The Effects of Mechanical Cyclic Loading on the Bond Strength of Orthodontic Brackets

Abstract

During treatment, orthodontic brackets are exposed to repeated loads that are below their ultimate bond strengths (UBS) and therefore do not cause bond failure. However, these loads may cause fatigue damage and thus decrease the UBS. The objective of this study was to accelerate fatigue damage and to determine its effect on UBS. Ormco's Ormesh ™ central incisor brackets were bonded to bovine teeth with Ormco's System 1 + TM adhesive. Each test group contained 17-20 specimens. An unfatigued group was used to determine the control shear-peel UBS (216N). The four experimental groups were defined by the applied shear-peel load (30% or 50% of UBS) and the number of sinusoidally applied load cycles (10,000 or 20,000). Group L1C1 was loaded at 30% of UBS for 10,000 cycles, L2C1 at 50% of UBS for 10,000 cycles, L1C2 at 30% of UBS for 20,000 cycles, and L2C2 at 50% of UBS for 20,000 cycles. The results suggest that there was no significant amount of fatigue damage occurring at the tested loads and cycles.