An experimental study on the fatigue characteristics of orthodontic brackets bonded to enamel

Choi, Hae Woon; Kim, Jeong Gee

Abstract

The purpose of this study is to evaluate the effects of mechanical and thermal fatigue on the shear bond strength(SBS) in orthodontic brackets bonded to human premolars with chemically cured adhesive(Mono-Lok(2), Rocky Mountain Orthodontics). Two types of metal brackets (Ormesh, Microloc) and three types of ceramic brackets (Fascination, Starfire, Transcend 2000) were used in this study. The 10(6) loadcycles of l7.4 x 10(2)sin2piftl g,cm and the 1,000 thermocycles of 15 second dwell time each In 5degrees C and 55degrees C baths were acturated as mechanical and thermal fatigue stress, and SBS were measured after each fatigue test. The fracture sites were examined by stereoscope and scanning electron microscope. The results obtained were summarized as follows ; 1. In static shear bond test, Fascination brackets showed the maximum SBS(20.78+/-3.45 MPa) and Microloc brackets showed the minimum SBS(14.88+/-3.10 MPa). Fascination and Starfire brackets showed significantly greater SBS than Microloc brackets(P<0.05). 2. In mechanical fatigue test, Fascination brackets showed the maximum SBS (20.19+/-3.45 MPa) and Starfire brackets showed the minimum SBS(9.10+/-8.33 MPa). The SBS of Transcend 2000 brackets(P<0.01) and Starfire brackets(P<0.05) significantly decreased after 106 loadcycles. 3. In thermocycling test, Ormesh brackets showed the maximum SBS (19.36+/-2.76 MPa) and Starfire brackets showed the minimum SBS(l1.94+/-6.86 MPa). The SBS of Transcend 2000(P<0.01), Microloc and Starfire brackets(P<0.05) significantly decreased after 10(3) thermocycles. 4. Failure sites of thermocycling groups were similar to those of static groups but after mechanical fatigue test, Ormesh and Transcend 2000 brackets failed at the bracket/resin interface and Microloc brackets failed within adhesive. Facination brackets failed at the enamel/resin interface irrespective of experimental condition.