Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 10 6 2013 12 15 501 5 Kiumarz Nazarimoghadam Associate Professor, Department of Endodontics, Dental School, Shahed University of Medical Sciences, Tehran, Iran. Hossein Labaf Assistant Professor, Department of Endodontics, Dental School, Shahed University of Medical Sciences, Tehran, Iran. 2015 10 16 The aim of this in-vitro study was to compare the accuracy of two new electronic apex-locator controlled handpieces (EALHs) using the first rotary Mtwo file while rotating in the canal.A total of 36 extracted mandibular molar teeth were selected. The lengths of the mesio-buccal canals to the major foramina were measured directly using a size 10 K-file introduced in the canal until the tip was visible under a loupe and then 0.5 mm was subtracted from the recorded lengths as the actual working lengths (AWLs). Subsequently, the teeth were randomly assigned to two groups and embedded in an alginate model. Auto-stop function of the EALHs was preset at "0.5" mark and then electrical working lengths (EWLs) in groups 1 and 2 were recorded by VDW GOLD and Dentaport ZX, respectively. Analysis of variance (ANOVA, 1-way) and Tukey pairwise multiple comparison intervals (0.05) were used to compare the accuracy of the two electronic devices.For VDW GOLD, 61.1% of the measurements were within ±0.5 mm and 88.9% were within ±1 mm of the AWL. For Dentaport ZX, 88.9% of the measurements were within ±0.5 mm and 94.4% were within ±1mm of the AWL. There was no significant difference between AWLs and EWLs (p=0.466 for Dentaport ZX and p=0.283 for VDW Gold) and between the accuracy of the two devices in determining the EWL (p=0.8).Both Dentaport ZX and VDW Gold were suitable for determining working length using a rotary file. To avoid over instrumenting the canal, we recommend setting the devices to automatically stop or reverse the rotary file at 1 mm level. https://fid.tums.ac.ir/index.php/fid/article/view/593 https://fid.tums.ac.ir/index.php/fid/article/download/593/568