title: Effects of Nd:YAG laser irradiation on the hybrid layer of different adhesive systems.
abstract: OBJECTIVE
  The aim of this in vitro study was to evaluate the microtensile bond strength (microTBS) and hybrid layer morphology of different adhesive systems, either followed by treatment with Nd:YAG laser irradiation or not. Previous studies have shown the effects of Nd:YAG laser irradiation on the dentin surface at restoration margins, but there are few reports about the significance of the irradiation on the hybrid layer.
  
  
  METHODS
  The flattened coronal and root dentin samples of 24 bovine teeth were randomly divided into 8 groups, according to the adhesive system used -- Scotchbond Multi Purpose (SBMP) or Clearfil SE Bond (CSEB) -- and were either irradiated with Nd:YAG or not, with different parameters: 0.8 W/10 Hz, 0.8 W/20 Hz, 1.2 W/10 Hz, 1.2 W/20 Hz. The left sides of specimens were the control groups, and right sides were irradiated. A composite crown was built over bonded surfaces and stored in water (24 h at 37 degrees C). Specimens were sectioned vertically into slabs that were subjected to microTBS testing and observed by SEM.
  
  
  RESULTS
  Control groups (27.81 +/- 1.38) showed statistically higher values than lased groups (21.37 +/- 0.99), and CSEB control group values (31.26 +/- 15.71) were statistically higher than those of SBMP (24.3 +/- 10.66). There were no significant differences between CSEB (20.34 +/- 10.01) and SBMP (22.43 +/- 9.82) lased groups. Among parameters tested, 0.8 W/10 Hz showed the highest value (25.54 +/- 11.74). Nd:YAG laser irradiation caused dentin to melt under the adhesive layer of both adhesive systems tested.
  
  
  CONCLUSIONS
  With the parameters used in this study, Nd:YAG laser irradiation of the hybrid layer promoted morphological changes in dentin and negatively influenced the bond strength of both adhesive systems.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, SP, Brazil.
authors.forename: Leila S
authors.initials: LS
authors.lastname: Ferreira
authors.forename: Lisiane Soares
authors.initials: LS
authors.lastname: Ferreira
authors.forename: Carlos
authors.initials: C
authors.lastname: Francci
authors.forename: Ricardo Scarparo
authors.initials: RS
authors.lastname: Navarro
authors.forename: Fernanda Calabró
authors.initials: FC
authors.lastname: Calheiros
authors.forename: Carlos de Paula
authors.initials: Cde P
authors.lastname: Eduardo
mesh_terms: D000269:Adhesives; D000818:Animals; D002417:Cattle; D003188:Composite Resins; D003442:Crowns; D003799:Dental Stress Analysis; D003804:Dentin / Q000528:radiation effects*; D003806:Dentin Permeability / Q000528:radiation effects; D053844:Lasers, Solid-State; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D011897:Random Allocation; D019279:Resin Cements / Q000528:radiation effects; D013718:Tensile Strength / Q000528:radiation effects
chemical_list: D000269:Adhesives; C438313:Clearfil SE Bond; D003188:Composite Resins; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose