Methods: Thirty-three bovine permanent mandibular incisors were embedded in acrylic blocks, with the buccal surfaces exposed, and divided into 2 groups. In each group, a different type of bracket was bonded to the specimens: in group 1 (n=16), policarbonate brackets (Morelli® Monoblock Roth System® code 10.15.208); and, in group 2 (n=17), metallic ones (Morelli® Roth System code 10.10.208). A light-cured composite resin (Unitek® Transbond XT®) was used as bonding agent in both groups. Shear testing was carried out using a Universal Testing Machine Emic DL500, at a crosshead speed of 0,5 mm/min.
Results: The mean shear bond strengths were 3,68 MPa and 6,52 MPa for groups 1 and 2, respectively. Student's t-test analysis showed statistically significant difference between the 2 groups (p≤0,05). In relation to ARI assessment, after debonding, most of the specimens showed none or less than half of bonding material left on tooth surface.
Conclusion: Besides the observed mean values, this study reached these conclusions: the evaluated metallic brackets demonstrated higher shear bond strength than the evaluated policarbonate ones and, in both types of bracket, the bond failure occurred predominantly at the enamel-adhesive interface.