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Published on: December 20, 2024
The influence of cyclic shear fatigue on the bracket-adhesive-enamel complex: an in vitro study
Nikolaos Daratsianos1, Ena Musabegovic, Susanne Reimann
1Department of Orthodontics, University of Bonn, Germany. nikolaos.daratsianos@uni-bonn.de
Objectives:
To describe the effect of fatigue on the strength of the bracket-adhesive-enamel complex and characterize the fatigue behavior of the materials tested.
Methods:
Upper 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 1Hz with a self-made testing machine. The survived specimens were subjected to shear strength testing.
Results:
The fatigued 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™.
Significance:
Fatigue 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.
