Background: the bond strength of bracket to the tooth substrate is a critical matter. The different surface treatments are introduced to achieve an appropriate bond strength. We aimed to investigate the shear bond strength(SBS) of metal brackets to amalgam surfaces with universal adhesive and compared the results with the enamel group.

Material and methods: in this in-vitro study, eighty specimens of amalgam in four groups and sixty specimens of the enamel in three groups were prepared. In amalgam groups, the control group was sandblasted and treated with transbond Xt whilst the other three groups prepared in the following order, group 2 sandblasted and treated with All Bond Universal(ABU), group 3 using diamond bur and ABU, and group 4 using self-etch mode of ABU. In enamel groups, control group was acid-etched and using transbond XT as a primer; in other two groups, the ABU was used as a primer in etched and self-etched mode. The specimens thermocycled and prepared for the SBS test. SEM analysis and ARI index were performed. pvalue≤ was considered significantly.

Results: SBS of enamel was significantly higher than amalgam. Within enamel groups, etched with ABU showed the highest SBS. In amalgam group, the highest SBS was related to surface treated with ABU only, and the lowest SBS was related to diamond bur group.

Conclusion: The etched surface of enamel showed the appropriate bond strength to bracket, and in the amalgam group, using mechanical preparation can decrease the oxide layer and compromise amalgam SBS.

Keywords: Dental amalgam, Enamel, shear strength, Adhesive