics of dimethacrylate resin-cements

ObjectivesTo determine polymerization shrinkage-strain (S_Y) and shrinkage-stress (S_Z) of six resin-cements and to compare their performance with the aid of degree of conversion (DC) data.MethodsVariolink 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 investigated. MS, MX and RX were self-adhesive; others require a bonding-agent. All measurements were conducted at 23 °C for 60 min (n = 5), except 80 min for RX, with materials self-cured only (sc) and dual-cured (dc); NX2 and VL2 were additionally light-cured only (lc). S_Y was measured by the bonded-disk method Watts DC, Cash AJ. Determination of polymerization shrinkage kinetics in visible-light-cured materials: methods development. Dent Mater 1991;7(4):281–7; Watts DC, Marouf AS. Optimal specimen geometry in bonded-disk shrinkage-strain measurements on light-cured biomaterials. Dent Mater 2000;16(6):447–51]; S_Z by the Bioman instrument Watts DC, Satterthwaite JD. Axial shrinkage-stress depends upon both C-factor and composite mass. Dent Mater 2008;24(1):1–8 Epub October 24, 2007]; Watts DC, Marouf AS, Al-Hindi AM. Photo-polymerization shrinkage-stress kinetics in resin-composites: methods development. Dent Mater 2003;19(1):1–11]. Light-cure was achieved by QTH at 500 mW/cm². The respective DCs were measured under the same conditions by FTIR–ATR spectroscopy. Data were analyzed by One-Way ANOVA plus Bonferroni test, and by t-test, at p < 0.05.ResultsDC by self-curing was less than the DC by dual-curing, for all cements. Shrinkage-strain ranged from 1.77 to 5.29% and shrinkage-stress from 3.36 to 10.37 MPa. NX2 and VL2 were not significantly different, when light-cured only. Except for RX, sc and dc shrinkage-strain varied maximally by 0.4%. MX showed the highest S_Y, RX the lowest. When sc, RX initially expanded by <0.5% (t ～ 5 min). For most materials, S_Y correlated with their filler loading. The highest stress with sc was exerted by MX, and when dc by MS, which was not statistically different from MX.SignificanceShrinkage data of resin-cements are of intrinsic clinical importance. Self-cure, despite a lower DC, did not necessarily result in a lower S_Y compared to dual-cure. S_Y-rate and S_Z development depend upon cure mode and S_Y upon filler fraction.