Objectives: The purpose of the study was to assess the shear bond strength of three different adhesive resins with reference to the base design of three different maxillary molar stainless steel brackets. Three different well known makes of stainless steel orthodontic molar brackets were bonded to human enamel specimens using three different adhesive resins. The bondable brackets used were Victory series (3M Unitek), Upper Molar (GAC) and Optimesh XRT (Ormco). The adhesives used were Transbond XT (3M Unitek), Enlight (Ormco) and Sure Ortho Light Bond (Sure Orthodontics). Methods: The enamel specimens (144) were randomly divided into nine groups and each group (n=16) was allocated to a bracket/adhesive combination. The brackets were bonded to the enamel according to the instructions of each adhesive resin manufacturer. The bonded specimens were temperature cycled and the shear bond strength measured. Results: The shear bond strengths of all three Ormco bracket/adhesive resin combinations (5.8-6.8 MPa) were significantly lower (p<0.05; Kruskal-Wallis) than the other six bracket adhesive combinations (9.4-12.1 MPa). The contact surface area of the Ormco brackets was significantly smaller (p<0.05) than that of both the 3M and GAC brackets. The Ormco bracket surface displayed a single mesh layer with smaller mesh apertures than that of the 3M and GAC brackets. The 3M bracket also displayed a single mesh design but with the mesh criss-crossing the base diagonally from corner to corner. The GAC bracket displayed a double mesh structure on the bracket surface. Conclusion: The base size, surface treatment, mesh strand diameter and aperture size of the bracket base mesh have a significant effect on the shear bond strength at the bracket/adhesive interface. |