The effects of mechanical and thermal fatigue on the shear bond strength of orthodontic adhesives

Shin, Wan Cheal; Kim, Jong Sung; Kim, Jong Ghee

Abstract

The purpose of this study was to examine the effects of mechanical and thermal fatigue on the shear bond strength(SBS) of stainless steel mesh brackets bonded to human premolar teeth with 3 no-mix adhesives. The stainless steel mesh bracket was Ormesh(Ormco, .022 slot) and three types of no-mix adhesives were Ortho-one(Bisco), Monolok2(RMO), System 1+(Ormco). The 10(6) loadcycles of 17.4x10(2)sin2piftlg . cm and the 1,000 thermocycles of 15 second dwell time in each bath of 5degrees C and 55degrees C were acturated as mechanical and thermal fatigue stress, and SBS were measured after each fatigue test. The fracture sites were analyzed by stereoscope and scanning electron microscope. The results obtained were summarized as follows; 1. Before thermocycles, Monolok2 showed the highest Knoop hardness number(KHN, 64.03kg/mm2) and System 1+ showed the lowest value(31.60kg/mm2). After thermocycling, Monolok2 also showed the highest KHN(38.03kg/mm2) and system 1+ showed the minimum(20.87kg/mm2). The KHN of Ortho-one, Monolok2, System 1+ significantly decreased after thermocycling(P<0.01).