PHOTOELASTIC COMPARISON OF STRESS-INDUCED BY USING STAINLESS-STEEL VERSUS NICKEL-TITANIUM SPREADERS IN-VITRO

The vertical force applied to an endodontic spreader generates stress along the canal walls. Recognizing the potential for this stress may r educe the incidence of vertical root fractures. A photoelastic acrylic model was fabricated to exhibit the stress produced during obturation of curved canals using the lateral condensation technique. Twenty sta ndardized models simulating curved canals (32 degrees) were formed wit hin PL-2 photoelastic acrylic resin blocks. The canals were fitted wit h a gutta-percha point, and either a stainless-steel or nickel-titaniu m finger spreader was inserted. An Instron 4502 universal testing mach ine applied a vertical force of 20 Newtons to the spreader. Quarter wa ve and polarizing filters were used with backlighting to generate the fringe patterns in the models. Photographs of the resulting stress lin es showed that the stainless-steel spreaders created three areas of co ncentrated stress. The nickel-titanium spreaders induced stress patter ns spread out along the surface of the canals, thus reducing the conce ntration of stress and the potential for vertical root fracture.