Design, metallurgical features, mechanical performance and canal preparation of six reciprocating instruments J. N. R. Martins 1,2,3 , E. J. N. L. Silva 4,5 , D. Marques 2,3,6 , F. Belladonna 5 , M. Sim~ oes-Carvalho 5 , V. T. L. Vieira 4 , H. S. Antunes 4 , F. M. B. Braz Fernandes 7 & M. A. Versiani 8 1 Department of Endodontics, Faculdade de Medicina Dent aria, Universidade de Lisboa, Lisbon; 2 Unidade de Investigac ß~ ao em Ci^ encias Orais e Biom edicas (UICOB), Faculdade de Medicina Dent aria, Universidade de Lisboa, Lisbon; 3 Centro de Estudo de Medicina Dent aria Baseada na Evid^ encia (CEMDBE), Faculdade de Medicina Dent aria, Universidade de Lisboa, Lisbon, Portugal; 4 Department of Endodontics, School of Dentistry, Grande Rio University (UNIGRANRIO), Rio de Janeiro; 5 Department of Endodontics, Fluminense Federal University, Niteroi, Brazil; 6 LIBPhys-FCT UID/FIS/04559/2013, Lisboa; 7 CENIMAT/I3N, Department of Materials Science, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica, Portugal; and 8 Dental Specialty Center, Brazilian Military Police, Minas Gerais, Brazil Abstract Martins JNR, Silva EJNL, Marques D, Belladonna F, Sim~ oes-Carvalho M, Vieira VTL, Antunes HS, Fernandes FMB, Versiani MA. Design, metallurgical features, mechanical performance and canal preparation of six reciprocating instruments. International Endodontic Journal, 54, 1623–1637, 2021. Aim To compare six reciprocating instruments regard- ing their geometric design, metallurgical characteristics, mechanical behaviour and ability to prepare root canals. Methodology A total of 246 new 25-mm NiTi instruments (41 per group) from six reciprocating sys- tems (Reciproc, Reciproc Blue, One Files, One Files Blue, Reverso Silver, and WaveOne Gold) were evaluated throughout a multimethod approach regarding their design using stereomicroscopy (number of blades and helix angle) and scanning electron microscopy (blades symmetry, cross section and surface finishing), nickel-ti- tanium composition, phase transformation temperatures, mechanical performance (cyclic fatigue, torsional and bending resistance) and unprepared canal surface area on anatomically matched mandibular molars assessed by micro-CT. One-way ANOVA and post hoc Tukey’s or Mood’s median tests were selected depending on sample distribution with significance level set at 5%. Results The instruments had similarities regarding their metal composition and unprepared canal area, whilst differences in phase transformation tempera- tures and geometric design (number of blades, surface finishing and tip geometry) were observed. Overall, no difference was observed regarding the maximum tor- que values (P > 0.05), whilst One Files (72 s) and One Files Blue (414 s) had the shortest and longest times to fracture, respectively (P < 0.05). Similar angles of rotation were observed in Reciproc (310°), One Files (285°) and Reverso Silver (318°) instru- ments (P > 0.05), which were significantly lower than Reciproc Blue (492°), One Files Blue (456°) and WaveOne Gold (492°; P < 0.05). Maximum bending load demonstrated that Reciproc Blue (201.3 gf) was significantly more flexible that the other instruments (P < 0.05). Conclusion Although there were similarities in metal composition and percentage of unprepared canal surface, the instruments had differences in the overall geometric design, phase transformation tem- peratures and in the four mechanical resistance parameters (time to fracture, maximum torque, angle of rotation and maximum bending load). Keywords: bending load, cyclic fatigue, differential scanning calorimetry, micro-CT, reciprocation, tor- sional strength. Received 18 December 2020; accepted 5 April 2021 Correspondence: Jorge N. R. Martins, Faculdade de Medicina Dent aria da Universidade de Lisboa, Cidade Universit aria, 1649- 003 Lisboa, Portugal (Tel: +351 96 52 64 0 63; e-mail: jnr_martins@yahoo.com.br). International Endodontic Journal, 54, 1623–1637, 2021 © 2021 International Endodontic Journal. Published by John Wiley & Sons Ltd doi:10.1111/iej.13529 1623