LAUSR

Introduction: The purpose of this study was to compare the formation of microcracks after canal preparation performed with different single‐file systems as One Shape (Micro‐Mega, Besancon, Cedex, France), F6 SkyTaper (Komet Italia Srl, Milan, Italy), HyFlex EDM (Coltene/Whaledent AG, Altstatten, Switzerland), WaveOne (Dentsply Maillefer, Ballaigues, Switzerland), Reciproc (VDW, Munich, Germany), and WaveOne Gold (Dentsply Maillefer). Methods: Eighty‐four human extracted mandibular central incisors (40–60 y) were selected and divided into 6 experimental groups (n = 12 teeth) and a control group (unprepared teeth): One Shape (group 1), F6 SkyTaper (group 2), HyFlex EDM (group 3), WaveOne (group 4), Reciproc (group 5), and WaveOne Gold (group 6). Roots were then sectioned at 3, 6, and 9 mm from the apex, and the surface was observed under a stereomicroscope. Data were analyzed using logistic regression (P < .05). Results: No cracks were observed in the control group. All the systems tested caused cracks, mainly in the apical section (3 mm). HyFlex EDM (33.3%) and WaveOne Gold (58.3%) showed fewer microcracks than other experimental groups (P < .01); however, no significant difference was found between them in crack formation (P > .05). There was no difference among the other experimental groups (P > .05). Conclusions: All the instruments tested created dentinal cracks. Within the limitations of this study, the flexibility of nickel‐titanium instruments because of heat treatment seems to have a significant influence on dentinal crack formation. HyFlex EDM and WaveOne Gold caused less microcracks than the other instruments tested. HighlightsThe effects of 6 single‐file systems on crack formation were evaluated.HyFlex EDM and WaveOne Gold produced less microcracks than other files.There was no difference among One Shape, F6 SkyTaper, Wave One, and Reciproc files.The apical section showed the major number of cracks for all instruments.The flexibility of nickel‐titanium alloy seems to have a great influence on crack formation.