Effect of thermocycling on the shear bond strength of a cyanoacrylate orthodontic adhesive.

The purpose of this study was to evaluate the effects of thermocycling on the shear bond strength of a cyanoacrylate adhesive system, specifically 24 hours after bonding when the adhesive has achieved most of its bond strength and after thermocycling. Forty freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned, polished, and randomly separated into 2 groups: group I, cyanoacrylate adhesive debonded after 24 hours immersion in deionized water at 37 degrees C; and group II, cyanoacrylate adhesive debonded after thermocycling at 5 degrees C and 55 degrees C. The results of the t test comparing the 2 groups (t = 6.84) indicated significant differences between them (P =.0001). The cyanoacrylate adhesive at 24 hours had significantly greater shear bond strength (macro x = 7.1 +/- 3.3 MPa) than after thermocycling 500 times between 5 degrees C and 55 degrees C (macro x = 1.5 +/- 1.4 MPa). The findings indicated that the cyanoacrylate adhesive tested has clinically adequate shear bond strength at 24 hours after initial bonding but loses about 80% of its strength after thermocycling. The clinician should consider all properties of the adhesive, including no need for a curing light, working time of 5 seconds before the adhesive starts to set, and the significant decrease in bond strength after thermocycling.