title: Effect of light activation on resin-modified glass ionomer shear bond strength.
abstract: OBJECTIVE
  Recent studies confirmed that resin-modified glass ionomers (RMGIs) set on the basis of two competing mechanisms, an acid-base reaction and a light-activated resin polymerization. This study evaluated the effect of the setting mechanism on bond strength by measuring the shear bond strength of three RMGIs to dentin with and without light activation.
  
  
  METHODS
  Sixty human molars were ground to midcoronal dentin and randomly divided into six even groups: 1) Ketac Nano (KN), 2) KN without light cure (woLC), 3) Fuji Filling LC (FF), 4) FF woLC, 5) Fuji II LC (FII), and 6) FII woLC. The dentin surfaces of the specimens were conditioned/primed according to the manufacturers' instructions. A 1.54-mm diameter plastic tube was filled with RMGI material and affixed to the dentin surface. Groups 1, 3, and 5 were light cured for 20 seconds, and groups 2, 4, and 6 were immediately placed in a damp dark box with no light curing at 37°C for 24 hours. Shear bond strength testing was performed in an Instron device at 1 mm/min. Data were analyzed with a one-way analysis of variance (ANOVA) and Tukey/Kramer test (α=0.05).
  
  
  RESULTS
  Mean ± standard deviation shear bond strength values (MPa) are: 7.1 ± 4.2 (KN), 11.7 ± 3.9 (FF), 10.2 ± 3.2 (FF woLC), 12.5 ± 5.1 (FII), and 0.3 ± 0.4 (FII woLC). Two KN, all KN woLC, and seven FII woLC specimens debonded before testing. Tukey/Kramer analysis revealed no significant differences in bond strength between the three light-cured RMGIs. KN and FII showed significantly lower bond strength without light cure, but no significant difference was observed between FF and FF woLC.
  
  
  CONCLUSIONS
  The results of this study strongly suggest that light activation is necessary to obtain optimal bond strength between RMGI and dentin. FF may contain components that chemically activate resin polymerization. Clinically, KN and FII need to be light cured after placement of these RMGIs.
authors.affiliation: University of Alabama, Birmingham, AL, USA. nlawson@uab.edu
authors.forename: N C
authors.initials: NC
authors.lastname: Lawson
authors.forename: D
authors.initials: D
authors.lastname: Cakir
authors.forename: P
authors.initials: P
authors.lastname: Beck
authors.forename: L
authors.initials: L
authors.lastname: Ramp
authors.forename: J O
authors.initials: JO
authors.lastname: Burgess
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000648:ultrastructure; D005898:Glass / Q000737:chemistry / Q000528:radiation effects; D005899:Glass Ionomer Cements / Q000737:chemistry / Q000528:radiation effects*; D006801:Humans; D008027:Light; D055115:Light-Curing of Dental Adhesives / Q000379:methods; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D011092:Polyethylene Glycols / Q000737:chemistry / Q000528:radiation effects; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry / Q000528:radiation effects; D011140:Polyurethanes / Q000737:chemistry / Q000528:radiation effects; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects*; D012117:Resins, Synthetic / Q000737:chemistry / Q000528:radiation effects; D033081:Shear Strength; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D015040:Zirconium / Q000737:chemistry / Q000528:radiation effects
chemical_list: C079765:Fuji II LC cement; D005899:Glass Ionomer Cements; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D019279:Resin Cements; D012117:Resins, Synthetic; C421283:poly(ethylene glycol)-dimethacrylate; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C005044:hydroxyethyl methacrylate; D015040:Zirconium; C028541:zirconium oxide