Efficacy of rotary instruments with greater taper in preparing oval root canals

Aim: To compare the preparation quality of two rotary systems and NiTi-hand files in oval root canals, and to evaluate the effect of canal dimensions on the preparation. Methodology: Ninety roots with oval root canals were selected. The middle third was cross sectioned at two levels and photographed. The maximum and minimum diameters of the root and canal were recorded. Teeth were distributed in three groups (n = 30) using stratified randomization, and prepared under simulated clinical conditions with Mtwo, ProTaper, or NiTi-hand files. The pre- and post-preparation photographs were traced and superimposed, the thickness of dentine removed was measured and the ratio of prepared canal outline was calculated. The impact of preparation system and canal dimensions on the quality of the preparation was evaluated using regression analysis. Results: With regards to the ratio of prepared canal outline, no statistical significant difference was found between Mtwo (0.75 [95%CI: 0.69; 0.81]) and ProTaper (0.75 [95%CI: 0.69; 0.80]), but both systems performed significantly better than NiTi-hand files (0.65 [95%CI: 0.60; 0.71]). In six root canals in Mtwo-group (20%), and eight root canals in ProTaper-group (27%), the minimal thickness of dentine-wall after preparation was less than 0.5 mm. In contrast to the maximum diameter of the root canal, the minimum diameter influenced the quality of the preparation (P = 0.0006). Conclusions: No instrumentation technique was able to circumferentially prepare the oval outline of root canals. Nevertheless, instruments with greater taper (ProTaper and Mtwo) were more efficient than NiTi- hand files, but this was, in some cases, at the expense of remaining dentine-wall thickness.