Mechanical properties of reciprocating thermally treated NiTi endodontic instruments / Propriedades mecânicas de instrumentos endodônticos de NiTi reciprocantes tratados termicamente

The aim of this study was to evaluate the flexibility, buckling resistance, dynamic cyclic fatigue resistance and roughness pattern of Reciproc R25 M-Wire (R25M), Reciproc Blue R25 (R25B) and WaveOne Gold Primary (WOGP) NiTi reciprocating instruments. Thirty-three R25M, 30 R25B e 30 WOGP, all with 25mm in length, were tested. The flexibility was determined by 45° bending tests according to the standard ANSI/ADA number 101 specification. To determine the buckling resistance an increasing axial load was applied to the instruments until the file underwent an elastic displacement of 1mm. A customized machine was used to perform the dynamic cyclic fatigue test measuring the time to fracture in a metallic stainless steel canal measuring 1.4 mm of diameter, 19 mm of total length, an angle of 86 degrees and 6 mm of curvature radius. The roughness was obtained using a profilometer. Results were analyzed using one-way ANOVA and Student-Newman-Keuls post-hoc test. Analysis were performed with the significance level (?) of 5%. The instruments presented the following order of flexibility: R25B > WOGP > R25M (P < 0.05); buckling resistance: R25M > R25B > WOGP (P < 0.05); and cyclic fatigue resistance: R25B > R25M > WOGP (P < 0.05). No differences were observed regarding the roughness pattern (P > 0.05). The R25B file presented superior flexibility and performance under fatigue tests. The R25M have higher buckling resistance. Instruments demonstrated similar characteristics of surface.