title: Delayed Photo-activation Effects on Mechanical Properties of Dual Cured Resin Cements and Finite Element Analysis of Shrinkage Stresses in Teeth Restored With Ceramic Inlays.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of delayed photo-activation on elastic modulus, Knoop hardness, and post-gel shrinkage of dual cure resin cements and how this affects residual shrinkage stresses in posterior teeth restored with ceramic inlays.
  
  
  METHODS
  Four self-adhesive (RelyX Unicem, 3M ESPE; GCem, GC; MonoCem, Shofu; and seT, SDI) and two conventional (RelyX ARC, 3M ESPE; and AllCem, FGM) dual cure resin cements for cementing posterior ceramic inlays were tested. Strain gauge and indentation tests were used to measure the post-gel shrinkage (Shr), elastic modulus (E), and Knoop hardness (KHN) when photo-activated immediately and 3 and 5 minutes after placement (n=10). Shr, E, and KHN results were analyzed using two-way analysis of variance followed by Tukey honestly significant difference post hoc tests (α=0.05). The experimentally determined properties were applied in a finite element analysis of a leucite ceramic inlay (Empress CAD, Ivoclar Vivadent) cemented in a premolar. Modified von Mises stresses were evaluated at the occlusal margins and cavity floor.
  
  
  RESULTS
  Shr, E, and KHN varied significantly among the resin cements (p<0.001). Highest overall Shr values were found for RelyX Unicem; GCem had the lowest. Increasing the photo-activation delay decreased Shr significantly. Delayed photo-activation had no effect on E (p=0.556) or KHN (p=0.927). RelyX Unicem had the highest E values; seT and MonoCem had the lowest E values. AllCem and RelyX Unicem had the highest KHN and MonoCem had the lowest KHN. Cements with high Shr and E values caused higher shrinkage stresses. Stresses decreased with delayed photo-activation for all cements.
  
  
  CONCLUSIONS
  KHN and E values varied among the different resin cements. Residual shrinkage stress levels decreased with increasing photo-activation delay with all resin cements.
authors.forename: C J
authors.initials: CJ
authors.lastname: Soares
authors.forename: A A
authors.initials: AA
authors.lastname: Bicalho
authors.forename: C
authors.initials: C
authors.lastname: Verissimo
authors.forename: Pbf
authors.initials: P
authors.lastname: Soares
authors.forename: D
authors.initials: D
authors.lastname: Tantbirojn
authors.forename: A
authors.initials: A
authors.lastname: Versluis