Avaliação da resistência à fadiga cíclica de limas rotatórias e reciprocantes

Abstract

Summary: The aim of this study was to evaluate in vitro, the cyclic fatigue resistance of three types of nickel-titanium rotary endodontic files (NiTi): ProtaperR, Wave OneR and ReciprocR. Method: The cyclic fatigue test was performed with ProtaperR F2, Wave OneR Primary and ReciprocR R25. Sixty instruments were used in two artificial canals with differents radius and arc lengths. The first canal was made with a radius of curvature of 6mm and arc length with 12,56 mm, the second measured radius of 9 mm and arc length with 9,42 mm. The files were tested according to manufacturers recommendations. ProtaperR F2 was used at a rate of 300 rpm continues rotate, while ReciprocR R25 300 rpm and Wave OneR Primary files 350 rpm reciprocation motions. The number of cycles to fracture was determined by measuring the time to fracture and the length of the broken fragments were recorded. A scanning electron microscope was used to characterize the topographic features of the fracture surfaces of broken files. Results: ReciprocR R25 was more resistant when tested in the canal measured 9,42 mm (p<0,001). No significant difference was found in NCF when compared the three files in canal 12,56 mm (P>0,05). ProtaperR F2 presented the same result when rotated in the simulated canals 1 and 2 (p>0,05). Statistical differences were observed in instrument separation files in the arc 9,42 mm (p<0,001), however the arc 12,56 mm demonstrated broken files with similar sizes (p>0,05). SEM analysis revealed no plastic deformation in the helical shaft of fractured instruments. Fracture surfaces exhibited characteristics of the ductile mode. Conclusion: Curvature geometry including the radius and arc lengths influence the number of cycles to fracture of rotary nickel-titanium instruments subjected to cyclic fatigue.