All systems were associated with apical debris extrusion when canals were prepared to a large apical size. The PTU system was associated with more debris extrusion.

This study assessed the percentage of untouched canal areas and the amount of debris accumulation after canal preparation with ProTaper Next (PTN) and Twisted File Adaptive (TFA) systems using micro-computed tomographic (micro-CT) imaging. Twenty isthmus-containing mesial roots of mandibular molars were anatomically matched through micro-CT evaluation and randomly assigned to one of the two experimental groups (n = 10), according to the system used for canal preparation: PTN (X1 and X2 files using rotary motion) and TFA (SM1 and SM2 files using adaptive motion). After canal preparation up to ISO size 25, the specimens were then scanned and the matched images of the mesial canals, before and after preparation, were examined from the furcation level to the apex to quantify the untouched surface canal areas and to evaluate the amount of accumulated debris. An independent samples t-test and a Mann-Whitney test were used, respectively, to compare these variables between the groups with a significance level set at 5%. Root canals prepared with either PTN or TFA systems were found to present similar untouched canal surface areas (P = 0.52) and hard-tissue debris accumulation (P = 0.39). Both systems produced a suboptimal and similar mechanical preparation of the mesial canals of mandibular molars and were not able to yield root canals completely free from packed hard-tissue debris.