title: Polymerization shrinkage kinetics of dimethacrylate resin-cements.
abstract: OBJECTIVE
  To 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.
  
  
  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 investigated. MS, MX and RX were self-adhesive; others require a bonding-agent. All measurements were conducted at 23 degrees C for 60min (n=5), except 80min 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 500mW/cm(2). 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.
  
  
  RESULTS
  DC 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 10.37MPa. 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 approximately 5min). 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.
  
  
  CONCLUSIONS
  Shrinkage 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.
authors.affiliation: Medical University of Vienna, Bernhard Gottlieb Universitätszahnklinik, Vienna, Austria. thomas@spinell.it
authors.forename: Thomas
authors.initials: T
authors.lastname: Spinell
authors.forename: Andreas
authors.initials: A
authors.lastname: Schedle
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D001840:Dental Bonding / Q000379:methods*; D003799:Dental Stress Analysis; D006244:Hardness; D007700:Kinetics; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates; D044367:Phase Transition; D019279:Resin Cements / Q000737:chemistry*; D055116:Self-Curing of Dental Resins; D013314:Stress, Mechanical
chemical_list: D008689:Methacrylates; D019279:Resin Cements