Smooth flexible versus active tapered shaft design using NiTi rotary instruments

AIM: The aim of this study was to evaluate the influence of a smooth flexible versus active tapered shaft design on canal preparation by NiTi rotary techniques. METHODOLOGY: A XMCT-scanner (SkyScan 1072) and developed software (Bergmans et al. 2001) were used to nondestructively analyze the mesial canals of 10 extracted mandibular molars in 3D with a spatial resolution of 30 microm. Specimens (n = 10 per group) were scanned before (PRE) and after (POST) preparation using Lightspeed (smooth flexible) or GT-rotary (active tapered) files. Numerical values for volumes, dentine removal (net) transportation and centring ability were obtained in addition to a visual inspection on canal aberrations. Data were analyzed by Shapiro Wilk test, multiway factorial anova, Tukey-Kramer test, Wilcoxon test and t-test. RESULTS: Results indicated that the active tapered shaft removed significantly more dentine in the middle to apical portion of the root compared to the smooth flexible design. Both groups demonstrated some straightening, but no significant differences were found with respect to instrument types. However, absolute values for net transportation and centering ratio were small and no canal aberrations could be found. CONCLUSIONS: The smooth flexible shaft design did not improve the morphological characteristics of canal preparation by NiTi rotary instruments when compared with the active tapered design. Therefore, system selection should be based upon other criteria.