Shear bond strength of composite to Sodium Ascorbate applied on bleached enamel

Bleaching technique is known to be an effective method for elimination of tooth discoloration but residual Oxygen after bleaching inhibits polymerization of resin based materials. The aim of this study was to evaluate the shear bond strength of composite to Sodium Ascorbate applied on bleached enamel. Methods & Materials: The study was carried out experimentally. Materials used were: Composite Z100 (3M), Single Bond (3M), Carbamide Peroxide 35% (Opalescence), Sodium Ascorbate 10%. The flattened labial surface of 75 maxillary premolars were subjected to 5 different treatments as follows:(1): No treatment, (2): Bleaching for 30 minutes, (3), (4), (5): Immersion in Sodium Ascorbate for 2, 10, 30 minutes, respectively, after bleaching. After bonding procedure, specimens were subjected to shear bond test after 24 hours. Data were analyzed by ANOVA and LSD post hoc tests. Shear bond strength of composite on enamel bleached with Carbamide Peroxide 35% was reduced significantly while it was increased by using Sodium Ascorbate 10% after bleaching with Carbamide Peroxide 35% although this increase was less than that occurred in control group (bonding to enamel without bleaching with Sodium Ascorbate 35%). Shear bond strength values in different groups were: (1) 29.06± 3.99, (2) 14.41± 3.31, (3) 24.46± 4.51, (4) 25.81±3.97, (5) 23.19± 4.27. ANOVA revealed no significant difference in shear bond strength when different times used to apply Sodium Ascorbate 35%. Stereomicroscopic evaluations showed most fractures in group 1 to be enamel cohesive, group 2, adhesive between tooth and composite, and other three groups to show all three fracture types (adhesive, enamel cohesive, composite cohesive). Although bonding to bleached enamel was improved by Sodium Ascorbate but duration of application had no significant effect on the shear bond strength of composite to bleached enamel.