Methods:Sixty extracted mandibular central incisors (40–60 y) were selected and divided into 3 experimental groups (n = 15 teeth) and a control group (unprepared teeth, n=15); Control, Reciproc (group 1) Wave One (group 2), and Wave One Gold (group 3). 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). Wave One Gold (53.3%) showed fewer microcracks than other experimental groups (P<.01). There was no significant difference among Reciproc and Wave One 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. Wave One Gold caused less microcracks than the other instruments tested.