effect of ascorbic acid on shear bond strength of orthodontic brackets bonded with resin-modified glass-ionomer cement to bleached teeth

background and aims. 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. materials and 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 magnification. data were analyzed using mann-whitney u test, one- and independent-samples t-test, and fisher’s exact 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 difference 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. conclusion. 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 deserves further studies.