The effect of thiourea on shear bond strengths of composite to bleached enamel

Background: Reduced composite-tooth bond strength after bleaching inhibits immediate tooth restoration. Objective: To determine the effect of thiourea as a free radical scavenger on shear bond strength of composite to bleached enamel. Methods: Enamel surfaces of 96 sound human premolars were randomly assigned to six experimental groups (n=12) which were bleached with %15 CP, and two control groups 1, 2 (n=12) bonded without bleaching. The specimens in groups 3 and 4 (n=24) were bonded 24 hours after bleaching. Groups 5 and 6 (n=24) were bleached with a mixture of %15 CP and thiourea followed by bonding. Groups 7 and 8 (n=24) were bleached, immersed in water and left for 1 week. In odd groups, single bond and in even groups Excite were used. Composite Cylinders were bonded and the shear bond strengths were determined 24 hours later. Data were subjected to one-way ANOVA and Tukey HSD at a significant levels of p<0.05. Findings: There was no statistically significant difference between diverse groups. Mean bond strength was lowest in groups 3 and 4 and highest mainly in group 8 and with a little decrease in group 5. Conclusion: Bleaching with 15% carbamid peroxide caused insignificant reduction in composite-enamel bond strengths in bonding either after 24 hours or one week following the application of 2 types of bonding agents. Application of thiourea in combination with bleaching agents may be useful for immediate composite restorations.