Effect of sodium ascorbate on the shear bond strength of orthodontic brackets to bleached enamel using universal dental adhesive

BACKGROUND: The aim of this study was to investigate the effect of bleaching agent, sodium ascorbate as an antioxidant, and delay time on the shear bond strength (SBS) of orthodontic brackets to enamel using Transbond XT and universal adhesive. MATERIALS AND METHODS: In this in vitro experimental study, 80 extracted maxillary premolars without any defect or decay were randomly divided into eight groups of 1: no bleaching + Transbond XT (NB/TX) bonding agent, 2: no bleaching + All-Bond Universal (NB/AB), 3: bleaching + Transbond XT (B/TX), 4: bleaching + All-Bond Universal (B/AB), 5: bleaching + sodium ascorbate + Transbond XT (B/SA/TX), 6: bleaching + sodium ascorbate + All-Bond Universal (B/SA/AB), 7: bleaching + Transbond XT after a 3-week delay (B/3W/TX), and 8: bleaching + All-Bond Universal after a 3-week delay (B/3W/AB). After thermocycling (1000 cycles, 5–55°C), the SBS was measured, and the adhesive remnant index scores were determined to assess the failure mode. Data were analyzed by one-way analysis of variance, Tamhane's post hoc test, Kruskal–Wallis, and Mann–Whitney U-test at the significance level of P < 0.05. RESULTS: The mean SBS range was 5.5–29.78 MPa. The highest SBS values were related to Group 2 (NB/AB) which were significantly higher than all groups (P < 0.05) and the lowest values were observed in Group 5 (B/SA/TX) which were significantly lower than all groups except Group 3 (B/TX) (P < 0.05). CONCLUSION: Bleaching with 40% hydrogen peroxide significantly decreased the SBS of orthodontic brackets, and 10% sodium ascorbate could not reverse the adverse effect of bleaching on SBS. Delaying the bonding procedure by 3 weeks using Universal adhesive considerably decreased the adverse effect of bleaching on SBS and increased the SBS to a clinically acceptable level for orthodontic treatment.