title: Effect of Ascorbic Acid on Shear Bond Strength of Orthodontic Brackets Bonded with Resin-modified Glass-ionomer Cement to Bleached Teeth.
abstract: OBJECTIVE
  Bleaching can considerably reduce shear bond strength (SBS) of orthodontic brackets bonded with composite adhesives. Application of antioxidants is a method to reverse the negative effect of bleaching on composite-to-enamel bond. However, the efficacy of antioxidants in increasing the SBS of brackets bonded using resin-modified glass-ionomer cement (RMGIC) has not been studied, which was the aim of this study.
  
  
  METHODS
  Fifty freshly extracted human maxillary first premolars were bleached with 35% hydrogen peroxide (Pola Office Bleaching, SDI). Sodium ascorbate 10% was applied to the experimental specimens (n=25). All the specimens were etched with 37% phosphoric acid (Ivoclar/Vivadent) and bonded using RMGIC (Fuji Ortho LC, GC). The specimens were subjected to incubation (37°C, 24h) and thermocycling (1000 cycles, 5-55°C, dwell time = 1 min). The SBS was measured at 0.5 mm/min debonding crosshead speed. The adhesive remnant index (ARI) was scored under ×10 magni-fication. Data were analyzed using Mann-Whitney U test, one- and independent-samples t-test, and Fisher'sexact test (α=0.05).
  
  
  RESULTS
  The mean SBS of experimental and control groups were 11.97 ± 4.49 and 7.7 ± 3.19 MPa, respectively. The dif-ference was statistically significant (P=0.000 by t-test). SBS of both control (P=0.014) and experimental (P=0.000) groups were significantly higher than the minimum acceptable SBS of 6 MPa, according to one-sample t-test.
  
  
  CONCLUSIONS
  Application of ascorbic acid can guarantee a strong bond when RMGIC is to be used. However, RMGIC might tolerate the negative effect of bleaching with minimum SA treatments (or perhaps without treatments), which de-serves further studies.
authors.affiliation: Associate Professor, Department of Orthodontics, Dental Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Behnam
authors.initials: B
authors.lastname: Khosravanifard
authors.forename: Vahid
authors.initials: V
authors.lastname: Rakhshan
authors.forename: Solmaz
authors.initials: S
authors.lastname: Araghi
authors.forename: Hadi
authors.initials: H
authors.lastname: Parhiz