Effect of Bleaching on Bond-Strength of a Resin to Tooth

Objectives: To investigate the effect of antioxidant treatment and delayed bonding after bleaching with carbamide peroxide (CP) on the shear bond strength (SBS) of composite resin to enamel and dentin. Methods: Forty flat enamel and 40 flat dentin surfaces were prepared from freshly extracted human molars using a low speed diamond saw (Isomet, Buehler). Then, each group was divided into three bleaching subgroups (n=10/subgroup) and a control group (n=10) Bleaching process was performed with 16% carbamide peroxide (Vivastyle,IvoclarVivadent). Group 1(Enamel-E1,Dentin-D1) consisted of specimens bonded immediately after bleaching. Group 2 (E2,D2) specimens were treated with an antioxidant agent, 10% sodium ascorbate, while Group 3 (E3,D3) specimens were immersed in artificial saliva for 1 week after bleaching. Specimens in the control group (E0,D0) were not bleached, but immersed in artificial saliva for 1 week before bonding. Eighty ceramic blocks (Empress2,Ivoclar) were prepared and luted to teeth using a dual-curing resin cement (Variolink II, Ivoclar) under a constant load of 600 g for 5 min. The specimens were thermocycled and the SBS tests were performed using a universal testing machine (Autograph, Shimadzu, crosshead speed: 0.5 mm/min). Fracture analysis of the bonded enamel and dentin surfaces were done using a SEM (Jeol JSM 5200,Kyoto). The SBS data were statistically analyzed (ANOVA, Duncan's Multiple Range Test, alpha=0.05). Results: SBS values (Mean±SD) (MPa) were as follows:

Substrate Control Group 1 Group 2 Group 3

Enamel(E) 38,8±4 36,6±14 41,7 ±1 37,5±8

Dentin(D) 22,1±2 11,9±3 26,3±7 20,7±6

There were no significant differences among E0, E1, E2 and E3 (P > 0.05). The SBS values of D1 were significantly lower than other dentin groups. No significant differences among D0, D2 and D3 were observed. Conclusion: Bleaching with CP immediately before bonding reduced the SBS of the composite resin to dentin.