title: Shear bond strength of resin composite bonded with two adhesives: Influence of Er: YAG laser irradiation distance.
abstract: BACKGROUND
  Dental surfaces prepared with different Er:YAG laser distance may have different characteristics compared with those prepared with conventional instruments. The aim of this study was to investigate the effect of Er:YAG laser irradiation distance from enamel and dentin surfaces on the shear bond strength of composite with self-etch and etch and rinse bonding systems compared with conventional preparation method.
  
  
  METHODS
  Two hundred caries-free human third molars were randomly divided into twenty groups (n = 10). Ten groups were designated for enamel surface (E1-E10) and ten for dentin surface (D1-D10). Er: YAG laser (2940 nm) was used on the E1-E8 (240 mJ, 25 Hz) and D1-D8 (140 mJ, 30 Hz) groups at four different distances of 0.5 (standard), 2, 4 and 11 mm. Control groups (E9, E10, D9 and D10) were ground with medium grit diamond bur. The enamel and dentin specimens were divided into two subgroups that were bonded with either Single Bond or Clearfil SE Bond. Resin composite (Z100) was dispensed on prepared dentin and enamel. The shear bond strengths were tested using a universal testing machine. Data were analyzed by SPSS12 statistical software using three way analysis of variance, Tukey and independent t-test. P < 0.05 was considered as significant.
  
  
  RESULTS
  There was a significant difference between enamel and dentin substrates (P < 0.001) and between lased and un-lased groups; the un-lased group had significantly higher bond strength (P < 0.001). Shear bond strength increased significantly with an increase in the laser irradiation distance (P < 0.05) on enamel surfaces (in both bonding agent subgroups) and on dentin surfaces (in the Single Bond subgroup).
  
  
  CONCLUSIONS
  Laser irradiation decreases shear bond strength. Irradiation distance affects shear bond strength and increasing the distance would decrease the negative effects of laser irradiation.
authors.affiliation: Dental Materials Research Center and Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Shirani
authors.affiliation: Torabinejad Dental Research Center and Department of Periodontics, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Birang
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Isfahan (Khorasgan Branch), Islamic Azad University, Isfahan, Iran.
authors.forename: Mohammad Reza
authors.initials: MR
authors.lastname: Malekipour
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Isfahan (Khorasgan Branch), Islamic Azad University, Isfahan, Iran.
authors.forename: Zahra
authors.initials: Z
authors.lastname: Hourmehr
authors.affiliation: Department of Health Policy and Administration, School of Public Health, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Shantia
authors.initials: S
authors.lastname: Kazemi
keywords: Dentin; Er: YAG laser; enamel; irradiation distance; resin composite; shear bond strength