title: Effect of bracket bonding with Er: YAG laser on nanomechanical properties of enamel.
abstract: BACKGROUND
  The aim of this study was to compare the effects of conventional acid etching and laser etching on the nano-mechanical properties of the dental enamel using nano-indentation test.
  
  
  METHODS
  In this experimental in vitro study, buccal surfaces of 10 premolars were divided into three regions. One of the regions was etched with 37% phosphoric acid and another etched with Er:YAG laser, the third region was not etched. The brackets were bonded to both of etched regions. After thermocycling for 500 cycles, the brackets were removed and the teeth were decoronated from the bracket bonding area. Seven nano-indentations were applied at 1-31 μm depth from the enamel surface in each region. Mean values of the hardness and elastic modulus were analyzed with repeated measures analysis of variance and Tukey HSD tests, using the SPSS software (SPSS Inc., version16.0, Chicago, Il, USA). P < 0.05 was considered as significant.
  
  
  RESULTS
  The hardness up to 21 μm in depth and elastic modulus up to 6 μm in depth from the enamel surface for laser-etched enamel had significantly higher values than control enamel and the hardness up to 11 μm in depth and elastic modulus up to 6 μm in depth for acid-etched enamel had significantly lower values than the control enamel.
  
  
  CONCLUSIONS
  The mechanical properties of the enamel were decreased after bracket bonding with conventional acid etching and increased after bonding with Er:YAG laser.
authors.affiliation: Dental Materials Research Center and Department of Orthodontics, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
authors.forename: Shiva
authors.initials: S
authors.lastname: Alavi
authors.affiliation: Department of Periodontics, Dental Implants Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Birang
authors.affiliation: Department of Orthodontics, School of Dentistry, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Hajizadeh
authors.affiliation: Department of Orthodontics, School of Dentistry, Arak University of Medical Sciences, Arak, Iran.
authors.forename: Hamed
authors.initials: H
authors.lastname: Banimostafaee
keywords: Elastic modulus; Er:YAG laser; enamel; hardness; nano-indentation test; orthodontic bracket