title: Microleakage and shear bond strength of orthodontc brackets bonded to hypomineralized enamel following different surface preparations.
abstract: OBJECTIVE
  This study investigated the effects of several conditioning methods on shear bond strength (SBS) and microleakage of orthodontic brackets bonded to demineralized enamel.
  
  
  METHODS
  One hundred premolars were selected and immersed in a cariogenic solution for 12 weeks. The teeth were randomly assigned into 5 groups. In groups 1 and 2, the teeth underwent acid etching for 30 and 120 seconds, respectively. In group 3, a combination of laser and acid etching was employed. A self-etch primer (SEP) was applied in group 4 and in group 5, the teeth were exposed to acidulated phosphate fluoride (APF) for 4 minutes before etching. After bracket bonding, the teeth were immersed in methylen blue for 12 hours and then were mounted in acrylic resin. SBS was determined with an Instron Universal Testing Machine and the amount of microleakage under the brackets was assessed under a stereomicroscope.
  
  
  RESULTS
  The lowest SBS was related to the SEP group and the highest one was observed in the specimens prepared by APF+acid etching. There was a significant difference in SBS (p=0.009), but not in microleakage (p=0.971) of the study groups. The SBS of the specimens treated with SEP was significantly Lower than the other groups, which were not significantly different from each other. The SEP group displayed a higher frequency of bond failure at the enamel-adhesive interface.
  
  
  CONCLUSIONS
  Enamel preparation with SEP provided the lowest SBS among the groups. All groups showed some degree of microleakage. There was no significant correlation between SBS and microleakage. Key words:Bond strength, microleakage, bonding, self-etch primer, Er:YAG laser.
authors.affiliation: DDS, MS, Associate Professor of Orthodontics. Dental Research Center, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Mostafa
authors.initials: M
authors.lastname: Shahabi
authors.affiliation: DDS, MS, Assistant Professor of Orthodontics. Dental Research Center, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Ahrari
authors.affiliation: DDS MS, Assistant Professor. Department of Operative Dentistry, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Hamideh
authors.initials: H
authors.lastname: Mohamadipour
authors.affiliation: DDS MS, Assistant Professor of Operative Dentistry. Dental Material Research Center, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Horieh
authors.initials: H
authors.lastname: Moosavi