Aim

To evaluate the shaping ability of several heat-treated nickel-titanium systems used to prepare root canals with moderate and severe curvature, in extracted mandibular molars, by micro–computed tomography, considering their variation in kinematics and design.

Methodology

Curved-mesial roots of mandibular molars were randomly selected and assigned into 4 balanced experimental groups (n = 10), established by determining homogeneous 3D parameters of volume and surface area: R-Motion size 30, .04 taper (RM; FKG Dentaire, Switzerland), Reciproc Blue size 25, .08 taper (RCB; VDW GmbH, Germany), HyFlex CM size 30, .04 taper (HFX; Coltène Whaledent, Switzerland) and XP-endo Shaper size 30, .01 taper (XPS; FKG Dentaire). The volume of irrigation was established at 10 mL of 2.5% NaOCl. Throughout the entire root canal preparation procedures, the samples were fixed in a vice submerged in a container with water monitored at 37ºC. Dimensional cross-sectional measures of area, perimeter, roundness, major/minor diameters and 3-dimensional (volume, surface area, structure model index-SMI) parameters as well as the smallest dentine thickness along the cervical and middle root thirds were evaluated by micro-CT. Data were analysed using analysis of variance and post-hoc Tukey tests (α=5%).

Results

RCB and XPS had significantly great, mean increases in cross-sectional area measurements, only in the middle third, when compared with RM and HFX (p < .05). RM, RCB, and XPS had a similar increase in measurements of length and width of perimeter (p > .05), and HFX had significantly lower mean increases in perimeter values only when compared with XPS (p < .05). RCB and XPS had significantly greater, mean increases in volume when compared with RM and HFX (p < .05). RM had a significantly lower difference in SMI after preparation, compared with RCB, HFX and XPS (p < .05). The smallest dentine thickness was observed after the use of RCB (p < .05), in the danger and safety zones.

Conclusions

XPS and RM had shaping ability similar to that of instruments with larger taper, achieved with less dentine thickness removal in danger and safe zones in curved-mesial canals of extracted molar teeth treated on a laboratory benchtop.