Methods: Computed tomography (CT) scans of the ML canals of 60 mandibular first molars were provided from areas within 1, 2, 3, and 4 mm of the furcation area and minimum initial root thickness (MIRT) of concave areas was measured at each level. The samples were divided into two groups (G1 and G2) which were prepared by the step-back and crown-down techniques, respectively. In both groups, anti-curvature filing was used. On secondary CT images of the samples in the same position, the minimum residual root thickness (MRRT) and the amount of removed dentin were analyzed by t-test and ANOVA.
Results: There was no significant difference for MIRT between the two groups. The MRRT was greater in the G2 group in all the sections, with no significant difference between them. The average of MRRT was not less than 0.5 mm in any of the groups or sections.
Conclusions: Based on the results of this study when the root thickness is appropriate at first, GG drills used in any sequence may be suitable, safe, and cost effective for pre-flaring of mesial canals of mandibular first molars with preserving the root thickness of furcation areas.