Background: Bleaching can considerably reduce shear bond strength (SBS) of orthodontic brackets. It is shown that application of antioxidants might reverse the negative effect of bleaching when using composite adhesives. However, no previous studies have assessed this, when resin-modified glass ionomer cement (RMGIC) is used as the bonding agent. The aim of this study was to evaluate this issue.
Methods: 50 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 specimens were etched with 37% phosphoric acid (Ivoclar/Vivadent) and were bonded using RMGIC (Fuji Ortho LC, GC) and were subjected to incubation (37°c, 24h) and thermocycling (1000 cycles, 5-55°c, dwell time = 1 min), respectively. The SBS was measured at 0.5 mm/min debonding speed. The adhesive remnant index (ARI) was scored under 10x magnification. The data were analyzed using Mann-Whitney U, one- and independent-samples t, and Fisher exact tests (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 = 6 MPa, according to one-sample t test.
Conclusion: The 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 this deserves further studies.

 Source: Journal of Dental Research, Dental Clinics, Dental Prospects

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