Micro-CT Evaluation of Canal Shaping Extent with Apex Locator– Integrated Endodontic Motors

This in vitro study evaluated the accuracy of the extent of canal shaping to apical constriction (AC) with electronic apex locator (EAL)-integrated endodontic motors using micro-computed tomography (MicroCT). A total of sixty human single-canal teeth were chosen from a pool of extracted teeth for reasons not related to the study. After tooth decoronation, the samples were scanned using microCT (SCANCO Medical AG, Brüttisellen, Switzerland) and distributed into three groups: Rooter Universal (RU; FKG Denatire, La Chaux-de-Fonds, Switzerland), Tri Auto ZX II (TA; J. Morita, Tokyo, Japan), and control group (n = 20 each). The working length (WL) was determined simultaneously during canal shaping using the auto-reverse function set at the 0.5 mark in the RU and TA groups. In the control group, the WL was measured before the shaping using Root ZX (J. Morita, Tokyo, Japan). In the three groups, canals were shaped using ProTaper Gold files (Dentsply Sirona, Ballaigues, Switzerland) until the preset mark was reached in the two experimental groups and to the measured WL in the control group. Afterwards, post-shaping microCT scans were taken. Scan superimposition was conducted to assess the absolute distance between the final shaping endpoint and AC. Negative and positive data were recorded when the measurements were found short or beyond the AC, respectively. Analysis of variance (ANOVA) and post-hoc Tukey tests were used to analyze the distance in each group. The chi-square test was applied to analyze the accuracy of the measurements with respect to the AC. The significance level was set at 5%. No over-shaping beyond the apical foramen was found in any sample. However, the control group was found to shape canals closer to the AC, compared to the RU and TA (p < 0.01). The measurement accuracy was found to be better in the control group compared to the RU and TA. In conclusion, all tested systems were able to maintain the canal shaping coronal to the apical foramen. In detecting the AC, the standalone EAL was found to be more accurate than the apex locators integrated in the tested endodontic motors.