An in vitro study of the bond strength of two light-cured composites used in the direct bonding of orthodontic brackets to molars.

This study examines methods of improving the bond strengths of the light-activated composites, Heliosit-orthodontic, and Transbond. Begg brackets were bonded onto each of the four surfaces of 50 molar teeth that had been previously extracted. The bonding systems used were Right-on (R), Heliosit-orthodontic (H), Heliosit with a precured composite resin on the mesh (HPC), Heliosit with a precured intermediate bonding resin on the mesh (HPR), Transbond (T), and Transbond with a precured layer of resin on the mesh (TPC). The shear bond strengths were tested on a M5K tensile tester, crosshead speed 0.5 mm/min. After bracket removal, the enamel surface of the bonding site was examined and assessed with the adhesive remnant index (ARI). The shear bond strength in mean mPa +/- 1 SD was found to be significantly greater for HPC, HPR, and TPC than for H (P < 0.001). The ARI scores suggest that bond failure is associated more with the micromechanical bond with enamel for HPC and HPR. The results indicate that the chemical properties of the two light-activated adhesives were improved by precuring on the mesh base of the bracket before bonding.