Effect of time on the shear bond strength of cyanoacrylate and composite orthodontic adhesives.

The purpose of this study was to compare the effects of time on the shear bond strength of a cyanoacrylate system and a composite adhesive system (1) within half an hour after bonding the bracket to the tooth, and (2) after 24 hours from the time of bonding when the adhesive had achieved most of its bond strength. Eighty freshly extracted molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleansed, polished, and randomly separated into 4 groups: (I), cyanoacrylate adhesive debonded within one-half hour from initial bonding; (II), cyanoacrylate adhesive debonded after 24 hours immersion in deionized water at 37 degrees C; (III), composite adhesive debonded within one-half hour from initial bonding; (IV), composite adhesive debonded after 24 hours immersion in deionized water at 37 degrees C. The results of the analysis of variance comparing the 4 experimental groups (F = 12.68) indicated significant differences between them (P =.0001). The composite adhesive at 24 hours had significantly greater shear bond strength than did the other 3 groups. In general, the shear bond strengths were greater in the 2 groups debonded after 24 hours. This was true for both the cyanoacrylate ((-)x 7.1 +/- 3.3 megaPascals [MPa]) and the composite ((-)x 10.4 +/- 2.8 MPa) adhesives. On the other hand, the shear bond strength was significantly lower in the 2 groups debonded within one-half hour of their initial bonding. The bond strength of the cyanoacrylate adhesive ((-)x 5.8 +/- 2.4 MPa) was not significantly different from that of the composite ((-)x 5.2 +/- 2.9 MPa) adhesive. Our findings indicated that the cyanoacrylate and the composite adhesives tested have clinically adequate shear bond strengths at half an hour and at 24 hours after initial bonding. The clinician needs to consider the properties of each adhesive: eg, the need to use a curing light and the ability to have more working time with the composite adhesive versus no light but only a 5-second working time before the cyanoacrylate adhesive starts to set.