An In Vivo Comparison of the Root ZX II, the Apex NRG XFR, and Mini Apex Locator by Using Rotary Nickel-Titanium Files

Introduction: The purpose of this study was to compare the accuracy of working length (WL) measurements by using the Root ZX II, Apex NRG XFR, and Mini Apex Locator with rotary nickel-titanium (NiTi) instruments. Methods: Twenty-eight teeth had their WLs determined with each electronic apex locator (EAL) by using 0.04 taper ProFiles sizes 40-20 in a crown-down technique until WL was reached. Four control teeth had their WL determined by using stainless steel hand files. The files were cemented at WL, and the teeth were extracted. The apical 4 mm of each root was shaved to the apical constriction, exposing the file. Photographs were taken under 15× and 30× magnification and projected at 360× and 720× for evaluation. Results: The accuracy of the Root ZX II, Apex NRG XFR, and Mini Apex Locator in locating the minor diameter within ±0.5 mm was 50%, 46.43%, and 39.29%, respectively. There was no statistically significant difference between the EALs in locating the minor diameter. The determination of WL by using hand files in the control teeth was more accurate. Conclusions: The Root ZX II, Apex NRG XFR, and Mini Apex Locator used with rotary NiTi files were able to locate the apical constriction within ±0.5 mm only 50% or less of the time.