The influence of cyclic shear fatigue on the bracket–adhesive–enamel complex: An in vitro study

Objectives cribe the effect of fatigue on the strength of the bracket–adhesive–enamel complex and characterize the fatigue behavior of the materials tested. s central incisor brackets (Discovery®, Dentaurum) were bonded with a light-curing (Transbond XT™, 3M Unitek) and a chemically-curing adhesive (Concise™, 3M Unitek) on bovine teeth embedded in cylindrical resign bases and stored in water at 37(±2) °C for 24 (±2) h. The first 15 specimens were tested with a universal testing machine ZMART.PRO® (Zwick GmbH & Co. KG, Ulm, Germany) for ultimate shear bond strength according to the DIN-13990-2-standard. The remaining three groups of 20 specimens underwent fatigue staircase testing of 100, 1000 and 3000 cycles at 1 Hz with a self-made testing machine. The survived specimens were subjected to shear strength testing. s tigued specimens showed decreased shear strength with both adhesives at all cycle levels. The shear strength after fatigue for 100, 1000 and 3000 cycles was in the Concise™-groups 34.8%, 59.0%, 47.3% and in the Transbond™ XT-groups 33.6%, 23.1%, 27.3% relative to the ultimate shear strength. The fatigue life of the Concise™-groups decreased with increasing stress and Transbond™ XT showed lower fatigue ratio with no obvious trend. The specimens bonded with Transbond™ XT showed typically favorable fracture modes in contrary to Concise™. icance e of the bracket–adhesive–enamel complex decreased its shear strength. The staircase method can provide a standardized experimental protocol for fatigue studies, however testing at various cycle numbers is recommended.