title: Effect of Photoactivation Timing on the Mechanical Properties of Resin Cements and Bond Strength of Fiberglass Post to Root Dentin.
abstract: OBJECTIVE
  This study tested the hypothesis that photoactivation timing and resin cement affect mechanical properties and bond strength of fiberglass posts to root dentin at different depths.
  
  
  METHODS
  Fiberglass posts (Exacto, Angelus) were luted with RelyX Unicem (3M ESPE), Panavia F 2.0 (Kuraray), or RelyX ARC (3M ESPE) using three photoactivation timings: light curing immediately, after three minutes, or after five minutes. Push-out bonding strength, PBS (n=10) was measured on each root region (coronal, middle, apical). The elastic modulus (E) and Vickers hardness (VHN) of the cement layer along the root canal were determined using dynamic indentation (n=5). A strain-gauge test was used to measure post-gel shrinkage of each cement (n=10). Residual shrinkage stress was assessed with finite element analysis. Data were analyzed with two-way analysis of variance in a split-plot arrangement and a Tukey test (α=0.05). Multiple linear regression analysis was used to determine the influence of study factors.
  
  
  RESULTS
  The five-minute delay photoactivation timing significantly increased the PBS for all resin cements evaluated. The PBS decreased significantly from coronal to apical root canal regions. The mean values for E and VHN increased significantly with the delayed photoactivation for RelyX Unicem and decreased from coronal to apical root regions for all resin cements with the immediate-curing timing.
  
  
  CONCLUSIONS
  The PBS of fiber posts to root dentin, E, and VHN values were affected by the root canal region, photoactivation timing, and resin cement type. Shrinkage stress values decreased gradually with delayed photoactivation for all the cements.
authors.forename: R D
authors.initials: RD
authors.lastname: Pereira
authors.forename: A D C M
authors.initials: AD
authors.lastname: Valdívia
authors.forename: A A
authors.initials: AA
authors.lastname: Bicalho
authors.forename: S D
authors.initials: SD
authors.lastname: Franco
authors.forename: D
authors.initials: D
authors.lastname: Tantbirojn
authors.forename: A
authors.initials: A
authors.lastname: Versluis
authors.forename: C J
authors.initials: CJ
authors.lastname: Soares
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate; D001840:Dental Bonding; D003738:Dental Cements / Q000737:chemistry; D003804:Dentin; D017220:Dentin-Bonding Agents / Q000737:chemistry; D005898:Glass; D005899:Glass Ionomer Cements; D006801:Humans; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D019279:Resin Cements / Q000737:chemistry
chemical_list: D003738:Dental Cements; D017220:Dentin-Bonding Agents; D005899:Glass Ionomer Cements; C438843:Panavia-Fluoro; D011109:Polymethacrylic Acids; C483701:Rely X Unicem; C462240:RelyX ARC; D019279:Resin Cements; C009753:fiberglass; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate