In vitro shearing force testing of the Australian zirconia-based ceramic Begg bracket

The purpose of this study was to investigate the condition of bond failure of the Australian zirconia-based ceramic Begg bracket (Elipse bracket) in comparison with that of a small-base metal Begg bracket (Solitaire bracket) under various environmental conditions. Shear tests were performed and sites of bond failure were also recorded. The results showed that (1) mean shear force of the bonded Elipse ceramic bracket is significantly higher than the metal one (2) shearing force at failure in both ceramic and metal groups, is considered clinically acceptable, (3) thermocycling (1000 cycles) had no significant additional effect on shearing force with both groups, (4) failure sites of the bonding were more likely to be at enamel/resin interfaces, and (5) there was no instance of fracture of the ceramic bracket and the enamel. A particular distinction is noted concerning the test results that measured shearing force rather than shear strength. It is questioned whether some published reports referring to "shear strength" have adequately accounted for bond surface area estimation necessary for proper calculation of strength values.